Larval Endoparasitoid Research Articles

Biocontrol performance and mass production potential of the larval endoparasitoid Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) against the fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

BackgroundThe fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an aggressive pest species that causes severe economic losses in outbreak regions. Use of FAW natural enemies, particularly native parasitoids, has been suggested as a promising control strategy. Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) is a solitary ichneumonid larval endoparasitoid with a broad host range that includes S. frugiperda. However, its parasitism rate, developmental stages, and population dynamics during parasitization of S. frugiperda remain unclear. A field survey was conducted to determine the emergence rate and sex ratio of C. chlorideae, evaluated the biological control performance, and investigated the production potential of it on the individually reared and group-reared S. frugiperda through age-stage, two-sex life tables, respectively.ResultsThe results showed that C. chlorideae parasitizing individually reared FAW resulted for the parasitoid in a lifetime total fecundity (F) of 301.5 ± 16.4 eggs/female, a net reproduction rate (R0) of 62.03 ± 9.07 adult females/female, an overall life span of females of 28.3 ± 0.52 days, and an intrinsic rate of increase (r) of 0.1946 ± 0.0076 day−1. In contrast, the parameters of F, R0, overall life span of females, and r were 87.71 ± 6.32 pupae/female, 6.02 ± 1.61 adult females/female, 25.21 ± 0.79 days, and 0.0918 ± 0.0148 day−1 in group-reared S. frugiperda.ConclusionsThis study suggests that C. chlorideae has a promising biological control potential against S. frugiperda. Future research should focus on developing methods to increase the production of C. chlorideae.

Weather Parameter’s Impact on Natural Parasitization by Campoletis chlorideae Uchida in Chickpea Ecosystem - New Alluvial Zone of West Bengal

Background: A major biotic constraint in chickpea (Cicer arietinum L.) production is gram pod borer, Helicoverpa armigera (Hübner). However, the population of this pest is reduced to some extent by a solitary endo-larval parasitoid, Campoletis chlorideae Uchida under field conditions. Climate change has a greater impact on natural enemies’ effectiveness used in field-level pest management. Therefore, the present study was conducted to understand the impact of weather factors on C. chlorideae parasitization rate of H. armigera in chickpea grown in the new alluvial agro-climatic zone of West Bengal. Methods: Chickpea was grown in a randomized complete block design (RCBD) with three replications during Rabi 2017-18, 2018-19 and 2019-2020, at Mondouri farm, Bidhan Chandra Krishi Visawavidayala, Mohanpur, West Bengal. To know the most significant weather parameter which influences C. chlorideae parasitization or parasitoid incidence, H. armigera larvae (2nd instar) collected from the field experiment were reared until cocoon formation and parasitization % was correlated with weather parameters and subsequently subjected to stepwise regression analysis. Result: The larval endo-parasitoid, C. chlorideae marked its first appearance from 3rd SMW after the appearance of H. armigera and its activity was high (68% to 72% parasitization) during the flowering to pod initiation stage and thereafter declined gradually. Among the weather variables, only temperature (maximum and minimum) had a consistent and significant negative correlation with C. chlorideae incidence and was responsible for nearly 50% C. chlorideae incidence. An increase in 1°C temperature results in a decrease of 4% parasitoid incidence. Thus, climate change in the near future will have a considerable influence on the overall survival, development and rate of parasitization of parasitoids.

Prospecting for fine scale establishment of exotic stem borer pupal parasitoid (Xanthopimpla stemmator Thunberg) in Kenya

