Prey preference of ladybird larvae and its impact on larval mortality, some life-history traits of adults and female fitness

Aphids are essential for aphidophagous ladybird beetle reproduction in natural conditions. The different species of aphids vary in quality and abundance from year to year. As a consequence, females may be forced to oviposit in suboptimal colonies of prey. The relationship between the choice of oviposition sites by adults and larval performances is poorly studied in predators. To determine the performance of larvae reared on optimal and suboptimal prey, two clutches of eggs from each of eight females of the two spot ladybird beetle, Adalia bipunctata, were used. The larvae hatching from each clutch of eggs were assigned in equal numbers to one of two groups. The larvae of one group were fed throughout their development on pea aphids (Acyrthosiphon pisum), which is a high quality prey, and the other group on cowpea aphids (Aphis craccivora), which is considered a suboptimal prey. Our results confirm that A. craccivora is a suboptimal prey for this ladybird as the adults developing from the larvae fed this aphid were lighter and had fewer ovarioles, and overall had a lower fitness than individuals reared on pea aphid. When offered a choice naive first instar larvae more frequently attacked cowpea than pea aphids. Fourth instar larvae attacked equally the two species of prey irrespective of the aphids they were previously fed. This study indicates that larvae do not show a preference for feeding on high quality aphids even though larvae that feed and complete their development on low quality prey are less fit than those that feed on high quality prey.