Sublethal effects of organophosphorus insecticide phoxim on patch time allocation and oviposition behavior in a parasitoid wasp Meteorus pulchricornis

Parasitoid wasps are key agents for controlling insect pests in integrated pest management programs. Although many studies have revealed that the behavior of parasitic wasps can be influenced by insecticides, the strategies of patch time allocation and oviposition have received less attention. In the present study, we forced the endoparasitoid Meteorus pulchricornis to phoxim exposure at the LC30 and tested the foraging behavior within patches with different densities of the host, the larvae of the tobacco cutworm Spodoptera litura. The results showed that phoxim treatment can significantly increase the patch-leaving tendency of female wasps, while host density had no impact. The number of oviposition and the number of previous patch visits also significantly influenced the patch time allocation decisions. The occurrence of oviposition behavior was negatively affected by phoxim exposure; however, progeny production was similar among patches with different host densities. Phoxim exposure shaped the offspring fitness correlates, including longer durations from cocoon to adult wasps, smaller body size, and shorter longevity. The findings of the present study highlight the sublethal effects that reduce the patch residence time and the fitness of parasitoid offspring, suggesting that the application of phoxim in association with M. pulchricornis should be carefully schemed in agroecosystems.

Proteo-Trancriptomic Analyses Reveal a Large Expansion of Metalloprotease-Like Proteins in Atypical Venom Vesicles of the Wasp Meteorus pulchricornis (Braconidae)

Meteorus pulchricornis (Ichneumonoidea, Braconidae) is an endoparasitoid wasp of lepidopteran caterpillars. Its parasitic success relies on vesicles (named M. pulchricornis Virus-Like Particles or MpVLPs) that are synthesized in the venom gland and injected into the parasitoid host along with the venom during oviposition. In order to define the content and understand the biogenesis of these atypical vesicles, we performed a transcriptome analysis of the venom gland and a proteomic analysis of the venom and purified MpVLPs. About half of the MpVLPs and soluble venom proteins identified were unknown and no similarity with any known viral sequence was found. However, MpVLPs contained a large number of proteins labelled as metalloproteinases while the most abundant protein family in the soluble venom was that of proteins containing the Domain of Unknown Function DUF-4803. The high number of these proteins identified suggests that a large expansion of these two protein families occurred in M. pulchricornis. Therefore, although the exact mechanism of MpVLPs formation remains to be elucidated, these vesicles appear to be “metalloproteinase bombs” that may have several physiological roles in the host including modifying the functions of its immune cells. The role of DUF4803 proteins, also present in the venom of other braconids, remains to be clarified.

Cytochrome P450s Are Essential for Insecticide Tolerance in the Endoparasitoid Wasp Meteorus pulchricornis (Hymenoptera: Braconidae)

With the widespread application of insecticides, parasitoid wasps may also be under risk when exposed to insecticides directly at their free-living stages. The endoparasitoid wasp Meteorus pulchricornis is the predominant natural enemy of many lepidopteran pests, such as Spodoptera litura and Helicoverpa armigera. The cytochrome P450 monooxygenases constitute a ubiquitous and complex superfamily of hydrophobic, haem-containing enzymes. P450s are involved in the detoxification of many xenobiotics. However, their exact roles in the tolerance mechanism in parasitoids toward insecticides has received less attention. Here, 28 P450 genes in M. pulchricornis were identified from a previously constructed transcriptome dataset. These P450 genes belonged to CYP2, -3, and -4, and mitochondrial clans. Subsequently, eight candidate MpulCYPs were selected from four CYP clans to validate their expression patterns under phoxim, cypermethrin, and chlorfenapyr exposure by qRT-PCR. The results showed that all three insecticides had significant effects on the expression of MpulCYPs. To further study the function of P450s, CYP369B3 was silenced, and its expression levels of CYP369B3 were significantly decreased. Survival analysis indicated that after dsRNA injection, the mortality rate of wasps was significantly increased when M. pulchricornis females were exposed to insecticides compared to control groups. Our findings provide a theoretical base for elucidating the mechanism of insecticide tolerance and promote functional research on P450 genes in parasitoid wasps.

