Dietary sucrose and oligosaccharide synthesis in relation to osmoregulation in the pea aphid, Acyrthoslphon pisum

Abstract. A major problem for aphids is the avoidance of dehydration due to a high dietary osmotic pressure. Their adaptations include a high osmotic pressure in the haemolymph and polymerization of dietary sugars to oligosaccharides. The pea aphid, Acyrthosiphon pisum (Harris), was fed on an artificial diet containing Relabelled sucrose, and the fate of dietary sucrose was studied using quantitative paper chromatography. The haemolymph of A. pisum , feeding on artificial diet containing 25% w/v (730 mM) sucrose, contained two main sugars: trehalose (255 nw) and fructose (129 mM). No sucrose was found in the haemolymph. The honeydew sugars (350 mM) of aphids fed the same diet were mainly oligosaccharides (220 mM). The polymerization of sucrose was responsible for a 34% reduction in molarity of sugars in the honeydew. At low dietary sucrose concentrations, the honeydew contained mainly mono- and disaccharides. At dietary sucrose concentrations of 15% or more, oligosaccharides were predominant. This is consistent with the idea that osmoregulation is carried out by oligosaccharide synthesis. Analysis of the stomach contents revealed that oligosaccharide synthesis occurs there, and tissue incubation showed that die gut is much more active in oligosaccharide synthesis than the eviscerated body tissues. The function of the filter chamber, found in some aphid species, is considered and it is suggested that this is a mechanism for reducing the osmotic pressure of the ingested diet.     

Living on a high sugar diet: the fate of sucrose ingested by a phloem-feeding insect,the pea aphid Acyrthosiphon pisum

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 and <5% 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.     

Interspecific symbiont transfection confers a novel ecological trait to the recipient insect

In Japan, pea aphids Acyrthosiphon pisum mainly feed on vetch and clover, and many aphid clones produce more progeny on vetch than on clover. In this context, particular genotypes of the facultative symbiont Regiella insecticola enhance reproduction of infected pea aphids specifically on clover, thereby broadening the suitable food plant range of the insect. A species that is sympatric to A. pisum, vetch aphids Megoura crassicauda, are commonly found on vetch but not on clover. Laboratory rearing of M. crassicauda strains revealed active reproduction on vetch but substantially no reproduction on clover. Experimental transfection of Regiella from A. pisum to M. crassicauda by haemolymph injection established stable and heritable infection in the recipients, although no Regiella infection has been detected in natural populations of M. crassicauda. Different strains of Regiella-transfected M. crassicauda grew and reproduced on vetch, but exhibited lower fitness in comparison with corresponding uninfected aphid strains. Strikingly, the Regiella-transfected M. crassicauda exhibited improved survival and some reproduction on clover. These results suggest that Regiella has the potential to confer an ecological trait, adaptation to clover, on novel insect hosts, and also account for why Regiella is able to infect M. crassicauda but is scarcely found in these aphid populations.     

Sucrose hydrolases from the midgut of the sugarcane stalk borer Diatraea saccharalis

A beta-fructosidase (EC 3.2.1.26) was isolated from the midgut of larval sugar cane stalk borer Diatraea saccharalis by mild-denaturing electrophoresis and further purified to near homogeneity by gel filtration. beta-Fructosidase hydrolysed sucrose, raffinose and the fructosyl-trisaccharide isokestose, but it had no activity against maltose, melibiose and synthetic substrates for alpha-glucosidases. Two other sucrose hydrolases, one resembling a alpha-glucosidase (EC 3.2.1.20) and the other one active specifically against sucrose (sucrase) were detected in the larval midgut of D. saccharalis. All three sucrose hydrolases were associated with the midgut epithelium of larval D. saccharalis. Relative molecular mass (M(r)) of the beta-fructosidase was estimated around 45,000 (by gel filtration). The other two sucrose hydrolases had M(r) of 54,000 (alpha-glucosidase) and 59,000 (sucrase). The pH optima of the sucrose hydrolases were 5-10 for both alpha-glucosidase and sucrase and 7-8 for beta-fructosidase. Considering V(max)/K(m) ratios, beta-fructosidase preferentially cleaves isokestose rather than raffinose and sucrose. In order to evaluate the possible contribution of microorganisms isolated from the midgut to the pool of sucrose hydrolases, washed midgut epithelia were homogenised and plated onto appropriate media. Seven bacterial and one yeast species were isolated. None of the sucrose hydrolases extracted from the microorganisms corresponded to the enzymes isolated from midgut tissue homogenates. This result suggests that the major sucrose hydrolases found in the midgut of larval D. saccharalis were probably produced by the insect themselves not by the gut microflora.     

