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International audience; Adult feeding on hosts is common among parasitic wasps. The ingested host fluid is rich in nutrients, especially proteins. A study on Eupelmus vuilleti (Hymenoptera: Eupelmidae), a host-feeding parasitoid of larvae of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), showed that the carbohydrates (maybe lipids) but not proteins, gained from host feeding accounted for the increased egg production. Thus, host protein is probably utilized for general adult metabolism, allowing conservation of carbohydrate and/or lipid resources for direct allocation to oocytes. In that case, there should be increased N excretion by female parasitoids. To test this, we studied the dynamics of excretion in E. vuilleti with and without host exposure. The aim of this work was threefold: (i) to identify the major N-containing compounds in adult excreta, (ii) to assess whether protein consumption during host feeding increased the amount of N excreted, and (iii), if so, to compare the increase in N excreted with the amount taken in during a single host feeding. We found that uric acid is the predominant N-containing metabolite in excreta, although small quantities of urea and traces of allantoin were also found. A calculation of the N budget showed that the extra quantity of N excreted following a host meal corresponds to the quantity ingested, confirming that host-feeding in this species offers little or no net quantitative benefit in N allocation to oocytes, although the allocation of specific amino acids from host feeding cannot be discounted. Interestingly, host-feeding in parasitoids appears analogous to vertebrate blood-feeding in mosquitoes, both in terms of the N-containing compounds excreted and the offset of acquired N to metabolism, rather than to oo-cytes. Further comparative and detailed investigations of N excretion in insects living on other N-rich fluids might establish further metabolic commonalities.

The plant mirid bugs, Lygus pratensis Linnaeus and Polymerus cognatus Fieber, are key pests on economically important cotton crops and ecologically important grassland in northwestern China. Lambda-cyhalothrin is frequently used against mirid bugs in the regions. In this study, we examined the sublethal and transgenerational effects of short-term exposure to lambda-cyhalothrin on biological traits using a miminal dose, LD5 [0.484 ng/L. pratensis adult, and 0.171 ng/P. cognatus adult], a low lethal dose, LD25 [1.353 ng/L. pratensis adult, and 0.781 ng/P. cognatus adult] and a moderate lethal dose, LD50 [2.766 ng/L. pratensis adult, and 2.243 ng/P. cognatus adult]. Direct exposure to LD50 of lambda-cyhalothrin led to decreased adult longevity, shorter female oviposition period and lower fecundity of the parental generation for both species, whereas treatment with LD5 lambda-cyhalothrin stimulated female fecundity on L. pratensis, but not on P. cognatus. The F1 generation underwent transgenerational effects, i.e. there was delayed egg-laying period and larval development and decreased hatchability for both species, decreased adult longevity and fecundity for L. pratensis, and shortened adult longevity for the LD50 group of P. cognatus. Compared with the untreated control group, the net reproductive rate (R0), the intrinsic rate of increase (rm), and finite rate of increase (λ) were significantly decreased for the groups treated with different doses of lambda-cyhalothrin, whereas the generation time (T) was increased. Our results demonstrate that sublethal effects of lambda-cyhalothrin can retard development and suppress population growth for both of these mirid species. Therefore, this insecticide can be used effectively against mirid bugs in northern China and its application strategy to control mirid bug is discussed.

The peach potato aphid, Myzus persicae is a globally distributed crop pest with a host range of over 400 species including many economically important crop plants. The intensive use of insecticides to control this species over many years has led to populations that are now resistant to several classes of insecticide. Work spanning over 40 years has shown that M. persicae has a remarkable ability to evolve mechanisms that avoid or overcome the toxic effect of insecticides with at least seven independent mechanisms of resistance described in this species to date. The array of novel resistance mechanisms, including several ‘first examples’, that have evolved in this species represents an important case study for the evolution of insecticide resistance and also rapid adaptive change in insects more generally. In this review we summarise the biochemical and molecular mechanisms underlying resistance in M. persicae and the insights study of this topic has provided on how resistance evolves, the selectivity of insecticides, and the link between resistance and host plant adaptation.

