Trichogramma | |
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Female Trichogramma dendrolimi on egg of armyworm (Noctuidae) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Hymenoptera |
Family: | Trichogrammatidae |
Subfamily: | Trichogrammatinae |
Tribe: | Trichogrammatini |
Genus: | Trichogramma Westwood, 1833 |
Species | |
230+, see text |
Trichogramma is a genus of minute polyphagous wasps that are endoparasitoids of insect eggs. [1] Trichogramma is one of around 80 genera from the family Trichogrammatidae, with over 200 species worldwide. [2] [3] [4]
Although several groups of egg parasitoids are commonly employed for biological control throughout the world, Trichogramma spp. have been the most extensively studied. [5] More than a thousand papers have been published on Trichogramma species, and they are the most used biological control agents in the world. [6]
Trichogramma spp. are also of interest in neuroscience research, having fewer than 10,000 neurons, approaching the theoretical lower limit of the size of an insect brain, yet exhibiting complex behaviors to sustain their lives. [7]
Trichogramma have highly developed chemosensory organs due to their need to discriminate host from nonhost in a crowded environment. [3] Zhang et al. 1979 finds 13 sensilla types on the antennae, eyes, mouthparts, wing, leg, and external genitalia of T. dendrolimi . This is considered to generalize to the entire genus, and there may be more still undiscovered. [8]
To locate host eggs, adult females use chemical and visual signals, such as egg shape and colour. [3] After she finds a suitable egg, an experienced female attempts to determine if the egg has previously been parasitized, using her ovipositor and antennal drumming (tapping on the egg surface). Females also use antennal drumming to determine the size and quality of the target egg, which determines the number of eggs the female will insert. [9] A single female can parasitize up to 10 host eggs a day.
Trichogramma wasps are small and very uniform in structure, which causes difficulty in identifying the separate species. [10] [11] As females are all relatively similar, taxonomists rely upon examination of males to tell the different species apart, using features of their antennae and genitalia. [12] [13]
The first description of a Trichogramma species was in North America in 1871, by Charles V. Riley. He described the tiny wasps that emerged from eggs of the viceroy butterfly as Trichogramma minutum. [3] In taxonomy, original specimens are very important, as they are the basis of reference for subsequent descriptions of species. The original specimens, however, were lost. Riley also described a second species in 1879 as Trichogramma pretiosum, but these specimens were also lost. To correct these errors, entomologists returned to the areas where Riley originally found the species and obtained neotype specimens of T. minutum and T. pretiosum. These specimens are now preserved properly in the United States National Museum. [3] Currently, the number of Trichogramma species is over 200, but as of 1960, only some 40 species of Trichogramma had been described. [14]
Wolbachia is a widespread bacterial genus that infects insects' organs, most commonly the reproductive organs. [15] Wolbachia has been observed to alter the host's reproductive success upon infection. [15] Through a series of manipulations, Wolbachia-infected hosts transmit this intracellular bacterium to uninfected individuals. [15] [16] These manipulations include male killing (increasing ratio of infected females that can reproduce), feminization (males become fertile females), parthenogenesis, and cytoplasmic incompatibility. [16] Horizontal transfer of parthenogenesis-inducing Wolbachia, which has been observed in Trichogramma wasps, causes infected females to asexually produce fertile females and nonfunctional males. [17] The effects of this include potential speciation of Trichogramma, if Wolbachia is maintained long enough for genetic divergence to occur and for a new species of asexual wasps to become reproductively isolated. [17]
Transmission of the bacterium through horizontal transfer has been observed within the same species and among different species of Trichogramma, including T. kaykai, T. deion, T. pretiosum, and T. atopovirilia; however, limitations to transmission exist. [16] In vitro successful horizontal transfer is uncommon within Trichogramma, which suggests that the density of Wolbachia must be relatively high inside of the hosts' ovaries. [16] Cytoplasmic incompatibility of the host and bacterium can also be the source of this unsuccessful transfer in-vitro. [16] These limitations in vitro suggest that in nature, horizontal transfer by parthenogenesis-inducing Wolbachia may be a difficult and rare phenomenon. However, when looking at the Wolbachia-host associations, the Trichogramma-Wolbachia form a monophyletic group based on several Wolbachia-specific genes, which may be explained by horizontal transfer of Wolbachia between different species. [16] Therefore, although interspecific horizontal transfer of Wolbachia is limited in vitro, it is likely to occur quite frequently in nature and is not well understood yet.