Oligosaccharide synthesis regulates gut osmolality in the ant-attended aphid Metopeurum fuscoviride but not in the unattended aphid Macrosiphoniella tanacetaria

Abstract:  An artificial phloem sap (APS) for Metopeurum fuscoviride and Macrosiphoniella tanacetaria , based on analysis of their host plant, Tanacetum vulgare , phloem sap, contained 308  μ g/ μ l (900  μ mol/ μ l) sucrose (and no other sugars) and a mixture of 14 amino acids with a total concentration of 82.5 nmol/ μ l. There was no significant difference in the total amino acid concentration of the honeydew of adult M. fuscoviride fed on the host plant and aphids fed on APS. Incubation of isolated guts in APS indicated no role of gut bacteria or gut enzymes on the amino acid pattern in the gut. The sugar composition of the honeydew of the ant-attended M. fuscoviride indicated a rapid digestion of sucrose into glucose and fructose, and the simultaneous synthesis of considerable amounts of melezitose and some trehalose. The sugar composition of the honeydew of the unattended M. tanacetaria in contrast showed only traces of trehalose and melezitose, but up to 20% erlose in plant-fed aphids. Incubation of isolated guts of M. fuscoviride in APS demonstrated a steady high rate of melezitose synthesis by gut enzymes over an 8-h period. Incubation of isolated guts of M. tanacetaria on the other hand demonstrated only a moderate rate of erlose synthesis and no detectable melezitose or trehalose. Melezitose in the aphid M. fuscoviride is a signal sugar for ants (ecological function), indicating the presence of abundant sugar rich honeydew [ Woodring et al. (2004) Physiol. Entomol. , vol. 29, pp. 311–319]. It was estimated that melezitose reduces the gut osmolality of M. fuscoviride to approximately 25–35% of what it would be without the synthetases (physiological function). M. tanacetaria on the other hand produces very little honeydew, is not attended by ants, and thus there is little need to synthesize large amounts of oligosaccharides to attract ants or for osmoregulation.     

Protein digestion in cereal aphids (Sitobion avenae) as a target for plant defence by endogenous proteinase inhibitors

Gut extracts from cereal aphids (Sitobion avenae) showed significant levels of proteolytic activity, which was inhibited by reagents specific for cysteine proteases and chymotrypsin-like proteases. Gut tissue contained cDNAs encoding cathepsin B-like cysteine proteinases, similar to those identified in the closely related pea aphid (Acyrthosiphon pisum). Analysis of honeydew (liquid excreta) from cereal aphids fed on diet containing ovalbumin showed that digestion of ingested proteins occurred in vivo. Protein could partially substitute for free amino acids in diet, although it could not support complete development. Recombinant wheat proteinase inhibitors (PIs) fed in diet were antimetabolic to cereal aphids, even when normal levels of free amino acids were present. PIs inhibited proteolysis by aphid gut extracts in vitro, and digestion of protein fed to aphids in vivo. Wheat subtilisin/chymotrypsin inhibitor, which was found to inhibit serine and cysteine proteinases, was more effective in both inhibitory and antimetabolic activity than wheat cystatin, which inhibited cysteine proteases only. Digestion of ingested protein is unlikely to contribute significantly to nutritional requirements when aphids are feeding on phloem, and the antimetabolic activity of dietary proteinase inhibitors is suggested to result from effects on proteinases involved in degradation of endogenous proteins.     