Lepidopteran stem borers are an important constraint to cereal production in Sub- Saharan Africa. The exotic Chilo partellus (Swinhoe) is one of the most economically important stem borer pest causing extensive losses on cereal crops in Kenya. This pest has also displaced indigenous species of stem borers while expanding its range in warm, mid and high altitude areas. In order to exert control on various developmental stages of this pest, both Cotesia flavipes Cameron (larval endoparasitoid) and Xanthopimpla stemmator Thunberg (pupal endoparasitoid) were imported and released in 2002 in the Eastern region of Kenya. This study was conducted to assess the establishment status, spread and impact of X. stemmator on C. partellus following its release in Kenya. Stem borer sampling was done on farms where the biocontrol agents had been released and on transects radiating outwards from them every 15km to assess spread. A total of 100 maize plants were inspected for stem borer infestation and destructive sampling done on 10 maize stems per farm to collect immature stem borer stages. Emerging parasitoids and adult moths were identified, counted and recorded. Results of this study showed that C. partellus was the most dominant stem borer species (constituted 71.2%) followed by Sesemia calamistis and Busseola fusca (26.0 and 2.8% respectively). A decrease in overall stem borer infestation (22.47±7.42%) with no significant difference across distances from parasitoid release points (F=0.4; df=3, 51; p>0.05) was also recorded. Seven parasitoid species were recovered, the most abundant being C. flavipes and this coupled with a significant increase in parasitism (25.27±3.27%) (V=1213, p˂0.05) from pre-release levels. The parasitoid of interest, X. stemmator was not recovered. This suggests a failure to establish though there is need to sample alternative hosts before this is declared. Key words: Classical biological control, lepidoptera, pupal parasitoid, post release survey, Xanthopimpla stemmator, Eastern Kenya

Direct and indirect host‐related volatile compounds attract a fruit fly parasitoid, Diachasmimorpha longicaudata

AbstractFruit fly pests (Diptera: Tephritidae) are a serious problem for fruit production and for local and international trade. Biological control is increasingly included as a pest control tool within integrated pest management (IPM) programmes, seeking to reduce pesticides and improve fruit quality. Ceratitis capitata Wiedemann, the Mediterranean fruit fly (medfly), is probably the most damaging fruit fly pest, with a global distribution and more than 200 host species. The solitary larval endoparasitoid Diachasmimorpha longicaudata Ashmead (Hymenoptera: Braconidae) is a biocontrol agent widely used against Tephritidae fruit fly pests. Previous studies showed that female wasps locate host larvae using visual, mechanical, and chemical cues. Here, we investigated the chemical basis of female parasitoid attraction to cues that guide D. longicaudata to the host, and thus unveil volatile organic compounds that might be used in IPM programmes. Female orientation to chemical cues was tested in a Y‐tube olfactometer, where attraction to C. capitata‐infested oranges, oranges with residues of larval activity, oranges infected with a green mould, and overripe oranges was confirmed. Volatiles from all these types of fruit were collected and used in gas chromatography‐electroantennographic detection (GC‐EAD) and GC‐mass spectrometry (MS) analyses. These studies allowed us to identify six candidate compounds that were present in all treated oranges but not in the control fruit (ripe and uninfested oranges): D‐limonene, acetophenone, linalool, nonanal, decanal, and eugenol. Electroantennography (EAG) showed that acetophenone, nonanal, and decanal triggered dose‐dependent responses, suggesting a relevant role in the process of host finding. Although responses to D‐limonene, linalool, and eugenol were independent of the dose, they could be involved in host location in areas with high probability of host presence. The fact that these six compounds are shared by the four behaviourally attractive sources opens new possibilities for the development of novel tools to improve biocontrol programmes.

Host-instar selection, interspecific competition, and reproductive capacity of extant and novel parasitoids (Hymenoptera: Braconidae) on Egyptian cotton leafworm

Abstract Background Cotesia marginiventris (Cresson) and Microplitis rufiventris Kok. (Hymenoptera: Braconidae) are larval endoparasitoids of Spodoptera frugiperda (Smith) and S. littoralis (Boisd.), respectively. Cotesia marginiventris was introduced in Egypt to control the recent invasive pest, S. frugiperda and local one, S. littoralis. Therefore, competition between the two parasitoid species may occur. Results When single females of C. marginiventris (Exp. 1), single females of M. rufiventris (Exp. 2), and one female each of C. marginiventris and M. rufiventris (Exp. 3) were offered a choice of 60 1st, 60 2nd, and 60 3rd instars, of the tested host species, S. littoralis and different parasitization levels were obtained. In the non-competitive context (Exps. 1, 2), all instars were parasitized, but C. marginiventris and M. rufiventris parasitized primarily 2nd and 3rd instar host larvae, respectively. In the competitive context (Exp. 3), the same preference pattern emerged but the percentage of parasitism was lower than in each of the two non-competitive contexts. Conclusions M. rufiventris appears to be a superior competitor when simultaneously exploiting the host with the other parasitoid species. The knowledge of this work can be used to predict and/or understand possible outcomes of a biological control program using the two biocontrol agents against one or the two pests species, and to gain insight into possible biotic interference between species at the same trophic level exploiting the same host. Graphical abstract

