Ground-level predation on artificial caterpillars indicates no enemy-free time for lepidopteran larvae

Abstract

Lepidoptera is one of the most diverse orders of insects, their larvae are very abundant in many habitats, and frequent prey of various predators. To decrease predation risk, caterpillars developed several means of defence, among them timing their activity to avoid predators (seeking enemy-free time). Although the enemy-free time hypothesis is often invoked to explain caterpillar behaviour, empirical evidence for it is scarce. We tested whether such enemy-free time exists in a temperate forest by comparing predation pressure on artificial caterpillars during day and night on the ground in forest fragments in Denmark. We found a high predation rate, 23.9%d -1 , and higher predation rate at night (30.9%d -0.5 ) than during the day (17.0%d -0.5 ), both by invertebrate (23.3%d -0.5 vs. 12.4%d -0.5 ) and vertebrate (8.5%d -0.5 vs. 3.3%d -0.5 ) predators. The most important predators were chewing insects (73.4% of all attacks) and small mammals (19.0%). Attack rates on red caterpillars were higher (30.0%d -1 ) than on green ones (19.5%d -1 ). Overall, these data do not support the idea that night activity can provide enemy-free time for solitary caterpillars on the temperate forest floor.

Ant assemblage composition explains high predation pressure on artificial caterpillars during early night

“…Unlike the previous studies which divided diel time into only day and night (Seifert et al ., ; Ferrante et al ., ), our study subdivided diel time into four time intervals (morning, afternoon, early and late night). We found that both total predation rate and predation by ants were highest during the early night (19.00–01.00 hours).…”

“…However, in a temperate forest, Ferrante et al . () found that predation rate at night was higher than during the day. Diel variability of predation pressure is still under debate, and potential drivers of such patterns are poorly understood.…”

“…Predators can shape morphological and chemical defence traits (Greeney et al ., ) and biological rhythms of prey (Heinrich, ). In response to prey availability and activity, predation pressure varies across different timescales, including diel, lunar, seasonal and annual cycles (Lima & Bednekoff, ; Ferrari et al ., ; Ferrante et al ., ).…”

“…Examples include common rabbit ( Oryctolagus cuniculus ) and mammalian mesopredators in southern Europe (Monterroso et al ., ), and wolves ( Canis lupus ) and moose ( Alces alces ) in North American boreal forest (Vander‐Vennen, ). Among invertebrates, lepidopteran larvae have been the subject of several empirical and theoretical studies that investigated temporal variability of their predation rate (Heinrich, ; Seifert et al ., ; Ferrante et al ., ). Lepidopteran caterpillars (hereafter ‘caterpillars’) mostly forage during the night to avoid the activity peak of their predators (e.g.…”

“…Assessing predation rate based on artificial caterpillars made of odourless and non‐toxic coloured plasticine is a simple measure of predation pressure, and has been widely employed (e.g. Posa et al ., ; Howe et al ., ; Tvardikova & Novotny ; Ferrante et al ., , ; Low et al ., ; Lövei & Ferrante, ; Roslin et al ., ). Here we used artificial caterpillars exposed on plant leaves in a natural rainforest at Xishuangbanna Tropical Botanical Garden, Yunnan Province, southwest China, to study the diel variability of predation rate on caterpillars.…”