Diurnal feeding as a potential mechanism of osmoregulation in aphids

Diurnal variation in phloem sap composition has a strong infuence on aphid performance.The sugar-rich phloem sap serves as the sole diet for aphids and a suite of physiological mechanisms and behaviors allowv them to tolerate the high osmotic stress.Here,we tested the hypothesis that night-time feeding by aphids is a behavior that takes advantage of the low sugar diet in the night to compensate for osmotic stress incurred while feeding on high sugar diet during the day.Using the electrical penetration graph(EPG)technique.we examined the eiects of diurmal rhythm on feeding behaviors of bird cherry-oat aphid(Rhopalosiphurm padi L.)on wheat.A strong diurmal rhythm in aphids as indicated by the presence of a cyclical pattern of expression in a core clock gene did not impact aphid feeding and similar feeding behaviors were observed during day and night.The major difference observed between day and night feeding was that aphids spent significantly longer time in phloem salivation during the night compared to the day.In contrast,aphid hydration was reduced at the end of the day-time feeding compared to end of the night-time fepding.Gene expression analysis of R.padi osmoregulatory genes indicated that sugar break down and water transport into the aphid gut was reduced at night.These data suggest that while diumal variation occurs in phloem sap composition,aphids use night time feeding to overcome the high osmotic stress incurred while feeding on sugar-rich phloem sap during the day.     

Molecular characterisation of a candidate gut sucrase in the pea aphid, Acyrthosiphon pisum

The hydrolysis of sucrose, the principal dietary source of carbon for aphids, is catalysed by a gut alpha-glucosidase/transglucosidase activity. An alpha-glucosidase, referred to as APS1, was identified in both a gut-specific cDNA library and a sucrase-enriched membrane preparation from guts of the pea aphid Acyrthosiphon pisum by a combination of genomic and proteomic techniques. APS1 contains a predicted signal peptide, and has a predicted molecular mass of 68 kDa (unprocessed) or 66.4 kDa (mature protein). It has amino acid sequence similarity to alpha-glucosidases (EC 3.2.1.20) of glycoside hydrolase family 13 in other insects. The predicted APS1 protein contains two domains: an N-terminal catalytic domain, and a C-terminal hydrophobic domain. In situ localisation and RT-PCR studies revealed that APS1 mRNA was expressed in the gut distal to the stomach, the same localisation as sucrase activity. When expressed heterologously in Xenopus embryos, APS1 was membrane-bound and had sucrase activity. It is concluded that APS1 is a dominant, and possibly sole, protein mediating sucrase activity in the aphid gut.     

Direct effects of snowdrop lectin (GNA) on larvae of three aphid predators and fate of GNA after ingestion

Plants genetically modified to express Galanthus nivalis agglutinin (GNA) have been found to confer partial resistance to homopteran pests. Laboratory experiments were conducted to investigate direct effects of GNA on larvae of three species of aphid predators that differ in their feeding and digestive physiology, i.e. Chrysoperla carnea, Adalia bipunctata and Coccinella septempunctata. Longevity of all three predator species was directly affected by GNA, when they were fed a sucrose solution containing 1% GNA. However, a difference in sensitivity towards GNA was observed when comparing the first and last larval stage of the three species. In vitro studies revealed that gut enzymes from none of the three species were able to break down GNA. In vivo feed-chase studies demonstrated accumulation of GNA in the larvae. After the larvae had been transferred to a diet devoid of GNA, the protein stayed present in the body of C. carnea, but decreased over time in both ladybirds. Binding studies showed that GNA binds to glycoproteins that can be found in the guts of larvae of all three predator species. Immunoassay by Western blotting of haemolymph samples only occasionally showed the presence of GNA. Fluorescence microscopy confirmed GNA accumulation in the midgut of C. carnea larvae. Implications of these findings for non-target risk assessment of GNA-transgenic crops are discussed.     

The effect on Aphis fabae of diel changes in their food quality

ABSTRACT. Marked diurnal changes in total soluble carbohydrates were found in broad bean leaves, with a maximum of c. 11% of dry weight at 18.00 hours to a minimum of c. 4% at 06.00 hours. If reflected in the phloem sap, this would mean that aphids receive different food from plants by night and by day. The growth rate of Aphis fabae was therefore compared on broad bean plants under light and darkness. Although the aphids showed the same mean gross growth rate under both conditions, those in the dark had a higher final percentage moisture content, their dry weight increase being negligible. Counts of honeydew droplets on a 'honeydew clock' indicated a reduction in excretion during the dark. Measurements of haemolymph concentration of Acyrthosiphon pisum were obtained by comparison of haemolymph vapour pressure with that of known sucrose solutions, using capillary tubes. Haemolymph samples collected at the end of the day showed a higher (mean 11.53 atm) and more variable osmotic pressure than those obtained at the end of the night (mean 8.62 atm). The more dilute sap in the plant at night may benefit the aphid by allowing it to compensate for osmotic stress incurred during daytime feeding. These results suggest that the diurnal change in total soluble carbohydrates in leaves of the broad bean is reflected in the phloem sap.     

