The influence of aphid-produced honeydew on parasitoid fitness and nutritional state: A comparative study

Honeydew is a sugar-rich resource excreted by many hemipteran species and is a key food source for other insect species such as ants and parasitoid wasps. Here, we evaluated the nutritional value of 14 honeydews excreted by 13 aphid species for the generalist aphid parasitoid Lysiphlebus testaceipes to test a series of hypotheses concerning variation in the nutritional value of honeydew. There was a positive correlation between the body sugar content of honeydew-fed parasitoids and their longevity. This information is valuable for biological control researchers because it demonstrates that the nutritional state of honeydew-fed parasitoids in the wild can indicate their fitness, independently of the honeydew source they have fed on.Although the carbohydrate content and longevity of L. testaceipes differed greatly among the different honeydews, we did not find a significant effect of aphid or host plant phylogeny on these traits. This result suggests that honeydew is evolutionarily labile and may be particularly subject to ecological selection pressures. This becomes apparent when considering host aphid suitability: Schizaphis graminum, one of the most suitable and commonly used hosts of L. testaceipes, produced honeydew of the poorest quality for the parasitoid whereas Uroleucon sonchi, one of the few aphids tested that cannot be parasitized by L. testaceipes, excreted the honeydew with the highest nutritional value. These data are consistent with the hypothesis that hemipterans are subject to selection pressure to minimize honeydew quality for the parasitoids that attack them.     

Nutritional ecology of a parasitic wasp: food source affects gustatory response, metabolic utilization, and survivorship

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 °C than at 27 °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.     

Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability

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.     

The nutritional value of aphid honeydew for non-aphid parasitoids

Intake of sugar-rich foods by adult parasitoids is crucial for their reproductive success. Hence, the availability of suitable foods should enhance the efficacy of parasitoids as biological control agents. In situations where nectar is not readily available, homopteran honeydew can be a key alternative food source. We studied the impact of honeydew feeding on the longevity of the larval endoparasitoids Cotesia marginiventris, Campoletis sonorensis and Microplitis rufiventris, all natural enemies of important lepidopteran pests. Females of these wasps lived longer when feeding on honeydew produced by the aphid Rhopalosiphum maidis on barley compared to control females provided with water only. However, they lived shorter than females fed with a sucrose solution. Further investigations with C. marginiventris showed that access to honeydew also increases the number of offspring produced, but less so than access to a sucrose solution. Moreover, it was found that females of this species need to feed several times throughout their life in order to reach optimal longevity and reproductive output. Analyses of the sugars in the honeydew produced by R. maidis on barley revealed that it contains mainly plant-derived sugars, but also several aphid-synthesized sugars. The sugar composition of the honeydew changed as a function of aphid colony size and time a colony had been feeding on a plant. In general, the higher the aphid infestation, the smaller the percentage of aphid-synthesized sugars in the honeydew. Experiments with honeydew sugar mimics allowed us to reject the hypothesis that the relatively poor performance of the parasitoid on a honeydew diet was due to the sugar composition. Instead, the results from additional feeding experiments with diluted honeydew showed that the nutritional value of pure honeydew is primarily restricted by its high viscosity. The possible consequences of these findings for biological pest control are discussed.     

Comparing floral nectar and aphid honeydew diets on the longevity and nutrient levels of a parasitoid wasp

We compared the effects of floral nectar from buckwheat, Fagopyrum esculentum Moench, and honeydew produced by the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), on longevity, nutrient levels, and egg loads of the parasitoid Diadegma insulare Cresson (Hymenoptera: Ichneumonidae). Diadegma insulare lived for 2 days in control treatments of water or clean soybean leaves, for 6–7 days with honeydew, and in excess of 2 weeks with buckwheat nectar. Potential reasons for the superiority of buckwheat nectar over soybean aphid honeydew for extending the longevity of parasitoids include: (i) parasitoids ingest more sugars from floral sources, (ii) oligosaccharides in honeydew have a lower nutritional value than nectar sugars, and (iii) honeydew has antagonistic compounds. Overall sugar levels were lower in honeydew‐ vs. nectar‐fed female wasps, suggesting a lower feeding rate, but other explanations cannot be excluded. Diadegma insulare eclosed with high levels of lipids and glycogen, and low levels of gut and storage sugars. All carbohydrates increased over the life of both nectar‐ and honeydew‐fed wasps, but remained low or decreased in starved wasps. Lipid levels declined over the lifespan of female wasps, but females fed floral nectar showed the slowest rate of lipid decline. Diet did not affect egg load, probably because the females were not given hosts in the experiment.     

