Effects of Scleroderma sichuanensis Xiao (Hymenoptera: Bethylidae) venom and parasitism on nutritional content regulation in host Tenebrio molitor L. (Coleoptera: Tenebrionidae)

Lipid Metabolism in Parasitoids and Parasitized Hosts

Parasitoids have an exceptional lifestyle where juvenile development is spent on or in a single host insect, but the adults are free-living. Unlike parasites, parasitoids kill the host. How parasitoids use such a limiting resource, particularly lipids, can affect chances to survive and reproduce. In part 1, we describe the parasitoid lifestyle, including typical developmental strategies. Lipid metabolism in parasitoids has been of interest to researchers since the 1960s and continues to fascinate ecologists, evolutionists, physiologists, and entomologists alike. One reason of this interest is that the majority of parasitoids do not accumulate triacylglycerols as adults. Early research revealed that some parasitoid larvae mimic the fatty acid composition of the host, which may result from a lack of de novo triacylglycerol synthesis. More recent work has focused on the evolution of lack of adult triacylglycerol accumulation and consequences for life history traits. In part 2 of this chapter, we discuss research efforts on lipid metabolism in parasitoids from the 1960s onwards. Parasitoids are also master manipulators of host physiology, including lipid metabolism, having evolved a range of mechanisms to affect the release, synthesis, transport, and take-up of lipids from the host. We lay out the effects of parasitism on host physiology in part 3 of this chapter.

Reproductive performance effects of rearing the quasi-social parasitoid, Sclerodermus brevicornis (Hymenoptera: Bethylidae), on a factitious host

Wasps in the genus Sclerodermus are ectoparasitoids that typically attack the larvae of woodboring coleopterans. Interest in these species is increasing as they are used in programs to control longhorn beetle pests of economic importance in China and have invasive pest control potential in Europe. Wasps may be mass reared for field release, but using the target host species can be time consuming and physically demanding. There is thus a need for factitious hosts with lower production costs and that are easier to rear. The present research focuses on Sclerodermus brevicornis, which was found in Italy in association with the invasive longhorn beetle, Psacothea hilaris hilaris, and can be laboratory reared on this longhorn beetle and on a factitious lepidopteran host, Corcyra cephalonica. As it is known that the biology of natural enemies can be influenced by the host they emerge from and that the behavior of S. brevicornis is relatively complex due to its degree of sociality (multiple foundress females cooperate to paralyze the host and produce offspring communally), we explored whether, and how, performance and behavioral traits of adult females are influenced by the host species on which they were reared, both when no choice or a choice of current host species was offered. We evaluated the survival of foundresses and their movements between offered hosts and their tendency to form groups with other foundresses according to kinship and host characteristics. We also evaluated the production of offspring and the timing of their development. We found that S. brevicornis reared from C. cephalonica do have some disadvantages compared with those that have developed on P. h. hilaris but also that they recognize, prefer, and can reproduce on P. h. hilaris. We conclude that the use of the more convenient factitious host for mass-rearing is unlikely to greatly compromise the potential of S. brevicornis to suppress longhorn beetle pests in the field.

Predicting the Distribution of Sclerodermus sichuanensis (Hymenoptera: Bethylidae) under Climate Change in China

Sclerodermus sichuanensis is the natural enemy of the longicorn beetle due to its strong attack ability and high parasitic rate. Its good resistance and fecundity make it have significant biological control value. The Maxent model and ArcGIS software were used to simulate the current distribution of S. sichuanensis in China by combining the known distribution information and environmental variables and predict the suitable area of the 2050s (2041-2060) and 2090s (2081-2000) under three climate scenarios (SSP1-2.6, SSP2-4.5. and SSP5-8.5). The results showed that the Mean Diurnal Range (bio2), Min Temperature of the Coldest Month (bio6), Precipitation of the Warmest Quarter (bio18), and Max Temperature of the Warmest Month (bio5) were the key environmental variables affecting the distribution of S. sichuanensis. Southwest China and part of North China are the main concentrations of the current high-suitability areas of S. sichuanensis. The moderately suitable areas are concentrated in South China and Central China. Under the SSP5-8.5 scenario, the suitable area predicted in the 2050s will expand significantly to North China and Northwest China, with a total increase of 81,295 km². This work provides an essential reference for future research on S. sichuanensis and the application of forestry pest control.

Galleria mellonella larvae fat body disruption (Lepidoptera: Pyralidae) caused by the venom of Habrobracon brevicornis (Hymenoptera: Braconidae)

The ability of Habrobracon brevicornis venom to elevate the nutritional suitability of a host by affecting the host larvae fat body condition was studied. To understand whether H. brevicornis crude venom impacts the host biochemical profile, the concentrations of total lipids and main sugars in the host larvae lymph were analyzed. All measurements were carried out during the first 3 days after envenomation. A significant increase in the lipid level was fixed only on the second day after envenomation. A significant increase in the total trehalose count was detected during all 3 days, while a significant increase in glucose concentration was noted only on the first day. Well-observed disruptions were fixed in thin and semithin sections of the G. mellonella larval fat body starting from the second day after envenomation. Significant increases in both phospholipase A₂ and C enzyme activity as well as acid proteases were detected in the wax moth fat body after envenomation during all experimental times. At the same time, imbalances in the antioxidant system, including changes in the activities of superoxide dismutase, peroxidases, catalase, and glutathione-S-transferase, were detected. The reliable increase in the expression of the gene encoding Hsp70 was fixed both for 24 and 48 h after envenomation, while a reliable increase in the expression of the gene encoding inhibitor of apoptosis protein was detected only 24 h after wax moth larvae envenomation. Considering the absence of DNA fragmentation, the imbalance in the "ROS/antioxidants" system, and the increased activity of phospholipases and acid proteases in the fat body cells from envenomated wax moth larvae, we can hypothesize that the fat body disruption occurs in a necrotic manner. The results of the work expand the knowledge about the biochemical aspects of interaction between ectoparasitoids and their hosts.

Host regulation by the ectophagous parasitoid wasp Bracon nigricans

The host regulation process has been widely investigated in endophagous parasitoid wasps, which in most cases finely interact with living hosts (i.e. koinobiont parasitoids). In contrast, only very limited information is available for ectophagous parasitoids that permanently paralyze and rapidly suppress their victims (i.e. idiobiont parasitoids). Here we try to fill this research gap by investigating the host regulation by Bracon nigricans, an ectophagous idiobiont wasp species. Parasitism, mainly by venom action, is able to redirect host metabolism in order to enhance its nutritional suitability for the developing parasitoid larvae and to provide the required metabolic support to host tissues. The observed alterations of the host titers of haemolymph proteins, carbohydrates and acylglycerols are associated with a parasitoid-induced mobilization of nutrients stored in the fat body. This tissue undergoes a controlled degradation mediated by a close surface interaction with haemocytes, where a cathepsin L activity is localized, as demonstrated by immunolocalization, biochemical and transcriptional data. B. nigricans parasitism does not markedly influence the survival of haemocytes, even though a persistent suppression of the immune competence is observed in parasitized hosts, which show a reduced capacity to encapsulate and melanize non-self objects. These immune alterations likely allow a more efficient food uptake and use by the ectophagous larvae. The obtained results indicate that the host regulation process in basal lineages of parasitic Hymenoptera is more complex than expected and shares functional similarities with adaptive strategies occurring in derived koinobiont species.