Parasitoid Eggs Research Articles

Differential immune responses in new and old fruit fly-parasitoid associations: Implications for their management.

The oriental fruit fly, Bactrocera dorsalis (Hendel), and marula fruit fly, Ceratitis cosyra (Walker), are major fruit-infesting tephritids across sub-Saharan Africa. Biological control of these pests using parasitic wasps has been widely adopted but with varying levels of success. Most studies investigating host-parasitoid models have focused on functional and evolutionary aspects leaving a knowledge gap about the physiological mechanisms underpinning the efficacy of parasitoids as biocontrol agents of tephritids. To better understand these physiological mechanisms, we investigated changes in the cellular immune responses of C. cosyra and B. dorsalis when exposed to the parasitic wasps, Diachasmimorpha longicaudata (Ashmaed) and Psyttalia cosyrae (Wilkinson). We found that B. dorsalis was more resistant to parasitisation, had a higher hemocyte count, and encapsulated more parasitoid eggs compared to C. cosyra, achieving up to 100% encapsulation when exposed to P. cosyrae. Exposing B. dorsalis to either parasitoid species induced the formation of a rare cell type, the giant multinucleated hemocyte, which was not observed in C. cosyra. Furthermore, compared to P. cosyrae-parasitized larvae, those of both host species parasitized by D. longicaudata had lower encapsulation rates, hemocyte counts and spreading abilities and yielded a higher number of parasitoid progeny with the highest parasitoid emergence (72.13%) recorded in C. cosyra. These results demonstrate that cellular immune responses are central to host-parasitoid interaction in tephritid fruit flies and further suggest that D. longicaudata presents greater potential as a biocontrol agent of B. dorsalis and C. cosyra in horticultural cropping systems.

Biological control in a changing climate: plant-mediated impact of elevated CO2 concentration on Lobesia botrana eggs and egg parasitism by Trichogramma cacoeciae

Climate change can affect biological pest control by altering trophic interactions. Elevated carbon dioxide (CO2) concentrations can reduce host plant quality and, in turn, alter herbivore and natural enemy preference and performance. Using the Geisenheim VineyardFACE (free-air carbon dioxide enrichment) facility, we studied plant- and herbivore-mediated bottom-up effects of elevated CO2 concentration on the European grapevine moth, Lobesia botrana, and the parasitoid Trichogramma cacoeciae. Grapevine inflorescences of two cultivars cultivated at ambient or elevated CO2 (aCO2 and eCO2: 400 and 480 ppm) in the VineyardFACE were incorporated into L. botrana artificial diet. Eggs laid by the respective adults were parasitized by T. cacoeciae. Egg size and emergence rate of L. botrana as well as parasitism rate, parasitoid emergence rate and egg size preference of T. cacoeciae were evaluated. We observed an indirect grapevine cultivar-dependent bottom-up effect of CO2 on both herbivore and egg parasitoid. Compared to aCO2, eCO2 resulted in larger host eggs and higher parasitism rates regarding Riesling-feeding but not regarding Cabernet Sauvignon-feeding L. botrana larvae. Parasitoid emergence rate was higher when L. botrana had fed on Riesling compared to Cabernet Sauvignon-diet. Egg size preference depended on the host’s diet: T. cacoeciae preferred larger L. botrana eggs when the larvae had fed on grapevine-containing diet but not when they fed on standard artificial diet. Our results highlight the importance of the host’s diet for the parasitoid’s preference and performance. They furthermore suggest that the future efficiency of L. botrana-biocontrol by T. cacoeciae will not decrease under elevated CO2 concentrations.

Laboratory evaluation of the compatibility of Beauveria bassiana with the egg parasitoid Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) for joint application against the oriental fruit moth Grapholita molesta (Lepidoptera: Tortricidae).

