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In New Zealand's ancient Fuscospora spp. or beech forests, two invasive Vespula social wasps Vespula vulgaris (L.) and Vespula germanica (F.) have become significant problems, adversely affecting native birds and invertebrate biodiversity. The nature of chemical communication in these two species is poorly understood, and this work was undertaken to identify the behaviourally active compounds in the venom of the common wasp, Vespula vulgaris (L.). Venom was removed from the stings of both workers and females and analyzed by coupled gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography/mass spectrometry (GC/MS). Two compounds were present in the venom that consistently elicited EAD responses from the antennae of males and workers. Mass spectrometry analysis and syntheses of candidate structures revealed the structures to be N-(3-methylbutyl)acetamide (MBA) and N-(3-methylbutyl)butanamide (MBB). Gyne venom contains significantly larger amounts of MBA and MBB than worker venom. When these two compounds were tested in the field individually or as binary blends in combination with the known food odour (honeydew volatiles), only N-(3-methylbutyl)butanamide or blends containing this compound showed a strong repellent effect on workers to honeydew volatiles at all doses tested. This is the first report of the occurrence of N-(3-methylbutyl)butanamide in nature and the third amide to be identified in the venom of any social wasp. In addition, this work is the first to report the chemical analysis of the venom of V. vulgaris gyne. The repellency effect observed in this study of the venom compound suggests that our definition and understanding of the function of the alarm pheromone need to be reassessed.

While adaptive responses to climate gradients are increasingly documented, little is known about how individuals alter their upper thermal tolerances. Long-term increases in dietary carbohydrates can elevate upper thermal tolerances in insects. We explored how the nutritional state of a Neotropical canopy ant governs its CT max – the temperature at which individuals lose muscle control. We predicted that Azteca chartifex workers recently fed a carbohydrate-rich diet, such as honeydew and extrafloral nectar, would use that energy to increase their CT max . Moreover, if a carbohydrate-rich diet increases CT max , then we predicted that ants from colonies with high CT max s feed at a lower trophic level, and thus have a higher carbon:nitrogen ratio. We used A. chartifex colonies from a long-term fertilization experiment where phosphorus addition increased A. chartifex foraging activity with respect to controls. As foraging activity can be governed by resource availability, we first measured CT max of field collected colonies. In freshly collected field colonies, CT max was 2 °C higher in control plots. This difference disappeared when ants were provided with only water for 10 h. Ants were then provided with a 10% sucrose solution ad lib which increased CT max by 5 °C. We thus support the hypothesis that enhanced carbohydrate nutrition enables higher thermal tolerance, but this does not appear to be linked to colony trophic status, higher carbon:nitrogen ratios, or higher total body phosphorus. This short-term thermal plasticity linked to carbohydrate nutrition demonstrates the importance of ant diet in shaping their physiological traits. It is especially relevant to ant species that maintain high abundance by feeding on plant exudates. In a rapidly warming world, carbohydrate availability and use may represent a new element for predicting population and community responses of herbivorous insects.

The availability of food sources is important for parasitoid survival, especially for those that inhabit ecosystems where nectar and honeydew are spatially or temporally scarce. Therefore, the value of even a single meal can be crucial for survival. Psyttalia lounsburyi is a parasitoid, and biological control agent, of the olive fruit fly, Bactrocera oleae. In order to improve our understanding of the basic nutritional ecology of P. lounsburyi and its role in survival we evaluated the effect of a single sucrose meal on the longevity of female and male wasps. We measured the duration of feeding, volume ingested, sucrose consumption, energy content, and longevity of wasps provided with different concentrations of sucrose (0.5, 1, and 2 M) at different times after emergence (0, 1, 2 or 3 days after emergence). Our results showed that longevity was significantly influenced by sucrose concentration and timing of feeding. For females, feeding on sucrose increased the likelihood of survival to varying degrees, ranging from 32.3% to 95.4%, compared to water-only controls. The longest duration of feeding was observed for the highest sucrose concentrations and oldest wasps. The amount of sugar ingested and energy uptake increased, up to a point, as sugar concentration increased. Our results suggest that P. lounsburyi derived greatest benefit from the intermediate concentration (1 M) of sucrose provided 2 or 3 days after emergence. Our study emphasizes the importance of finding balance between increasing longevity and limiting the duration of feeding, and concomitant uptake of nutrients, that is fundamental for survival of the wasp in nature.

