The olive fruit fly (''Bactrocera oleae'') is a species of
fruit fly which belongs to the subfamily
Dacinae
The Dacinae are a subfamily of the fruit fly family Tephritidae. Its 41 genera are distributed among three tribe (biology), tribes:
* Tribe Ceratitidini:
** ''Capparimyia''
** ''Carpophthoromyia''
** ''Ceratitella''
** ''Ceratitis''
** ''Eumict ...
. It is a
phytophagous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
species whose
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
e feed on the fruit of olive trees, hence the common name. It is considered a serious pest in the cultivation of olives.
Until 1998, the fly had not been detected in the United States, and its range coincided with the range of the olive tree in the Eastern Hemisphere: northern, eastern, and southern Africa, Southern Europe, the Canary Islands, India, and western Asia. In the Western Hemisphere, it is currently restricted to California, Baja California, and Sonora. The olive fruit fly was first detected in North America infesting olive fruits on landscape trees in Los Angeles County in November 1998. It can now be found throughout the state of California.
History
In the final years of the 18th century, Italian scientist
Giuseppe Maria Giovene
Giuseppe Maria Giovene (23 January 1753 – 2 January 1837) was an Italian archpriest, naturalist, agronomist, geologist, meteorologist, entomologist and ichthyologist. elogio-storico, pag. 9, note 8 He is best known for his studies on the "n ...
(1753–1837), in his work ''Avviso per la distruzione dei vermi che attaccano la polpa delle olive'' (1792), provided some suggestions for peasants to effectively destroy the fly ''musca oleae'', which infested the pulp of
olive trees
The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' 'M ...
.
Distribution and importance
This species is associated with plants of the genus ''
Olea
''Olea'' ( ) is a genus of about 40 species in the family Oleaceae, native to warm temperate and tropical regions of the Middle East, southern Europe, Africa, southern Asia, and Australasia. They are evergreen trees and shrubs, with small, opp ...
''. It is found throughout the
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
basin and in
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
. Since the late 1990s, it has also been present in
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
and may have spread throughout the area of olive cultivation in the
Nearctic
The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface.
The Nearctic realm covers most of North America, including Greenland, Central Florida, and the highlands of Mexico. The parts of North America t ...
region. It is considered the most serious pest of olives in regions where it lives, significantly affecting both the amount and quality of production in most olive-growing areas.
The impact of its attacks tends to worsen in the more humid and cooler growing areas, with significant variations depending on the variety grown, where it affects
olive cultivars
The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' 'M ...
and areas that have hot summers and less drought.
Morphology
The egg is around 0.7 to 1.2 mm long, elongated, and slightly flattened in its stomach, with a small, white microfleece nodule, which is important for the respiration of the embryo.
The
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
is
Caecilian
Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
and has a conical-cylindrical, narrow front. It develops through three stages (larva, first, second and third stage). The mature
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
is 6–7 mm long, white-yellowish in colour, elongated, and subconical. The front sensors are bipolar and the second conic feature, the rear sensor, has eight sensilla. The cephalopharyngeal skeleton has very short dorsal and ventral
apodemes, the hypostomal
scleritis
Scleritis is a serious inflammatory disease that affects the white outer coating of the eye, known as the sclera. The disease is often contracted through association with other diseases of the body, such as granulomatosis with polyangiitis or ...
is triangular. It lacks a subhypostomal and the jaws are hooked. The oral lobes have 10–12 indents, preceded on each side by a sensory plate similar to the larva of the ''Ceratitis capitata''. The frontal
stigmas have 9–10 lobes. The three larval stages can be distinguished in different ways by their cephalopharyngeal structures. The different shapes of the frontal stigmas allow determination of the larvae of the second and third stages, while the larva at its first stage is
metapneustic, equipped with one pair of posterior stigmas.
The
pupa
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
l stage takes place inside the
puparium
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
, an elliptical shell formed by the last
exuvial transformation of the
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
. The puparium is 3.5 to 4.5 mm long, varying in colour from creamy white to yellow-brown, when it is dry. The change in colour of the puparium can determine the age of the pupa.
Adults
An adult is a human or other animal that has reached full growth. In human context, the term ''adult'' has meanings associated with social and legal concepts. In contrast to a "minor", a legal adult is a person who has attained the age of majori ...
are 4–5 mm long. In
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
, they are easily recognized in conjunction with other
Tephritidae
The Tephritidae are one of two fly families referred to as fruit flies, the other family being the Drosophilidae. The family Tephritidae does not include the biological model organisms of the genus ''Drosophila'' (in the family Drosophilidae), w ...
for the small dark spot at the apex of the wing and the length of the narrow, elongated anal cell.
