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

Abstract

AbstractBrassolis sophorae (Linnaeus), the coconut palm caterpillar, is a pest in the Northeast region of Brazil. Despite its great importance, information about the biology and behaviour of this insect is scarce. B. sophorae caterpillars are gregarious, and they remain in a nest during the daytime and only come out at dusk to feed. When caterpillars leave the nest to forage, they lay down a trail of silk that leads the group to the feeding site. In spite of this, there is no scientific evidence showing whether trail‐following behaviour in B. sophorae caterpillars is mediated by silk‐associated chemical cues. This gregarious behaviour has probably hampered biological studies of this species. We determined biological parameters (number of instars and development time of each instar) of the larvae and conducted behavioural assays to assess whether trail‐following behaviour of B. sophorae is mediated by chemical (silk extract) or physical (solvent‐washed silk) cues, or a combination of both. Measurements of the head capsule width showed that B. sophorae larvae pass through six instars in an average period of 12 days per instar. Dual‐choice tests in a Y‐shaped arena showed that the larvae significantly preferred to walk on a silk‐covered surface over a clean one and on a silk extract over hexane alone. When caterpillars were given the choice of walking on silk or on solvent‐washed silk, they did not show a preference for either treatment. These results demonstrate the presence of pheromonal compounds in the silk of B. sophorae although the communication between caterpillars of B. sophorae is also mediated by physical cues. The results of this study broaden knowledge on the trail‐following behaviour of immature larvae as well as the biology, morphology and behaviour of this insect.