Host plant recognition in monophagous weevils: Specialization ofCeutorhynchus inaffectatus to glucosinolates from its host plantHesperis matronalis

Several aphid honeydews were incorporated into sucrose solutions and presented to hop aphids, Phorodon humuli (Schrank), as artificial diets in free-choice bioassays. Small additions of honeydew collected from two species of aphid feeding on hop, Humulus lupulus L., arrested the searching behavior of the hop aphid and appeared to stimulate prolonged periods of ingestion. This effect was more dependent on the host plant honeydew source than the species of aphid that produced the honeydew. Aphid honeydews collected from plants other than hop (non-hosts to P. humuli) contained hop aphid phagostimulants that were less effective. Our results indicate that analysis of aphid honeydew could help describe chemical cues involved in the recognition of appropriate host plants by aphid species.     

Energy reserves of parasitoids depend on honeydew from non‐hosts

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Effect of six carbohydrate sources on the longevity of a whitefly parasitoid Eretmocerus hayati (Hymenoptera: Aphelinidae)

Parasitoid adults often acquire carbohydrates by feeding on floral nectar and honeydew which provides them with energy and prolongs their life span. The concentration and type of saccharide in nectar and honeydew are variable by species of plant and insect. To explore the effects of various sugar type and concentrations on parasitoid fitness, we compared 5%, 10% and 20% (w/v) solutions of six different sugar resources (glucose, fructose, sucrose, trehalose, melezitose and honey) on the longevity of Eretmocerus hayati, a larval parasitoid of the whitefly Bemisia tabaci in China. Male and female longevity was increased by all of the sugar diets, but female wasps survived longer than the males when the same sugar diet was supplied. Female parasitoids feeding on 10% glucose and 10% honey increased longevity, respectively up to 6.2- and 5.9-fold longer than distil water; 5% honey and 10% fructose had the greatest effects on male longevity, up to 3.5- and 3.3-fold. All six sugar diets, no matter which concentration, significantly changed the survival curves. Glucose, sucrose and honey were optimal sugar diets for this wasp, and 10% was the optimal concentration. Our results could provide an insight into the nutritional requirements of E. hayati under laboratory conditions. Such information can be a basis to improve the longevity of this biological control agent by sugar feeding during the indoor mass-rearing process.     

Nectar to improve parasitoid fitness in biological control: Does the sucrose:hexose ratio matter?

The consumption of saccharide-rich foods such as floral nectar is crucial for the survival of many adult parasitoid wasps. The importance to parasitoids of nectar quality, with regards to its sucrose:hexose ratio, was investigated. Nectar, an aqueous solution of sugars, amino acids and other compounds, differs between plant species. Nectar composition is dominated by sucrose, glucose and fructose. Previous studies have shown that the ratio of sucrose to hexose (glucose+fructose) sugars can explain nectar associations in a range of flower visiting arthropods. It has been suggested that this ratio may be important in terms of parasitoid fitness. Analysis of floral nectar from fourteen plant species confirmed that the sucrose/hexose ratio significantly differed between species. An opportunity to select floral resources based on this measure of nectar quality arose and highlighted the potential to utilize native flowering plant species in place of the seven most commonly deployed, which are usually not native to the countries in which they are used.Results presented in this paper indicate, however, that the sucrose/hexose ratio is not a significant factor explaining parasitoid longevity. The hymenopteran parasitoids Diadegma semiclausum (Ichneumonidae) and Dolichogenidea tasmanica (Braconidae) were fed 40% w/w sugar solutions, differing in their sugar ratios. Solutions were classified as either sucrose-dominant (ratio >0.99), sucrose-rich (ratio 0.5–0.99), hexose-rich (ratio 0.1–0.499) or hexose-dominant (ratio <0.1). No significant differences in parasitoid longevity were found between the different treatments for either species. This suggests there is not an optimal sucrose/hexose ratio for parasitoid wasps, although a greater number of parasitoid species should ideally be tested to confirm if this is true for the wider parasitoid taxonomic groups.     