The adult male has a hardened wing at the top of the anal cell, which is longer than the female's. The third urite shows the pectorals.
The adult female has a yellowish head with two strong circular spots under the antennae close to the compound eyes, whilst the eyes are bluish-green. The chest can show various specks instead of the typical bands and lines. The mesonotum is bluish-gray with three blackish longitudinal lines. The humeral callus and areas mesopleurali, metapleurali, and mesoscutello are ivory. The wings are hyaline, with part of the
pterostigma
The pterostigma (plural: pterostigmata) is a group of specialized cells in the outer insect wing, wings of insects, which are often thickened or coloured, and thus stand out from other cells. It is particularly noticeable in dragonfly, dragonfli ...
with brown specks at the apex. The abdomen is light brown with variable colourings: typically there are pairs of blackish spots on the first to fourth urotergit, which often come together in bands. The
ovipositor
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
is clearly visible, partly invaginated in the seventh urite, which is always black. The length is 4–5 mm.
In the Asian variety, the whole body of the mesonotum is yellowish with strong, visible dark lines.
Life cycle
The females lay their eggs in the summer when the olive is at least 7–8 mm in diameter. Egg-laying is done by making a puncture with the ovipositor into the skin of the olive, leaving only one egg in the hollow below. The bite has a characteristic triangular shape due to an optical effect. A puncture has a dark green colour, whilst older bites have a yellowish-brown colour as a result of wound healing.
Hatching occurs over a variable period depending on weather conditions: from 2–3 days in summer, to about 10 days in autumn. The newly hatched larva initially digs a tunnel on the surface, but later moves deeper into the flesh to the core, which is not affected in any way. During larval development, two changes occur, which in turn increase the size of the larva.
Around the third change, larvae at their third stage move toward the surface and prepare the exit hole for the adult, gnawing at the flesh to leave a thin surface layer. During this phase, the olive clearly shows signs of the attack because its appears darker in conjunction with the tunneling. On the surface, a circular hole due to the remaining residual skin becomes apparent. The pupae remain dormant in the hollow below, protected within the exuviae produced by the mature larvae.
At maturity, the adult breaks the exuvia and emerges from the pupa. It breaks the skin surface left by the larva by force and leaves the exit hole. In late autumn and winter, its behaviour changes; the mature larva emerges from the olive and drops onto the ground, where pupation takes place.
Adults are
glycogenic and feed primarily on
honeydew. Since their basic
diet
Diet may refer to:
Food
* Diet (nutrition), the sum of the food consumed by an organism or group
* Dieting, the deliberate selection of food to control body weight or nutrient intake
** Diet food, foods that aid in creating a diet for weight loss ...
is low in
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
, they are particularly attracted to materials that emit volatile nitrogenous substances, such as bird droppings, for purposes of supplementing their protein requirements. This behavior is important because it can be used in programs for the fly's control and monitoring by using attractants such as
hydrolysate proteins and
ammonium salt
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
s.
Environmental needs
The development cycle is closely linked to environmental conditions, in particular the
climate
Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...
and the state of the olives. Knowing these parameters, together with the monitoring of the population, is needed to implement effective pest management programs.
The climate influences the cycle, especially with the temperature and less humidity. The duration of each stage is summarized below:
The duration of young larva therefore varies from a minimum of 20 days to a maximum of 5 months in the overwintering generation.
Temperature has an important role on the viability and rhythms of reproduction. Temperatures above 30 °C cause resorption of ovarian follicles by reducing the fecundity of females; a female lays two to four eggs on average per day in summer and 10-20 eggs in autumn. Persistent temperatures above 32 °C for several hours a day also cause mortality of over 80% of the eggs and larvae of that age.
Low temperatures, therefore, have very limited effects because its activity is undermined by temperatures below 0 °C. Given ordinary climatic conditions, low temperatures and harsh winters clearly interfere with population dynamics only in the northernmost areas of olive vegetation.
In general, the optimum temperatures for oviposition and larval development are between 20 and 30 °C, together with a need for humid weather.
