''Rhizoglyphus'' is a genus of mites in the family Acaridae. It has a worldwide distribution and is often associated with the

bulb In botany, a bulb is structurally a short stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs duri ...

corm A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem that serves as a storage organ that some plants use to survive winter or other adverse conditions such as summer drought and heat (perennation). The word ' ...

s or

tuber Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing ...

s of plants.

Description and life cycle

''Rhizoglyphus'' begin their lives as whitish, ellipsoidal

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s that are 0.12 mm long. These hatch into larvae, which are oval, white and have three pairs of legs. Larvae are 0.15-0.2 mm long on hatching and grow to 0.25 mm long. Larvae then develop into protonymphs, which are 0.4 mm long and (compared to larvae) gain an additional leg pair and two genital suckers. Under certain conditions such as high population density, protonymphs develop into deutonymphs (or hypopi), a quiescent stage that does not feed. This life stage is convex dorsally and flattened ventrally, brown in colour, 0.2-0.3 mm long, heavily

sclerotised Sclerotin is a component of the cuticle of various Arthropoda, most familiarly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, a form of tanning in which qui ...

, lacks mouthparts and has a ventral sucker plate. The purpose of the deutonymph stage is to attach to insects and be carried to other bulbs ( phoresis). Deutonymphs are resistant to starvation and desiccation during adverse conditions. The tritonymph stage follows the protonymph (or deutonymph). Tritonymphs are about 0.5 mm long and have three or four genital suckers. They eventually develop into adults. Adults are 0.5-0.9 mm long, shiny, white and somewhat transparent, and have reddish brown appendages. Unlike tritonymphs, they have distinct genital apertures. Some features which distinguish adult ''Rhizoglyphus'' from other mites are: 4 pairs of prodorsal

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

e and 12 pairs of dorsal hysterosomal setae, external vertical setae small/vestigial and situated about halfway along sides of prodorsal shield, supracoxal setae smooth, and tarsi I and II each with a proximal conical spine near bases of solenidion and famulus. The duration of the life cycle depends on ''Rhizoglyphus'' species, diet, temperature and relative humidity. At a temperature of 25 °C, it can be as short as 12.2 days for ''Rhizoglyphus robini'' and 13.9 days for ''R. echinopus''. Adults live longer (for up to 121 days) at lower temperatures. Males tend to live twice as long as females in this genus.

Host arthropods

As noted previously, ''Rhizoglyphus'' deutonymphs ride on other, larger arthropods for dispersal. They have been collected from scarab beetles,

weevils Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, ...

, various flies and

flea Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...

Host plants

''Rhizoglyphus'' feed on a range of ornamental (e.g. '' Dahlia'', '' Eucharis'', '' Gladiolus'', ''

Hyacinthus ''Hyacinthus'' is a small genus of bulbous, spring-blooming perennials. They are fragrant flowering plants in the family Asparagaceae, subfamily Scilloideae and are commonly called hyacinths (). The genus is native to the area of the eastern M ...

'', ''Iris'',

lily ''Lilium'' () is a genus of Herbaceous plant, herbaceous flowering plants growing from bulbs, all with large prominent flowers. They are the true lilies. Lilies are a group of flowering plants which are important in culture and literature in mu ...

, ''Narcissus'',

orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of flowering ...

, tulip) and crop plants (e.g.

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

carrot The carrot ('' Daucus carota'' subsp. ''sativus'') is a root vegetable, typically orange in color, though purple, black, red, white, and yellow cultivars exist, all of which are domesticated forms of the wild carrot, ''Daucus carota'', nat ...

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

onion An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus ''Allium''. The shallot is a botanical variety of the onion ...

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

sweet potato The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledonous plant that belongs to the Convolvulus, bindweed or morning glory family (biology), family, Convolvulaceae. Its large, starchy, sweet-tasting tuberous roots are used as a r ...

taro Taro () (''Colocasia esculenta)'' is a root vegetable. It is the most widely cultivated species of several plants in the family Araceae that are used as vegetables for their corms, leaves, and petioles. Taro corms are a food staple in Africa ...

). While underground plant parts are most commonly attacked, the mites have also been collected from leaves, stems and seeds.

Biochemistry

''Rhizoglyphus'' secrete an alarm pheromone from opisthonotal glands. This pheromone has neryl-formate as its main component and citral and α-acaridial as minor components. Its secretion triggers escape behaviour in other mites and it may be involved in mite defense against predators. Citral and α-acaridial also have

antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as crypto ...

activity. These mites also have a range of

cuticular A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

chemicals. Hexyl rhizoglyphinate is another antifungal, while the roles of other chemicals remain unknown.

Pest status

As noted previously, ''Rhizoglyphus'' feed on a range of plants. Infested bulbs may rot and fail to produce new growth, or new growth may be discoloured, stunted and distorted. In tulips, ''Rhizoglyphus'' may enter prematurely opened buds and cause bud necrosis. Bulbs that are damaged or infested with ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' fungus are more vulnerable to attack. Due to their pest status, these mites are classified as quarantine species by many countries such as Australia and New Zealand.

Control measures

Rough handling of bulbs should be avoided as this can cause damage that allows ''Rhizoglyphus'' to enter. Keeping bulbs dry also generally prevents them from being attacked, since the mites cannot withstand drought. A range of

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 ...

s have been used, but ''Rhizoglyphus'' are resistant to a number of pesticides and there is concern about pesticides affecting non-target species. There has been research on biological control of this genus of mites. Most of this has involved predatory mites, but entomopathogenic nematodes have also been considered.

Species

* '' Rhizoglyphus actinidia'' Zhang, in Zhang, Jiang & Zeng 1994 * '' Rhizoglyphus algericus'' Fain, 1988 * '' Rhizoglyphus algidus'' Berlese, 1920 * '' Rhizoglyphus alliensis'' Nesbitt, 1988 * '' Rhizoglyphus allii'' Bu & Wang, 1995 * '' Rhizoglyphus balmensis'' Fain, 1988 * '' Rhizoglyphus costarricensis'' Bonilla, Ochoa & Aguilar, 1990 * '' Rhizoglyphus echinopus'' (Fumouze & Robin, 1868) * '' Rhizoglyphus eutarsus'' Berlese, 1920 * '' Rhizoglyphus frickorum'' Nesbitt, 1988 * '' Rhizoglyphus fumouzi'' Nesbitt, 1993 * '' Rhizoglyphus globosus'' Berlese, 1920 * '' Rhizoglyphus longispinosus'' Ho & Chen, 2001 * '' Rhizoglyphus narcissi'' Lin & Ding, 1990 * '' Rhizoglyphus occidentalis'' (Sevastianov & Tamam-Nasem-Marros, 1993) * '' Rhizoglyphus occurrens'' Berlese, 1920 * '' Rhizoglyphus robini'' Claparédè, 1869 * '' Rhizoglyphus robustus'' Nesbitt, 1988 * '' Rhizoglyphus sportilionis'' Lombardini, 1947 * '' Rhizoglyphus termitum'' Womersley, 1941 * '' Rhizoglyphus trouessarti'' Berlese, 1897 * '' Rhizoglyphus tsutienensis'' Ho & Chen, 2000

References

External links

{{Taxonbar, from=Q2595410 Acaridae