The effects of Wolbachia in Trichogramma have several evolutionary implications. Commonly, uninfected wasps are unable to breed with infected wasps. [18] Many generations of reproductive isolation of these different groups may result in speciation. [18] In addition, some hosts can evolve with a dependency on Wolbachia for core reproductive functions, such as oogenesis, so that eventually an infection is a requirement for successful reproduction. [18] Finally, Wolbachia can influence gender determination in its hosts so that more females are successfully born. This results in a reversal in sexual selection, where females must compete for male mates, which has evolutionary implications as it exposes different phenotypes to natural selection. [18]
Trichogramma spp. have been used for control of lepidopteran pests for many years. They can be considered the Drosophila of the parasitoid world, as they have been used for inundative releases and much understanding today comes from experiments with these wasps. [19] [20]
Entomologists in the early 1900s began to rear Trichogramma spp. for biological control. T. minutum is one of the most commonly found species in Europe and was first mass reared in 1926 on eggs of Sitotroga cerealella . [21] T. minutum has been investigated as a method of biological control of the Choristoneura fumiferana, a major pest of spruce and fir forests. [22]
Nine species of Trichogramma are produced commercially in insectaries around the world, with 30 countries releasing them. Trichogramma wasps are used for control on numerous crops and plants; these include cotton, sugarcane, vegetables, sugarbeets, orchards, and forests. [23] Some of the pests controlled include cotton bollworm ( Helicoverpa armigera ), codling moth ( Cydia pomonella ), lightbrown apple moth ( Epiphyas postvittana ), and European corn borer ( Ostrinia nubilalis ).
Trichogramma species vary in their host specificity. This can lead to nontarget hosts being parasitized. This, in turn, can cause problems by reducing the amount of parasitism of the target host, and depending on the rate of parasitism, nontarget effects could be significant on nontarget host populations. Research is being done on the use of Trichogramma wasps to control populations of spruce bud moth ( Zeiraphera canadensis), which damages white spruce trees. [24]
Trichogramma began to be seriously used in the 1990s in China. Since then some applications have fallen out of use due to the rise of Bt crops because Bt is also toxic to the parasitoid. Future expansion of Bt in China is expected, and this threatens some uses of Trichogramma, however for some crops/pests it remains the better option and so is expected to continue instead of expanded Bt in those applications. Trichogramma will be especially necessary for resistance management if Bt maize/Bt corn is widely adopted. [8]
In 2021 the National Trust in England embarked on a trial of using Trichogramma evanescens , which parasitises clothes moth eggs, in conjunction with pheromones to control common clothes moths, which cause serious damage to carpets, furniture, clothing and other wool and silk objects in historic buildings. [25] The trial was abandoned in 2023; while the microwasps performed well at reducing moth populations in combination with pheromones, they were no better than pheromones alone. It was suspected that the high interiors may not have been suitable and the Trust may continue to use the wasps in smaller stores or where they can be sited close to a known infestation source. [26] [27]
The most commonly used species for biological control are T. atopovirilia , T. brevicapillum , T. deion , T. exiguum , T. fuentesi , T. minutum , T. nubilale , T. platneri , T. pretiosum , and T. thalense . [3]
T. pretiosum is the most widely distributed species in North America. [3] It is a more generalized parasitoid, able to parasitise a range of different species. It has been the focus of many research studies and has been successfully reared on 18 genera of Lepidoptera. T. pretiosum was introduced into Australia in the 1970s as part of the Ord River Irrigation Area IPM scheme. [28] [29]
Trichogramma carverae is mainly used for light brown apple moth and codling moth control, and is predominately used in orchards. [30] In Australia, T. carverae is used for biological control of light brown apple moth in vineyards. Though Australia has its own native Trichogramma species, not much work has been undertaken to use them commercially for biological control within Australia. [31]
Light brown apple moth is common throughout Australia and is polyphagous on more than 80 native and introduced species. The larvae cause the most damage, especially to grape berries, as their feeding provides sites for bunch rot to occur. [32] Losses in the crops can amount up to $2000/ha in one season. It is very predominant in areas such as the Yarra Valley. Insecticide use is not a choice method for most growers, who prefer a more natural means of controlling pests. As a result, Trichogramma wasps were considered a good candidate for biological control, even more so as the moth larvae are difficult to control with insecticide. Moreover, light brown apple moths are relatively vulnerable to egg parasitism, with their eggs being laid in masses of 20–50 on the upper surfaces of basal leaves in grapevines.
Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also involves an active human management role. It can be an important component of integrated pest management (IPM) programs.
Chalcid wasps 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, meaning the vast majority have yet to be discovered and described. The name "chalcid" is often confused with the name "chalcidid", though the latter refers strictly to one constituent family, the Chalcididae, rather than the superfamily as a whole; accordingly, most recent publications (e.g.,) use the name "chalcidoid" when referring to members of the superfamily.
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 parasitism, distinguished by the fatal prognosis for the host, which makes the strategy close to predation.
