Spinosad
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Spinosad is an insecticide based on chemical compounds found in the bacterial species ''
Saccharopolyspora spinosa ''Saccharopolyspora spinosa'' is a species of actinobacterium first isolated from soil in a rum still in an abandoned sugar mill on the Virgin Islands. It was discovered and described by researchers Mertz and Yao while collecting specimens to be ...
''. The genus ''
Saccharopolyspora ''Saccharopolyspora'' is a genus of bacteria within the family Pseudonocardiaceae. Species ''Saccharopolyspora'' comprises the following species: * '' S. antimicrobica'' Yuan et al. 2008 * '' S. aridisoli'' Saygin et al. 2022 * "'' S. auranti ...
'' was discovered in 1985 in isolates from crushed
sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...
. The bacteria produce yellowish-pink aerial hyphae, with bead-like chains of spores enclosed in a characteristic hairy sheath. This genus is defined as aerobic, Gram-positive, nonacid-fast
actinomycetes The Actinomycetales is an order of Actinomycetota. A member of the order is often called an actinomycete. Actinomycetales are generally gram-positive and anaerobic and have mycelia in a filamentous and branching growth pattern. Some actinomycete ...
with fragmenting substrate mycelium. ''S. spinosa'' was isolated from soil collected inside a nonoperational sugar mill rum still in the
Virgin Islands The Virgin Islands ( es, Islas Vírgenes) are an archipelago in the Caribbean Sea. They are geologically and biogeographically the easternmost part of the Greater Antilles, the northern islands belonging to the Puerto Rico Trench and St. Cro ...
. Spinosad is a mixture of chemical compounds in the spinosyn family that has a generalized structure consisting of a unique tetracyclic ring system attached to an amino sugar (D-forosamine) and a neutral sugar (tri-''Ο''-methyl-L-rhamnose). Spinosad is relatively nonpolar and not easily dissolved in water. Spinosad is a novel mode-of-action insecticide derived from a family of natural products obtained by fermentation of ''S. spinosa''. Spinosyns occur in over 20 natural forms, and over 200 synthetic forms (spinosoids) have been produced in the lab. Spinosad contains a mix of two spinosoids, spinosyn A, the major component, and spinosyn D (the minor component), in a roughly 17:3 ratio.


Mode of action

Spinosad is highly active, by both contact and ingestion, in numerous insect species. Its overall protective effect varies with insect species and life stage. It affects certain species only in the adult stage, but can affect other species at more than one life stage. The species subject to very high rates of mortality as larvae, but not as adults, may gradually be controlled through sustained larval mortality. The mode of action of spinosoid insecticides is by a neural mechanism. The spinosyns and spinosoids have a novel mode of action, primarily targeting binding sites on nicotinic acetylcholine receptors (nAChRs) of the insect nervous system that are distinct from those at which other insecticides have their activity. Spinosoid binding leads to disruption of acetylcholine neurotransmission. Spinosad also has secondary effects as a γ-amino-butyric acid (GABA) neurotransmitter agonist. It kills insects by hyperexcitation of the insect nervous system. Spinosad so far has proven not to cause
cross-resistance Cross-resistance is when something develops resistance to several substances that have a similar mechanism of action. For example, if a certain type of bacteria develops resistance to one antibiotic, that bacteria will also have resistance to sev ...
to any other known insecticide.


Use

Spinosad has been used around the world for the control of a variety of insect pests, including
Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...
,
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 ...
,
Thysanoptera Thrips (order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
,
Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
, Orthoptera, and
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 ...
, and many others. It was first registered as a pesticide in the United States for use on crops in 1997. Its labeled use rate is set at 1 ppm (1 mg a.i./kg of grain) and its maximum residue limit (MRL) or tolerance is set at 1.5 ppm. Spinosad's widespread commercial launch was deferred, awaiting final MRL or tolerance approvals in a few remaining grain-importing countries. It is considered a natural product, thus is approved for use in organic agriculture by numerous nations. Two other uses for spinosad are for pets and humans. Spinosad has recently been used in oral preparations (as Comfortis) to treat '' C. felis'', the cat flea, in canines and felines; the optimal dose set for canines is reported to be 30 mg/kg. Spinosad is sold under the trade names, Comfortis, Trifexis, and Natroba. Trifexis also includes
milbemycin oxime Milbemycin oxime, sold under the brand name Interceptor among others, is a veterinary medication from the group of milbemycins, used as a broad spectrum antiparasitic. It is active against worms (anthelmintic) and mites (miticide). Mechanism of a ...
. Comfortis and Trifexis brands treat adult fleas on pets; the latter also prevents heartworm disease. Natroba is sold for treatment of human head lice. Spinosad is also commonly used to kill
thrips Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
.