Life history and host preferences of Tetrastichus julis (Walker) (Hymenoptera: Eulophidae), the principal parasitoid of the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae)

Tetrastichus julis is the key larval endoparasitoid of the cereal leaf beetle, Oulema melanopus. The beetle has recently invaded cereal growing regions of western Canada, and classical biological control with T. julis is a viable management option. Although the general biology of T. julis is known, several knowledge gaps on life history traits still remain particularly in relation to host preferences and their consequences for parasitoid-beetle interactions. We investigated life history parameters and host preferences of T. julis with reference to a number of developmental parameters including survivorship, clutch size, ovipositional preferences for larval stages and their influences on realized clutch size of the parasitoid. Salient features of T. julis biology observed in this study were a short developmental time, a female-biased sex ratio, which is slightly more pronounced in larger instars, extended longevity of females, sibling mating, and more importantly, the capacity of females to live longer in the absence of hosts. The seasonal trend in parasitism rate of T. julis indicated a peak in activity in mid-June. This investigation revealed that T. julis females can discriminate among host instars and can adjust clutch size accordingly and to some extent increase production of females more than males in larger instars. In laboratory and field trials, given a choice, females laid more eggs in fourth instars than in first instars. The sex ratio was female biased and was positively correlated with clutch size. At least one male emerged from most clutches (>2) and sibling mating was common. Parasitism rates were higher after an exposure period of 48 h than 24 h. Mass rearing of T. julis can be enhanced by exposing mated T. julis females for at least 48 h to fourth-instar larvae of O. melanopus. Understanding T. julis biology can enhance mass rearing to relocate parasitoids and improve sustainable management of the cereal leaf beetle as it expands its geographic range.

Host immunity, non-reproductive effects and kleptoparasitism from novel interactions: A case study with the fruit fly parasitoid Psyttalia fletcheri (Hymenoptera: Braconidae)

Interactions between a parasitoid and its host may result in successful parasitism, unsuccessful parasitism due to host immunity, or parasitoid-induced host mortality especially in a novel interaction (non-reproductive effects). Previous parasitism by a suitable parasitoid may suppress a host’s immune response, allowing a non-suitable parasitoid to develop from the host (kleptoparasitism). This study illustrated these interactions and outcomes between the solitary larval endoparasitoid Psyttalia fletcheri (Hymenoptera: Braconidae) and its co-evolved (Zeugodacus cucurbitae) and novel (Bactrocera dorsalis, B. latifrons, and Ceratitis capitata) (all Diptera: Tephritidae) hosts in the aftermath of biological control introductions against these invasive pests in Hawaii. We demonstrated that the parasitoid could accept all four hosts for oviposition. As a reproductive host, however, B. dorsalis was not suitable, as the parasitoid’s eggs and first instars were encapsulated and only 0.4% of the parasitoid’s progeny developed to adults; B. latifrons was moderately suitable, with a 15.3% emergence rate; C. capitata was as suitable as Z. cucurbitae. After B. dorsalis was parasitized first by its most effective parasitoid, Diachasmimorpha longicaudata (Hymenoptera: Braconidae), 1.9% of P. fletcheri offspring developed to adults in B. dorsalis. Similarly, Z. cucurbitae was not suitable for D. longicaudata, but after Z. cucurbitae was first parasitized by P. fletcheri, followed by D. longicaudata, 1.4% of the latter species developed to adults. Parasitization by P. fletcheri induced high host mortalities in unsuitable hosts. Extensive surveys did not recover any P. fletcheri from 22,359 puparia of B. dorsalis, B. latifrons, and C. capitata collected from various host fruits on the Hawaiian Islands, and this parasitoid emerged only from Z. cucurbitae. We discuss the implications of these results for host specificity assessment in biological control of tephritid fruit flies.

