Sugar Feeding Research Articles

Diel Patterns of Female Host Seeking, Male Swarming, and Sugar Feeding in Fannia conspicua (Diptera: Muscidae) in Southern California

Adult Fannia conspicua Malloch were captured by sweep net at a southern California coastal mountain community to determine diel flight activity and crop/gut sugar (gut sugar) concentration. Male swarming activity was monitored by visual estimation of swarm numbers. Gut sugar content of captured flies was determined by cold anthrone assay. Peak host seeking by female flies generally occurred in early morning (0700-0800) and early evening (1900-2000). Variation in female host-seeking activity was significantly explained by the time elapsed since sunrise or time remaining until sunset, with temperature, humidity, and wind speed having small, but significant effects on activity. Male swarming activity occurred more generally throughout the day, with peaks in mid-morning and mid-afternoon and reduced swarming during periods of highest female host-seeking activity. Male swarming behaviors were only minimally explained by environmental variables. Flies of both sexes commonly fed on fructose sugars with 99.94% of host-seeking female flies (n = 1,647), and 98.93% of swarming male flies (n = 1,398) with gut sugar levels exceeding those of starved flies. Host-seeking female flies had significantly higher overall sugar content than swarming male flies. Male flies had peak gut sugar levels at 0800-0900 and 2000. Female flies had broad peaks in gut sugar level from 0700 to 1200 and 1600 to 1900. Stepwise regression showed that variation in gut sugar level was poorly explained by environmental variables for both sexes.

Dengue Control: The Challenge Ahead

Dengue Control: The Challenge Ahead

A survival and reproduction trade-off is resolved in accordance with resource availability by virgin female mosquitoes

The first 2-4 days after an Anopheles gambiae female mosquito emerges are critical to her survival and reproductive success. Yet, the order of behavioural events (mating, sugar feeding, blood feeding) during this time has received little attention. We discovered that among female cohorts sampled from emergence, sugar feeding had a higher probability than blood feeding of occurring first, and mating rarely occurred before a meal was taken. The night after emergence, 48% of females fed on sugar in mesocosms, and 25% fed on human blood; in the absence of sugar, 49% of females fed on human blood. After 5 days, 39% of the sugar-supplied females had blood fed and mated, and were fructose negative, whereas only 8% of the sugar-denied females had both blood fed and mated by this time. The model that best explained the transitions suggests that females made use of two distinct behavioural pathways, the most common one being to sugar-feed, then mate, and then seek blood. Other females sought blood first, then mated, and forwent a sugar meal. Lipid levels were higher in females with access to sugar than in females without access to sugar, particularly for those in later gonotrophic stages, while glycogen levels in the sugar-supplied group were higher throughout. In single-night experiments with females having had access to sucrose since emergence, those given a blood meal 1 day before spending a night with males had higher insemination rates than those not receiving the blood meal. These results indicate that the trade-off between survival and immediate reproduction is resolved by young adult females in accordance with availability of resources and gonotrophic state.

Differential attraction of Aedes albopictus in the field to flowers, fruits and honeydew

Sugar is the main source of energy for the activities of mosquitoes; however, information on the vital sugar feeding of Aedes albopictus in the field is scanty and often anecdotal. Using glue traps and baits, we evaluated the attraction of Ae. albopictus to 28 different, potential sugar sources. Control traps were baited with either sugar–water solution or water alone, and since there was no significant difference between these controls, the water control was used as the standard for comparison. The total catch amounted to 1347 females and 1127 males. An attraction index (mean number of mosquitoes attracted to the baits/mean number of mosquitoes attracted to the control) was used to compare the relative attraction of the baits. The attraction index of significantly attractive baits ranged from 2.5 to 50.0 and the index of others ranged from 0.50 to 2.75. None of the baits were repellent. Significantly high attraction was observed for four of six ornamental flowers (Tamarix chinensis, Vitex agnus-castus, Polygonum baldchuanicum, Buddleja davidii), four of eleven wild flowers (Prosopis farcta, Ziziphus spina-christi, Polygonum equisetiforme, Ceratonia siliqua), the only tested seed pod when damaged and fermenting (C. siliqua), and all five of the tested fruits: Opuntia ficus indica (sabra), Ficus carica (fig), Punica granatum (pomegranate, damaged), Eriobotyra japonica (loquat), and Rubus sanctus (raspberry). Unlike damaged, fermenting carob seed pods and pomegranates, the fresh fruits were not attractive. Attraction to foliage soiled with honeydew excretion of three different aphid species was also not significant. The potential to use attractive sugar sources for mosquito control is discussed.

