Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

Ilka Vosteen,Jonathan Gershenzon,Grit Kunert

doi:10.1111/een.12636

Ilka Vosteen, Jonathan Gershenzon + Show 1 more

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https://doi.org/10.1111/een.12636

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Abstract

1. Predatory larvae often have to face food shortages during their development, and thus the ability to disperse and find new feeding sites is crucial for survival. However, the dispersal capacity of predatory larvae, the host finding cues employed, and their use of alternative food sources are largely unknown. These aspects of the foraging behaviour of the aphidophagous hoverfly (Episyrphus balteatus De Geer) larvae were investigated in the present study.2. It was shown that these hoverfly larvae do not leave a plant as long as there are aphids available, but that dispersing larvae are able to find other aphid colonies in the field. Dispersing hoverfly larvae accumulated on large aphid colonies, but did not distinguish between different pea aphid race–plant species combinations. Large aphid colonies might be easier to detect because of intensified searching by hoverfly larvae following the encounter of aphid cues like honeydew that accumulate around large colonies.3. It was further shown that non‐prey food, such as diluted honey or pollen, was insufficient for hoverfly larvae to gain weight, but prolonged the survival of the larvae compared with unfed individuals. As soon as larvae were switched back to an aphid diet, they rapidly gained weight and some pupated after a few days. Although pupation and adult hatching rates were strongly reduced compared with hoverflies continuously fed with aphids, the consumption of non‐prey food most probably increases the probability that hoverfly larvae find an aphid colony and complete their development.

Highlights

The survival of insects depends on several crucial events such as finding the right food or avoiding predation
Whilst herbivorous larvae are often attracted by volatiles from their host plants (e.g. Visser, 1986; Dickens, 2002; Castrejon et al, 2006; Becher & Guerin, 2009; Soler et al, 2012), studies considering the orientation of predatory larvae are rare (Branco et al, 2006), even though predatory larvae are more likely than herbivorous larvae to encounter food shortages
As nothing is known about the dispersal behaviour of hoverfly larvae, we aimed to find out whether movement between aphid colonies is a general behaviour in E. balteatus larvae and under what circumstances they leave a plant

Summary

Introduction

The survival of insects depends on several crucial events such as finding the right food or avoiding predation. Unpredictability of food sources or trade-offs between female foraging and offspring performance (Thompson, 1988; Scheirs & De Bruyn, 2002) might lead the egg-laying female to make suboptimal decisions. In these cases it would be an advantage if developing larvae could disperse and find new feeding sites. Visser, 1986; Dickens, 2002; Castrejon et al, 2006; Becher & Guerin, 2009; Soler et al, 2012), studies considering the orientation of predatory larvae are rare (Branco et al, 2006), even though predatory larvae are more likely than herbivorous larvae to encounter food shortages This is especially true if predatory larvae are specialised on prey with an unpredictable distribution. The development of ladybird larvae usually takes more than 2 weeks

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