The Tachinidae are a large and variable family of true flies within the insect order Diptera, with more than 8,200 known species and many more to be discovered. Over 1,300 species have been described in North America alone. Insects in this family commonly are called tachinid flies or simply tachinids. As far as is known, they all are protelean parasitoids, or occasionally parasites, of arthropods, usually other insects. The family is known from many habitats in all zoogeographical regions and is especially diverse in South America.
Wolbachia is a genus of gram-negative bacteria infecting many species of arthropods and filarial nematodes. The symbiotic relationship ranges from parasitism to obligate mutualism. It is one of the most common parasitic microbes of arthropods, and is possibly the most widespread reproductive parasite bacterium in the biosphere. Its interactions with hosts are complex and highly diverse across different host species. Some host species cannot reproduce, or even survive, without Wolbachia colonisation. One study concluded that more than 16% of neotropical insect species carry bacteria of this genus, and as many as 25 to 70% of all insect species are estimated to be potential hosts.
Manduca quinquemaculata, the five-spotted hawkmoth, is a brown and gray hawk moth of the family Sphingidae. The caterpillar, often referred to as the tomato hornworm, can be a major pest in gardens; they get their name from a dark projection on their posterior end and their use of tomatoes as host plants. Tomato hornworms are closely related to the tobacco hornworm Manduca sexta. This confusion arises because caterpillars of both species have similar morphologies and feed on the foliage of various plants from the family Solanaceae, so either species can be found on tobacco or tomato leaves. Because of this, the plant on which the caterpillar is found does not indicate its species.
The almond moth or tropical warehouse moth is a small, stored-product pest. Almond moths infest flour, bran, oats, and other grains, as well as dried fruits. It belongs to the family of snout moths (Pyralidae), and more specifically to the tribe Phycitini of the huge snout moth subfamily Phycitinae. This species may be confused with the related Indian mealmoth or the Mediterranean flour moth, which are also common pantry pests in the same subfamily.
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps (Pompilidae) exclusively attack spiders.
The Trichogrammatidae are a family of small endoparasitoid wasps in the superfamily Chalcidoidea that include some of the smallest of all insects, with most species having adults less than 1 mm in length, with species of Megaphragma having an adult body length less than 300 μm. Over 840 species are placed in about 80 genera; their distribution is worldwide.
The Mediterranean flour moth or mill moth is a moth of the family Pyralidae. It is a common pest of cereal grains, especially flour. This moth is found throughout the world, especially in countries with temperate climates. It prefers warm temperatures for more rapid development, but it can survive a wide range of temperatures.
Encarsia formosa is a species of chalcidoid wasp and a well known parasitoid of greenhouse whitefly, one of the first to be used commercially for biological pest control, from the 1920s. Its use fell with commercial pesticides in the 1940s, but rose again from the 1970s.
Choristoneura fumiferana, the eastern spruce budworm, is a species of moth of the family Tortricidae native to the eastern United States and Canada. The caterpillars feed on the needles of spruce and fir trees. Eastern spruce budworm populations can experience significant oscillations, with large outbreaks sometimes resulting in wide scale tree mortality. The first recorded outbreaks of the spruce budworm in the United States occurred in about 1807, and since 1909 there have been waves of budworm outbreaks throughout the eastern United States and Canada. In Canada, the major outbreaks occurred in periods circa 1910–20, c. 1940–50, and c. 1970–80, each of which impacted millions of hectares of forest. Longer-term tree-ring studies suggest that spruce budworm outbreaks have been recurring approximately every three decades since the 16th century, and paleoecological studies suggest the spruce budworm has been breaking out in eastern North America for thousands of years.
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.
Zeiraphera canadensis, the spruce bud moth, is a moth of the family Tortricidae. It is a small brown moth mainly found in North America, specifically New Brunswick, Quebec, and the north-eastern United States. The adult moth flutters quickly, and stays low among trees during the day and higher above tree cover after sunset. The spruce bud moth relies primarily on the white spruce tree as a host plant. Both male and female spruce bud moths mate multiply, however males have the ability to secrete accessory gland proteins that prevent female re-mating. The moth is univoltine, meaning only one generation hatches per year, and its eggs overwinter from July to May. The species Z. ratzeburgiana is very similar to Z. canadensis and can only be distinguished by the presence of an anal comb in Z. canadensis.
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Trichogramma japonicum is a minute wasp parasitoid from the Trichogrammatidae family in the order Hymenoptera. T. japonicum parasitizes the eggs of many pest species, especially Lepidoptera found in many monocultures. They are entomophagous parasitoids that deposit their eggs inside the host species' egg, consuming the host egg material and emerging from the egg once development is complete. T. japonicum can be found naturally in rice ecosystems, but are dispersed commercially to many monocultures as a biological control. The mitochondrial genomes of T. japonicum are significantly rearranged when comparing it to related insects.
Tetrastichus coeruleus is a gregarious koinobiont wasp which can be used as a biological control agent for the common asparagus beetle.