Natural Plant Sugar Sources of Anopheles Mosquitoes Strongly Impact Malaria Transmission Potential

An improved knowledge of mosquito life history could strengthen malaria vector control efforts that primarily focus on killing mosquitoes indoors using insecticide treated nets and indoor residual spraying. Natural sugar sources, usually floral nectars of plants, are a primary energy resource for adult mosquitoes but their role in regulating the dynamics of mosquito populations is unclear. To determine how the sugar availability impacts Anopheles sergentii populations, mark-release-recapture studies were conducted in two oases in Israel with either absence or presence of the local primary sugar source, flowering Acacia raddiana trees. Compared with population estimates from the sugar-rich oasis, An. sergentii in the sugar-poor oasis showed smaller population size (37,494 vs. 85,595), lower survival rates (0.72 vs. 0.93), and prolonged gonotrophic cycles (3.33 vs. 2.36 days). The estimated number of females older than the extrinsic incubation period of malaria (10 days) in the sugar rich site was 4 times greater than in the sugar poor site. Sugar feeding detected in mosquito guts in the sugar-rich site was significantly higher (73%) than in the sugar-poor site (48%). In contrast, plant tissue feeding (poor quality sugar source) in the sugar-rich habitat was much less (0.3%) than in the sugar-poor site (30%). More important, the estimated vectorial capacity, a standard measure of malaria transmission potential, was more than 250-fold higher in the sugar-rich oasis than that in the sugar-poor site. Our results convincingly show that the availability of sugar sources in the local environment is a major determinant regulating the dynamics of mosquito populations and their vector potential, suggesting that control interventions targeting sugar-feeding mosquitoes pose a promising tactic for combating transmission of malaria parasites and other pathogens.

Sugar feeding by coccinellids under field conditions: the effects of sugar sprays in soybean

Sucrose was applied weekly throughout the growing season at three US locations (South Dakota [SD], Maryland [MD], and Kentucky [KY]), and coccinellids and aphids (Aphis glycines Matsumura [Hemiptera: Aphididae]) were sampled 24 h later. Total coccinellid densities were 50–77% greater in sugar-sprayed soybean than in untreated plots. Coccinella septempuncata L., Hippodamia convergens Guerin-Meneville, and Harmonia axyridis Pallas were more abundant where sugar was applied. Coleomegilla maculata (DeGeer) was found in equally low numbers in all treatments. Aphid densities were similar in both treatments, and only reached economically threatening levels in SD. Coccinellids digested sugar meals within 1 h of consumption (measured using the cold anthrone test). Despite this narrow window of detection, field-collected coccinellids frequently tested positive for fructose. Under natural conditions, sugar is commonly ingested by coccinellids and sugar sprays increase coccinellid densities and their consumption of sugar. Sugar sprays did not enhance biological control of aphids in this experiment.

Patterns of sugar feeding and host plant preferences in adult males of An. gambiae (Diptera: Culicidae)

Sugar feeding by male mosquitoes is critical for their success in mating competition. However, the facets of sugar source finding under natural conditions remain unknown. Here, evidence obtained in Western Burkina Faso indicated that the distribution of An. gambiae s.s. (M and S molecular forms) males across different peri-domestic habitats is dependent on the availability of potential sugar sources from which they obtain more favorable sites for feeding or resting. Among field-collected anophelines, a higher proportion of specimens containing fructose were found on flowering Mangifera indica (Anacardiaceae), Dolonix regia (Fabaceae), Thevetia neriifolia (Apocynaceae), Senna siamea, and Cassia sieberiana (both Fabaceae) compared to that recorded on other nearby plants, suggesting that some plants are favored for use as a sugar source over others. Y-tube olfactometer assays with newly-emerged An. gambiae s.s. exposed to odors from individual plants and some combinations thereof showed that males use odor cues to guide their preference. The number of sugar-positive males was variable in a no-choice cage assay, consistent with the olfactory response patterns towards corresponding odor stimuli. These experiments provide the first evidence both in field and laboratory conditions for previously unstudied interactions between males of An. gambiae and natural sugar sources.

