Adult Parasitoids of Honeydew-Producing Insects Prefer Honeydew Sugars to Cover their Energetic Needs

Abstract

To meet their carbohydrate requirements, adult parasitoids exploit a broad range of sugar resources, including floral and extrafloral nectar and honeydew. Although honeydew might be the predominant sugar source, especially in agricultural systems, it often is nutritionally inferior to sugar sources like nectar. Given its broad availability, it may be expected that sugar-feeding insects have evolved specialized adaptations to deal with this typically inferior sugar source. This would apply especially to organisms that have a close association with honeydew producers. Here, we hypothesized that parasitoids of honeydew-producing insects should show a pronounced response to sugars, such as fructose, sucrose, melezitose, and trehalose, and to a lesser extent glucose. To test this hypothesis, we investigated sugar consumption, feeding behavior and survival of the aphid parasitoid Aphidius ervi on several sugars (equiweight solutions). Our results show that A. ervi adults consumed typical honeydew sugars (sucrose, fructose, trehalose, and melezitose) the most, while consuming considerably less glucose or melibiose. Rhamnose, which does not occur in aphid honeydew, was not, or was only marginally, consumed. When different sugars were provided at the same time, A. ervi adults preferred sucrose or fructose over glucose or melezitose. Furthermore, pre-exposure to sucrose or fructose significantly reduced subsequent intake of glucose, suggesting an acquired distaste for glucose after being previously exposed to highly preferred sugars such as sucrose and fructose. Altogether, this study shows that A. ervi adults prefer sugars (fructose, melezitose, trehalose, and sucrose) that are overrepresented in aphid honeydew and show a lower preference to one (glucose) that is underrepresented in honeydew.

Attraction of Aphidius ervi (Hymenoptera: Braconidae) and Aphidoletes aphidimyza (Diptera: Cecidomyiidae) to Sweet Alyssum and Assessment of Plant Resources Effects on their Fitness

“…On the other hand, when aphids were present, the provision of additional resources did not increase A. ervi longevity, suggesting that the combination of honeydew and hosts is adequate to keep females alive. In fact, several studies have shown that parasitoids, including A. ervi, are well adapted to the use of insect-produced honeydew which is the predominant sugar source in many agricultural systems (Burger et al 2004, Lenaerts et al 2016.…”

Nectar bacteria affect life history of a generalist aphid parasitoid by altering nectar chemistry

“…To test whether the changes in nectar chemistry induced by the tested bacteria affected nectar consumption by the insects, a previously developed assay, using a capillary feeder (CAFE) system was used (Lenaerts, Abid, et al., ). Briefly, a plastic insect cage (height: 12.5 cm; diameter: 10.0 cm) was provided with four calibrated glass micropipettes (5.0 μl, Blaubrand Intramark, Wertheim, Germany) filled with 4.0 μl of the synthetic nectar solution and an overlay of inert mineral oil (1.0 μl) to minimize evaporation.…”

“…In a third experiment, we assessed the effects of bacterial inoculation on insect longevity. The experiment was performed using the no‐choice CAFE assay outlined above (Lenaerts, Abid, et al., ), and was performed for a total of 225 parasitoid individuals divided over 15 cages, each with 15 individuals. Experiments were conducted under controlled conditions of 22°C, 70% relative humidity and with a 16:8 hr light:dark cycle, starting with the light period.…”

“…In a third experiment, we assessed the effects of bacterial inoculation on insect longevity. The experiment was performed using the nochoice CAFE assay outlined above (Lenaerts, Abid, et al, 2016), and synthetic nectar medium described above, at concentrations measured in Experiment 1 (Table S2). Furthermore, we tested the effect of different pH values (pH 3, 4 and 5; Table S2).…”

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

“…When honeydew is present near their hosts, parasitoids have to invest less time in searching for sugar sources, and they can minimise energy and risks associated with searching for nectar, which may be located further away . Indeed, longevity of aphid parasitoids is generally supported by honeydew, but not all honeydew types are equal in this respect (Hogervorst et al, 2007;Tena et al, 2018), probably because some honeydew carbohydrates have a larger impact on longevity than do others (Lenaerts et al, 2016). Indeed, many factors contribute to variation in the composition of dietary sugars in honeydew, including host plant species (e.g.…”