Does host‐feeding on GNA‐intoxicated aphids by Aphelinus abdominalis affect their longevity and/or fecundity?

Transgenic potatoes have been transformed with a gene coding the snowdrop lectin Galanthus nivalis agglutinin (GNA) and they have been shown to be partially resistant to aphids. GNA binds to insect gut cells, including those of aphids, consequently inducing disruption of nutrient assimilation. Aphid parasitoids are important natural biocontrol agents of aphids and some species such as Aphelinus abdominalis are commercially available. Aphid parasitoids are endoparasitoids during their larval stages and free-living insects as adults. They could be directly or indirectly affected by GNA during both these stages. In this work, we present data on the potential direct and indirect effects of GNA on adult A. abdominalis. Aphelinus abdominalis is a synovigenic species (eggs are matured throughout the adult life) which needs a diet relatively rich in proteins and amino-acids to produce anhydropic eggs (large, yolk-rich eggs that do not expand in the host during embryonic stages). Adult A. abdominalis females feed on aphid haemolymph and they may be directly exposed to the entomotoxin or indirectly affected by a change in aphid haemolymph quality due to intoxication by GNA. We conducted a first tier experiment to investigate this potential risk. A. abdominalis females were offered either aphids reared on control diet or aphids reared on GNA 0.1% diet as hosts (i.e., as food and oviposition sites). No trace of GNA was found in females fed with GNA-aphids but no GNA could be detected in the haemolymph of aphids fed a 0.1% GNA diet. Longevity and fecundity were not affected suggesting that the quality of the haemolymph necessary for A. abdominalis egg maturation and production was not significantly altered.     

Interaction of the Bacillus thuringiensis delta endotoxins Cry1Ac and Cry3Aa with the gut of the pea aphid, Acyrthosiphon pisum (Harris)

Hemipteran pests including aphids are not particularly susceptible to the effects of insecticidal Cry toxins derived from the bacterium Bacillus thuringiensis. We examined the physiological basis for the relatively low toxicity of Cry1Ac and Cry3Aa against the pea aphid, Acyrthosiphon pisum (Harris). Cry1Ac was efficiently hydrolyzed by aphid stomach membrane associated cysteine proteases (CP) producing a 60 kDa mature toxin, whereas Cry3Aa was incompletely processed and partially degraded. Cry1Ac bound to the aphid gut epithelium but showed low aphid toxicity in bioassays. Feeding of aphids on Cry1Ac in the presence or absence of GalNAc, suggested that Cry1Ac gut binding was glycan mediated. In vitro binding of biotinylated-Cry1Ac to gut BBMVs and competition assays using unlabeled Cry1Ac and GalNAc confirmed binding specificity as well as glycan mediation of Cry1Ac binding. Although Cry3Aa binding to the aphid gut membrane was not detected, Cry3Aa bound 25 and 37 kDa proteins in aphid gut BBMV in ligand blot analysis and competition assays confirmed the binding specificity of Cry3Aa. This, combined with low toxicity in feeding assays, suggests that Cry3Aa does bind the gut epithelium to some extent. This is the first systematic examination of the physiological basis for the low efficacy of Cry toxins against aphids, and analysis of Cry toxin-aphid gut interaction.     