Previously, we demonstrated that sex pheromone production in mated female Heliothis virescens moths is dependent upon hemolymph trehalose concentration (HTC), which is influenced by activities such as the feeding of adults on sucrose. In this paper we demonstrate, for the first time, that this effect also occurs in starved (i.e., sugar-stressed) virgin females. Females allowed to feed on sugar for 6 days, following eclosion, had significantly greater titers than females that had fed only on water (i.e., were starved). No differences in pheromone titer were observed between sugar- and water-fed females at shorter (1 or 3 days) periods following eclosion. The relatively short-term effects of HTC on sex pheromone titer of virgins, were demonstrated by feeding experiments, in which starved (for 4 days) virgins fed on 10% sucrose solution had significantly greater HTC and pheromone titers than ones fed only on water; an increase in HTC was apparent within an hour, while the increase in pheromone titer was apparent within 2.5 h, of sugar feeding. Starvation also showed similar effects on titers of pheromone gland fatty acids (pheromone intermediates) and HTC. Over 6 days of starvation, fatty acid titers and HTC declined gradually. After feeding on sucrose, titers of hexadecanoic, (Z)-9-hexadecanoic, (Z)-11-hexadecanoic and (Z)-9-octadecanoic, acids, as well as HTC, increased significantly 24 h later, but titers of octadecanoic and (Z,Z)-9,12-octadecanoic (linoleic) acids did not. Lepidoptera cannot biosynthesize polyunsaturated acids, but the lack of change in octadecanoic acid titer suggests this acid may not participate in pheromone biosynthesis. In addition to these short-term changes in pheromone and fatty acid production, mediated by HTC, a longer-term effect of age, regardless of HTC, on pheromone titer was observed. Overall, these results are consistent with hemolymph trehalose and glandular fatty acids acting as twin metabolite reservoirs for pheromone biosynthesis. Hemolymph trehalose, able to be refilled through feeding on exogenous sugars, has a one-way flow of metabolites for synthesis of glandular free fatty acids (FFAs) and pheromone, while glandular glycerolipids provide a reversible reservoir for metabolites, accepting surplus FFAs when glandular concentrations are high, and providing FFAs for pheromone biosynthesis when concentrations are low.

Deuterium-labeled hexadecanoic acid (D4-16:COOH), a sex pheromone biosynthetic intermediate, and heptadecanoic acid (D3-17:COOH), an acid that cannot be converted to sex pheromone, were topically applied to the pheromone gland of female Heliothis virescens, and the fate of the label determined. Both acids were incorporated similarly into the glycerolipids, with by far the greatest amount found in the triacylglycerols (TGs), and relatively small amounts found in other neutral and polar classes. For D4-16:COOH, the labeled pheromone precursor, (Z)-11-hexadecenoate, was also found predominantly in the TGs but relatively (compared to labeled hexadecanoate) high amounts were also found in the phospholipids. Within the TGs, both acids, as well as the pheromone precursor, were found almost exclusively on the sn-3 position of the glycerol backbone. This demonstrates that the major fate, in the glycerolipids, of free fatty acids is addition to 1,2-diacylglycerols. A relatively large amount of the applied acid was also found in the gland in the form of the acyl-CoA thioester. In a 24-h time-course study, this form remained at a relatively high level for the duration of the assay, and decreased at a rate comparable to the titer of this acid in the TGs, suggesting that titers of fatty acids in the glycerolipids and acyl-CoA thioesters may be in equilibrium. A time-course assay with D4-16:COOH demonstrated that peak pheromone titer after application was reached before peak titers of both total hexadecanoate and hexadecanoyl-CoA. Combined with a dose-response experiment, which showed that labeled pheromone titer did not increase above an applied concentration of 20 mg/ml, these data suggest that the final step in pheromone biosynthesis, reduction of Z11-16:Acyl-CoA, may be inhibited by increased acyl-CoA titers in the gland. Overall, our data are consistent with the glycerolipids modulating acyl-CoA concentrations in the pheromone gland.