The brown planthopper (Nilaparvata lugens Stal, BPH) is one of the most destructive pests in rice production, and rice resistance is thought to be an economical and environmentally friendly strategy against BPH. Although resistant rice cultivars have been widely applied to control BPH, little is known regarding the impact of the ingestion of resistant plant phloem on the BPH physiological metabolism. In this study, the differences in the metabolic responses of BPH nymphs during the first 72 h after ingesting susceptible TN1 and resistant IR56 plant phloem were compared. The results showed that BPH nymphs feeding on IR56 plants exhibited significant decreases in honeydew excretion and body weight, and significantly lower concentrations of most of the detected sugars, vitamins and some essential amino acids but higher levels of most amides, free fatty acids and some non-essential amino acids. These findings indicate that the energy metabolism and nutrition supply of these nymphs were disturbed by the resistant rice plants. The qPCR results revealed that BPH could actively adapt to IR56 plants by upregulating the gene expression levels of some detoxification enzymes, including GST, CarE and POD, to some extent. These results provide additional information to improve our understanding of physiological mechanism underlying the loss of BPH fitness caused by resistant rice varieties.

Parasitoids commonly forage in agricultural settings where the predominant sugar source is homopteran honeydew. The aphidiine braconid, Binodoxys communis, is an Asian parasitoid currently being released against the soybean aphid, Aphis glycines, in North American soybean fields. We conducted a number of laboratory experiments evaluating the quality of A. glycines honeydew as a sugar source for this parasitoid. Wasps readily fed on droplets of A. glycines honeydew, honey and 50% sucrose solution, but the length of feeding bouts on honey was significantly longer than on the other foods. Parasitoids lived significantly longer when fed honey or sucrose than honeydew, while starved wasps had the shortest lifespan. At 21+/-1 degrees C and 25+/-5% R.H., male B. communis that were fed honey lived for a maximum of 14 days, while females lived up to 20 days. Honeydew-fed wasps of both sexes lived approximately 3 days on average, which was 2-3 times longer than when they were only allowed access to water. Anthrone tests of whole insects showed that total sugar and glycogen levels of honey or sucrose-fed individuals were consistently higher than those fed honeydew or water. The glycogen levels of honeydew-fed wasps increased significantly after one day of feeding. HPLC analyses revealed that B. communis readily assimilates A. glycines honeydew oligosaccharides such as erlose, while others (e.g., raffinose) did not degenerate. Raffinose was present in much higher amounts in honeydew-fed wasps than in wasps fed other diets, so this sugar could be used as a 'signature' sugar for this species. Honeydew-fed wasps also had significantly lower fructose/(fructose+glucose) ratios than those from other diet treatments. Although A. glycines honeydew might be the main carbohydrate source within a soybean field, other sugar sources such as floral nectar appear to be more optimal foods for B. communis from a physiological standpoint. We discuss the results from the perspective of classical biological control of the soybean aphid in North America.

Protease inhibitors (PIs) have been shown to cause lethal and sublethal effects on aphids depending on the kind of PI and aphid species. Therefore, these proteins might affect aphid parasitoids directly by inhibiting their digestive proteolysis or indirectly via their development in a less suitable host. In our study, the risk of exposure and the potential effects of soybean Bowman-Birk inhibitor (SbBBI) and oryzacystatin I (OCI) on the aphid endoparasitoid Aphidius ervi were investigated using artificial diet to deliver PIs. Immunoassays showed that both SbBBI and OCI were detected in the honeydew of aphids reared on artificial diet containing these recombinant proteins at 100 microg/mL. However, only SbBBI was detected in parasitoid larvae, while this PI could not be detected in adult parasitoids emerged from PI-intoxicated aphids. Enzymatic inhibition assays showed that digestive proteolytic activity of larvae and adults of A. ervi predominantly relies on serine proteases and especially on chymotrypsin-like activity. Bioassays using SbBBI and OCI on artificial diet were performed. A. ervi that developed on intoxicated aphids had impaired fitness. Thus development and parasitism success of parasitoids exposed to OCI were severely affected. On the contrary, SbBBI only altered significantly female size and sex ratio. Direct exposure to PIs through adult food intake did not affect female's longevity, while SbBBI and OCI (100 microg/mL) induced 69% and 30% inhibition of digestive protease activity, respectively. These studies made it possible to estimate the risk of exposure to plant PIs and the sensitivity of the aphid parasitoid A. ervi to these entomotoxins, by combining immunological, biochemical and biological approaches. First it pointed out that only immature stages are affected by PIs. Secondly, it documented two different modes of effect, according to the nature of the PIs and both host and parasitoid susceptibility. OCI prevented the development of A. ervi mainly due to the host susceptibility, whereas SbBBI only induced sublethal effects on the parasitoid, possibly due to both direct action on the parasitoid susceptible proteases, and host-mediated action through size reduction.