Effects of aphid honeydew sugars on the longevity and fecundity of the aphidophagous gall midge Aphidoletes aphidimyza

The predatory gall midge Aphidoletes aphidimyza, which is used for augmentative biological control of aphids in greenhouses, uses aphid honeydew as an energy source. Currently, Rhopalosiphum padi on barley plants and Melanaphis sacchari on sorghum plants are used as the banker plant systems for A. aphidimyza to control Aphis gossypii on eggplant in Japan. We analyzed the sugar components of the honeydew of these three species by HPLC. The major components of honeydew were sucrose, fructose, and melezitose for A. gossypii; glucose and fructose for R. padi; and glucose, fructose, and melezitose for M. sacchari. Maltose and trehalose were minor components of the honeydew of these species. We investigated the influence of sugars, including three artificial aphid honeydews, six sugar components, and distilled water, on the longevity of unmated A. aphidimyza. Both females and males attained the greatest longevity on sucrose and artificial honeydew of A. gossypii. Mean longevities of both females and males were shortest when they were provided only with water. We conducted another experiment in which a mated female was released in a cage with an eggplant seedling infested with A. gossypii and fed with sucrose or only water. Females fed with sucrose lived significantly longer and had higher lifetime fecundity than those fed only water.     

Aphid parasitoid responses to semiochemicals — Genetic, conditioned or learnt?

Parasitoid foraging behaviour is known to be influenced by interactions of genetic, physiological, environmental and experiential factors. Although the role of genetics, learning and conditioning in determining responses to foraging cues has been studied in lepidopteran parasitoids, aphid parasitoids have been less intensively researched. Using the tritrophic system,Vicia faba — Acyrthosiphon pisum — Aphidius ervi, evidence for the role of genetics and learning in parasitoid foraging is presented, and the difficulty of differentiating between genetic responses and those conditioned during parasitoid development is discussed. Aphidius ervi responds to aphid sex pheromones both in the field and in the laboratory. Since laboratory reared individuals have never experienced sexual aphids, the response must be genetic as it cannot have been conditioned during development. An example of a response conditioned during development is the variable response ofA. rhopalosiphi to different wheat cultivars depending upon host feeding. Aphid parasitoids also are adept at learning as shown by their responses to plant-derived cues which are learnt as Conditioned Stimuli (CS). Host products such as honeydew, as well as the host itself, can act as the Unconditioned Stimulus (US) in the learning process. Aphidius ervi offers a good model for investigating the role of these factors in parasitoid foraging behaviour. Finally, the value of such research for biological control programmes involving aphid parasitoids is discussed.     

Sugar feeding by the aphid parasitoid Binodoxys communis: how does honeydew compare with other sugar sources?

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.     

Snowdrop lectin (Galanthus nivalis agglutinin) in aphid honeydew negatively affects survival of a honeydew- consuming parasitoid

1 Insecticidal proteins can be excreted in the honeydew when sap-sucking insects feed on insect-resistant transgenic plants. Honeydew can be an important source of carbohydrates, thus potentially exposing a broad range of honeydew-feeding insects to transgene products.
2 Snowdrop lectin ( Galanthus nivalis agglutinin; GNA) dissolved in a 2 m sucrose solution had no antifeedant effect on female aphid parasitoids ( Aphidius ervi ) but had a direct negative effect on their longevity.
3 When feeding on honeydew from Rhopalosiphum padi feeding on a GNA-containing artificial diet, Aphidius ervi suffered a longevity reduction that was more pronounced than was to be expected based on the detected GNA concentration in the honeydew.
4 Analysis of carbohydrate and amino acid composition revealed that a change in honeydew composition caused by a GNA-effect on the aphids could be a possible explanation for the additional reduction in parasitoid longevity.
5 When comparing the effect of honeydew from Sitobion avenae and R. padi feeding on GNA-expressing or nontransformed wheat plants on A. ervi longevity, aphid species was found to have a significant effect, whereas the wheat variety had no effect. The latter result was probably due to low GNA expression levels in the plants. Differences in nutritional suitability between honeydew from R. padi and S. avenae could be explained by differences in carbohydrate and amino acid composition.
6 This is the first study to demonstrate that GNA ingested by aphids and transported into the honeydew can negatively affect the parasitoids consuming this honeydew.
7 We recommend that honeydew should be considered as a route of exposure to transgene products in future risk assessment studies.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.     