The second controlling environmental factor is the obvious characteristics of the olives and the phenological stage of the plant. Females receive sensory stimuli to denote the degree of receptivity of the olive, a phenomenon that allows them to choose the olive; before oviposition, the female first "analyses" the size, colour and odour and, it seems, the presence of certain bacterial species. They are especially frequent in summer, caused by the females with a sterile puncture to test the receptivity of the olive. The ethology of the fly has been paid particularly regard in recent years when analysing study control methods based on the use of prior insect repellents (copper,
kaolin
Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
, etc.).
Larval development is instead influenced by the consistency of the pulp and especially the size of drupe. In table olives, in fact, mortality of the larva is lower in summer because they can escape the lethal effects of high temperatures by migrating deeper. The consistency of the pulp is instead an intrinsic characteristic. Not even susceptibility of olive fruit fly attacks make much difference according to
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
.
Population dynamics
Unlike other species, the succession of generations of the ''Bactrocera oleae'' is not markedly different for the scaling of ovipositioning and longevity of adults. Within a year, generally three to five generations occur, but in many years, a sixth generation can grow in the spring on the olive tree, but does not remain on the tree.
The population size varies throughout the year, but with two peaks: the first in the middle of spring, at the development of the winter generation of adults, and the second, more intense, in early autumn when the olives are at the highest degree of receptivity, the temperatures drop slightly and the climate becomes wetter. In
Sardinia
Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label=Algherese and Catalan) is the second-largest island in the Mediterranean Sea, after ...
, the larval population peaks typically occur during the months of April–May and September–October.
Predisposing factors
The predisposition to the flies' attacks is tied to several factors, both intrinsic and extrinsic. The main ones are climatic (temperature and rainfall), so marked differences can occur from year to year. However, other
genetic or
agronomic
Agricultural economics is an applied field of economics concerned with the application of economic theory in optimizing the production and distribution of food and fiber products.
Agricultural economics began as a branch of economics that specif ...
factors should not be overlooked.
Ultimately, the environmental conditions favorable to fly attacks are:
* Conditions of moderate heat, with temperatures not exceeding 32-34 °C
* A humid climate
* Premature
cultivation
* Mass or dual purpose cultivation
* Cultivation under irrigation
Because of these factors, the incidence of olive fruit fly attacks increase, passing from the southern to northern areas, and coastal to inland regions. As for the season in general, the summer infestations are usually contained with the exception of cooler environment and more susceptible cultivars. On the other hand, infestation peaks happen from the months of September until cold weather arrives, especially with a rainy climate.
Another unique factor is the relationship between the alternation of production, a phenomenon in which the olive tree is particularly susceptible, and the intensity of the attacks. The attacks are usually most intense in years of low production and high production. The cause of this behaviour is partly biological, partly agricultural.
In low seasons following a high one, usually, a significant amount of olive residue is left on the plants from the previous year, so it has a higher population at its production peak in spring, and a higher reproductive potential occurring with more intense and earlier attacks. The attacked olives fall early in autumn and this causes a higher incidence of mortality during the winter.
In the subsequent good year for the population of first generation olives, production is quite low, with modest reproductive potential. The attacks will therefore be later and help a mass-production.
Damages
The damages caused by the olive fruit fly are of two types: quantitative and qualitative.
From a quantitative point of view, the damage is caused by larvae of second and especially third stages, by the removal of the significant proportion of the pulp which as a consequence results in reduction in the yield of olives. Part of the production is also lost due to premature falling of the attacked fruit. Olive bites and holes dug by the larvae in the initial phase do not have a significant impact on the yield. In table olives, however, the damage extends to the sterile punctures, which cause the variation in production.
A qualitative aspect to be considered is the significant deterioration in the quality of the oil extracted from olives with a high percentage of attacks by larvae of the third stage. The oil obtained from infected olives has a high
acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
level (expressed as
oleic acid
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated omega ...
, from 2% to 10% depending on the percentage of the infestation) and a lower shelf life as it has a higher
peroxide value
Detection of peroxide gives the initial evidence of rancidity in unsaturated fats and oils. Other methods are available, but peroxide value is the most widely used. It gives a measure of the extent to which an oil sample has undergone primary oxida ...
. Secondarily qualitative impairments of varying severity derive from the olive fruit fly attacks due to the arrival of
mold
A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...
through the eclosions. This deterioration in quality is evident in significantly flawed oils obtained from olives harvested from the ground or stored for several days before pressing.
