Spatial proximity between two host plant species influences oviposition and larval distribution in a leaf beetle

Abstract

Everything else being equal, insect herbivores can be expected to oviposit on host plants that provide the qualitatively and quantitatively best food for larvae. However, the selection of a plant for oviposition may be influenced by such ecological factors as natural enemies, host distribution, host patch size or host patch density. We performed a field study to test whether spatial proximity between two host plant species influences the oviposition patterns and larval distribution of the alpine leaf beetle Oreina elongata. In the population studied, O. elongata oviposits and feeds on two host plants, that belong to the same family (Asteraceae): Adenostyles alliariae and Cirsium spinosissimum. The first species contains pyrrolizidine alkaloids that are sequestered by the beetle as a chemical defence, whereas the second plant does not contain any alkaloids but has hairy and spiny leaves that might give some mechanical protection to beetle larvae. During two consecutive summers, we quantified oviposition and larval distribution on randomly chosen C. spinosissimum that grew spatially isolated from A. alliariae, on C. spinosissimum that grew in leaf contact with A. alliariae and on A. alliariae that grew in leaf contact with C. spinosissimum (isolated A. alliariae was not considered, because it is rare in the study population). In both years, more eggs were laid on C. spinosissimum than on A. alliariae and more on those C. spinosissimum that were growing close to A. alliariae than on those growing isolated. Large numbers of larvae moved from C. spinosissimum to A. alliariae during the season. Patch size did not influence egg and larval numbers. Eggs survived better on C. spinosissimum than on A. alliariae in the field. The data suggest that C. spinosissimum may provide eggs with better protection against stormy weather. In a separate study of the same population, we found that larval performance was better on A. alliariae than on C. spinosissimum. Our present data suggest that O. elongata preferentially oviposits on plants of the species that maximizes egg survival and that grow in close proximity to plants of the species that provides better food and chemical defence.

Conserved oviposition preferences in alpine leaf beetle populations despite host shifts and isolation

“…It is seen in the wild at the Col du Petit Saint-Bernard site, where more eggs are laid on Cirsium than on A. alliariae ( Ballabeni et al , 2001a ). This seems to be a response to the lower level of egg predation on Cirsium , which results from the protection offered by the spines and complex shape of its leaves ( Ballabeni et al , 2001b ).…”

“…This would remove the tendency for host ranking or specificity to diverge in populations that lack this host, as the selection pressure induced by wasting time is absent. The fine gradient of preference may have evolved as a general response to the patch fidelity and typical habitat of Oreina species, where ovipositing females find themselves in patches dominated by suitable host plants ( Ballabeni et al , 2001a ). The ecology of the beetle may therefore circumvent the selection pressure for local adaptation, by making preferences among the three suitable hosts effectively neutral in most populations.…”

“…The fi nal column shows the signifi cance of the reductions due to these effects. specificity is strong enough that most eggs are laid on Cirsium in simultaneous choice experiments and in the wild ( Ballabeni et al , 2001a ). Yet in the absence of a choice, females of all populations are sufficiently motivated to oviposit on any of the three host plants rather than waiting for Cirsium .…”

“…This would have a strong impact on these beetles because at high altitudes their breeding season is extremely limited, with the habitat only free of snow between late June and early September. In the field, females lay eggs singly from early July to mid August ( Ballabeni et al , 2001a ), and in the laboratory can lay several hundred eggs during a season (unpublished data). However, as eggs take 15 -20 days to hatch ( Ballabeni et al , 2001b ) and larval growth requires » 30 days , there is a very limited period in which females can lay eggs that stand a chance of completing development before the winter.…”

Spatial associations among algae affect host use in a herbivorous marine amphipod

“…The dispersal of terrestrial herbivores among habitat patches may be strongly influenced by attributes of habitat structure (Wiens 1995), including the nature of matrix habitat (Rand 1999;Jonsen et al 2001) and the proximity of available hosts (Kareiva 1985;Ballabeni et al 2001). Few studies have considered how the spatial arrangement of plants affects the dispersal of marine invertebrates associated with vegetated substrates .…”