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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.