Auxiliaries antagonised by the olive fruit fly
Few natural enemies prey on the olive fruit fly, but they can play a significant role in containing populations in
biological
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary in ...
and
integrated pest control
Integrated pest management (IPM), also known as integrated pest control (IPC) is a broad-based approach that integrates both chemical and non-chemical practices for economic control of pests. IPM aims to suppress pest populations below the econ ...
. However, these biological factors by themselves cannot counterweigh the economic effects they cause, in particular due to the reproductive differences between flies and antagonists. In fact, they can manage the attacks of the olive fruit fly when its population is contained, but less so in the case of heavy infestations. The enemies of the fly that play a significant role are mostly
parasitoids
In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasi ...
.
*
Hymenoptera
Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
Ichneumonoidea
The superfamily Ichneumonoidea contains one extinct and three extant families, including the two largest families within Hymenoptera: Ichneumonidae and Braconidae. The group is thought to contain as many as 100,000 species, many of which have not ...
**''
Opius concolor
''Opius'' is a genus of wasps in the family Braconidae. This genus has a wide geographic range and contains the majority of species in the subfamily Opiinae.
Species
* ''Opius abbyae''
* ''Opius abditiformis''
* ''Opius abditus''
* ''Opius aber ...
'' (
Braconidae
The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analysis ...
) is an
endoparasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
of various Diptera Tefritidi including ''B. oleae''. Naturally found in the African continent, after its discovery in 1910, it was introduced in many other regions; however, it is difficult to acclimate in the Italian regions, except, perhaps, Sicily. It is used as a replacement of the larvae ''
Ceratitis capitata
''Ceratitis capitata'', commonly known as the Mediterranean fruit fly or medfly, is a yellow-and-brown fly native to sub-Saharan Africa. It has no near relatives in the Western Hemisphere and is considered to be one of the most destructive frui ...
'' (Mediterranean fruit fly).
*
Hymenoptera
Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
Chalcidoidea
Chalcid wasps (, , for their metallic colour) are insects within the superfamily Chalcidoidea, part of the order Hymenoptera. The superfamily contains some 22,500 known species, and an estimated total diversity of more than 500,000 species, me ...
**''
Pnigalio mediterraneus'' (
Eulophidae
The Eulophidae are a large family of hymenopteran insects, with over 4,300 described species in some 300 genera. The family includes the genus ''Elasmus'', which used to be treated as a separate family, "Elasmidae", and is now treated as a subf ...
) is one of the most active of the
ectoparasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
larvae of ''B. oleae''. Although polyphagous, its summer generations are usually associated with the fly.
**''
Eupelmus urozonus'' (
Eupelmidae
Eupelmidae is a family of parasitic wasps in the superfamily Chalcidoidea. The group is apparently polyphyletic, though the different subfamilies may each be monophyletic, and may be elevated to family status in the near future. As presently defi ...
) is another polyphagous
ectoparasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
associated with olives and has two or three summer generations associated with the ''B. oleae'' larva. Come autumn, it moves to another Tefritide associated with the
Dittrichia. It can be used as a replacement of the fruit fly. It has a definite activity as a
hyperparasite
A hyperparasite, also known as a metaparasite, is a parasite whose host, often an insect, is also a parasite, often specifically a parasitoid. Hyperparasites are found mainly among the wasp-waisted Apocrita within the Hymenoptera, and in two othe ...
against other parasitoids of the fly.
**''
Eurytoma martellii'' (
Eurytomidae
The Eurytomidae are a family within the superfamily Chalcidoidea.
Unlike most chalcidoids, the larvae of many are phytophagous (feeding in stems, seeds, or galls), while others are more typical parasitoids, though even then the hosts are usually ...
) is an ectoparasite of the ''B. oleae'' larvae, but not much information on its biology is known. In local contexts, it can become the most common antagonist of the fly.
**''
Cyrtoptyx latipes'' (
Pteromalidae
The Pteromalidae are a very large family of mostly parasitoid wasps, with some 3,450 described species in about 640 genera (the number was greater, but many species and genera have been reduced by synonymy in recent years). The subfamily-level d ...
). is an ectoparasite of the ''B. oleae'' larvae. It is an antagonist of minor importance, as it is rare.
*
Diptera
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
**''
Lasioptera berlesiana'' (
Cecidomyiidae
Cecidomyiidae is a family of flies known as gall midges or gall gnats. As the name implies, the larvae of most gall midges feed within plant tissue, creating abnormal plant growths called galls. Cecidomyiidae are very fragile small insects usu ...