Field experiments of Anopheles gambiae attraction to local fruits/seedpods and flowering plants in Mali to optimize strategies for malaria vector control in Africa using attractive toxic sugar bait methods

BackgroundBased on recent studies in Israel demonstrating that attractive toxic sugar bait (ATSB) methods can be used to decimate local anopheline and culicine mosquito populations, an important consideration is whether the same methods can be adapted and improved to attract and kill malaria vectors in Africa. The ATSB approach uses fruit or flower scent as an attractant, sugar solution as a feeding stimulant, and an oral toxin. The ATSB solutions are either sprayed on vegetation or suspended in simple bait stations, and the mosquitoes ingesting the toxic solutions are killed. As such, this approach targets sugar-feeding female and male mosquitoes. This study examines the attractiveness of African malaria vectors to local fruits/seedpods and flowering plants, key biological elements of the ATSB approach for mosquito control.MethodsThree field experiments were conducted at sites in Mali. The attraction of Anopheles gambiae s.l. to 26 different local fruits and seedpods was determined at a site in the semi-arid Bandiagara District of Mali. Wire mesh glue traps with fruits/seedpods suspended on skewers inside were set along a seasonal lagoon. Seven replicates of each fruit/seedpod species were tested, with a water-soaked sponge and a sugar-soaked sponge as controls. The attraction of An. gambiae s.l. to 26 different types of flowering plants was determined at a site near Mopti in Mali. The flowering plants held in a water-filled buried container were tested using the same glue traps, with controls including water only and sugar solution. Six replicates of each selected plant type were tested on transects between rice paddies. Additional studies using CDC light traps were done to determine the relative densities and periodicity of An. gambiae s.l. attraction to branches of the most highly attractive flowering plant, branches without flowers, human odor, and candescent light.ResultsOf the 26 fruits and seedpods tested, 6 were attractive to An. gambiae s.l. females and males, respectively. Guava (Psidium guajava) and honey melon (Cucumis melo) were the two most attractive fruits for both females and males. Of the 26 flowering plants tested, 9 were significantly attractive for females, and 8 were attractive for males. Acacia macrostachya was the most attractive flowering plant. Periodicity studies using this plant showed peaks of An. gambiae s.l. attraction between 1930 and 2200 h and 0400-0500 h, which differed considerably from the response to human odors, which expectedly peaked at around midnight.ConclusionThese field experiments in Mali highlight that female and male An. gambiae s.l. have pronounced differences in attraction for diverse types of indigenous fruits/seedpods and flowering plants. The identification of attractive fruits and seedpods shows that a variety of indigenous and locally abundant natural products could potentially be used as juices to make ATSB solution for mosquito control. As well, the simple methods used to identify the most attractive flowering plants provide valuable insights into the natural history of sugar feeding for An. gambiae s.l. These observations can be used to guide future strategies for employing ATSB methods for malaria vector control in Africa. They also provide a basis for subsequent chemical analysis and development of attractive baits for mosquito control.

Seed pods of the carob tree Ceratonia siliqua are a favored sugar source for the mosquito Aedes albopictus in coastal Israel

The sugar feeding of Aedes albopictus was studied. In outdoor cages they fed avidly on carob ( Ceratonia siliqua L., Caesalpiniaceae) seed pods soiled with sugary exudates. Feeding was either from the surface or by piercing the tissue which is indicated by the presence of plant tissue residues in the gut. More than 90% were sugar positive and about a third had plant tissue residues in the gut after overnight exposure. Similar exposure to clean undamaged seed pods resulted in about two thirds sugar positive mosquitoes and all of these had plant-tissue residues in the gut. In an irrigated, field site, with abundance of sugar sources in the summer 68% of the females and 75% of the males were sugar positive whereas, 1.2% of the females and no males had plant tissue in the gut. The proportion of sugar positive mosquitoes was similar in the autumn and plant tissue was not found in 150 females and 13 males. In the dry site in the summer 42% females and 33% males were sugar positive while 22% females and 33% males contained plant tissue. In the autumn 73% females and 80% males were sugar positive while 2% females and none of the males contained plant tissue.