Companion crops alter olfactory responses of the fall armyworm (Spodoptera frugiperda) and its larval endoparasitoid (Cotesia icipe)

BackgroundThe fall armyworm (FAW), Spodoptera frugiperda, is a devastating invasive pest and a threat to food security in Africa, with yield losses of 20–50%. Recent studies highlighted the importance of cereal crops such as maize and sorghum as the most preferred host plants for FAW oviposition. In the current work, we investigated the olfactory responses of FAW and its key larval endoparasitoid Cotesia icipe to odours from the preferred host (maize) in the presence of six potential companion crops including beans, groundnut, sweet potato, greenleaf- and silverleaf desmodium, and cassava. We hypothesized that odours released by companion crops in maize-based intercropping systems would alter host preferences of FAW for oviposition and its parasitoid responses.ResultsIn dual choice oviposition bioassays, FAW laid significantly more eggs on maize than on the other plants. However, in the multiple-choice bioassays, significantly fewer eggs were laid on maize when companion plants were present except cassava. While wind tunnel bioassays confirmed the differential behavioural responses of FAW, we found that its larval endoparasitoid C. icipe was attracted to volatiles from the companion plants tested individually and/or when they were combined with maize. Coupled gas chromatography–mass spectrometry (GC–MS) analysis detected several potential behaviour-modifying compounds including (Z)-3-hexenyl acetate, (E)-β-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-caryophyllene, camphor, methyl salicylate and (E, E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene.ConclusionsOur findings provide evidence supporting diversified maize cropping system could reduce FAW damage by repelling the pest while simultaneously recruiting its natural enemies. Hence, diversifying cereal cropping system with companion crops could serve as an ecologically sustainable FAW management strategy.Graphical

Evaluation of suitable reference genes for expression analysis using quantitative real-time polymerase chain reaction in the parasitoid Exorista sorbillans (Diptera: Tachinidae).

The parasitoid Exorista sorbillans (Diptera: Tachinidae) is a larval endoparasitoid of the silkworm Bombyx mori, causing severe damage to silkworm cocoon industry. It is also an important natural enemy resource of insect pests in agriculture and forestry. Despite their roles in biocontrol and pest status on sericulture, there has been limited research on the functional studies of dipteran parasitoids. Quantitative real-time polymerase chain reaction (qRT-PCR) is the most commonly used to address gene functions. Using qRT-PCR, stably expressed reference genes under different experimental conditions are required to normalize the expression of target genes. However, no information regarding suitable qRT-PCR reference genes in dipteran parasitoids has been reported. In this study, we evaluate the expression stability of nine commonly used reference genes in insects including eukaryotic translation elongation factor 1δ (eEF1δ), elongation factor 2, 18S ribosomal RNA (18S rRNA), tubulin 3, actin87, ribosomal protein 49 (RP49), ribosomal protein S15, glyceraldehyde-3-phosphate dehydrogenase, and TATA-box binding protein (TBP) in E. sorbillans under different treatments, including tissues, developmental stages, genders, feeding density and pesticide stress, using ∆Ct , BestKeeper, geNorm, Normfinder and RefFinder, respectively. The results showed that the genes RP49, eEF1δ and 18S rRNA were recommended as the most suitable reference genes in E. sorbillans across all experimental conditions. This finding provides the necessary foundation for future functional studies in E. sorbillans and its effective use in both sericulture and pest control.

Host Transcriptome Analysis of Spodoptera frugiperda Larvae Parasitized by Microplitis manilae

