Silk drives aggregation and following in the neotropical caterpillar Mechanitis menapis (Nymphalidae: Ithomiini)

Abstract

Gregarious larvae that use chemical communication to feed and move together are widespread among folivorous insects, although social behaviour has been studied almost exclusively in a few temperate zone genera. The Menapis (or variable) tigerwing butterfly Mechanitis menapis mantineus Hewitson (Lepidoptera, Nymphalidae, Danainae, Ithomiini) is a neotropical species whose larvae feed gregariously on Solanaceae host plants. In laboratory experiments conducted in the Ecuador cloud forest, M. menapis caterpillars are attracted to silk produced by conspecifics and show no evidence of pheromone production. Indeed, caterpillars consistently choose arenas with silk over bare arenas but do not show a preference for arenas marked with abdominal cuticular surface residues. Mechanitis menapis caterpillars on silk‐coated plants are both more mobile and more cohesive than those on control plants. Nonetheless, caterpillars move independently over unmarked surfaces and groups do not make rapid collective choices between two food sources. Collective behaviour in M. menapis thus appears to be based on aggregation on collectively produced silk to facilitate feeding, as well as using this silk to maintain cohesion. Silk production is common in caterpillars, although M. menapis appears to be unique among species studied so far in using silk to maintain group cohesion.

Caterpillars Cooperate to Overcome Plant Glandular Trichome Defenses

“…Two potentially complementary mechanisms exist by which grouping can facilitate feeding initiation on trichome-bearing plants: first, previous work suggests that caterpillars collectively lay down silk to avoid trichome exudates (Rathcke and Poole, 1975), and second, the present study shows that individuals share the feeding edge created by one of their neighbors. M. menapis collectively lay down a network of silk threads to move around suspended above the trichomes (Despland and Santacruz-Endara, 2016), and this behavior was observed on control leaves in our experiment (Supplementary Image 1). However, larvae on washed leaves were observed walking directly on the leaf surface, around the base of non-glandular trichomes (Supplementary Videos 1, 2), suggesting that the silk bridge is used to avoid glandular trichomes and their exudates.…”

“…The genus Mechanitis is specialized on the trichome-bearing Leptostemonum clade within the mega-genus Solanum, and many species are gregarious (Giraldo and Uribe, 2012). Mechanitis menapis actually exhibits relatively small group-sizes and flexible behavior (Despland and Santacruz-Endara, 2016) compared to some congenerics (Young and Moffett, 1979b;Young, 1983;Brown and Freitas, 1994;Arantes, 2001;Giraldo and Uribe, 2010). Previous work has suggested that other Mechanitis larvae cut trichomes prior to feeding, leading to the accumulation of piles of uneaten trichomes near the feeding hole (Young and Moffett, 1979b), and that they use silk to cover plant trichomes and to facilitate movement and feeding (Rathcke and Poole, 1975), suggesting that adaptations to overcoming trichomes are widespread in this genus that specializes on trichome-defended plants.…”

Ciclo de vida y enemigos naturales de Mechanitis menapis mantineus (Lepidoptera: Ithomiini)

“…En condiciones de cautiverio, PGS observó que distintas hembras de M. menapis mantineus depositaron sus huevos de forma aledaña en las mismas hojas, haciendo indistinguibles las distintas posturas en un grupo de ocho huevos. Este comportamiento fue reportado para Mamestra configurata Walker, 1856 (Lepidoptera: Noctuidae) (Ulmer, Gillott, & Erlandson, 2003), pero no ha sido reportado previamente para ninguna otra especie del género Mechanitis ni de la tribu Ithomiini, a diferencia de la agregación de las larvas, registrada para la especie recientemente (Despland & Santacruz, 2016). Así pues, se requieren observaciones adicionales en campo para corroborar que las hembras adultas de M. menapis favorecen el gregarismo de las larvas en campo como estrategia ecológica para incrementar la supervivencia de su descendencia.…”

“…Finalmente, los efectos del gregarismo sobre el forrajeo, evitando el consumo de los tricomas de la plantas hospedera, fueron expuestos para M. polymnia varias décadas atrás (Rathcke & Poole, 1975). Esta idea fue soportada en trabajos recientes, donde se sugiere que la producción de seda facilita la alimentación y ayuda a mantener la cohesión del grupo larvario (Despland & Santacruz, 2016).…”

Peer Review #1 of "Top-down and bottom-up controls on an herbivore on a native and introduced plant in a tropical agricultural landscape (v0.1)"

“…Solanum subgenus Leptostemonum (Robinson et al, 2010), the 'spiny Solanums', characterized by sharp epidermal prickles and stellate trichomes (Levin et al, 2006). Caterpillars are gregarious and feed collectively, using silk to avoid plant trichome defenses (Despland, 2019;Despland and Santacruz-Endara, 2016).…”