Repeated bouts of dehydration deplete nutrient reserves and reduce egg production in the mosquito Culex pipiens

In this study of the mosquito, Culex pipiens, we examined the impact of multiple bouts of dehydration and rehydration on survival, depletion of metabolic reserves and egg production in both non-diapausing and diapausing females. Mosquitoes provided with access to sugar during rehydration survived longer than those allowed to rehydrate without sugar, and their survival was similar to that of mosquitoes of the same age that were not dehydrated. Among mosquitoes not provided with sugar, each dehydration bout reduced the mosquito's dry mass - an effect likely to be due to the utilization of carbohydrates and lipid reserves. The toll on glycogen and lipid reserves is likely to be especially costly for diapausing mosquitoes that are dependent on these stored reserves for winter survival. Egg production in both non-diapausing and post-diapausing C. pipiens was also reduced in response to multiple bouts of dehydration. Although egg quality was not compromised, the number of eggs produced was reduced. Both non-diapausing and diapausing females can compensate for the nutrient loss due to dehydration by sugar feeding but the opportunity to feed on sugar is likely to be rarely available in the overwintering habitat of diapausing females, thus the impact of dehydration may be especially pronounced in overwintering populations of C. pipiens.

Effect of body size and sugar meals on oviposition of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Effect of body size and sugar meals on oviposition of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Feeding and hemolymph trehalose concentration influence sex pheromone production in virgin Heliothis virescens moths

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

Exploiting mosquito sugar feeding to detect mosquito-borne pathogens

Arthropod-borne viruses (arboviruses) represent a global public health problem, with dengue viruses causing millions of infections annually, while emerging arboviruses, such as West Nile, Japanese encephalitis, and chikungunya viruses have dramatically expanded their geographical ranges. Surveillance of arboviruses provides vital data regarding their prevalence and distribution that may be utilized for biosecurity measures and the implementation of disease control strategies. However, current surveillance methods that involve detection of virus in mosquito populations or sero-conversion in vertebrate hosts are laborious, expensive, and logistically problematic. We report a unique arbovirus surveillance system to detect arboviruses that exploits the process whereby mosquitoes expectorate virus in their saliva during sugar feeding. In this system, infected mosquitoes captured by CO(2)-baited updraft box traps are allowed to feed on honey-soaked nucleic acid preservation cards within the trap. The cards are then analyzed for expectorated virus using real-time reverse transcription-PCR. In field trials, this system detected the presence of Ross River and Barmah Forest viruses in multiple traps deployed at two locations in Australia. Viral RNA was preserved for at least seven days on the cards, allowing for long-term placement of traps and continuous collection of data documenting virus presence in mosquito populations. Furthermore no mosquito handling or processing was required and cards were conveniently shipped to the laboratory overnight. The simplicity and efficacy of this approach has the potential to transform current approaches to vector-borne disease surveillance by streamlining the monitoring of pathogens in vector populations.

Chronic sugar intake dampens feeding-related activity of neurons synthesizing a satiety mediator, oxytocin

Increased tone of orexigens mediating reward occurs upon repeated consumption of sweet foods. Interestingly, some of these reward orexigens, such as opioids, diminish activity of neurons synthesizing oxytocin, a nonapeptide that promotes satiety and feeding termination. It is not known, however, whether consumption-related activity of the central oxytocin system is modified under chronic sugar feeding reward itself. Therefore, we examined how chronic consumption of a rewarding high-sucrose (HS) vs. bland cornstarch (CS) diet affected the activity of oxytocin cells in the hypothalamus at the time of meal termination. Schedule-fed (2h/day) rats received either a HS or CS powdered diet for 20 days. On the 21st day, they were given the same or the opposite diet, and food was removed after the main consummatory activity was completed. Animals were perfused 60 min after feeding termination and brains were immunostained for oxytocin and the marker of neuronal activity, c-Fos. The percentage of c-Fos-positive oxytocin cells in the hypothalamic paraventricular nucleus was significantly lower in rats chronically exposed to the HS than to the CS diet, regardless of which diet they received on the final day. A similar pattern was observed in the supraoptic nucleus. We conclude that the chronic rather than acute sucrose intake reduces activity of the anorexigenic oxytocin system. These findings indicate that chronic consumption of sugar blunts activity of pathways that mediate satiety. We speculate that a reduction in central satiety signaling precipitated by regular intake of foods high in sugar may lead to generalized overeating.