The entomopathogenic fungus Beauveria bassiana and the egg parasitoid Trichogramma dendrolimi can both contribute to biological control of the global fruit borer Grapholita molesta. To derive insights for optimizing their combined application in augmentation programs, we assayed fungal pathogenicity to both G. molesta (eggs, larvae and adults) and adult parasitoids, and assessed wasp acquisition and transmission of fungal spores following their emergence from B. bassiana-treated host eggs. Concentrations of 108 conidia mL-1 of B. bassiana and higher caused virtually complete mortality of G. molesta larvae, but less than 30% mortality of eggs, and female moths surviving treatments had reduced fecundity. More than 80% of adult T. dendrolimi survived B. bassiana treatments of 107 conidia mL-1 , and more than 60% survived 109 conidia mL-1 , with surviving females achieving reproductive success equivalent to controls. Parasitoid females preferred healthy eggs over B. bassiana-infected ones in choice tests; wasps emerging from treated eggs carried about 104 conidia each and contributed an additional 11% host mortality in trials combining both agents. Our results indicate that combined applications of B. bassiana and T. dendrolimi can have complimentary impacts on G. molesta, the wasps compensating for low fungal pathogenicity to eggs and their progeny potentially aiding in subsequent disease transmission. Although foraging wasps tended to avoid infected eggs, negative interactions between the two agents might be further mitigated by timing B. bassiana applications from late instar larva to early moth stage, and T. dendrolimi releases several days later to coincide with peak oviposition periods. © 2022 Society of Chemical Industry.

Biology of Apanteles Baoris Wilkinson (Hymenoptera: Braconide) A Larval Parasitoid of Chapra Maathas Fab

ApantelesbaorisWilkinson is potential biocontrol agent of Chapramathias Fab. a paddy pest in Kolhapur. It attacks about 86% caterpillars of C. mathias. In the present paper life cycle, longevity, Sex ratio and behavioral aspects viz; mating and oviposition have been studied in detail. The life cycle of the parasitoid egg to adult emergence have been completed within 17 days. Egg hatching period was 3 days, larval period was 8-9 days and pupal period was 5-6 days. Mating takes place within one hour of their emergence from cocoons. Mating occurred at morning hours. Oviposition is completed within 3 seconds. In a single host the parasitoid can lay on an average 55 eggs of which progeny production obtained was 46 (average). Sex ratio of adult parasitoids was found favoring females. The results are useful for mass rearing of the above parasitoids.

Reduction of larval resistance and adult reproductive capacity in Spodoptera littoralis at different degrees of superparasitization by Microplitis rufiventris

AbstractThe solitary endoparasitoid, Microplitis rufiventris Kok, attacks and can develop in the first three instars of Spodoptera littoralis (Boisd.) larvae with preference for third‐instar. We used the last three instars to show the effect of increasing superparasitization on host resistance and reproductive capacity of surviving moths of S. littoralis that had been parasitized during their newly moulted fourth, fifth and sixth instar larvae. The degree of resistance of late instars and reproductive capacity of surviving moths varied significantly as a function of both, the virulence factors (number of wasp eggs, venom and polydnavirus) and size of host instars. Increasing number of parasitism events overcame resistance in larger host instars. The host survival was increased with the host instar and decreased with the number of ovipositions, while the chances that at least one wasp emerges follow a reverse pattern. When the survived parasitized hosts were able to pupate, parasitism usually reduced their weight, but sometimes the host pupal weight was increased. Furthermore, for surviving hosts, the weight of egg masses produced in female moths, decreased with increasing superparasitization, that is, the number of ovipositions during their larval stage. The ‘threshold’ number of parasitoid eggs, which allows the development of host, accounts for three parasitoid eggs in the fourth and fifth host instar and five parasitoid eggs in the sixth instar. The survived parasitized hosts (L4–L6) exhibited fitness‐related costs in terms of smaller size and lower reproductive output.

