Neonates know better than their mothers when selecting a host plant

Abstract

Evolutionary ecological theory predicts that among insect herbivores ‘mothers know best’ when selecting a plant to deposit their eggs. Host‐plant selection is usually studied for the adult stage exclusively, although mothers have not always been reported to know best. Here, we investigate the host‐plant selection behaviour of caterpillars, which are considered to be completely dependent on their mothers’ choices. We use a system that offers a biologically relevant framework to compare the degree of participation of adults and juveniles in host‐plant selection. Our results show that neonate Pieris brassicae caterpillars can actively discriminate between conspecific Brassica oleracea plants with or without aphid (Brevicoryne brassicae) infestation. The caterpillars prefer aphid‐infested plants on which their performance is significantly better, while their mothers, the female butterflies, did not discriminate. We compared caterpillar preferences of individuals released individually or in groups, because P. brassicae is a gregarious species. We found that the strength of the preference for aphid‐infested plants was not affected by the degree of grouping. Caterpillar choices were made before contact with the plants, indicating that plant odours were used for orientation. However, the composition of the volatile blends emitted by plants with and without aphids did not show strong differences. Similarly, like with aphid‐infested plants, plants treated with salicylic acid (SA) were also preferred by neonates over untreated control, indicating that the infestation by aphids may have rendered the plants more attractive to the neonates via changes related to interference with JA‐signaling. The main parasitoid of the caterpillars did not discriminate between plants with hosts in the presence or absence of aphids, showing that top–down forces do not influence the relative suitability of the different food sources for the caterpillars. These data are discussed in the context of mothers and offspring having both important, but different roles in the process of host‐plant selection. Butterflies may select the plant species patch, while their offspring adjust and/or update the choices of their mothers at the local scale, within the micro‐habitat selected by the adult.

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

“…In these cases it would be an advantage if developing larvae could disperse and find new feeding sites. Whereas dispersal of insect larvae has been reported (Doak, 2000), little is known about their actual dispersal capacities and how they orient if they switch feeding sites (Chew, 1977;Bernays & Chapman, 1994;Berdegué et al, 1998;Soler et al, 2012). Whilst herbivorous larvae are often attracted by volatiles from their host plants (e.g.…”

“…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. This is especially true if predatory larvae are specialised on prey with an unpredictable distribution.…”

Plants under dual attack : consequences for plant chemistry and parasitoid behavior

“…Though the multivariate data analysis did not segregate the volatile blends by treatment, wasps may be picking up on subtle changes in the blend characteristics that current GC-MS technology is not sensitive enough to detect, or alternatively, only the specific subset of volatiles used by the wasps is different between treatments. However, our results are similar to what has previously been found in cultivated B. oleracea using the same aphid, lepidopteran and parasitoid species, also looking at the systemic effects of aphid induction (Soler et al, 2012b). Though of a longer induction period than in this study, volatile profiles of single and dually infested plants could not be separated in the multivariate space, and likewise wasps did not differentiate between the two treatments, and this also at two different aphid densities.…”

“…These results, in combination with my own, and other work from our lab (e.g. Soler et al, 2012b) show that C. glomerata is rather flexible in its use of volatile cues, or relies on other, non-volatile cues as well. The aphid parasitoid Diaeretiella rapae was also unaffected by non-host presence, supporting previous work with this species (Agbogba & Powell, 2007), though unexpectedly I found strong negative effects of increasing host density: as host density increased, volatiles from these plants became less attractive to the wasps.…”

Insect host plant selection in complex environments

“…Recently, the role that pathogenic and beneficial organisms have on insect choices has also received considerable attention [5][6][7][8]. Furthermore, in some species the larval stages are able to leave the plant chosen by the female and select new host plants themselves [9,10]. This would reduce the selective pressure on female preference in relation to larval diet and allow more emphasis on needs directly connected to female or egg survival.…”