Planthopper harbour yeast-like symbionts in the mycetocyte. A possible role that the symbionts may play for the host insect is nitrogen recycling, i.e. conversion of nitrogenous waste products of the insect into compounds of nutritional value. To examine this possibility, we determined the uric acid content in the honeydew and the whole tissues of control and symbiont-depleted brown planthoppers, Nilaparvata lugens . The symbiont-depleted insects were obtained by exposing newly hatched nymphs to 35 °C for three days. In the honeydew, uric acid was not detected regardless of the presence or absence of symbionts. Nevertheless, a considerable amount of uric acid was found in the insect tissues, and the content was markedly higher in heat-treated insects than in controls. We also determined the uricase activity in the insect whole tissues and in the isolated symbionts. While in control insects uricase was detectable, there was no uricase activity in heat-treated insects. Isolated symbionts had uricase activity 15 times higher than in the whole tissues of control insects. These results suggested that uric acid synthesized by the insect is stored in insect tissues rather than excreted, and that uric acid is recycled in the planthopper with the aid of its endosymbionts.

Aposymbiotic pea aphids Acyrthosiphon pisum (i.e. aphids lacking functional symbiotic bacteria) were generated by treatment with the antibiotic rifampicin. Eight-day-old aposymbiotic aphids produced honeydew containing 16–30 mol% glutamine, while the honeydew of symbiotic aphids (containing bacteria) contain

Pea aphids (Acyrthosiphon pisum) whose symbiotic bacteria were disrupted with the antibiotic chlortetracycline over the first 5 days after birth (i.e. aposymbiotic aphids), were able to feed from the host plant Vicia faba, as indicated by the regular production of honeydew droplets and by electrical penetration graph (EPG) recordings of stylet penetration through the plant tissues to the sieve elements. No difference was identified in the time taken by adult symbiotic and aposymbiotic aphids [24 ± 2.4 and 24 ± 3.0 min (mean ± SE), respectively] to penetrate the plant tissues and puncture the sieve elements during the probes which resulted in sustained phloem feeding. 7/8-day-old aposymbiotic larvae produced less honeydew (0.43 ± 0.038 mg/aphid) over 24 h than symbiotic aphids (0.79 ± 0.079 mg/aphid), but this difference was attributed primarily to the greater body size of the symbiotic aphids, suggesting that feeding by these larval aphids was not substantially impaired. The aposymbiotic larvae produced smaller honeydew droplets more frequently than symbiotic larvae, and no difference between the number of droplets produced in the first and second 12 h in the 24 h recording period was found. Aposymbiotic adults, in contrast, fed relatively poorly. Both EPG and honeydew production studies indicated that all symbiotic adults, but only 60–66% of aposymbiotic adults, had initiated phloem ingestion within a 10 h test period. It is proposed that the deleterious effects of bacterial disruption may be cumulative, and become increasingly severe and nonspecific with time since antibiotic treatment. It is recommended that studies on the nutritional physiology of aposymbiotic aphids are conducted with recently-generated aposymbionts, whose feeding responses are not impaired.

Many aphids are known to engage in a trophic mutualism with ants, whereby the aphids secrete sugaryrich honeydew which is collected by the ants for food, and the ants, in exchange, protect the aphids against natural enemies. Previous results, however, suggest that the production of some of the honeydew sugars, such as the ant-attractant trisaccharide melezitose, may induce an indirect cost to the aphids. This led us to believe that large differences in the nature of the secreted honeydew might exist, due to some clones capitalizing more or less on their mutualistic interaction with ants, or due to some ‘‘cheater’’ clones foregoing the production of particular sugars, instead taking advantage of the ant-attracting effect of other non sugar-deficient clones, co-occurring on the same plant. Here we present data on clonal variation in the composition of honeydew of the black bean aphid Aphis fabae which confirm this prediction. In particular, our results show that there was large interclone variation in the amount of glucose, melezitose and total sugar produced. The variation in the production of melezitose, however, showed particularly large differences, with 54% (7 out of 13) of the clones screened being virtually deficient for the production of this sugar, irrespective of whether the aphid colonies were ant-tended or not. The consequences of this finding in the context of the evolution and maintenance of the ant–aphid mutualism, as well as the adaptive benefits of oligosaccharide synthesis in aphids and other insects are discussed. 2011 Elsevier Ltd. All rights reserved.