Sugar in moderation: sugar diets affect short-term parasitoid behaviour

The biological control potential of parasitic wasps in the field is expected to increase with the provisioning of sugar sources, which increase longevity and replenish carbohydrate reserves. Apanteles aristoteliae is an important parasitoid of Argyrotaenia franciscana, the orange tortrix, an economic pest in fruit crops. In the present study, the effect of sugar diet on the physiological status of A. aristoteliae is investigated in the laboratory, as well as the effects of nutritional status on short-term olfactory orientation and parasitism behaviour, and the association between olfactory orientation and immediate parasitism activity. Levels of glycogen, fructose, total sugars, proportional weight gain and volume consumed are higher among females fed 25% sucrose solution than 10% sucrose solution, and lowest for those fed water. Sugar feeding also affects behaviour: wasps with higher levels of fructose or weight gain have a lower probability of making a choice in the olfactometer. Wasps with intermediate fructose levels or weight gain have a higher probability of orienting towards hosts than wasps with low or high levels. Among wasps that make a choice in the olfactometer, wasps fed 10% or 25% sucrose significantly prefer host versus food cues, whereas starved wasps are just as likely to select food cues as host cues.

An insight into the sialotranscriptome of the West Nile mosquito vector, Culex tarsalis

BackgroundSaliva of adult female mosquitoes help sugar and blood feeding by providing enzymes and polypeptides that help sugar digestion, control microbial growth and counteract their vertebrate host hemostasis and inflammation. Mosquito saliva also potentiates the transmission of vector borne pathogens, including arboviruses. Culex tarsalis is a bird feeding mosquito vector of West Nile Virus closely related to C. quinquefasciatus, a mosquito relatively recently adapted to feed on humans, and the only mosquito of the genus Culex to have its sialotranscriptome so far described.ResultsA total of 1,753 clones randomly selected from an adult female C. tarsalis salivary glands (SG) cDNA library were sequenced and used to assemble a database that yielded 809 clusters of related sequences, 675 of which were singletons. Primer extension experiments were performed in selected clones to further extend sequence coverage, allowing for the identification of 283 protein sequences, 80 of which code for putative secreted proteins.ConclusionComparison of the C. tarsalis sialotranscriptome with that of C. quinquefasciatus reveals accelerated evolution of salivary proteins as compared to housekeeping proteins. The average amino acid identity among salivary proteins is 70.1%, while that for housekeeping proteins is 91.2% (P < 0.05), and the codon volatility of secreted proteins is significantly higher than those of housekeeping proteins. Several protein families previously found exclusive of mosquitoes, including only in the Aedes genus have been identified in C. tarsalis. Interestingly, a protein family so far unique to C. quinquefasciatus, with 30 genes, is also found in C. tarsalis, indicating it was not a specific C. quinquefasciatus acquisition in its evolution to optimize mammal blood feeding.

Methods of short-term storage of cultures of the blowfly Calliphora Vicina R.-D. (Diptera, Calliphoridae)