Parasitism of Diaphorina citri (Hemiptera: Liviidae) by Tamarixia radiata (Hymenoptera: Eulophidae) on residential citrus in Texas: Importance of colony size and instar composition

Diaphorina citri (Hemiptera: Liviidae) is an invasive citrus pest that colonizes young flush shoots and spreads huanglongbing, a lethal citrus disease. Effects of D. citri colony size (nymphs per shoot) and instar composition on parasitism rates by the nymphal ectoparasitoid, Tamarixia radiata (Hymenoptera: Eulophidae), were evaluated on residential citrus in South Texas. From 2016 to 17, D. citri colony sizes and apparent parasitism (T. radiata adult emergence) were monitored monthly on grapefruit, lemon, lime, and orange trees at 12 residential sites. In 2019, size and instar composition of colonies and actual parasitism (mummies and nymphs with parasitoid larvae or eggs) were monitored biweekly on citrus trees at a residential park. Psyllid nymphs were found year-round at these sites with highest densities from late summer to fall and lowest densities in winter. Mean apparent parasitism was independent of citrus species and ranged from 23% in April 2016 to 4% in February 2017. Mean actual parasitism ranged from 1.5% in August to 33.4% in November 2019. Because actual parasitism of 3rd or younger instars was very rare, a ‘host patch’ was defined as the cluster(s) of 4th to 5th instars within a colony infesting a shoot. Based on apparent or actual parasitism, host density was positively related to discovery of D. citri colonies but inversely related to percent parasitism by T. radiata. The inability of T. radiata to achieve high rates of field parasitism under a wide range of host densities could explain, in part, its low impact against D. citri on residential citrus.

Parasitoid age and host age interact to improve life history parameters and rearing of Trichogramma euproctidis

ABSTRACT Trichogramma euproctidis (Girault) is an egg parasitoid under consideration for mass production and augmentative biological control of major lepidopteran pests in Iran and other countries. The main objective of this research was to determine the effects of T. euproctidis female age and Ephestia kuehniella Zeller egg age on life history parameters of T. euproctidis. Experimental design involved exposing 1-, 2-, 3-, or 4-d-old E. kuehniella eggs to 1-, 2-, 3-, or 4-d-old T. euproctidis females in glass test tubes. Results indicated that host egg age and parasitoid female age interacted significantly to improve parasitism rate, progeny emergence rate, sex ratio, longevity, and fecundity of T. euproctidis. The age of T. euproctidis females affected parasitism rate; 1-d-old females, rather than the other ages, parasitised more E. kuehniella eggs. The highest mean total fecundity (81.62 eggs) was recorded from adult progeny produced by 1-d-old T. euproctidis females reared from 1-d-old E. kuehniella eggs. Trichogramma euproctidis development time increased as the age of E. kuehniella eggs increased, but the parasitoid female age and host egg age interaction was not significant. A life table analysis confirmed the results that 1-d-old T. euproctidis females and 1-d-old E. kuehniella eggs resulted in optimal effects on T. euproctidis life history. This study implies that mass rearing systems designed to expose young-aged T. euproctidis females to young-aged E. kuehniella eggs would maximise T. euproctidis progeny production.

Amount of venom that Leptopilina species inject into Drosophila melanogaster larvae in relation to parasitic success

The Drosophila endoparasitoid wasps Leptopilina boulardi and L. heterotoma (Hymenoptera: Cynipidae) are pro-ovigenic species, i.e., females contain their lifetime number of mature eggs at emergence. They are therefore able to immediately parasitize many hosts when present. In response to parasitoid oviposition, the larval host D. melanogaster can mount an immune response, encapsulation, that can destroy the parasitoid eggs. This response is counteracted by the venom the wasp injects during oviposition. Here, we estimated the amount of venom injected into a D. melanogaster host larva using immunodetection of venom proteins and we attempted to correlate this amount with the number of eggs a female can lay on successive days. The venom reservoir of L. boulardi contains enough venom for at least 100 ovipositions while that of L. heterotoma contains venom for about 16 ovipositions. While a female L. boulardi may have enough venom for three days of parasitism when 20 or 40 larval hosts were presented each day, L. heterotoma certainly needs to synthesize new venom to parasitize the number of hosts offered. Interestingly, parasitism stopped (L. boulardi), egg protection (L. heterotoma) and egg hatching decreased (both species) after three days of parasitism. Thus, although venom does not appear to be a limiting factor for parasitism, our data suggest that it may have less effectiveness on the egg protection and on egg/host development after high repetitive egg laying.

