Abstract. 1. Sugar from nectar or from honeydew can prolong parasitoids' lifespan, enhance their fecundity and foraging ability, and thereby increase their pest suppression efficiency. Sugar sources within crop monocultures are considered to be limiting for parasitoids. Nevertheless, only few studies have measured the sugar feeding of parasitoid assemblages in agricultural areas or in surrounding non-crop habitats.2. We used cold anthrone tests to compare the frequency of sugar feeding in parasitoid communities, inside pomegranate orchards and in adjacent natural areas, over two consecutive years. Overall, 40% of the 1610 sampled individuals belonging to 135 species scored positive for sugar.3. Sugar-feeding frequency was lower within the orchards than in the neighbouring natural areas. The proportion of sugar-fed wasps increased with herbaceous vegetation cover, both within and outside the orchards, suggesting that herbs are a sugar-rich habitat. Parasitoids sampled from trees and from herbs within the orchards had similar frequencies of sugar feeding, despite differences in wasp species composition.4. Our results probably overestimate sugar-feeding frequencies in the field because sugar-fed individuals have higher longevity and hence are more likely to be sampled. We propose a simple model to approximate this over-sampling bias and apply it to Encarsia inaron (Aphelinidae), one of the most abundant parasitoids in the samples.5. We conclude that sugar availability potentially limits parasitoid fitness in this agro-ecosystem. This may be due to the low density of plants in natural areas during the Mediterranean summer, and to herbicide applications within the orchards that further suppress non-crop herbs.

Temperature and precipitation are major components of climate that have a pervasive effect on the phenotype and physiology of insects. The Oriental hornet has a wide geographical distribution and is the only vespid species found in a desert environment. Recently, it has extended its geographic distribution due to climate change and human activities. We compared the standard metabolic rate, diapause metabolic rate and body size of workers and gynes in two different climatic regions, 150 km apart along the northern part of the Great Rift Valley in Israel: In the north, high elevation Mediterranean habitat and in the south, low elevation, warm and dry desert. The brood in the desert region developed in higher ambient temperatures than in the Mediterranean, but only the workers of the desert had a smaller body size as adults. Worker hornets from the Mediterranean region had a higher standard metabolic rate (SMR) at the environmental temperature of main activity compared to desert hornets. Queens had a typical discontinuous gas exchange cycles (DGC) pattern, with Mediterranean queens having a 30% lower SMR. Such lower SMR might reflect an adaptation for prolonged and more profound diapause typical to the cold and long winter conditions in this region.

Fatty acids (FA) are the primary metabolic fuel for many organisms and the fundamental component of membranes of all living organisms. FAs can be saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA). PUFA are not synthesized by most animals and are considered as essential nutrients. We examined the effect of climate on the saturation level of polar (mostly membranal) and neutral lipids in the body of the Oriental hornet (Vespa orientalis) from two extreme climatic zones: Mediterranean high elevation; and hot arid desert. In contrast to previous reports, the environmental temperature was shown to affect the hornet colonies’ thermal environments. The hornets nonetheless maintained their colony temperature within a narrow range. Analyses of the hornets’ unsaturation levels of polar and non-polar body lipids revealed caste differences: gynes and males contained less unsaturated lipids than workers. However, there were no differences in the respective castes between the two different climate zones tested. Experimentally manipulating the diet of queenless hornet colonies to a high Omega-3 diet (salmon) or a high Omega-6 diet (crickets) had only a minor effect on the worker-born males’ lipid composition. Although salmon-fed males had a higher Omega-3 content than cricket-fed ones, the proportion of these fatty acids was still low (below 1%). Cricket-fed males had significantly higher levels of Omega-6 than salmon-fed males. Our data show that the specific lipid composition of the hornet body is highly regulated and deficient in essential PUFA, even under different climates or high Omega-3 or Omega-6 PUFA diet. PUFA, especially Omega-3, is considered to have a beneficial effect on physiological processes. Our finding that these FA, when common in the diet, are almost absent in the body raises questions about how they affect animals’ physiology.

The main challenge facing a parasite of social insects lies in deceiving its host’s detection and defense systems in order to enter and survive within the host colony. Sphecophaga orientalis is an ichneumonid wasp that parasitizes the pupae of the Oriental hornet Vespa orientalis. In Israel’s Mediterranean region, this parasitoid infects on average 23.48% (8–56%) of the host pupal cells. Observation of colonies brought to the laboratory revealed that the parasite moves around within the colony without being aggressed by the host workers. To assess how the parasite evades host detection and defense, we compared the cuticular hydrocarbon (CHC) profiles of both species. There was little similarity between the parasite and the host workers’ CHC, refuting the hypothesis of chemical mimicry. The parasite’s CHCs were dominated by linear alkanes and alkenes with negligible amounts of branched alkanes, while the host workers’ CHCs were rich in branched alkanes and with little or no alkenes. Moreover, the parasite cuticular wash was markedly rich in oleic acid, previously reported as a cue eliciting necrophoric behavior. Since nests of Oriental hornets are typified by large amounts of prey residues, we suggest that, due to its unfamiliar CHCs and the abundance of oleic acid, the parasite is considered as refuse by the host. We also detected rose oxide in the parasitoid head extracts. Rose oxide is a known insect repellent, and can be used to repel and mitigate aggression in workers. These two factors, in concert, are believed to aid the parasite to evade host aggression.