Carbohydrate analysis of beech honeydew

Abstract

Honeydew from the beech scale insect, Ultracoelostoma assimile, infesting the beech species Nothofagus fusca and N. solandri var. solandri contained fructose, sucrose, glucose, and several non-reducing oligosaccharides composed of glucose and fructose residues. Although the total carbohydrate content varied from 5 to 64 g/100 g, and was dependent on rainfall in the sampling area, there were no significant differences between the honeydews of N. fusca and N. solandri sampled on the same day in the absence of recent rain. The mean proportional composition (±SD) of such samples were 42±5% fructose, 23±8% sucrose, 1 ± 0.4% glucose, and 33±6% oligosaccharides. A refractometer calibrated against sucrose slightly overestimated total carbohydrate of honeydew and such data should be divided by a correction factor of 1.145. The energy value of honeydew carbohydrate was estimated to be 16J mg^?1 (dry weight). Honeydew contained little protein (<50 mg g^?1).     

Plutella xylostella (diamondback moth) and its parasitoid Diadegma semiclausum show different gustatory and longevity responses to a range of nectar and honeydew sugars

Parasitoids as well as many of their herbivorous hosts, depend on carbohydrate‐rich food during the adult stage. Different types of nectar and honeydew vary with regard to their sugar composition. In order to successfully exploit a food source, the insect must show a positive gustatory response to its component sugars and be able to digest and metabolise them. Here we tested the herbivore Plutella xylostella L. (Lepidoptera: Plutellidae) and its parasitoid Diadegma semiclausum (Hellén) (Ichneumonidae: Campopleginae) with respect to their feeding response and longevity when provided with one of nine sugars (fructose, glucose, lactose, maltose, melibiose, melezitose, raffinose, sucrose, or trehalose). Both species responded to and showed a prolonged life span on a broad range of sugars. The impact of food supply on life span was about sixfold higher for the parasitoid than for the herbivore. In general, there was a good fit between gustatory response and achieved longevity, with some outliers. Both species showed only weak responses to melibiose, which significantly prolonged life span. The parasitoid showed a gustatory response to melezitose, which did not prolong its life span. The parasitoid and its herbivorous host responded differently to trehalose. These differences in gustatory response and longevity show the potential for application of selective sugar sources in conservation biological control. At the same time it also reveals a risk that the indiscriminate application of sugar sources may stimulate herbivory.     

Nutritional state of the pollen beetle parasitoid Tersilochus heterocerus foraging in the field

Many laboratory studies have demonstrated that parasitoids of various species depend on sugar sources such as nectar or honeydew. However, studies about nectar acquisition by parasitoids foraging in the field are scarce. Tersilochus heterocerus Thomson is one of the more abundant and widespread parasitoids of the pollen beetle (Meligethes aeneus F.) but nothing is known about the nutritional ecology of this species. In this study we examined the nutritional state of T. heterocerus at the time of emergence and at various time periods throughout the season while foraging in the field using high-performance anion-exchange chromatography. We found that: (i) T. heterocerus emerge with relatively small amounts of sugar, composed mainly of trehalose, glucose and fructose; (ii) the first parasitoids caught just after they appeared in the field at the beginning of oilseed rape flowering had already consumed significant amounts of sugar reserves; and (iii) the total amount of sugar at the end of flowering was always significantly higher than the total amount of sugar at the beginning of flowering. This study provides valuable insights into the acquisition of sugar in the field by the parasitoid T. heterocerus and suggests that nectar acquisition takes place in the oilseed rape field or in the surrounding landscape.     