Survival rates of the first and second offspring of Echthrodelphax fairchildii Perkins (Hymenoptera: Dryinidae) under self and conspecific superparasitism: The effects of body size of ovipositing females

AbstractThe effects of ovipositing female body size on the survival of the first and second offspring under self and conspecific superparasitism have not been determined. Here, we report the importance of the body size of ovipositing females for three intervals (0, 1, and 24 h) between first and second ovipositions using a semi‐solitary ectoparasitoid, Echthrodelphax fairchildii, and fourth‐instar nymphs of its host, the planthopper Laodelphax striatellus. We addressed the case in which the first and second parasitoid eggs were laid on different sides of the same host. The second ovipositing female killed the previous offspring using the sting, but when the oviposition intervals were 0 and 1 h, the elimination was unprofitable because both offspring often emerged under non‐probing superparasitism. The survival rate of the second offspring decreased with increasing oviposition intervals under non‐probing superparasitism, whereas that of the first offspring was independent of oviposition intervals. Under non‐probing superparasitism, the survival rates of the first and second offspring were higher under conspecific superparasitism than under self superparasitism, especially when the first and/or second ovipositing females were small. Large mothers ensured high survival rates of their offspring under non‐probing superparasitism, except the survival rate of the second offspring under conspecific superparasitism, which was negatively associated with the first female's size. Thus, the first offspring from small mothers were likely to lose the competition to the second offspring. Under probing superparasitism, the second offspring survival rate was positively associated with the mother's size, suggesting that offspring, not ovipositing females, release agents affecting the mother‐size effect.

The effects of floral nectar, extrafloral nectar and hemipteran honeydew on the fitness of Tamarixia radiata (Hymenoptera: Eulophidae), a parasitoid of Diaphorina citri

Tamarixia radiata parasitizes nymphs of Diaphorina citri, a global citrus pest that vectors a bacterium that causes a lethal citrus disease, huanglongbing. The effects of four species of potted flowering native California plants, potted flowering buckwheat (Fagopyrum esculentum) and Euphorbia marginata (both non-native), honeydew from D. citri and Coccus hesperidum, cut flowers from lemon and orange trees, 50% honey-water, and water only on the longevity, survivorship and reproduction of T. radiata was investigated in the laboratory. Fecundity was measured by counting egg load of parasitoid cohorts ~15 h of age at time of set up and those that were removed for dissection from test arenas at 1, 6, and 18 days after introduction, or at time of death. Maximum survival of female T. radiata was 34 days on honey-water. Survival on honey-water, buckwheat and C. hesperidum honeydew was statistically equivalent, and these three food treatments significantly enhanced parasitoid survival when compared with all remaining food treatments. Female T. radiata fed on D. citri honeydew survived an average of 5 days, which was 3 days longer, on average, than those provided with water only. Parasitoid egg load significantly decreased with increasing days alive, thereby demonstrating the synovigenic nature of T. radiata. Parasitoids that fed on buckwheat flowers and died from natural causes had, on average, 5 more mature eggs in their ovaries at time of death when compared to parasitoids that died when provided access to other experimental sugar sources that were tested. These results suggest that buckwheat may be a useful insectary plant in citrus orchards that could enhance the efficacy of T. radiata against D. citri.

Impact of Temperature on the Immune Interaction between a Parasitoid Wasp and Drosophila Host Species.