Pea aphids (Acyrthosiphon pisum) containing their symbiotic bacteria do not require a dietary supply of the essential amino acid tryptophan over two generations on chemically-defined diets; but aphids, whose bacteria are disrupted by chlortetracycline, die as first-generation larvae on tryptophan-free diet. Consistent with the interpretation that the symbiotic bacteria in the aphids synthesize tryptophan, tryptophan synthetase activity was detected in both symbiont-bearing aphids and isolated bacteria, but not in chlortetracycline-treated aphids. Aphids reared on tryptophan-free diet produced honeydew containing 0.32 mM tryptophan, from which it can be calculated that each bacterial cell in the aphid releases at least 0.04 fmol tryptophan d−1.

This study concerns the responses of the pea aphid Acyrthosiphon pisum to chemically-defined diets containing different concentrations of nitrogen (45–270 mM amino acids) and how these responses are influenced by the antibiotic chlortetracycline, which selectively disrupts the aphids' symbiotic bacteria. The chlortetracycline-treated aphids ingested less diet than untreated controls, and the difference between the two groups of insects could be ascribed largely to the greater size of the untreated aphids. Diet uptake increased with decreasing dietary amino acid concentration, in the range 202-89 mM for untreated aphids and 202-135 mM for chlortetracycline-treated aphids. This compensatory feeding response contributed to the close similarity of aphid growth rates on these diets. The honeydew of untreated and chlortetracycline-treated aphids contained 6–10 and 10–30 mol% of the dietary amino acid concentration, respectively, and the values (in percentage terms) did not vary consistently with dietary nitrogen. The concentration of non-essential amino acids, but not essential amino acids, was significantly higher in the honeydew of chlortetracycline-treated aphids than in untreated aphids' honeydew. The selective utilization of non-essential amino acids by untreated aphids is consistent with the hypothesis that the symbiotic bacteria utilize non-essential amino acids as a nitrogen source for essential amino acid synthesis, a process known as nitrogen upgrading.

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.

Catechol oxidase (EC 1.10.3.1) and peroxidase (EC 1.11.1.7) were detected in the gut of the rose aphid. Both enzymes also occur in the saliva and catalyse the oxidation of catechin, a feeding deterrent that occurs in the parenchymal and vascular tissues of the rose. The oxidation products of catechin are phagostimulant, however, and the aphids will feed on tissues and on aqueous diets containing low concentrations of catechin. No catechin was detected in the gut, haemolymph or honeydew of aphids collected from roses but the presence in the gut and honeydew of phenolics that differed from those in the haemolymph was consistent with the ingestion and intraintestinal conversion of phenolics of plant origin. Evidence of the presence of catechin in the phloem sap was obtained, but whether the insects ingested phenols exclusively from phloem sap or from other tissues as well remained uncertain.

Acyrthosiphon pisum , whose symbiotic bacteria have been selectively disrupted by chlortetracycline, are known as aposymbionts. These aphids had significantly higher free amino acid content (108 nmol mg −1 fresh weight) than aphids containing their bacteria (65 nmol mg −1 fresh weight), but their protein content was depressed (0.034 and 0.041 mg mg −1 fresh weight for aposymbiotic and control aphids, respectively). Chlortetracycline treatment also influenced the amino acid composition of both the aphids and their honeydew. The carcasses of the aposymbionts had disproportionately high levels of the nitrogen-rich amino acids, asparagine and glutamine, and low levels of phenylalanine, isoleucine and threonine; and their honeydew was dominated by asparagine and glutamine, while that of untreated aphids contained high concentrations of arginine and histidine. It is suggested that: (a) protein synthesis in aposymbiotic aphids is limited by low availability of essential amino acids, which untreated aphids derive from their symbiotic bacteria; and (b) ammonia, a major nitrogenous waste product of the aphid, is utilized by the bacteria in untreated aphids, but it is detoxified, primarily by incorporation into glutamine in the aposymbiotic aphid. These data are consistent with the view that the bacteria contribute to the nutrition of aphids by the synthesis of essential amino acids.