Three methods of short-term storage of the blowfly Calliphora vicina strains are considered based on the experimental study of 21 strains originating from different parts of the species range. The colony can be preserved as diapausing adults at 6° and darkness for 2–3 months or more, depending on the geographical origin of the population. During the first five days of adult life the flies should be kept at 12° and short day on a sugar diet, after which they should be transferred into a refrigerator. During artificial hibernation the flies also require periodic sugar feeding every 20 days (3–4 h at 20°C) to maintain their vital functions. The combination of temperatures of 20–23°C and a protein diet terminates reproductive diapause, and oviposition starts in 10–17 days. The fly strain may be preserved as reproductive females at 6°C and darkness with sugar feeding. Flies also require periodic sugar feeding at 20°C (3–4 hours). In this case the flies start laying eggs 2–3 days after being transferred to 20–23°C. The preservation of diapausing larvae is a more reliable method of prolonged strain storage. In this case the flies of maternal generation are maintained at 20–23°C on sugar and protein diet. The egg rafts laid during 5–6 hours are then transferred into 12°C and short day until hatchment. The hatched larvae should be immediately placed into a refrigerator (2–3 or 5–6°C), where they feed during 1–1.5 months and enter diapause. For strain restoration, the diapausing larvae should be transferred into 20–25°C, where they pupariate in 3–5 days and the flies emerge in nearly 10 days.

Sugar feedingviatrehalose haemolymph concentration affects sex pheromone production in matedHeliothis virescensmoths

Long-distance, female-produced sex pheromones are widespread among moths. Larval feeding provides most of the nutrients for development of these insects but is not thought to influence the de novo production of the fatty-acid derived compounds used as pheromones by most species. Feeding on plant nectar (sugar) by adult moths is important for increasing female fitness and also for the pollination of many plant species. In this paper, I show that feeding on sucrose solution, as opposed to water, increases sex pheromone titre in mated, but not virgin, female Heliothis virescens. Mating caused a rapid decrease in haemolymph trehalose concentration, which was restored to near-virgin levels by sugar ingestion. When isolated mated female abdomens were cultured with different concentrations of trehalose, pheromone titre increased with increasing trehalose concentration. This effect was not observed when abdomens were cultured on saline containing the sugar rhamnose, which insects cannot metabolise to glucose. Virgins injected with the juvenile hormone (JH) analogue, methoprene, showed the same effects as mated females with respect to pheromone titre and haemolymph trehalose concentration. Thus, following mating increases in JH titre increase demand for, and lowering of, blood sugar to develop oocytes, which can be compensated for by sugar ingestion. Haemolymph trehalose concentration probably influences glycolysis in gland cells and, consequently, levels of cytosolic citrate and acetyl-CoA for pheromone biosynthesis. This increase in pheromone titre in sugar-fed, mated females may facilitate further mating and increased fecundity. Thus, exogenous sugar feeding is behaviourally and physiologically integrated with endogenous JH titre to maximise female fitness.

Nectar‐providing plants enhance the energetic state of herbivores as well as their parasitoids under field conditions

Abstract 1. The use of flowering vegetation has been widely advocated as a strategy for providing parasitoids and predators with nectar and pollen. However, their herbivorous hosts and prey may exploit floral food sources as well.2. Previous laboratory studies have shown that not all flower species are equally suitable in providing accessible nectar. Relatively little is known about actual nectar exploitation under field conditions.3. The present study investigates nectar exploitation by the pest, Plutella xylostella, and its parasitoid, Diadegma semiclausum, under field conditions and examines whether floral nectar exploitation in the field can be predicted based on controlled laboratory studies.4. Insects were collected from fields bordered by flowering margins containing Fagopyrum esculentum, Lobularia maritima, Anethum graveolens, Centaurea jacea or the grass Lolium perenne (control). Whole insect bodies were individually assayed by HPLC to establish their sugar profile as a measure of the level of energy reserves and the degree of food source use.5. The average overall sugar content of P. xylostella and D. semiclausum collected in fields bordered by flowering margins was significantly higher than those of individuals collected from grass‐bordered control plots. To the authors’ knowledge, this represents the first demonstration that nectar‐providing plants enhance the energetic state of herbivores under field conditions.6. In contrast to earlier laboratory studies, the present study did not find elevated sugar contents in P. xylostella and D. semiclausum individuals collected from fields bordered by buckwheat (F. esculentum).7. The present study shows widespread sugar feeding by both the herbivore and its parasitoid. It also shows that laboratory studies establishing nectar exploitation under controlled conditions can not always be extrapolated to actual exploitation under field conditions. This emphasises the importance of studying field‐collected insects with regard to food source use and nutritional status.

A study on the concentration of actively sugar feeding for ants ( Formica japonica)

A study on the concentration of actively sugar feeding for ants ( Formica japonica)