Binary mixtures of deuterium-labeled palmitic acid and an excess of different fatty acids were applied to the sex pheromone gland of female Heliothis virescens and the effects on the terminal steps of pheromone biosynthesis, including incorporation of fatty acids into the glandular lipids, observed. Relative to labeled palmitic acid applied alone, application of all the binary mixtures resulted in decreased levels of the labeled pheromone component, (Z)-11-hexadecenyl acetate (Z11-16:OAc), but there was generally no decrease in the amounts of labeled pheromone precursor, (Z)-11-hexadecenoate, nor labeled palmitate in the glandular lipids. These data suggest that the excess of fatty acid in the gland inhibits Delta11-desaturation. However, in the case of excess myristoleic acid, the amount of labeled (Z)-11-hexadecenoate increased significantly, suggesting that this acid inhibited fatty acid reduction. Dose-response tests with certain of the fatty acids were consistent with the above interpretations and further indicated that the gland had a high capacity for rapidly activating and incorporating excess fatty acids into the glandular lipids. Finally, application of the various fatty acids resulted in increased levels of these acids in the gland and, in the cases of myristoleic, palmitoleic and myristic acids, it also resulted in increased levels of the corresponding aldehydes, which had previously been detected in the gland of female H. virescens. This suggests that the fatty acid reductase in H. virescens is not highly specific for the major component, and that the final ratio of pheromone components is determined in part by the availability of their corresponding fatty acids in the gland.

The peach-potato aphid, Myzus persicae, provides an excellent demonstration of how genetic and ecological factors can interact to determine the dynamics of resistance and influence success of resistance management. The diversity of resistance mechanisms, based on both enhanced detoxification of insecticides and modifications to their target sites, that this species shows is now well understood at the genotypic, biochemical and molecular levels. These developments have yielded rapid and precise methods for detecting individual mechanisms, and for monitoring frequency changes in the presence and absence of insecticide selection. One factor influencing the prediction of these changes in the UK is the occurrence of prolonged periods of parthenogenesis in M. persicae, which results in non-random associations between particular resistance genes through the absence of genetic recombination. This has important implications for the rate at which resistance genes can accumulate in populations under selection by insecticides, and also for the speed at which they will decline when selection is relaxed. Although it is becoming apparent that resistance can be associated with various fitness costs, the relative contribution of individual resistance genes to these effects is still under investigation. However, the overall effect of the `ups’ and `downs’ of resistance in M. persicae, in the UK at least, has been to help maintain resistance phenotypes at manageable levels in most seasons. Unfortunately, the increasing genetic diversity of resistance in this species is progressively eroding the supply of effective insecticides. This in turn highlights the importance of ensuring sufficient chemical diversity to combat existing resistance mechanisms and to restrict the use of novel insecticides in order to sustain their effectiveness.

Sex pheromone-associated behavior of two tortricid moths in New Zealand, Planotortrix notophaea and P. octo , was studied in a laboratory. Most males of both species changed their antennal posture responding to the change from light to dark phase. Three antennal postures in both sexes were designated by dorsal view: antennae in resting position, those extended less than 80° from body axis, and those extended more than 80° from the body axis. In P. notophaea , antennal posture of males appeared as an external indicator representing the physiological readiness for pheromone perception; males with antennae extended more than 80° from the body axis responded better than those in resting position. Bioassays with medicine droppers indicated that threshold concentrations for male response to crude female pheromone extract were 3 × 10 −3 female equivalents (FE) and 3 × 10 −7 FE in P. notophaea and P. octo , respectively. In P. octo , threshold concentrations for male response to known pheromone compounds, (Z)-8-tetradecenyl acetate and tetradecyl acetate, were 10 fg and 100 fg, respectively. Female calling appeared continuous rather than being pulsed. In P. notophaea , stronger male responses were elicited toward females with antennae extended more than 80° from the body axis than those in resting position.