Abdominal gland secretion ofBledius rove beetles as an effective defence against predators

Recent investigations indicated thatBacillus thuringiensis delta-endotoxins (DET) possess aphidicidal activity in an artificial diet bioassay. Crystalline preparations of CryIIA, CryIIIA and CryIVD solubilized in a slightly alkaline sucrose/amino acid diet clearly imparted toxicity toward adults of potato aphid,Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) after 4–5 days of continuous feeding. No obvious feeding deterrence was noted in these assays, as copious honeydew was produced and aphids often died in a feeding position. CryIIIA which was solubilized in aphid diet, but filtered to remove spores or crystalline toxin lacked aphidicidal activity. Spores from an acrystalliferous strain (EG2205) were not toxic by themselves at 7.75×10⁵ spores/ml aphid diet, but did restore toxicity to the filtered CryIIIA solution. Therefore, low levels of spores may be very effective in concert with DET for aphicidal activity. Results also clearly demonstrated that a suspension of crystalline CryIIIA alone, without spores, exhibited toxicity. Therefore, DET may be more toxic to the aphids when imbibed as a fine suspension, perhaps indicating the need for slow solubilization into the aphid midgut.     

Impact of the entomopathogenic fungus Verticillium lecanii on development of an aphid parasitoid, Aphidius colemani

The parasitoid Aphidius colemani developed normally (approximately 90% adult emergence) when its cotton aphid (Aphis gossypii) host was treated with Verticillum lecanii conidia 5 or 7 days after parasitization. Fungus exposure 1 day before or up to 3 days after parasitization, however, reduced A. colemani emergence from 0 to 10%. Also, numbers of spores and mycelial fragments in aphid homogenates were much higher in aphids exposed to the fungus up to 3 days after parasitization than in aphids treated after 5 or 7 days. Our results suggest that the parasitoid and fungus may be used together for aphid biocontrol as long as fungus applications are timed to allow late-instar development of the parasitoid.     

The cabbage aphid: a walking mustard oil bomb

The cabbage aphid, Brevicoryne brassicae, has developed a chemical defence system that exploits and mimics that of its host plants, involving sequestration of the major plant secondary metabolites (glucosinolates). Like its host plants, the aphid produces a myrosinase (beta-thioglucoside glucohydrolase) to catalyse the hydrolysis of glucosinolates, yielding biologically active products. Here, we demonstrate that aphid myrosinase expression in head/thoracic muscle starts during embryonic development and protein levels continue to accumulate after the nymphs are born. However, aphids are entirely dependent on the host plant for the glucosinolate substrate, which they store in the haemolymph. Uptake of a glucosinolate (sinigrin) was investigated when aphids fed on plants or an in vitro system and followed a different developmental pattern in winged and wingless aphid morphs. In nymphs of the wingless aphid morph, glucosinolate level continued to increase throughout the development to the adult stage, but the quantity in nymphs of the winged form peaked before eclosion (at day 7) and subsequently declined. Winged aphids excreted significantly higher amounts of glucosinolate in the honeydew when compared with wingless aphids, suggesting regulated transport across the gut. The higher level of sinigrin in wingless aphids had a significant negative impact on survival of a ladybird predator. Larvae of Adalia bipunctata were unable to survive when fed adult wingless aphids from a 1% sinigrin diet, but survived successfully when fed aphids from a glucosinolate-free diet (wingless or winged), or winged aphids from 1% sinigrin. The apparent lack of an effective chemical defence system in adult winged aphids possibly reflects their energetic investment in flight as an alternative predator avoidance mechanism.     

A phloem-sap feeder mixes phloem and xylem sap to regulate osmotic potential

Phloem-sap feeders (Hemiptera) occasionally consume the dilute sap of xylem, a behaviour that has previously been associated with replenishing water balance following dehydration. However, a recent study reported that non-dehydrated aphids ingested xylem sap. Here, we tested the hypothesis that the consumption of xylem sap, which has a low osmolality, is a general response to osmotic stresses other than dehydration. Alate aphids were subjected to different treatments and subsequently transferred onto a plant, where electrical penetration graph (EPG) was used to estimate durations of passive phloem sap consumption and active sucking of xylem sap. The proportion of time aphids fed on xylem sap (i.e., time spent feeding on xylem sap/total time spent feeding on phloem plus xylem sap) was used as a proxy of the solute concentration of the uptake. The proportion of time alate aphids fed on xylem sap increased: (1) with the time spent imbibing an artificial diet containing a solution of sucrose, which is highly concentrated in phloem sap and is mainly responsible for the high osmotic potential of phloem sap; (2) with the osmotic potential of the artificial diet, when osmotic potential excess was not related to sucrose concentration; and (3) when aphids were deprived of primary symbionts, a condition previously shown to lead to a higher haemolymph osmotic potential. All our results converge to support the hypothesis that xylem sap consumption contributes to the regulation of the osmotic potential in phloem-sap feeders.     