The active ingestion of xylem sap by aphids is hypothesised to be an important mechanism for rehydration. When starved bird cherry-oat aphids (Rhopalosiphum padi) were allowed to feed on wheat (Triticum aestivum) treated with a sublethal dose of the xylem-mobile neonicotinoid thiamethoxam, analysis of feeding behaviours using the electrical penetration graph revealed a reduction in xylem feeding that was reversed on removal of the toxin. To test the importance of xylem-feeding behaviour as a rehydration mechanism, the effects of the sublethal dose of thiamethoxam on aphid water content, honeydew excretion, growth and fecundity were investigated. Body water contents of starved R. padi feeding on wheat treated with thiamethoxam were significantly reduced compared to aphids feeding on wheat treated with distilled water (74.5+/-0.23 and 75.6+/-0.18%, respectively). In addition, the sublethal dose of thiamethoxam had detrimental effects on aphid performance. At reproductive maturity, aphids that had been born on wheat treated with thiamethoxam were significantly smaller (as measured by body plan area; 1.07+/-0.03mm(2)), lighter (0.31+/-0.04mg) and less fecund (2.85+/-0.36nymphs/day) than aphids born on wheat treated with distilled water (1.87+/-0.02mm(2), 0.72+/-0.03mg, 11.28+/-0.58nymphs/day, respectively). Regardless of whether the observed impairment of xylem feeding is due to a neurotoxic or an antifeedant effect, these results have important implications for commercial crop protection as the behaviour-modifying effects of the sublethal dose of thiamethoxam may change the efficacy of this pesticide throughout the growing season.

A Florida strain of sweet potato whitefly, Bemisia tabaci (Gennadius), was found to have an expanded range which includes several new food crops. To determine why, we examined how it processes plant nutrients. The amino acid and carbohydrate content of phloem sap from poinsettia and pumpkin and of honeydew produced by the Florida strain were analysed. Honeydews produced by a strain from Arizona feeding on both plants were also analysed. Poinsettia phloem sap contained 15 amino acids; 14 of these were in pumpkin phloem sap. Almost all the same amino acids were in the honeydews produced by the two strains on the two hosts. Approximately half of the amino acids found in the honeydew were at concentrations which were significantly lower than concentrations in the phloem sap. Honeydew from both hosts contained six additional amino acids. The major one was glutanine which may be used to expel nitrogen. Carbohydrates in phloem sap and honeydew were common transport sugars, like sucrose. Both honeydews contained trehalulose, a disaccharide not previously associated with insects. Both strains processed phloem sap and honeydew from both plants in the same manner, but the Florida strain produced significantly larger quantities of honeydew; it is therefore assumed to process more phloem sap. Since this strain has access to more phloem sap it also has access to more of the amino acids which are in short supply in the phloem sap of some plants allowing it to broaden its range.

In an attempt to establish the roles played by intracellular symbionts in the nitrogen metabolism of aphids, the level of uric acid, ammonia and amino acids in the honeydew of symbiotic and aposymbiotic pea aphids, Acyrthosiphon pisum , were determined. It was shown that the honeydew of neither symbiotic nor aposymbiotic aphids contained any detectable amount of uric acid. A small amount of ammonia was present in the honeydew of both symbiotic and aposymbiotic aphids. The amino acid composition of the honeydew was compared with that in the phloem sap on which the aphids feed. Asparagine and glutamine were the two most abundant amino acids in the phloem sap. It was found that the amino acid composition of the honeydew changed with the age of the aphid. Amounts of asparagine and glutamine were smaller in the honeydew of symbiotic adults (21–23 day) than in that of sterile, aposymbiotic adults at the same age, suggesting that these amino acids were utilized efficiently by symbiotic aphids. In the honeydew from old symbiotic aphids (42–48 day) that no longer produced progeny, asparagine was the only amino acid in appreciable amount. In the honeydew excreted by old aposymbiotic aphids, not only asparagine but also glutamine was abundant.

The success of biological control is partly mediated by the longevity and reproductive success of beneficial insects. Availability of nectar and honeydew can improve the nutrition of parasitic insects, and thereby increase their longevity and realized fecundity. The egg parasitoid, Anaphes iole, showed strong gustatory perception of trehalulose, a carbohydrate found in homopteran honeydew. Chromatographic analysis demonstrated that enzymatic hydrolysis of sucrose, a common nectar sugar, proceeded at a faster rate than that of melezitose, a sugar common in aphid honeydew. A long-term bioassay showed that longevity was greater at 20 degrees C than at 27 degrees C, and at both temperatures survival was generally greatest for wasps provisioned with the three major nectar sugars, sucrose, glucose, and fructose. Patterns of food acceptance and utilization showed that A. iole accepted and utilized a broad range of sugars found in nature, including those found in nectar as well as honeydew. Glucose, fructose, and several oligosaccharides composed of these monosaccharide units appear to be more suitable for A. iole than other sugars tested. Evidence suggests that individual fitness benefits afforded by food sources are important for a time-limited parasitoid, and that continued investigations on the interface between nutrition and biological control are warranted for A. iole.