Simple SummaryGlobal warming affects most species and their interaction s. Insects are ectotherms, meaning their body temperature is affected by the ambient temperature. This is particularly important for koinobiont parasitoids, insects that keep their host insect alive during development of their eggs and larvae, the host eventually being consumed before adult parasitoids emerge. Temperature changes could therefore affect parasitoids directly and/or indirectly through their impact on the host. Here, we tested the effect of temperature on the parasitic success of two parasitoid lines on two host species, and on each partner independently, to determine whether the host immune response and/or the parasitoid venom proteins, injected with the egg to counteract the host immune response, were affected. The host’s immune defense consists of forming a capsule surrounding the parasitoid egg. In half of the interactions tested, the parasitic success increased with temperature. For one, the increase appeared to result solely from an increased capacity of the parasitoid to escape from a capsule, while for the second, it also appeared to involve a decrease in host encapsulation capacity. Finally, we observed a strong change in venom composition depending on the rearing temperature which may partially explain the change in parasitic success.Temperature is particularly important for ectotherms, including endoparasitoid wasps that develop inside another ectotherm host. In this study, we tested the impact of three temperatures (20 °C, 25 °C and 30 °C) on the host–parasitoid immune interaction using two Drosophila host species (Drosophila melanogaster and D. yakuba) and two parasitoid lines of Leptopilina boulardi. Drosophila’s immune defense against parasitoids consists of the formation of a melanized capsule surrounding the parasitoid egg. To counteract this response, Leptopilina parasitoids rely on the injection of venom during oviposition. Here, we tested the effect of temperature on parasitic success and host encapsulation capacity in response to a parasitoid egg or other foreign body. Increased temperature either promoted or did not affect the parasitic success, depending on the parasitoid–host pairs considered. The mechanisms behind the higher success seemed to vary depending on whether the temperature primarily affected the host immune response or also affected the parasitoid counter-immune response. Next, we tested the effect of parasitoid rearing temperature on its success and venom composition. Venom composition varied strongly with temperature for both parasitoid lines, partially consistent with a change in their parasitic success. Overall, temperature may have a significant impact on the host–parasitoid immune interaction.

Proteomics of purified lamellocytes from Drosophila melanogaster HopTum-l identifies new membrane proteins and networks involved in their functions

In healthy Drosophila melanogaster larvae, plasmatocytes and crystal cells account for 95% and 5% of the hemocytes, respectively. A third type of hemocytes, lamellocytes, are rare, but their number increases after oviposition by parasitoid wasps. The lamellocytes form successive layers around the parasitoid egg, leading to its encapsulation and melanization, and finally the death of this intruder. However, the total number of lamellocytes per larva remains quite low even after parasitoid infestation, making direct biochemical studies difficult. Here, we used the HopTum-l mutant strain that constitutively produces large numbers of lamellocytes to set up a purification method and analyzed their major proteins by 2D gel electrophoresis and their plasma membrane surface proteins by 1D SDS-PAGE after affinity purification. Mass spectrometry identified 430 proteins from 2D spots and 344 affinity-purified proteins from 1D bands, for a total of 639 unique proteins. Known lamellocyte markers such as PPO3 and the myospheroid integrin were among the components identified with specific chaperone proteins. Affinity purification detected other integrins, as well as a wide range of integrin-associated proteins involved in the formation and function of cell-cell junctions. Overall, the newly identified proteins indicate that these cells are highly adapted to the encapsulation process (recognition, motility, adhesion, signaling), but may also have several other physiological functions (such as secretion and internalization of vesicles) under different signaling pathways. These results provide the basis for further in vivo and in vitro studies of lamellocytes, including the development of new markers to identify coexisting populations and their respective origins and functions in Drosophila immunity.

The remarkable biology of a new species of Gelis Thunberg, 1827 (Ichneumonidae, Phygadeuontinae), a solitary endoparasitoid of fresh eggs of Timarcha (Coleoptera, Chrysomelidae)

A new species, Gelis timarchae Schwarz, Shaw & Kan, is figured and described from specimens reared as a solitary endoparasitoid of fresh eggs of Timarcha nicaeensis in the south of France. Oviposition behaviour of the adult parasitoid, directly into the host cytoplasm, is described and links to videos are given. This appears to be the first record of any ichneumonid developing as an endoparasitoid of an insect egg, and it is a major departure from hitherto known ectoparasitoid (or spiders’ egg-predation) behaviour in the genus Gelis. Fluid from the host egg issuing from the base of the parasitoid’s ovipositor early in the oviposition process is interpreted as a necessary reduction of hydrostatic pressure before the parasitoid egg can be forced down the ovipositor. The egg and first instar larva are figured; the latter is caudate, with the caudal appendage very unusual in being bifurcate. The complex phenology and diapause of the parasitoid were investigated partly experimentally; it is broadly bivoltine with a prepupal diapause in summer, but extra generations and prolonged diapause were both also seen.