It has been extensively found that parasitoids manipulate host physiology to benefit the survival and development of their offspring. However, the underlying regulatory mechanisms have not received much attention. To reveal the effects of parasitization of the larval solitary endoparasitoid Microplitis manilae (Hymenoptera: Braconidae) on host Spodoptera frugiperda (Lepidoptera: Noctuidae), one of the most destructive agricultural pests in China, deep-sequencing-based transcriptome analysis was conducted to compare the host gene expression levels after 2 h, 24 h, and 48 h parasitization. A total of 1861, 962, and 108 differentially expressed genes (DEGs) were obtained from the S. frugiperda larvae at 2 h, 24 h, and 48 h post-parasitization, respectively, compared with unparasitized controls. The changes in host gene expressions were most likely caused by the injection of wasp parasitic factors, including PDVs, that were injected along with the eggs during oviposition. Based on the functional annotations in GO and KEGG databases, we revealed that most DEGs were implicated in host metabolism and immunity. Further analysis of the common DEGs in three comparisons between the unparasitized and parasitized groups identified four genes, including one unknown and three prophenoloxidase (PPO) genes. Moreover, 46 and 7 common DEGs involved in host metabolism and immunity were identified at two or three time points after parasitization, respectively. Among these, most DEGs showed increased expressions at 2 h post-wasp parasitization while exhibiting significantly decreased expression levels at 24 h post-parasitization, demonstrating the expression regulations of M. manilae parasitization on host metabolism and immune-related genes. Further qPCR verification in 20 randomly selected DEGs confirmed the accuracy and reproducibility of the gene expression profiles generated from RNA-seq. This study reveals the molecular regulatory network about how host insects respond to wasp parasitism, laying a solid foundation for revealing the physiological manipulation of wasp parasitization on host insects, which facilitates the development of biological control practices for parasitoids.

First report on classical biological control releases of the larval parasitoid Ganaspis brasiliensis against Drosophila suzukii in northern Italy

Current management strategy of the invasive fruit fly Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) exploits different tools but relies mainly on chemical control. In the invaded areas, the local natural enemy community mostly consists of generalist pupal parasitoids unable to control the pest efficiently. Conversely, in the pest native area, there are more specialized sympatric larval parasitoids attacking D. suzukii. Following foreign explorations and quarantine risk assessments, the larval endoparasitoid Ganaspis brasiliensis (Ihering) (Hymenoptera: Figitidae) was selected as the best candidate for classical biological control programs. In 2021, the first ever propagative biocontrol program using a Japanese G1 lineage of G. brasiliensis started in Italy. Here we report the results of the first year of releases in the province of Trento (Northeast Italy), wherein G. brasiliensis was released in 12 locations. Pre- and post-release samplings on fresh and fallen fruits were performed around the release points to assess the recapture rate, the impact of the exotic parasitoid on D. suzukii and its potential interactions with local non-target species. After releases, G. brasiliensis was recovered at 50% of the locations. The exotic parasitoid only emerged from D. suzukii, mostly from fresh fruit still on the plant. Post-overwintering monitoring revealed the presence of a four G. brasiliensis individuals at two release locations.

Sex pheromone communication in an insect parasitoid, Campoletis chlorideae Uchida

Sex pheromones are pivotal for insect reproduction. However, the mechanism of sex pheromone communication remains enigmatic in hymenopteran parasitoids. Here we have identified the sex pheromone and elucidated the olfactory basis of sex pheromone communication in Campoletis chlorideae (Ichneumonidae), a solitary larval endoparasitoid of over 30 lepidopteran pests. Using coupled gas chromatography-electroantennogram detection, we identified two female-derived pheromone components, tetradecanal (14:Ald) and 2-heptadecanone (2-Hep) (1:4.6), eliciting strong antennal responses from males but weak responses from females. We observed that males but not females were attracted to both single components and the blend. The hexane-washed female cadavers failed to arouse males, and replenishing 14:Ald and 2-Hep could partially restore the sexual attraction of males. We further expressed six C. chlorideae male-biased odorant receptors in Drosophila T1 neurons and found that CchlOR18 and CchlOR47 were selectively tuned to 14:Ald and 2-Hep, respectively. To verify the biological significance of this data, we knocked down CchlOR18 and CchlOR47 individually or together in vivo and show that the attraction of C. chlorideae to their respective ligands was abolished. Moreover, the parasitoids defective in either of the receptors were less likely to court and copulate. Finally, we show that the sex pheromone and (Z)-jasmone, a potent female attractant, can synergistically affect behaviors of virgin males and virgin females and ultimately increase the parasitic efficiency of C. chlorideae. Our study provides new insights into the molecular mechanism of sex pheromone communication in C. chlorideae that may permit manipulation of parasitoid behavior for pest control.

