Effects of starvation on death‐feigning in adult Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

Abstract

In insects, death‐feigning is an effective defence strategy. Eucryptorrhynchus brandti, a major borer pest in China, has a weak flight ability and exhibits obvious death‐feigning behaviour when disturbed. Despite a large number of studies of its biological and ecological properties as well as control methods, the death‐feigning behaviour has not been specifically described. In laboratory conditions, we recorded the survival rate under starvation and feeding conditions and evaluated the effect of starvation on the duration and occurrence of death‐feigning. In a continuous experiment, we examined variation in the death‐feigning duration every day over 7 day. Then, we evaluated the effects of starvation for 3, 6 and 9 day in a non‐continuous experiment and further observed variation in the death‐feigning intensity. We found that starvation significantly affected the survival rate. Survival time was significantly longer in the starvation group than in the feeding group, and females had longer survival times than males (female: 14 day, male: 8 day). In the continuous experiment, starved E. brandti had the longest duration of death‐feigning at 2 day, followed by a significant decrease. In the non‐continuous experiment, the duration and proportion of death‐feigning decreased significantly as the duration of starvation increased and were significantly lower than feeding. These observations suggest that starvation is a non‐negligible factor in the death‐feigning behaviour of E. brandti adults, facilitating the interpretation of future ecological and behavioural data of thanatosis.

Death‐feigning propensity varies within dice snake populations but not with sex or colour morph

“…DF is a complex behaviour that often involves a set of features, such as immobility and leg‐folding, supination, display of colour pattern, mouth opening or expulsion of nauseating/noxious secretions (e.g. Miyatake et al ., 2004; Honma, Oku & Nishida, 2006; Humphreys & Ruxton, 2018; Mesquita et al ., 2018; Li et al ., 2019; Ramalho et al ., 2019; Segovia et al ., 2019). DF is observed widely across the animal kingdom and thus is assumed to confer substantial fitness benefits in many circumstances; yet, it is also a risky strategy because individuals become very easy prey (Humphreys & Ruxton, 2018, 2019).…”

Behaviour and metabolism during tonic immobility (death-feigning) in Eucryptorrhynchus scrobiculatus and E. brandti (Coleoptera: Curculionidae)

“…To induce TI behaviour, forceps were used to touch the metaventrite (the metathorax between the middle and hind legs) (Fig. 2) (Li et al, 2019). If a weevil did not respond, the same stimulus was applied a second or third time; if there was no response after three stimuli, the duration of TI was zero.…”

“…When some insects are disturbed by predators they curl up and remain motionless or fall from their original resting places and behave as if dead , and in the absence of further stimulation recover and resume activity after a few minutes (Humphreys & Ruxton, 2018). This is called tonic immobility (TI), death feigning, thanatosis, animal hypnosis, playing dead, immobilization catatonia, playing possum or quiescence (Ruxton, 2006;Acheampong & Mitchell, 2010;Li et al, 2019) and is widely used by animals to limit injury and as a means of escape.…”

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For example, specifi c sounds (alarm calls) can increase the duration of TI in Gallus gallus (Pochron & Thompson, 2019) and in two species of Callosobruchus, C. chinensis and C. maculatus (Miyatake et al, 2008a), high incidence of TI is associated with low temperatures (15°C and 20°C) and its duration is correlated negatively with increase in ambient temperature when TI is induced by touching. Thus, the variation in TI in different species associated with environmental factors is worthy of further study.Recent studies indicate that TI behaviour also depends on the sex and weight of an insect (Li et al, 2019; Konishi et al, 2020). For example, TI in C. chinensis stimulated by touching, is longer in heavy females than males (Hozumi & Miyatake, 2005

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“…Recent studies indicate that TI behaviour also depends on the sex and weight of an insect (Li et al, 2019; Konishi et al, 2020). For example, TI in C. chinensis stimulated by touching, is longer in heavy females than males (Hozumi & Miyatake, 2005…”