Preferential Parasitism of Ooencyrtus mirus (Hymenoptera: Encyrtidae) on Bagrada hilaris (Hemiptera: Pentatomidae) Regardless of Rearing Host

Abstract The invasive stink bug, Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), is a serious pest of cole crops. Studies are underway to assess the potential of an exotic egg parasitoid from Pakistan, Ooencyrtus mirus Triapitsyn & Power (Hymenoptera: Encyrtidae), as a biological control agent for this pest. In the present study, the ovipositional preference of O. mirus reared for multiple generations on B. hilaris, Thyanta pallidovirens (Stal), or Nezara viridula (Linnaeus) (Hemiptera: Pentatomidae) for eggs of these three stink bug species was evaluated. The first host accepted for oviposition, the number of parasitoid eggs (as indicated by pedicels) laid on each host egg at different time intervals, and the number of wasps that emerged from parasitized eggs were recorded. Results show that O. mirus prefers eggs of its primary host, B. hilaris, for oviposition over the alternate hosts tested regardless of whether the parasitoids were reared on the primary or alternate hosts. The percent parasitism in the first 2 h of exposure also was higher on B. hilaris eggs although it was not significantly different from T. pallidovirens eggs for parasitoids reared on B. hilaris and N. viridula eggs. For all parasitoid populations, the mean number of emerged wasps per host egg ranged from 0.9 to 1.1 with no significant differences. Bagrada hilaris eggs were significantly smaller than T. pallidovirens and N. viridula eggs and female wasps that emerged from B. hilaris eggs had significantly shorter body length and head width than those that emerged from T. pallidovirens and N. viridula eggs.

Parasitoid-mediated indirect interactions between unsuitable and suitable hosts generate apparent predation in microcosm and modeling studies.

Parasitoids used as biological control agents often parasitize more than a single host species and these hosts tend to vary in suitability for offspring development. The population dynamics of parasitoids and hosts may be altered by these interactions, with outcomes dependent on the levels of suitability and acceptance of both host species. Parasitism of individuals of an unsuitable host species may indirectly increase populations of a suitable host species if eggs laid into unsuitable hosts do not develop into adult parasitoids. In this case, the unsuitable host is acting as an egg sink for parasitoids and this can reduce parasitism of suitable hosts under conditions of egg limitation. We studied parasitoid‐mediated indirect interactions between two aphid hosts, Aphis glycines (the soybean aphid) and A. nerii (the milkweed, or oleander aphid), sharing the parasitoid Aphelinus certus. While both of these aphid species are accepted by A. certus, soybean aphid is a much more suitable host than milkweed aphid is. We observed a drastic reduction of parasitoid offspring production (45%) on the suitable host in the presence of the unsuitable host in microcosm assays. Aphelinus certus females laid eggs into the unsuitable hosts (Aphis nerii) in the presence of the suitable host leading to egg and/or time limitation and reduced fitness. The impact of these interactions on the equilibrium population sizes of the three interacting species was analyzed using a consumer–resource modeling approach. Both the results from the laboratory experiment and the modeling approaches identified apparent predation between soybean aphid and milkweed aphid, in which milkweed aphid acts as a sink for parasitoid eggs leading to an increase in the soybean aphid population. The presence of soybean aphids had the opposite effect on milkweed aphid populations as it supported increases in parasitoid abundance and thus reduced the fitness and abundance of this aphid species.