) is a
predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
of several insects, including ''B. oleae''. This species contributes to containment of the first summer infestations.
Control measures
Background
One of the first authors to describe the damage caused by the olive fruit fly is Girolamo Caruso,
[Antonio Saltini (1989). ''Storia delle scienze agrarie. Volume IV'': 256-259.] dean of the
faculty in
Pisa
Pisa ( , or ) is a city and ''comune'' in Tuscany, central Italy, straddling the Arno just before it empties into the Ligurian Sea. It is the capital city of the Province of Pisa. Although Pisa is known worldwide for its leaning tower, the cit ...
from 1872 to 1917, author of the famous ''monografo dell’olive''. Caruso (chapter XV paragraph 14) calls the insect ''Dacus olea'' (Fabr.), providing other scientific names proposed by different authors in dialect:
*''Musca oleae'' (Rossi, Lin., Gmelin, Fabr., Petagna, Olivier)
*''Tephritis olea'' (Latr., Risso)
*''Chiron, keirun, mouche de l'olive'', the ''olive de ver'', in southern France
*Olive fly, olive fruit fly, worm, olives, olive bug, ''pidocchina'' in various Italian regions
It follows a detailed description of all stages of the lifecycle, focusing on the larvae and the damage caused by them.
The remedies suggested are empirical. Among the undoubted merits of Caruso is that he suggested a designated control zone to farmers.
Chemical pest management
The chemical battle against the olive fruit fly can be implemented against larvae by using preventive treatments against adults.
The treatments are carried out by spraying the olive trees with insecticides (
dimethoate
Dimethoate is a widely used organophosphate insecticide and acaricide. It was patented and introduced in the 1950s by American Cyanamid. Like other organophosphates, dimethoate is an acetylcholinesterase inhibitor which disables cholinesterase, an ...
,
deltamethrin
Deltamethrin is a pyrethroid ester insecticide. Deltamethrin plays a key role in controlling malaria vectors, and is used in the manufacture of long-lasting insecticidal mosquito nets; however, resistance of mosquitos and bed bugs to deltamethrin ...
, and
phosmet). Dimethoate is commonly used for its effectiveness and relatively low cost. It may be preferable because it would leave few residues in
olive oil
Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
, since it is water-soluble and would pass through the
amurca
Amurca is the bitter-tasting, dark-colored, watery sediment that settles out of unfiltered olive oil over time. It is also known as "olive oil lees" in English. Historically, amurca was used for numerous purposes, as first described by Cato the E ...
. In the near future, legislative authorization for the withdrawal of use of dimethoate is to be implemented. Among the products with low impact,
azadirachtin
Azadirachtin, a chemical compound belonging to the limonoid group, is a secondary metabolite present in neem seeds. It is a highly oxidized tetranortriterpenoid which boasts a plethora of oxygen-bearing functional groups, including an enol ether, a ...
is a natural repellent extracted from the fruits of the
neem tree
''Azadirachta indica'', commonly known as neem, nimtree or Indian lilac, is a tree in the mahogany family Meliaceae. It is one of two species in the genus ''Azadirachta'', and is native to the Indian subcontinent and most of the countries in Afri ...
. However, its effectiveness against the olive fruit fly has not yet been sufficiently tested. Among the organic insecticide literature,
rotenone
Rotenone is an odorless, colorless, crystalline isoflavone used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the seeds and stems of several plants, such as the jicama vine plant, and the roots of several member ...
is also mentioned, but the use of this active ingredient, not readily available, must be authorized by established competent bodies after demonstrating the need for it.
The larvicidal treatment is carried out according to the criteria of the scheduled pest management, pest management and integrated pest management.
Scheduled pest management usually occurs with periodic preventive treatments from the period when the larvae appear during an average infestation (from midsummer in areas with higher incidence or in September in areas with lower incidence). The treatment is repeated on average every 20 days (in the case of dimethoate) or at the
interval of active use. The downside to the scheduled treatment is the risk of carrying out unnecessary treatments.
Pest management and integrated pest management is used if the problem exceeds the threshold. This can be estimated each week by noting the trend of the population of adults with the use of traps for monitoring or detecting the number of active infestation (bites and fertile mine of larvae I and II age). To be reliable, the system first requires a suitable response in the trial, because the intervention thresholds vary depending on the type of trap and the environment. In northern
Sardinia
Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label=Algherese and Catalan) is the second-largest island in the Mediterranean Sea, after ...