Honeydew composition and its effect on life-history parameters of hyperparasitoids

1. Diets that maximise life span often differ from diets that maximise reproduction. Animals have therefore evolved advanced foraging strategies to acquire optimal nutrition and maximise their fitness. The free-living adult females of parasitoid wasps (Hymenoptera) need to balance their search for hosts to reproduce and for carbohydrate resources to feed. 2. Honeydew, excreted by phloem-feeding insects, presents a widely available carbohydrate source in nature that can benefit natural enemies of honeydew-producing insects. However, the effects of variation in honeydew on organisms in the fourth trophic level, such as hyperparasitoids, are not yet understood. 3. This study examined how five different honeydew types influence longevity and fecundity of four hyperparasitoid taxa. Asaphes spp. (Pteromalidae) and Dendrocerus spp. (Megaspilidae) are secondary parasitoids of aphid parasitoids and are thus associated with honeydew-producing insects. Gelis agilis and Acrolyta nens (both Ichneumonidae) are secondary parasitoids of species that do not use honeydew-producing hosts. 4. Most honeydew types had a positive or neutral effect on life span and fecundity of hyperparasitoids compared with controls without honeydew, although negative effects were also found for both aphid hyperparasitoids. Honeydew produced by aphids feeding on sweet pepper plants was most beneficial for all hyperparasitoid taxa, which can partially be explained by the high amount of honeydew, but also by the composition of dietary sugars in these honeydew types. 5. The findings of this study underline the value of aphid honeydew as a carbohydrate resource for fourth-trophic-level organisms, not only those associated with honeydew-producing insects but also ‘interlopers’ without such a natural association.     

Using the stable isotope marker 13C to study extrafloral nectar uptake by parasitoids under controlled conditions and in the field

Parasitic wasps are prominent natural enemies of crop pests. They usually feed on floral resources during the adult stage (nectar, pollen, or honeydew). Extrafloral nectar is an alternative source of sugar easily accessible to adult parasitoids. We developed an original method of nectar labelling based on the injection of labelled sugar solution into the plant stem in order to analyse the nectar uptake by parasitoids (cotton wick method). This method was used to artificially enrich extrafloral cornflower, Centaurea cyanus L. (Asteraceae), nectar with the stable isotope ¹³C. We analysed (1) the transfer of ¹³C from the sugar solution into extrafloral nectaries, (2) the uptake of labelled nectar by parasitoids under laboratory conditions, and (3) the ability of the method to discriminate, in an oilseed rape (Brassica napus L., Brassicaceae) field, between labelled parasitoids (i.e., those who have fed on labelled cornflowers located adjacent to the field) and unlabelled parasitoids to track parasitoid movements from the margin into the field. The extrafloral nectar of all test plants was ¹³C‐labelled. Most (66%) of the parasitoids were identified as marked after 96 h of exposure to labelled plants in the laboratory. We could also detect labelled parasitoids inside the field, but the detection rate was only 1%. The experiments clearly demonstrate that the cotton wick method is appropriate to label extrafloral nectar and parasitoids feeding on this labelled nectar. Further research is needed on the amount of labelled extrafloral nectar required to obtain a sufficient marker level to track parasitoid movements in the field.     

Evaluating potential sugar food sources from the olive grove agroecosystems for Prays oleae parasitoid Chelonus elaeaphilus

Chelonus elaeaphilus Silvestri (Hymenoptera: Braconidae) is a host-specific parasitoid of the olive moth, Prays oleae (Bernard), that can cause parasitism rates of up to 80% in Mediterranean olive groves. A laboratory study was carried out to assess the potential of sugars provided by wild plant species in olive grove agroecosystem to enhance the fitness of C. elaeaphilus. Insects were reared in a climate-controlled chamber at 25?±?2°C, 60?±?5% relative humidity (RH) with a photoperiod of 16:8 (L:D) h. Five naturally occurring wild plant nectar sugars (sucrose, fructose, glucose, maltose and mannose) were tested for their effect on insect longevity. The nectar sugar content of sucrose, fructose and glucose in 12 selected olive grove agroecosystem plant species was analysed and categorised on the basis of sugar ratios. Female insect longevity was increased when they were fed on both sucrose and glucose compared to either maltose or fructose, suggesting that sucrose-dominant nectars would bene?t this parasitoid. Sucrose was predominant in the nectar of five of the studied plant species (Silene gallica, Borago officinalis, Echium plantagineum, Lavandula stoechas and Lonicera hispânica). The results are discussed in terms of potential enhancement of the biological control of P. oleae.