Tuberaphis styraci is a social aphid that produces 2nd instar soldiers with morphological, behavioral and reproductive division. High aphid density was shown to induce soldier production in T. styraci, although direct cue of soldier induction associated with high density has been unknown. In order to identify the proximate environmental cue underlying the density-dependent soldier production, a series of experiments was conducted using an artificial diet rearing technique. When adult aphids were reared with live normal nymphs, live soldiers, dead normal nymphs, shed skins, honeydew globules and excreted wax, only live normal nymphs effectively induced soldier production. In order to gain insights into the nature of soldier-inducing cue associated with normal aphids, we performed artificial diet experiments using partitioned and non-partitioned chambers, in which direct contact between aphids was either inhibited or allowed. Induction of soldiers was observed only when direct contact was allowed. Therefore, it was shown that the soldier-inducing cue is neither volatile in the air nor diffusible through the diet, but is transmitted between normal non-soldier aphids via direct contact. On the basis of these results, we suggest that the soldier-inducing cue might be physical stimulus combined with non-volatile surface chemicals whose properties differ between normal aphids and soldiers.

The effect of plant nitrogen (N) status on the content and distribution of free amino acids in the bodies and honeydew of silverleaf whiteflies Bemisia tabaci (Gennadius) Biotype B (= B. argentifolii Bellows and Perring) was determined. Whiteflies fed for 4 days on cotton leaves that received high or low N fertility. For low-N plants, photosynthesis and leaf total N levels were decreased, and a much-reduced amount of free amino acids was recovered in phloem sap. Low N fertility did not affect whitefly total N content, but did markedly decrease the free amino acid content. Glutamine, alanine and proline accounted for over half of the insect free amino acid pool for both N treatments. On a relative basis, adjustments in glutamine levels in response to plant N status were much larger compared to the other amino acids. Large amounts of amino N, especially asparagine, were excreted from whiteflies fed on high-N plants whereas amino N excretion essentially ceased for whiteflies fed on low N plants. The distribution of amino acids in the insects and honeydew was not closely related to the phloem sap amino acids. However, total amino acid excretion was quite indicative of the plant N status and the quality of the insect diet. The results indicated that whitefly free amino acid pools and excretion of amino N were rapidly altered by plant N status.

The intensity of the mutualistic relationship between aphids and ants depends mainly on the composition and amount of honeydew. We used the model system Tanacetum vulgare–Metopeurum fuscoviride to study age-related differences in honeydew production and composition and its effect on the mutualism between M. fuscoviride and the ant Lasius niger. First and second instar larvae of M. fuscoviride produced only half of the amount of honeydew as older larvae or adults. There were, however, no differences between age classes in the total honeydew sugar concentration, which averaged approx. 80 μg sugar/μl honeydew. Honeydew sugar composition also did not differ between age classes, and melezitose was the dominant sugar (59% in all classes). The amino acid concentration, by contrast, increased significantly with aphid age, reaching 22.6 nmol per μl honeydew in adult M. fuscoviride. This increase was mainly caused by asparagine and glutamine, while there were no differences in the concentrations of the five other regularly detected amino acids and cystine, respectively. The intensity of ant-attendance was significantly lower in colonies of first and second instar larvae than in colonies of older age classes. Ant-attendance correlated with the amount of honeydew produced, and not with the total amino acid concentration.

Transgenic rice plants expressing snowdrop lectin (Galanthus nivalis agglutinin; GNA) were screened for resistance to green leafhopper (Nephotettix virescens; GLH), a major homopteran pest of rice. Survival was reduced by 29% and 53% (P,0.05) respectively, on plants where GNA expression was tissue-specific (phloem and epidermal layer) or constitutive. Similar levels of resistance in GNA-expressing transgenic rice were previously reported for rice brown planthopper (Nilaparvata lugens; BPH). GNA binding to glycoproteins in gut tissues showed that BPH contained more “receptors” than GLH, and that the binding affinity was stronger, particularly in the midgut. Subsequent toxicity of GNA is thus unlikely to be directly related to the amount of lectin bound. GNA was not detected in the honeydew of either insect species when they were fed on GNA-expressing plants, in contrast to results from artificial diet studies. This result suggests that GNA is not being delivered to the insect efficiently. When offered a free choice vs control plants, BPH nymphs tended to avoid plants expressing GNA; avoidance was less pronounced and took longer to develop on plants where GNA expression was tissue-specific, In contrast to BPH, GLH nymphs were attracted to plants expressing GNA, whether constitutively or in a tissue-specific manner. © 2000 Elsevier Science Ltd. All rights reserved.