Orientation response of Cotesia plutellae Kurdjumov (Hymenoptera : Braconidae) towards nineteen straight-chain hydrocarbons ​​

The Cotesia plutellae (Kurdjumov) (Hymenoptera : Braconidae) is a larval endoparasitoid of the major crucifer pest, diamondback moth Plutella xylostella L. (Lepidoptera : Plutellidae). The oriental responses of C. plutellae towards 19 straight-chain hydrocarbons were scrutinized by Y tube choice bioassays. Stimulation for parasitoid elicited on application with 10 and 100 mg/l concentrations varied for each hydrocarbon. The study was conducted during the cole crop cultivation season in the winters of 2021-22 (January 2021-March 2022 at 28°32'7.8612'' N, 77°23'27.7044'' E). Out of all selected 19 hydrocarbons, Icosane emerged to be the best attractant with the highest percentage effectiveness of 1200%. The least attractancy was exhibited by Docosane. The possible behavioural manipulation of this specialist parasitoid using the desired concentration of hydrocarbon may be formulated and browbeaten for effective biological control of the diamondback moth.

A Fuzzy-Based Model to Predict the Spatio-Temporal Performance of the Dolichogenidea gelechiidivoris Natural Enemy against Tuta absoluta under Climate Change.

Simple SummaryTuta absoluta is an invasive pest threatening the productivity of the tomato crop. Dolichogenidea gelechiidivoris was imported and released as a natural enemy of Tuta absoluta. Mapping the efficacy of Dolichogenidea gelechiidivoris can improve its use as a control agent against Tuta absoluta. The Dolichogenidea gelechiidivoris efficacy map provides a tool for its targeted deployment as a Tuta absoluta natural enemy.The South American tomato pinworm, Tuta absoluta, causes up to 100% tomato crop losses. As Tuta absoluta is non-native to African agroecologies and lacks efficient resident natural enemies, the microgastrine koinobiont solitary oligophagous larval endoparasitoid, Dolichogenidea gelechiidivoris (Marsh) (Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae) was released for classical biological control. This study elucidates the current and future spatio-temporal performance of D. gelechiidivoris against T. absoluta in tomato cropping systems using a fuzzy logic modelling approach. Specifically, the study considers the presence of the host and the host crop, as well as the parasitoid reproductive capacity, as key variables. Results show that the fuzzy algorithm predicted the performance of the parasitoid (in terms of net reproductive rate (R0)), with a low root mean square error (RMSE) value (<0.90) and a considerably high R2 coefficient (=0.98), accurately predicting the parasitoid performance over time and space. Under the current climatic scenario, the parasitoid is predicted to perform well in all regions throughout the year, except for the coastal region. Under the future climatic scenario, the performance of the parasitoid is projected to improve in all regions throughout the year. Overall, the model sheds light on the varying performance of the parasitoid across different regions of Kenya, and in different seasons, under both current and future climatic scenarios.

Effects of extreme temperature events on the parasitism performance ofDiadegma semiclausum, an endoparasitoid ofPlutella xylostella

AbstractWith climate change, the occurrence of extreme weather events such as heatwaves is expected to increase. Extreme temperature events are short periods of high temperature (i.e., &gt;95th percentile of temperature distribution), and their occurrences are difficult to predict. These extreme temperature events pose great challenges to living organisms, especially ectotherms such as insects whose body temperature is greatly influenced by environmental temperature. Temperature is known to play an essential role in driving insect performance as well as inducing behavioral changes. Exposure to extreme temperatures causes physiological damage leading to potential long‐lasting effects on insect performance. We aimed at assessing the impact of direct (i.e., current) and indirect (previously experienced) exposure to extreme temperature on the oviposition success ofDiadegma semiclausumHellén (Hymenoptera: Ichneumonidae).Diadegma semiclausumis a larval endoparasitoid ofPlutella xylostellaL. (Lepidoptera: Plutellidae), a worldwide pest of brassicaceous crops. Oviposition success, measured as the percentage of parasitizedP. xylostella, was significantly lower at 33 °C than at 25 °C. However, previous exposure to 33 °C did not significantly impact the egg‐laying performance ofD. semiclausum, indicating that, after a heatwave, the egg‐laying performance can recover. Neither the direct nor indirect exposure to extreme temperature alteredD. semiclausumhost‐instar preference. These results indicate that temperature directly impactsD. semiclausumparasitism performance, although more detailed research is needed to disentangle direct physiological mechanisms from behavioral responses. Overall, these study results confirm others, suggesting that control ofP. xylostellabyD. semiclausumis likely to be impaired by more frequent heatwaves predicted under climate change scenarios.