Lipid Dynamics, Identification, and Expression Patterns of Fatty Acid Synthase Genes in an Endoparasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae)

In insect parasitoids, fatty acid synthases (FASs) have received less attention and their roles associated with lipogenesis loss are far from clear. Meteorus pulchricornis is a solitary endoparasitoid wasp of many larvae of lepidopteran pests. The lipid content during developmental stages of M. pulchricornis was measured; it was higher in the larval and pupal stages but declined from six-day-old pupae. Lipid accumulation constantly decreased in the adult stage, even after feeding on honey solutions. To investigate the roles of FASs in lipid synthesis in M. pulchricornis, four FAS genes (MpulFAS1~4) were identified from the transcriptome database of M. pulchricornis. All FAS genes included full-length open reading frames and shared 72–79% similarity with the sequences of Microplitis demolitor. qRT-PCR validation showed that all four FASs had the highest expression after the adult wasps were fed on honey diets. MpulFAS1 and MpulFAS2 reached their expression peaks at the adult stage but MpulFAS3 and MpulFAS4 peaked at the larval stage. To further study the function of FASs, dsRNA injection knocked down the expression of four MpulFASs and resulted in a significant decline of lipid content at the adult stage in M. pulchricornis. Results from this study suggest that M. pulchricornis adults cannot accumulate lipid content effectively and FASs may still contribute to lipid synthesis in the adult stage. This broadens the knowledge on the ability of lipid synthesis in parasitoid wasps and provides insight into the roles of FASs in insects with parasitic life-history traits.

Braconid and ichneumonid (Hymenoptera) parasitoid wasps of Lepidoptera from the Maltese Islands

Fourteen species of Ichneumonidae are here recorded from the Maltese Islands. Of these, all were reared from Lepidoptera hosts with the exception of Netelia (Paropheltes) inedita (Kokujev) which was collected from a malaise trap. Of these, the following species (or genera) are here reported for the first time from the Maltese Islands: Chirotica meridionalis Horstmann, Gelis carbonarius (de Stefani), G. exareolatus (Fӧrster), G. seyrigi Ceballos, Glypta sp., Meloboris sp., Netelia (Paropheltes) inedita (Kokujev), Ophion obscuratus Fabricius and Orthizema sp. Twenty-five species of Braconidae are also here reported from Lepidoptera hosts with the exception of Homolobus (Phylacter) meridionalis van Achterberg which was collected from a malaise trap. Of these, the following species (or genera) represent new records for the Maltese Islands: Apanteles metacarpalis (Thomson), Ascogaster sp., Clinocentrus excubitor (Haliday) [previously misidentified as C. exsertor (Nees) by Papp (2015)], Cotesia vestalis (Haliday) [previously misidentified as C. ruficrus (Haliday) by Papp (2015)], Dolichogenidea britannica (Wilkinson), Homolobus (Phylacter) meridionalis van Achterberg, Iconella ? meruloides (Nixon), Lysitermus tritoma (Bouček), Lysitermus suecius (Hedqvist), Microgaster messoria Haliday, Meteorus pulchricornis (Wesmael), Pholetesor circumscriptus (Nees) [previously misidentified as P. bicolor (Nees) by Papp (2015)] and Spathius pedestris Wesmael. Thus previous records of Clinocentrus exsertor and Pholetesor bicolor from Malta were found to be based on misidentifications and are here excluded from the braconid fauna of Malta. Maltese records of Cotesia abjecta (Marshall) and Cotesia jucunda (Marshall) by Papp (2015) were found to be misidentifications and should both refer to C. glomerata (Linnaeus). Thus, both Cotesia abjecta and Cotesia jucunda are also here removed from the braconid fauna of Malta. The record of Cotesia tibialis (Curtis) by Papp (2015) was also based on a misidentification and should be attributed to C. ruficrus (Haliday). Thus, C. tibialis is also removed from the braconid fauna of Malta.