Probiotic effects of beta-glucuronidase on the peach-potato aphid Myzus persicae (Aphididae)

beta-glucuronidase (GUS) is a reporter protein commonly expressed in transgenic plants allowing the visualization of the transformed individuals. In our recent work, we showed that consumption of transformed potato plants expressing this GUS enzyme improves performance of the phloem feeding aphid Myzus persicae. Those results led us to the conclusion that the expression of GUS in potato plants might be responsible for the probiotic effect measured in feeding aphids. In the present paper, artificial diets were used to provide active GUS (10 and 500 microg ml(-1)), inactivated heated GUS (500 microg ml(-1)), glucuronic acid (10, 100 and 500 microg ml(-1)), and bovine serum albumin (500 microg ml(-1)) to M. persicae. Our results reveal that these chemicals provided as food intake might influence the biological parameters of this aphid. Experiments showed a probiotic effect of 500 microg ml(-1) GUS diet, resulting in reduced larval mortality, and increased adult reproduction period and fecundity, which led to an increased population growth potential (r(m)=0.17+/-0.01 versus r(m)=0.12+/-0.03 for aphids fed on control diet). A lower amount of added GUS led to fewer variations, biological parameters being only slightly altered (r(m)=0.14+/-0.03). Statistically similar alterations of the biological parameters were obtained when comparing aphids fed on the diet added with inactivated GUS or the non-structural bovine serum albumin protein (r(m)=0.15+/-0.02 and 0.14+/-0.03, respectively). Feeding assays conducted with glucuronic acid supplemented diets enhanced longevity and nymph production of the adult aphids and reduced larval mortality, resulting in r(m)=0.15+/-0.02 for the highest dose (500 microg ml(-1)). Although 100 microg ml(-1) glucuronate diet did not induce any effect on M. persicae (r(m)=0.12+/-0.03), aphids fed on 10 microg ml(-1) glucuronate diet exhibited unexpected reduced demographic parameters (r(m)=0.10+/-0.03). Immuno-histological analysis showed GUS labeling along the whole digestive epithelium of adults and in various tissues including embryos and bacteriocytes. These results suggest that GUS crosses through the digestive tract. Western blots performed with protein extracts of transformed potato plants expressing the gus gene showed a unique band of molecular weight 76 kDa. On the contrary, in extracts from aphids fed on transgenic potato plants or bred on GUS 500 microg ml(-1) artificial diet, several proteins of lower molecular weight were hybridized, revealing proteolysis of ingested GUS. It is concluded that GUS protein, and more precisely GUS activity, is responsible for the probiotic effects on aphid feeding. The possible pathways of induction of such physiological alterations by GUS are discussed.     

Oral activity of FMRFamide-related peptides on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut

Insect myosuppressins and myosuppressin analogues were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Acyrthosiphon pisum myosuppressin (Acypi-MS) and leucomyosuppressin (LMS) had significant dose-dependent effects (0.1-0.5μg peptide/μl diet) on feeding suppression, mortality, reduced growth and fecundity compared with control insects, but Acypi-MS was more potent than LMS. One hundred percent of aphids had died after 10days of feeding on 0.5μg Acypi-MS/μl diet whereas 40% of aphids feeding on 0.5μg LMS/μl diet were still alive after 13days. Myosuppressins were degraded by aphid gut enzymes; degradation was most likely due to a carboxypeptidase-like protease, an aminopeptidase and a cathepsin L cysteine protease. The estimated half-life of Acypi-MS in a gut extract was 30min, whereas LMS was degraded more slowly (t?=54min). No toxicity was observed when the analogues δR(9) LMS and citrolline(9) Acypi-MS or FMRFamide were fed to the pea aphid. These findings not only help to better understand the biological effects of myosuppressins in aphids but also demonstrate the potential use of myosuppressins in a strategy to control aphid pests.