Disentangling thermal effects using life cycle simulation modelling on the biology and demographic parameters of Dolichogenidea gelechiidivoris, a parasitoid of Tuta absoluta

Dolichogenidea gelechiidivoris (Marsh) (Syn. Apanteles gelechiidivoris) (Hymenoptera: Braconidae), a konoibiont larval endoparasitoid of the South American tomato pinworm Tuta absoluta (Meyrick), was imported into Kenya in 2017 for the first classical biological control of T. absoluta in Africa. We determined the thermal thresholds of D. gelechiidivoris, with T. absoluta as host, using life cycle simulation modelling. Life-table data of D. gelechiidivoris were generated at six constant temperatures (10, 15, 20, 25, 30, and 35 °C, 65 ± 5% RH, and 12L: 12D photoperiod). Multiple non-linear functions were fitted to model some aspects of the biology of the parasitoid, including its longevity, mortality, reproduction, and senescence using Insect Life Cycle Modelling (ILCYM) software. The phenology models established were used to estimate life table parameters. Except at 35 °C, D. gelechiidivoris completed its development (i.e., egg-larval-pupa-adult) at all tested temperatures. The minimum temperature threshold from egg to cocoon was 7.0 °C and 5.9 °C from cocoon to adult wasp, while the maximum temperature thresholds were 34 °C and 36 °C, respectively. The optimal temperature for immature survival was 20–25 °C, while fecundity was optimum at 22.5 °C, with 69.5 eggs per female. Simulations of the population growth parameters indicated that the intrinsic rate of increase (rm) was maximum at 20 °C with 15 daughters per female per generation. Based on our findings the release of D. gelechiidivoris for inoculative augmentation in countries with temperatures ranging between 15 and 30 °C could be considered to control the pest.

High temperatures do not decrease biocontrol potential for the host-killing parasitoid Neochrysocharis formosa (Hymenoptera: Eulophidae) on agromyzid leafminers

Temperature, as a critical abiotic factor, might influence the effectiveness of biological control by parasitoids in host-parasitoid systems. In this study, Neochrysocharis formosa (Westwood), a larval endoparasitoid, is used to investigate the efficacy of biological control on a vegetable agriculture pest, Liriomyza sativae Blanchard, reared on kidney bean (Phaseolus vulgaris L.), at four constant temperatures (26, 29, 32, and 35°C) under laboratory conditions. Our results show that high temperatures (29, 32, and 35°C) do not significantly affect lifetime host-killing events of female adults by increased daily host-killing events compared to temperature of 26°C, although their lifespans decrease with an increase in temperatures. Each life-history trait of female adults (lifespan, parasitism, stinging, or non-reproductive host-killing events) present a linear relation with temperatures and host-feeding events, respectively. Our findings contribute to a better understanding of biocontrol efficacy of parasitoid N. formosa against agromyzid leafminers at high-temperature seasons or environments.

A female-biased odorant receptor tuned to the lepidopteran sex pheromone in parasitoid Microplitis mediator guiding habitat of host insects

IntroductionThe parasitoid wasp Microplitis mediator is an important natural enemy of the turnip moth Agrotis segetum and other Noctuidae pests. In our field observation, it was fortuitously discovered that sex pheromone traps used for A. segetum also attract female wasps, verified by a simulated field condition dual-choice laboratory assay. Therefore, it was hypothesized that olfactory recognition could be crucial in this process. In this regard, a female-biased odorant receptor of the wasp, MmedOR49, attracted our attention. ObjectivesTo unravel the significance of the female-biased MmedOR49 regulating host pheromone recognition. MethodsExpression analysis (fluorescence in situ hybridization; quantitative realtime PCR), in vitro (two-electrode voltage-clamp recordings) and in vivo (RNAi combined with behavioral assessments) functional studies, and bioinformatics (structural modeling and molecular docking) were carried out to investigate the characteristics of MmedOR49. ResultsMmedOR49 expression was detected in the antennae of females by FISH. Quantification indicated that the expression level of MmedOR49 increased significantly after adult emergence. In vitro functional study revealed that MmedOR49 was specifically tuned to cis-5-decenyl acetate (Z5-10:Ac), the major sex pheromone component of A. segetum. Molecular docking showed that Z5-10:Ac strongly bound to the key amino acid residues His 80, Ile 81, and Arg 84 of MmedOR49 through hydrogen bonding. Behavioral assays indicated that female wasps were significantly attracted by Z5-10:Ac in a three-cage olfactometer. RNAi targeting further confirmed that MmedOR49 was necessary to recognize Z5-10:Ac, as female wasps lost their original behavioral responses to Z5-10:Ac after down-regulation of the MmedOR49 transcript. ConclusionAlthough M. mediator is a larval endoparasitoid, female wasps have a behavioral preference for a sex pheromone component of lepidopteran hosts. In this behavior, for female M. mediator, MmedOR49 plays an important role in guiding the habitat of host insects. These data provide a potential target for enhancing natural enemy utilization and pest control.

