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Adult parasitoids depend on sugar-rich foods such as nectar and honeydew to meet their energy requirements and control insect pests. However, it is poorly known whether parasitoids can detect and feed on honeydew in agroecosystems, where it is the primary carbohydrate source, because this sugar source is less apparent in comparison to nectar and sometimes contains repellent compounds for parasitoids., High-performance liquid chromatography ( HPLC) analyses were carried out to test whether Aphytis melinus DeBach (Hymenoptera: Aphelinidae), a parasitoid whose host does not produce honeydew, feeds on honeydew from non-hosts. In addition, the correlation between the parasitoid's sugar reserves and honeydew abundance was determined. To do this, both the levels of honeydew producers and the sugar levels of individual collected parasitoids were assessed during different seasons. The overall sugar content was treated as an indicator of energy reserves and the erlose-melezitose ratio as an indicator of honeydew feeding., The data show that A. melinus fed commonly on honeydew from non-host hemipterans. More than 50% of the female parasitoids collected in spring and summer had recently fed on honeydew and most of them showed a high sugar content., However, in autumn, when the number of honeydew producers was three times lower than in spring and summer, less than 20% of A. melinus were found to have fed on honeydew, with the average total sugar content being reduced by a factor of three., This study demonstrates that A. melinus commonly feeds on honeydew in the field, even though its host does not produce honeydew. The results also suggest that the exploitation of honeydew by A. melinus is a function of the density and species of honeydew producers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

1. The Argentine ant, Linepithema humile, tends honeydew-excreting homopterans and can disrupt the activity of their natural enemies. This mutualism is often cited for increases in homopteran densities; however, the ant’s impact on natural enemies may be only one of several effects of ant tending that alters insect densities. To test for the variable impacts of ants, mealybug and natural enemy densities were monitored on ant-tended and ant-excluded vines in two California vineyard regions. 2. Ant tending increased densities of the obscure mealybug, Pseudococcus viburni, and lowered densities of its encyrtid parasitoids Pseudaphycus flavidulus and Leptomastix epona. Differences in parasitoid recovery rates suggest that P. flavidulus was better able to forage on ant-tended vines than L. epona. 3. Densities of a coccinellid predator, Cryptolaemus montrouzieri, were higher on ant-tended vines, where there were more mealybugs. Together with behavioural observations, the results showed that this predator can forage in patches of ant-tended mealybugs, and that it effectively mimics mealybugs to avoid disturbance by ants. 4. Ant tending increased densities of the grape mealybug, Pseudococcus maritimus, by increasing the number of surviving first-instar mealybugs. Parasitoids were nearly absent from the vineyard infested with P. maritimus. Therefore, ants improved either mealybug habitat or fitness. 5. There was no difference in mealybug distribution or seasonal development patterns on ant-tended and ant-excluded vines, indicating that ants did not move mealybugs to better feeding locations or create a spatial refuge from natural enemies. 6. Results showed that while Argentine ants were clearly associated with increased mealybug densities, it is not a simple matter of disrupting natural enemies. Instead, ant tending includes benefits independent of the effect on natural enemies. Moreover, the effects on different natural enemy species varied, as some species thrive in the presence of ants. [ABSTRACT FROM AUTHOR]

Abstract. 1. The wasp Diaeretiella rapae uses honeydew emitted by its host, the cabbage aphid Brevicoryne brassica, as a kairomone (chemicals emitted by an organism as part of its activity and used by its natural enemies to their advantage). The role of the kairomone in foraging decisions by the parasitic wasp was explored by manipulating the amount of honeydew and the number of aphids in a colony independently. The count-down patch-exploitation mechanism (Iwasa et al., 1981) was employed to predict the results of these manipulations and contrast them with the predictions of Waage's (1979) model. 2. Kairomonal activity of honeydew decreased as the honeydew aged and lost its activity completely within 72 h. 3. The wasp was exposed to different amounts of honeydew on (a) aphid-free leaves and (b) leaves bearing colonies of 150 aphids. The parasitoid search time on both leaf types increased with increasing honeydew contamination. On aphid-bearing leaves, the number of attacked aphids in the colonies also increased with increasing honeydew contamination. The presence of aphids reduced the parasitoid search time compared to search time on aphid-bearing leaves with the same level of honeydew contamination, as predicted by the count-down model. 4. Parasitoids exposed to the same amount of honeydew, but a different number of aphids in a colony on the leal, first increased the number of aphids attacked in relation to the number of aphids in the colony. But as the colony reached a certain size, the number of aphids attacked levelled off, despite the increase in the number of aphids in the colony. Search time was variable but did not exhibit any trend as the number of aphids in the colonies increased. 5. These results suggest that honeydew level is used by D. rapae as a cue for assessment of the number of aphids in the colony. In such cases, a count-down exploitation mechanism gives the best results to a forager. Many parasitoids may use kairomones for patch assessment... [ABSTRACT FROM AUTHOR]