Spinosyn A

Spinosyn A does not appear to interact directly with known insecticidal-relevant target sites, but rather acts via a novel mechanism. Spinosyn A resembles a GABA antagonist and is comparable to the effect of
avermectin The avermectins are a series of drugs and pesticides used to treat parasitic worms and insect pests. They are a group of 16-membered macrocyclic lactone derivatives with potent anthelmintic and insecticidal properties. These naturally occurring c ...
on insect neurons. Spinosyn A is highly active against neonate larvae of the tobacco budworm, ''
Heliothis virescens ''Chloridea virescens'', commonly known as the tobacco budworm, is a moth of the family Noctuidae found throughout the eastern and southwestern United States along with parts of Central America and South America. It is a major pest of field cro ...
'', and is slightly more biologically active than spinosyn D. In general, spinosyns possessing a methyl group at C6 (spinosyn D-related analogs) tend to be more active and less affected by changes in the rest of the molecule. Spinosyn A is slow to penetrate to the internal fluids of larvae; it is also poorly metabolized once it enters the insect. The apparent lack of spinosyn A metabolism may contribute to its high level of activity, and may compensate for the slow rate of penetration.


Resistance

Spinosad resistance has been found in ''
Musca domestica The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common f ...
'' by Liu & Yue 2000, in ''
Plutella xylostella The diamondback moth (''Plutella xylostella''), sometimes called the cabbage moth, is a moth species of the family Plutellidae and genus '' Plutella''. The small, grayish-brown moth sometimes has a cream-colored band that forms a diamond along ...
'' by Sayyed et al 2004, in ''
Bactrocera dorsalis ''Bactrocera dorsalis'', previously known as ''Dacus dorsalis'' and commonly referred to as the oriental fruit fly, is a species of tephritid fruit fly that is endemic to Southeast Asia. It is one of the major pest species in the genus ''Bactro ...
'' by Hsu & Feng 2006, in ''
Frankliniella occidentalis The western flower thrips 'Frankliniella occidentalis'' (Pergande)is an invasive pest insect in agriculture. This species of thrips is native to the Southwestern United States but has spread to other continents, including Europe, Australia (whe ...
'' by Bielza et al 2007, and in ''
Cydia pomonella The codling moth (''Cydia pomonella'') is a member of the Lepidopteran family Tortricidae. They are major pests to agricultural crops, mainly fruits such as apples and pears. Because the larvae are not able to feed on leaves, they are highly d ...
'' by Reyes et al 2007; see
Insecticide Resistance Action Committee The Insecticide Resistance Action Committee (IRAC) was formed in 1984 and works as a specialist technical group of the industry association CropLife to be able to provide a coordinated industry response to prevent or delay the development of insect ...

Arthropod Pesticide Resistance Database
for continued updates.


Safety and ecotoxicology

Spinosad has high efficacy, a broad insect pest spectrum, low mammalian toxicity, and a good environmental profile, a unique feature of the insecticide compared to others currently used for the protection of grain products. It is regarded as natural product-based, and approved for use in organic agriculture by numerous national and international certifications. Spinosad residues are highly stable on grains stored in bins, with protection ranging from 6 months to 2 years.
Ecotoxicology Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology ...
parameters have been reported for spinosad, and are: * in rat (''
Rattus norvegicus ''Rattus'' is a genus of muroid rodents, all typically called rats. However, the term rat can also be applied to rodent species outside of this genus. Species and description The best-known ''Rattus'' species are the black rat (''R. rattus'') ...
'' ), acute oral:  >5000 mg/kg (nontoxic) * in rat (''R. norvegicus''), acute dermal: LD50 >2000 mg/kg (nontoxic) * in California quail (''
Callipepla californica The California quail (''Callipepla californica''), also known as the California valley quail or Valley quail, is a small ground-dwelling bird in the New World quail family. These birds have a curving crest or '' plume'', made of six feathers, tha ...
'' ), oral toxicity: LD50 >2000 mg/kg (nontoxic) * in duck ('' Anas platyrhynchos domestica'' ), dietary toxicity: LC50 >5000 mg/kg (nontoxic) * in
rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
(''Oncorhynchus mykiss'' ), LC50-96h = 30.0 mg/L (slightly toxic) * in Honeybee (''
Apis mellifera The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bees worldwide. The genus name ''Apis'' is Latin for "bee", and ''mellifera'' is the Latin for "honey-bearing" or "honey carrying", ...
'' ), LD50 = 0.0025 mg/bee (highly toxic if directly sprayed on and of dried residues). Chronic exposure studies failed to induce tumor formation in rats and mice; mice given up to 51 mg/kg/day for 18 months resulted in no tumor formation. Similarly, administration of 25 mg/kg/day to rats for 24 months did not result in tumor formation.


Further reading


The non‐target impact of spinosyns on beneficial arthropodsSpinosad toxicity to pollinators and associated risk


References


External links

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