, an intervention threshold – for
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
s of oil – was reliably evaluated, with a weekly catch of 10 adults per sticky trap in summer and 30 adults per trap in October. Further reliable information used is the sampling of olives to estimate the extent of infestation. In this case, the threshold for intervention of an active infestation is recommended between 10-15% on
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
s for oil production and 5% for table cultivars. Sampling is carried out weekly and taken randomly over a large area for an olive tree at head height. A sample is separated from samples of 100-200 olives, which are to detect the presence of live and uninfected eggs and larvae at first and second stages. The presence of eclosions, larvae and pupal third stages should not be counted because the damage has already occurred and the treatment would be worthless.
The preventive treatments are carried out by spraying the olive grove with poisoned protein baits. The adults, being glycogenic, are attracted by nitrogenous substances necessary to supplement their low
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
diet. The substances used as bait for the flies are protein hydrolysates and are poisoned with organophosphate insecticides (usually dimethoate). The treatment should be carried out by spraying only part of the canopy of the trees, preferably the highest point nearest the sun. The
intervention threshold for adulticide treatments are quite low (two or three adults per trap per week). Recently, the introduction of ready-made protein baits containing Dow Agrosciences
Spinosad®biological insecticide also are authorized in organic farming.
Preventive treatments with baits have the advantage of requiring lower costs and have less environmental impact, also of preventing adult egg-laying and blocking the infestations directly. Generally, they are applied to only 50% of the canopy of plants, preferably facing south, with a diameter of 50–60 cm, with limited use of water. The main problem is they are not always effective. In general, the treatments with protein baits are effective in summer seasons in areas with low incidence, whilst from September–October, usually no larvicide treatments are needed.
Among the recent preventive measures acquired, together with the idea of pest management and integrated pest management, the treatment with
copper-based pesticides has also been cited.
Copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, although a
pesticide
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...
, was found to exert a repellent effect against flies; the females turn their attention instead to oviposition on untreated olives. The basis for this action would be the advance biocidal effect of copper against the symbiotic
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, interfering with the physiology of the digestive system of the larvae. These bacteria, which appear on the surface of plants and other materials, infest adult females and transmit them to their offspring through the egg. This bacterial population would have a preferential attraction against flies, which can explain the repellent action. Repellent action would take place by
kaolin
Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
, also altering the perception of the olive colour of ripening by females. Overall, these measures should not be interpreted as solution methods, including on the basis of the information on the cases, as it is still limited. Nevertheless, they are interesting because they are compatible with biological control and integrated pest management, which, therefore may play a priceless role in a strategy for integrated pest management.
Biological and integrated pest management control
Biological pest management control, carried out so far with experiments on the ''
Opius concolor
''Opius'' is a genus of wasps in the family Braconidae. This genus has a wide geographic range and contains the majority of species in the subfamily Opiinae.
Species
* ''Opius abbyae''
* ''Opius abditiformis''
* ''Opius abditus''
* ''Opius aber ...
'', for now, offers only partial results and in any case is particularly costly. Biological pest management controls have recently been carried out on ''
Bacillus thuringiensis
''Bacillus thuringiensis'' (or Bt) is a gram-positive, soil-dwelling bacterium, the most commonly used biological pesticide worldwide. ''B. thuringiensis'' also occurs naturally in the gut of caterpillars of various types of moths and butterflie ...
'', but in this case, the biological measures showed a limited effectiveness, mainly because of difficulty reaching deep inside the larva.
Integrated pest management
Integrated pest management (IPM), also known as integrated pest control (IPC) is a broad-based approach that integrates both chemical and non-chemical practices for economic control of pests. IPM aims to suppress pest populations below the econ ...
is a more effective option, as it uses the measures of nature by weathering (high summer temperatures) and natural enemies. Where appropriate, integrated pest management can be assisted with the release of parasitoids in late summer. The main criteria to be taken for the integrated pest management are:
* Choosing less susceptible cultivars
* Advance of collections, particularly for susceptible cultivars
* Use of insecticides with low environmental impact, in particular, wisely-used insecticides used for larvicide treatments should be excluded because they are harmful to useful insect fauna.