The natural diet of aphids, plant phloem sap, generally contains high concentrations of sucrose. When pea aphids (Acyrthosiphon pisum) were fed on chemically defined diets containing sucrose radiolabelled in the glucose or fructose moiety, 2 to 12-fold and 87 to 110-fold more radioactivity was recovered from the tissues and honeydew, respectively, of aphids that ingested [U-(14)C-glucose]-sucrose than from those ingesting [U-(14)C-fructose]-sucrose. The total radioactivity recovered was 70% of the ingested [U-(14)C-glucose]-sucrose and5% of ingested [U-(14)C-fructose]-sucrose. The dominant honeydew sugars produced by aphids feeding on 0.75 M sucrose diets were oligosaccharides comprising glucose. In vitro the guts of pea aphids had high sucrase activity, 1-5 U mg(-1) protein, generating equimolar glucose and fructose except at high sucrose concentrations where glucose production was inhibited (K(si)=0.1 M). These data suggest that the fructose moiety of ingested sucrose is assimilated very efficiently and may be preferentially respired by the aphid, and that the glucose moiety of sucrose is incorporated into oligosaccharides by the transglucosidase activity of the gut sucrase at high sucrose concentrations. These differences in the fate of sucrose-derived glucose and fructose are important elements in both the carbon nutrition and osmoregulation of aphids.

The major soluble carbohydrates in the silverleaf whitefly, Bemisia argentifolii, were glucose, α,α-trehalose and an unknown sugar. Analysis of the unknown sugar and its chemical and enzymatic digestion products by high-performance liquid chromatography (HPLC) showed that it was probably a trisaccharide, consisting entirely of glucose, and containing both α,α-trehalose and isomaltose moieties. Matrix-assisted laser desorption mass spectrometry, mass spectrometry and 13 C and 1 H nuclear magnetic resonance spectroscopy confirmed that the sugar was a trisaccharide with the following structure: O-α- d -glucopyranosyl-(1→6)-O-α- d -glucopyranosyl-(1↔1)-α- d -glucopyranoside. This trisaccharide, found primarily in the bodies of B. argentifolii and not in their honeydew, is structurally similar to bemisiose [O-α- d -glucopyranosyl-(1→4)-O-α- d -glucopyranosyl-(1↔1)-α- d -glucopyranoside], a sugar first identified in Bemisia honeydew. Consequently, the common name isobemisiose is proposed for the newly identified sugar. Isobemisiose, which has not been previously reported to occur in nature, constituted as much as 46% (w/w) of the ethanol-soluble sugars in adult B. argentifolii, equivalent to approximately 10% of their dry weight. It was also found in similar quantities in immature B. argentifolii. Isobemisiose was detected in two other whitefly species and in several species of aphids, but at lesser concentrations than in B. argentifolii. Labeling and pulse-chase experiments using [ 14 C ]sucrose supplied to B. argentifolii in an artificial diet revealed that label accumulated in and was chased from isobemisiose more slowly than for either glucose or trehalose. Incubation of isobemisiose with cell-free extracts of B. argentifolii demonstrated that these whiteflies contained the necessary complement of enzymes to fully degrade isobemisiose to glucose. These labeling and digestion experiments indicate that isobemisose is probably a storage carbohydrate in B. argentifolii.

Sterols were analysed to investigate the sterol source in Laodelphax striatellus and three other rice plant-sucking homopterous insects. In L. striatellus, cholesterol, 24-methylenecholesterol and β-sitosterol were detected. The host plant (rice) contained campesterol, stigmasterol and β-sitosterol. From the honeydew excreted by L. striatellus, cholesterol, β-sitosterol and negligible amounts of campesterol were recovered. Laodelphax striatellus possesses yeastlike symbiotes which can be destroyed by high temperature. Fifth instar nymphs, which have been exposed to 35°C for 3 days in their 1 st instar, showed lower cholesterol concentration and markedly reduced amounts of 24-methylenecholesterol. From the results it is concluded that L. striatellus has two sterol sources: one from the host plant and the other from the yeastlike symbiotes which appear to provide 24-methylenecholesterol.

The dry matter content of honeydew produced by Myzus persicae feeding on artificial diets increased with increasing sucrose concentrations of the diet. Whereas the diet osmolalities ranged from 828 to 1800 milliosmolal, the honeydew osmolality was relatively constant (about 500 milliosmolal). This osmoregulatory capacity is achieved largely by variations in the mean molecular weight of glucose-containing honeydew oligosaccharides.