Biological parameters of three Argentinian populations of Pseudapanteles dignus, a larval endoparasitoid of Tuta absoluta, at various temperatures

Understanding important aspects of the adaptation of a biological control agent population to different abiotic conditions (e.g., temperature) is essential to ensure its success once it is released in the field. In this context, we assessed different biological parameters of three Argentinian populations of Pseudapanteles dignus (from Salta, Buenos Aires and Río Negro provinces), a larval endoparasitoid of the South American tomato pinworm, Tuta absoluta, a key pest of tomato crops worldwide, under various regimes of temperature (25, 28 and 30 °C). All local populations of P. dignus showed density-independent parasitism at the temperatures tested, and sex ratios did not deviate from 1:1 except for Salta population at 30 °C. Intra and inter-population comparisons revealed differences in pre-imaginal development times according to the temperature regimes. These results may be exploited to improve mass rearing of P. dignus and to implement biological control programs of T. absoluta in Argentina.

Can the Combined Use of the Mirid Predator Nesidiocoris tenuis and a Braconid Larval Endoparasitoid Dolichogenidea gelechiidivoris Improve the Biological Control of Tuta absoluta?

Simple SummaryCombining natural enemies may lead to synergistic, additive, or antagonistic effects on the control of insect pests. An investigation into the nature and outcome of the interaction between a generalist mirid predator, Nesidiocoris tenuis, and a specialist koinobiont larval endoparasitoid, Dolichogenidea gelechiidivoris, in the control of a co-shared host/prey, Tuta absoluta, was undertaken under laboratory conditions. We found that the presence of N. tenuis did not affect oviposition performance or progeny production by D. gelechiidivoris. When both natural enemies were combined, the efficacy in reducing T. absoluta populations was significantly higher than that of either natural enemy used alone. Nesidiocoris tenuis preferentially reduced the densities of T. absoluta eggs, while D. gelechiidivoris reduced the larval stages of the pest. The combined use of N. tenuis and D. gelechiidivoris could potentially help reduce the overall infestation level of T. absoluta in tomato agroecosystems.The koinobiont solitary larval endoparasitoid Dolichogenidea gelechiidivoris (Marsh) (Syn.: Apanteles gelechiidivoris) (Hymenoptera: Braconidae) and the predatory bug Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) are important natural enemies of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a serious pest of tomato. Although N. tenuis preferentially feeds on T. absoluta eggs, it is also recorded as a predator of first and second instar larval stages. Dolichogenidea gelechiidivoris preferentially seeks these early larval stages of T. absoluta for oviposition. The occurrence of intraguild predation between N. tenuis and D. gelechiidivoris and the consequences on the oviposition performance of D. gelechiidivoris were investigated in the laboratory. Regardless of the manner of introduction (i.e., the sequence of combinations with D. gelechiidivoris) or density (i.e., number of N. tenuis combined with D. gelechiidivoris), the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris or the parasitoid’s progeny. Combination assays revealed that the efficacy of the combined use of N. tenuis and D. gelechiidivoris in controlling T. absoluta populations was significantly higher than that of either natural enemy alone. Our results highlight the potential of combining mirid predators and koinobiont larval endoparasitoids to control T. absoluta. The findings further contribute to data supporting the release of D. gelechiidivoris in tomato agroecosystems for the control of T. absoluta in Africa, where N. tenuis is widespread and abundant.