* Chemical treatment to be made only upon exceeding the
intervention threshold
* Preventive treatment with poisoned protein baits
* Preventive treatments and repellents with copper-based products (Bordeaux mixture, copper hydroxide, copper oxychloride)
* Removal of entire production to prevent outbreaks of infestation in the spring
* Monitoring of climatic conditions
* Use of
biotechnical pest management control methods
Biotechnical pest management
Biotechnical pest management is currently mostly practiced on experimental or pilot farms or as an adjunct to the use of integrated pest traps, according to the function. It can be divided into two types:
* Monitoring traps (trap-tests) are used to detect the trends of the population of adults to estimate the threshold. Their density depends on the type and how the trap is used. The traps are strewn with a sticky entomological plastic substance.
* Traps for mass trapping (trap mass) are used to capture adults in mass to remove the population to levels that keep infestations below the threshold. Their density must be high (one trap per plant with a sexual attraction and/or food).
Mass trapping has so far given results comparable to those of the chemical pest management test implemented with the protein bait and only if implemented on a large scale. It therefore pays for pest management programs in the area, while not offering excellent results if done at enterprise level, especially on limited foundations. In the 1970s, not yet having discovered the fly pheromone, mass trapping tests were carried out using yellow traps, but this technique, requiring the placement of at least five traps per plant, was discarded as uneconomic, and had a strong negative impact on useful entomofauna.
Until the 1990s, the traps that have offered the best results were hand-crafted, made of wood soaked in a potent and long-lasting insecticide concentrate. Among the various insecticides, the best results are obtained with
deltamethrin
Deltamethrin is a pyrethroid ester insecticide. Deltamethrin plays a key role in controlling malaria vectors, and is used in the manufacture of long-lasting insecticidal mosquito nets; however, resistance of mosquitos and bed bugs to deltamethrin ...
. These traps have been carried out, mass-trapping for over a decade with about 130,000 plants in Sardinia with results comparable to those obtained with the adulticide treatments using the protein bait.
Since the late 1990s, traps are commercially available on an industrial scale (Ecotrap) for the mass trapping of the olive fruit fly.
[ (Scheda tecnica in sito a finalità commerciali)] The Ecotrap is triggered by using a form of double attraction: the pheromone of the olive fruit fly and the
ammonium bicarbonate
Ammonium bicarbonate is an inorganic compound with formula (NH4)HCO3. The compound has many names, reflecting its long history. Chemically speaking, it is the bicarbonate salt of the ammonium ion. It is a colourless solid that degrades readily to ...
, with biocidal action carried out by deltamethrin. Despite the limited series of tests carried out in recent years in some areas of the Mediterranean regions, the results are judged to be positive.
Three types of attractants are used in traps:
* ''Colour'' is used for its attractiveness in sticky traps. The adult olive fruit fly is attracted to the colour yellow. Since the yellow colour is not available, these traps can only be used for monitoring purposes.
* ''Pheromones'', for example, 1,7-dioxaspiro-5,5-undecane, which a sex pheromone emitted by the female to attract the male. Because of its selectivity, it is ideal for mass trapping, but the traps baited with the pheromone only show results that are not very effective: the pheromone of the olive fruit fly is in fact very volatile, and three to four weeks after the maximum capacity, is substantially less effective. Until the 1990s, the devices using gradual release of the pheromone proved unsuitable and it was necessary to replace them every 30–40 days.
* ''Food attractants'' are volatile nitrogenous substances that attract the flies to search for protein supplements to their diet. Protein hydrolysates and ammonium salts may be used as attractants. The disadvantage of these are that their function is affected by atmospheric conditions (temperature and relative humidity). The best results are achieved by combining a protein hydrolyzed with an ammonium salt in the same tra
or a combination of an attractive food with the pheromone.
Currently, sticky traps are the most reliable way of monitoring, as the thresholds calibrated with the traps have been extensively tested, whilst threshold assessments are still uncertain with chemiotropic traps. These are best suited, however, for mass trapping by combining two or three attractants, preferably one sexual and one food-based.
References
Bibliography
*
*
External links
*
Resources about the olive fruit flyfrom UC Davis
on the
University of Florida
The University of Florida (Florida or UF) is a public land-grant research university in Gainesville, Florida. It is a senior member of the State University System of Florida, traces its origins to 1853, and has operated continuously on its ...
/
IFAS Featured Creatures Web site
OliveOilSourceU.S.A. Site.
Online map net trapping updated in real time in France.
{{Taxonbar, from=Q2207329
Bactrocera
Agricultural pest insects
Olives
Diptera of Africa
Insects described in 1790