Thigmotaxis maintains processions of late‐instar caterpillars of Ochrogaster lunifer

Abstract

Abstract. Processionary behaviour is a distinctive feature of the dispersal of caterpillars of a number of Lepidoptera, including Ochrogaster lunifer Herrich‐Schäffer (Lepidoptera: Notodontidae) from Australia. By cutting hairs on either the first or last three segments of the bodies of caterpillars and re‐introducing them into processions of normal caterpillars, the present study provides strong evidence that thigmotaxis is the mechanism that maintains single‐file, head‐to‐tail movement of groups of individuals. The inclusion of caterpillars whose posterior hairs have been cut results in the breakage of processions, whereas the inclusion of caterpillars whose anterior hairs have been cut rarely results in the breakage of processions. The breakage of processions occurs because caterpillars whose posterior hairs had been cut are difficult to follow and they will not stop when those behind became detached. The speed of movement of processions incorporating caterpillars whose hairs on the posterior segments of their bodies have been cut also has a significant effect on the likelihood of maintaining processionary movement; faster‐moving processions are more likely to break than are more slowly‐moving processions.

Wing pattern polyphenism in two behavioural forms of Ochrogaster lunifer (Lepidoptera: Notodontidae)

“…Although aspects of the basic entomology and biology of the species were documented many years ago, few of the published works allow an interested observer to know that males and females have different phenotypes, why there is variation in wing pattern or that wing pattern is linked to larval behaviour which varies with habitat. The findings presented herein, together with Steinbauer (), explain phenomena associated with the larvae and adults which regularly capture public attention. In addition, this work provides new biological information about the species and its ecology.…”

“…Consequently, data acquired when nests are likely to be empty are not expected to reflect conditions directly affecting larval development. Steinbauer () reported conducting behavioural experiments on caterpillars returning to nests until 12:00 pm but did not present data on when larvae left nests to forage. Therefore, I consider trends in temperature and humidity between 11:00 and 17:00 because these are periods when larvae are most likely to be in their nests and ambient conditions at their hottest and driest during the Austral summer and early autumn.…”

“…The Processionary caterpillar is a very familiar species which occurs in all Australian States and Territories except Tasmania. The name Processionary caterpillar derives from the behaviour of the hairy larvae to move in single‐file, head‐to‐tail processions on host plants and on the ground; this behaviour is maintained by thigmotaxis (Steinbauer ). The name Bag‐shelter moth dates from around the turn of the last century and derives from the silken nests that hang from hosts which are constructed by some populations (Fig.…”

Trail‐following behaviour and biological aspects of the gregarious caterpillar Brassolis sophorae (Lepidoptera: Nymphalidae)

“…However, Roessingh () found that in addition to tactile cues, Y. cagnagellus responds to pheromonal compounds extracted from the silk. According to Steinbauer (), processionary behaviour in Ochrogaster lunifer is mainly driven by thigmotaxis. Nevertheless, the authors agree with Fitzgerald () that physical cues may take precedence to semiochemical stimuli.…”

“…Others use chemical cues, which are present in the silk as long‐living non‐volatile pheromonal compounds (Roessingh and references therein; Pescador‐Rubio et al ). There are also a few reports that contact stimuli (thigmotaxis) mediate processionary behaviour in Lepidoptera species (Steinbauer ).…”