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

Antipredation strategies are important for the survival and fitness of animals, especially in more vulnerable life stages. In insects, eggs and early juvenile stages are often either immobile or unable to rapidly flee and hide when facing predators. Understanding what alternative antipredation strategies they use, but also how those change over development time, is required to fully appreciate how species have adapted 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. Our results show that the eggs are significantly more chemically defended than the first two mobile life stages, but not than the third instar. Tonic immobility is also favored by hatchlings, but less so by subsequent instars. We argue the case that over development time, tonic immobility is a useful defensive strategy until adequate chemical protection is achieved over an extended feeding period.

Immature stages of Murgantia histrionica (Hemiptera: Pentatomidae)

Immature stages of Murgantia histrionica (Hemiptera: Pentatomidae) are described using light and scanning electron microscopy. Specimens of all life stages of M. histrionica were collected on Peritoma arborea (Cleomaceae) in Palm Springs, California. Specimens were observed in light and scanning microscopies, imagens taken and described based on specimens and photographs. We provide images of the eggs and immatures in light microscopy, and SEM of the eggs and first and fifth instars. Eggs of M. histrionica are barrel-shaped, white, with brown band and circular spot; the corium surface carinated, forming hexagonal cells; carinae irregular apically. The nymphal color pattern; the reflexed lateral margins of pro- and mesothorax; and the scattered punctuation of the tegument are a combination of characteristics enabling M. histrionica identification in its nymphal stages. The eggs of M. histrionica are similar in shape, color, and size to other Strachiini genera, such as Bagrada, Eurydema and Stenozygum. Among the Strachiini, the correct identification of M. histrionica based on immatures is possible by the shape of the head and pronotum, overall size of immatures, and coloration patterns.