How the seed coat affects the mother\u2019s oviposition preference and larval performance in the bean beetle (Acanthoscelides obtectus, Coleoptera: Chrysomelidae, Bruchinae) in leguminous species

Árpád Szentesi

doi:10.1186/s12862-021-01892-9

Abstract

BackgroundThe host specificity and host range of the dry bean beetle, Acanthoscelides obtectus (Coleoptera: Chrysomelidae, Bruchinae), a seed predator of beans, is poorly known. In addition, the female oviposition preference and larval performance relationship is complicated by the respective importance of seed coat and cotyledon, because, paradoxically, females lay eggs on the basis of stimuli of the seed coat alone, without directly being able to assess the quality of the cotyledon’s suitability for larval development. Conversely, the thickness of seed coat may prevent first instar larvae from entering the seeds, even if cotyledons are suitable for development.MethodsThe seeds of 62 leguminous species and 75 cultivars and accessions occurring in Hungary were evaluated for preference-performance relations. The preference of female bean beetles for seeds was measured in no-choice egg-laying tests. The ability of first instar larvae to overcome the seed coat as a physical barrier was tested with intact seed coat, while pre-drilled seed coats allowed the larvae to assess the suitability of cotyledon for development. The number of emerging adults was recorded. The thickness of seed coats and the weight of seeds were measured. Nonparametric tests and logistic regression were used for the statistical analyses of data and effect sizes were also calculated.ResultsSeeds of 18 leguminous species (35% of them Lathyrus) supported larval development to adults if the seed coat was pre-drilled; however, only nine leguminous species supported development to adults if the seed coat was intact. Seed coat thickness beyond a critical threshold of 0.1 mm strongly influenced survival of first instar larvae. There was no overall positive correlation between oviposition preference and larval performance, except for 16 so-called acceptable non-hosts (Kendall’s τ = 0.3088). A. obtectus females also showed an ovipositional hierarchy of legume species even in no-choice tests.ConclusionsThe results suggest that whereas the use of some acceptable non-host species by the A. obtectus is possible in seed stores, the same is unlikely under outdoor conditions, where the recognition of a diverse set of seed pod-related compounds would be necessary to induce egg-laying.

Highlights

The host specificity and host range of the dry bean beetle, Acanthoscelides obtectus (Coleoptera: Chrysomelidae, Bruchinae), a seed predator of beans, is poorly known
Janzen [1] became one of the pioneers of female preference-larval performance studies, asking whether insect mothers optimally select substrates for larval development, and whether oviposition on novel or non-hosts are attempts of host range expansions [2, 3]. The latter hypothesis is supported by the fact that the range of plant species promoting survival of larvae is often wider than the egg-laying preference of the mother [4, 5]
Besides the two Phaseolus species, rearing in laboratories is possible on chickpea through generations [18, 40], and occasional infestations occur in stores on garden peas or faba beans (Szentesi unpubl. results)

Summary

Introduction

The host specificity and host range of the dry bean beetle, Acanthoscelides obtectus (Coleoptera: Chrysomelidae, Bruchinae), a seed predator of beans, is poorly known. Janzen [1] became one of the pioneers of female preference-larval performance studies, asking whether insect mothers optimally select substrates for larval development, and whether oviposition on novel or non-hosts are attempts of host range expansions [2, 3]. The latter hypothesis is supported by the fact that the range of plant species promoting survival of larvae is often wider than the egg-laying preference of the mother [4, 5]. The negative relationships refer to the lack of adaptation due to metabolic trade-offs, but to the importance of hitherto unconsidered life history components and environmental factors [8, 13, 14]

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Conclusion