Chemical defense and tonic immobility in early life stages of the Harlequin cabbage bug, Murgantia histrionica (Heteroptera: Pentatomidae)

Abstract

Antipredation strategies contribute to the lifetime reproductive success of organisms, particularly in more vulnerable life stages that look to survive until reproduction. In insects, eggs and larval stages are often immobile or unable to rapidly flee and hide from predators. Understanding what alternative antipredation strategies they use, but also how these change over development time, is required to fully appreciate how species adapt to biotic threats. Murgantia histrionica is a stink bug, conspicuously colored from egg to adult, known to sequester defensive glucosinolates from its cruciferous hosts as adults. We sought to assess whether this chemical defense is also present in its eggs and early nymphal instars and quantified how it fluctuates among life stages. In parallel, we looked at an alternative antipredation strategy, described for the first time in this species: tonic immobility (i.e., death feigning). We also qualitatively investigated ultraviolet reflectance in eggs and adults as a proxy of conspicuousness against UV-absorbing leaves. Our results show that the eggs are significantly more chemically defended than the first two but not third mobile life stages, yet compound concentrations do not statistically differ across nymphal instars. Tonic immobility is favored by hatchlings, but less so by subsequent instars. Eggs also had obvious ultraviolet reflectance, suggesting that they would contrast against a leaf substrate and, considering their chemical load, that they may be aposematic. We argue that there are two possible interpretations of our results. One is that, throughout ontogeny, tonic immobility is a useful defensive strategy until adequate chemical protection is achieved over an extended feeding period. The other is that both aposematism and tonic immobility are used by this species, but variation in strategy use throughout ontogeny is decoupled.

Protective geometry and reproductive anatomy as candidate determinants of clutch size variation in pentatomid bugs

“…Other species, such as predators in the genus Podisus , often lay relatively small, loosely clustered (non-aggregated) eggs with highly suboptimal protective geometry. There is some evidence that in some of these species with clutch sizes too small to protect a large number of eggs, other strategies have evolved to protect eggs from predation and/or parasitism, such as camouflage, occupying enemy-reduced microhabitats (Torres-Campos et al 2016) or sequestering toxic chemical compounds from host plants (Guerra-Grenier et al 2021). In the latter case, there is preliminary evidence that egg patterning may act as an aposematic signal to predators; if so, laying eggs in 2-by- n lines would maximize the strength of this signal.…”

“…) or sequestering toxic chemical compounds from host plants (Guerra-Grenier et al 2021). In the latter case, there is preliminary evidence that egg patterning may act as an aposematic signal to predators; if so, laying eggs in 2-by-n lines would maximize the strength of this signal.…”

Evaluation of Ten Alternative Treatments for the Management of Harlequin Bug (Murgantia histrionica) on Brassica Crops

“…This damage reduces the appearance of leaves at harvest, making plants less marketable. Traditionally, harlequin bug has been difficult to manage due to its mobility and its chemical defenses to deter natural enemies, both of which result in a lack of predators [ 9 ]. Indeed, harlequin bug has few natural enemies apart from generalist predators and hymenopterous egg parasitoids, making biological control challenging and largely ineffective [ 10 ].…”