Sex pheromone titre in the tortricid moth Epiphyas postvittana follows a pattern commonly observed in other species of moths: an increase to a peak some time after eclosion (2–3 days), and then a slow decline as the female ages. Previous work has shown that this decline is not regulated by the pheromone biosynthesis activating neuropeptide PBAN. Using in vivo and in vitro enzyme assays, and fatty acid methyl ester (FAME) analyses of pheromone precursors in the gland, we have investigated this senescent decline in pheromone titre. The enzyme assays have shown that in older females the fatty acid reductase and fatty acid synthesis enzyme systems decrease in activity (relative to younger females), whereas other enzyme systems involved in pheromone biosynthesis, including limited β -oxidation (2-carbon chain-shortening), ( E )-11-desaturation, and acetylation (by an acetyl transferase) remain unchanged in their activity. Of the two enzymatic processes involved, the more important one contributing to the decline appears to be the fatty acid reductase. This is consistent with FAME analyses of pheromone glands in old and young females, which show little difference in levels of saturated FAME, but a significant increase in the level of the putative precursor, ( E )-11-tetradecenoate, of the sex pheromone component ( E )-11-tetradecenyl acetate. Thus, this decline in fatty acid reductase activity results in a buildup of the precursor as the female ages. The near ubiquity of fatty acid reductases in moth sex pheromone systems suggests that this may be a common mechanism for the senescent decline of sex pheromone titre in moths.

Activation of sex pheromone production in virgin female moths has been intensively studied over the last few years. In contrast, little is known about the reciprocal process, inactivation of pheromone production in mated females. In females of the lightbrown apple moth, Epiphyas postvittana, mating results in the permannent inactivation of pheromone production. Injection of mated female haemolymph or extracts of male accessory glands or whole reproductive tracts into virgins failed to induce this effect, suggesting that whatever elicits the inactivation is not transported humourally. When pairs were artificially forced apart during copulation, females without a spermatophore in their bursa copulatrix all produced levels of pheromone similar to virgins, while of the remales with a spermatophore in their bursa copulatrix, 47% produced levels similar to virgins and the remainder produced levels similar to mated females. This suggests that mechanical factors are not responsible for inducing inactivation of pheromone production. However, when the ventral nerve cord of females was transected before mating, the resultant mated females produced levels of pheromone similar to virgins, indicating that inactivation of pheromone production is induced by a neural signal, originating from the abdomen, which travels up the ventral nerve cord to a higher centre. Data are presented to support the hypothesis that the signal functions by switching off the release of pheromone biosynthesis-activating neuropeptide, or a like neuropeptide from the corpora cardiaca.

Virgin female Hessian flies biosynthesize sex phermone in a cyclical fashion throughout their lifetime. Pheromone titre is relatively high early in the photophase, coinciding with the period of sexual activity, and decreases to a low level some 8 h later in the photophase. Mating results in the cessation of pheromone biosynthesis. Injection of male abdomen extract into virgin females suggested that this is due to the transfer of a chemical factor from the male to the female during mating. Decapitated female Hessian flies did not biosynthesize sex pheromone. However, injection of female head extract into these decapitated females resulted in the biosynthesis of sex pheromone, indicating that pheromone biosynthesis is initiated by a factor located in the female head. Injection of synthetic pheromone biosynthesis activating neuropeptide of Heliothis zea into Hessian fly females also initiated some pheromone biosynthesis, and it is believed that this neuropeptide or a related neuropeptide is responsible for initiation of pheromone biosynthesis. Analysis of the fatty acyl groups present in the pheromone gland of virgin female Hessian flies revealed the unusual compound (E)-9-dodecenoate. This compound may be an intermediate in the biosynthesis of the pheromone component (2S)-(E)-10-tridecen-2-yl acetate.

GeMe 2 H 2 reacts under mild conditions with [{Co 2 (CO) 7 } 2 Ge] to replace one bridging CO and give [Co 4 (CO) 13 Ge(GeMe 2 )]. GeH 4 similarly yields a trace of [Co 6 (CO) 20 Ge 2 ], which may be made in high yield from [Co 2 (CO) 8 ] and Ge 2 H 6 or Me 2 Si(GeH 3 ) 2 . Spectroscopic evidence suggests structures of linked GeCo 2 triangles.