Parasitoid wasp venom vesicles (venosomes) enter Drosophila melanogaster lamellocytes through a flotillin/lipid raft-dependent endocytic pathway

ABSTRACT Venosomes are extracellular vesicles found in the venom of Leptopilina endoparasitoids wasps, which transport and target virulence factors to impair the parasitoid egg encapsulation by the lamellocytes of their Drosophila melanogaster host larva. Using the co-immunolocalization of fluorescent L. boulardi venosomes and one of the putative-transported virulence factors, LbGAP, with known markers of cellular endocytosis, we show that venosomes endocytosis by lamellocytes is not a process dependent on clathrin or macropinocytosis and internalization seems to bypass the early endosomal compartment Rab5. After internalization, LbGAP colocalizes strongly with flotillin-1 and the GPI-anchored protein Atilla/L1 (a lamellocyte surface marker) suggesting that entry occurs via a flotillin/lipid raft-dependent pathway. Once internalized, venosomes reach all intracellular compartments, including late and recycling endosomes, lysosomes, and the endoplasmic reticulum network. Venosomes therefore enter their target cells by a specific mechanism and the virulence factors are widely distributed in the lamellocytes’ compartments to impair their functions.

Oviposition decisions in an endoparasitoid under self-superparasitism conditions

Superparasitism is a widespread phenomenon. Having accepted superparasitism, mated female parasitoids must decide on the sex of each egg they subsequently lay into the same host. Theory predicts that this decision is either based on host quality, when more male eggs are laid in hosts that are already parasitized because they are perceived to be of poorer quality; or more eggs are laid of the sex that is most likely to be a strong larval competitor, i.e. generally females. Anastatus disparis is a facultative endoparasitic egg parasitoid. We used ‘artificial’ hosts to explore outcomes of decision making by A. disparis during superparasitism under a manipulated absence of larval competition. When only one egg was laid it was always female. As the number of eggs laid increased, so more of them were male. This supports the theory that oviposition decisions are based on host quality; more male eggs were laid in hosts that were already parasitized and thus of poorer quality. In a second experiment, eggs were exposed to parasitoids for different periods of time. Half the eggs were dissected to determine the number of parasitoid eggs that had been laid. The remaining eggs were incubated and the number and sex of offspring that ultimately emerged, following larval competition, were recorded. Under superparasitism conditions fierce larval competition ensued; only one offspring survived and they were predominantly female. In conclusion, oviposition decisions by female A. disparis accepting self-superparasitism were made based on host quality.

Developmental biology of Platygaster diplosisae Risbec and Aprostocetus procerae Risbec

Platygaster diplosisae (Risbec, 1956) and Aprostocetus procerae (Risbec, 1956) are ovo-larval and pupal parasitoids, respectively of Orseolia oryzivora (H & G). The reproductive biology of the two parasitoids was studied by authors, but their developmental biology was not yet explored. Mature rice galls due to O. oryzivora were collected from irrigated rice fields of Karfiguela and Boulbi, located in Western and Central Burkina Faso respectively. They were kept in wooden cages (45.5 cm × 44.7 cm × 59.5 cm) or plastic buckets (32 cm × 29 cm) covered with a fine mesh mosquito net to prevent insects from escaping after emergence. Fourteen-day rice plants of the variety FKR 28 were infested by adults of O. oryzivora in two metal cages (1.52 m × 1.26 m 1.65 m) (10 pairs of adults for each cage). In this way, it was possible to maintain a continuous culture of O. oryzivora that allowed the mass rearing of the parasitoids. The studied biological parameters of the parasitoids included, duration of post-embryonic development, lifespan, fecundity and fertility. The results revealed that the development time of A. procerae from egg to adult was 28 ± 6.18 days and that of P. diplosisae 33 ± 6.94 days. The mean incubation time of P. diplosisae eggs was 16 ± 1.98 days and that of A. procerae was 3.2 ± 1.78 days. Each of the two parasitoids exhibited three stages of larval development. The mean durations of the three larval stages of A. procerae were 5 ± 2.78, 3 ± 1.14 and 3 ± 0.55 days, respectively. For P. diplosisae, these figures were 2.2 ± 0.54 and 3 ± 0,71 days respectively. The pupal development time of P. diplosisae was 10 ± 2.26 days while that of A. procerae was 15 ± 3.92 days. The average number of ovarian eggs of the female of P. diplosisae was 213 ± 32.34 while the average number of parasitoid eggs inside the larva of O. oryzivora was 106 ± 18.43. The average number of ovarian eggs of A. procerae was 11 ± 2.93. The lifespan of adult females of A. procerae (15 ± 3.64 days) fed with honey was longer than that of males (7 ± 4.77 days) fed under the same conditions. Male’s longevity was significantly different from that of the female depending on food and temperature. Longevity of honey-fed adult females of P. diplosisae (6 ± 3.31 days) was longer than that of honey-fed adult males (3 ± 0.55 days). The life span of unfed adult females (3 ± 0.71 days) as well as that of unfed adult males (1 ± 0.15 day) were shorter. The results obtained from the two parasitoids associated with Orseolia oryzivora could be used for the development of a biological control of Orseolia oryzivora.

