Chemical defence in ladybird beetles (Coccinellidae). I. Distribution of coccinelline and individual variation in defence in 7-spot ladybirds (Coccinella septempunctata)

Abstract

Summary7-spot ladybirds secrete alkaloid (coccinelline)-rich fluid (reflex blood) from leg joints as a defence mechanism against predators. A technique is described that enables the collection and accurate quantification of reflex blood produced, and the amount of coccinelline therein. Coccinelline was found distributed throughout the body, although concentrated in the reflex blood. Reflex blood was collected from a large set of beetles at several time points. Significant variation was found among beetles in the amount of reflex blood produced (for males and for females corrected for body weight) and the coccinelline concentration of the reflex blood. The results are discussed in relation to automimicry and the maintenance of variation through energy trade-offs. The relationships between tendency to aggregate, ability to reflex bleed and the possession of aposematic coloration are also considered.

The relative importance of colour, taste and smell in the protection of an aposematic insect Coccinella septempunctata

“…la). It has been shown (Holloway et al 1991) that these beetles need over a week to replace their full quota of reflex blood after bleeding. It may be that enough toxin is retained in the beetle's body to maintain full avoidance despite inability to bleed in response to attack.…”

“…In these cases there was always at least a week between the bleedings to let them replenish their reflex blood and coccinelline (Holloway et al 1991).…”

“…The reflex blood was collected and its alkaloid content measured by gas chromatography as described by Holloway et al (1991). No significant differences between hibernation sites were found (Mann Whitney tAtest: t/=94 0, jV=10, 10, P=0-427).…”

“…nestlings (Marples et al 1989) and contains two alkaloids, coccinelline and its free base precoccinelline (Pasteels et al 1973), which taste bitter. The alkaloid is distributed throughout the body of the adult seven-spot ladybird, but is more concentrated in the reflex blood that exudes from the tibia/femur joint of the legs, when the ladybird is attacked (Kay et al 1969;Holloway et al 1991). Reflex bleeding involves the exudation of fluid through pores in the knee joints of all six legs which serves to transport defensive compounds to the surface (Cuenot 1896;Hodek 1973;Holloway et al 1991).…”

Better the devil you know: avian predators find variation in prey toxicity aversive

“…One problem for predators regulating their intake of toxins is that individuals within an aposematic prey species often vary in their toxicity [7,8]. 'Automimicry' is characterized by the presence of non-toxic individuals ('automimics') in a population of otherwise aposematic prey ('automodels') [9,10].…”