Amino acid levels were determined in the honeydew of pea aphids infected with A. smithi , and compared to those of the holidic diet of the host in order to study the effect of parasitism on amino acid assimilation. Honeydew of both normal and infected aphids contained large amounts of arginine, histidine and homoserine but little of the other 20 amino acids and amides present in the diet. Aphids infected with an egg stage of the parasite assimilated amino acids at reduced rates compared to controls, possibly indicating that infection inhibited protein synthesis in the host aphid. Larval growth of the parasite caused renewed amino acid utilization in the host, the effect being more pronounced for homoserine than for arginine and histidine. The results suggest that the growing A. smithi larva depletes the host of specific nutrients according to its own requirements, thus causing regulatory responses in host feeding and food assimilation.

Six phytosterols are present in radish seedlings (Raphanus sativus) and in the excreta (honeydew) of the aphid, Myzus persicae fed on the seedlings. The possiblity that these compounds are transported in the phloem and utilized by the aphids is discussed.

A technique was devised for measuring the rate and frequency of honeydew excretion by the pea aphid, Acyrthosiphon pisum (Harr.), reared on pea plants, Pisum sativum L., under greenhouse conditions. The average droplet volume and the mean frequency and rate of excretion increased from the first-instar larva to the adult stage and decreased slightly during parthenogenetic reproduction. Quantitative chromatographic analyses of honeydew yielded 19 free amino acids and amides that are present also in the pea plant and the aphid blood. The total concentration of these compounds in honeydew was similar to that in aphid blood, but was 2–10 times as high as that in pea plant juice.

Single amino compounds absorbed via the petiole of pea leaves (Pisum sativum L.) were recovered in higher amounts in the leaf juice. Most absorbed compounds were partially metabolized by the leaves into other free amino compounds. The growth of pea aphids (Acyrthosiphon pisum (Harr.)) feeding on such treated leaves was slightly accelerated, but the difference in growth rate between treated leaves and checks was significant only when dl -homoserine, or a mixture of l -asparagine and l -glutamine, was used. The latter three compounds, plus leucines and valine, were recovered in increased amounts in pea leaf juice, aphid haemolymph, and honeydew; aspartic, glutamic acid, and serine increased in honeydew and haemolymph; and proline increased in haemolymph. These increases indicated a direct influence of the aphid diet on the qualitative and quantitative amino acid content of haemolymph and honeydew. The possible significance of amides and of homoserine in pea varietal resistance to aphids is discussed.

Starch substrate was utilized only in the absence of a bacteriostat, when honeydew or gut homogenate of the pea aphid, Acyrthosiphon pisum, was incubated at various pH values in appropriate starch mixtures. It was not attacked in the controls nor in the blanks. These results suggest that substrate utilization was carried out by micro-organisms (bacteria) present in the gut and honeydew of the pea aphid and was not due to any starch hydrolysing enzyme secreted by the gut.

Sorbitol was found to be the major C14-containing compound transferred from the insect Psylla pyricola (Foer.) to pear seedlings. Other C14 components were also present in the seedlings but the amounts were too small to be identified. The psylla larvae transferred considerably more C14 to the seedlings than did the adults. Analysis of psylla honeydew revealed that it contained 65 per cent sorbitol, 22 per cent sucrose, and 12 per cent reducing sugars on a dry weight basis.

Peptidase activity in gut homogenates from the pea aphid, Acyrthosiphon pisum (Harr.), was maximum at pH 7·0, 40°C, during the first few hours of incubation, and with a low substrate concentration varying from 0·05 to 0·1 per cent. A large number of dipeptides and two tripeptides were acted upon, and the mode of action suggested the presence of at least two different types of peptidases. Occasional and weak peptidase activity in the freshly excreted honeydew suggested that the enzyme was not mainly intracellular, but was being secreted into the lumen of the gut. No proteinase activity could be detected in the gut homogenates.

The chemical composition of the leaf sap of the radish, a host plant for the mustard aphid, Lipaphis erysimi , is compared with the composition of the honeydew that is excreted. The results indicate that the aphid utilizes sugars in a descending order of glucose, pentose sugars, fructose, and dextrins. Dextrin is utilized in very small amounts if at all and there is some evidence that the dextrin from honeydew has a larger molecule than the dextrin in the plant sap. Nitrogenous excretory products, when compared with the leaf sap materials, indicate the utilization of the essential amino acids and the elimination of nitrogen principally as arginine. Urea was detected and there were traces of ammonium salts. Amides and carbamyl compounds occur in significant concentrations high enough to indicate that the excretory mechanism of the aphid could be severely taxed to provide for their elimination.