Successful biological control of the ambermarked birch leafminer, Profenusa thomsoni (Hymenoptera: Tenthredinidae), in Anchorage, Alaska: Status 15 years after release of Lathrolestes thomsoni (Hymenoptera: Ichneumonidae)

In Anchorage, Alaska, larvae of the invasive ambermarked birch leafminer (AMBLM), Profenusa thomsoni Konow (Hymenoptera: Tenthredinidae), are parasitized in leafmines by Lathrolestes thomsoni Reshchikov and L. soperi Reshchikov (Hymenoptera: Ichneumonidae). The first species was introduced to Alaska from Alberta and the Northwest Territories of Canada beginning in 2004 after it was noted to be associated with the collapse of an outbreak of AMBLM in Alberta. The second species, L. soperi, was described in 2010 after it was found attacking AMBLM larvae in mines in Anchorage. In previous studies, we documented that after the release of L. thomsoni in Anchorage, AMBLM densities declined from 70% leaves mined in 2006, to 19% in 2011, and that parasitism of AMBLM larvae in mines by the two Lathrolestes species combined rose from 8% in 2006 to 32% in 2011. Here we conduct another post-release survey and find that the percentage of leaves mined has been reduced even further to 9%, and that parasitism rates by the Lathrolestes species have reached 70% in 2019. We then used DNA sequencing to determine the relative dominance of the two species of Lathrolestes by dissecting out individual parasitoid eggs or larvae from 249 parasitized AMBLM larvae collected in August 2019. In total, 207 parasitoid eggs or larvae were successfully sequenced and identified from 200 leafminer larvae, of which seven were supernumerary larvae in four host larvae. DNA sequencing indicated that of AMBLM larvae that were parasitized, 71% (n = 142) were parasitized by L. thomsoni, and 29% (n = 58) were parasitized by L. soperi. AMBLM now appears to be at non-pest densities at most sites in Anchorage, with the majority of biological control services provided by the introduced L. thomsoni.

Reprograming of epigenetic mechanisms controlling host insect immunity and development in response to egg-laying by a parasitoid wasp.

Parasitoids are insects that use other insects as hosts. They sabotage host cellular and humoral defences to promote the survival of their offspring by injecting viruses and venoms along with their eggs. Many pathogens and parasites disrupt host epigenetic mechanisms to overcome immune system defences, and we hypothesized that parasitoids may use the same strategy. We used the ichneumon wasp Pimpla turionellae as a model idiobiont parasitoid to test this hypothesis, with pupae of the greater wax moth Galleria mellonella as the host. We found that parasitoid infestation involves the suppression of host immunity-related effector genes and the modulation of host genes involved in developmental hormone signalling. The transcriptional reprogramming of host genes following the injection of parasitoid eggs was associated with changes in host epigenetic mechanisms. The introduction of parasitoids resulted in a transient decrease in host global DNA methylation and the modulation of acetylation ratios for specific histones. Genes encoding regulators of histone acetylation and deacetylation were mostly downregulated in the parasitized pupae, suggesting that parasitoids can suppress host transcription. We also detected a strong parasitoid-specific effect on host microRNAs regulating gene expression at the post-transcriptional level. Our data therefore support the hypothesis that parasitoids may favour the survival of their offspring by interfering with host epigenetic mechanisms to suppress the immune system and disrupt development.