Abstract
Studies of predation of ladybird beetles (Coccinellidae) have focused on a limited number of predator taxa, such as birds and ants, while other potential predators have received limited attention. I here consider amphibians as predators of ladybirds. Published amphibian gut analyses show that ladybirds are quite often eaten by frogs and toads (Anura), with recorded frequencies reaching up to 15% of dietary items. Salamanders (Caudata) eat ladybirds less frequently, probably as their habits less often bring them into contact with the beetles. Amphibians do not appear to be deleteriously affected by the potentially toxic alkaloids that ladybirds possess. Amphibians, especially frogs and toads, use primarily prey movement as a release cue to attack their food; it is thus likely that their ability to discriminate against ladybirds and other chemically defended prey is limited. Because of this poor discriminatory power, amphibians have apparently evolved non-specific resistance to prey defensive chemicals, including ladybird alkaloids. Although amphibian-related ladybird mortality is limited, in certain habitats it could outweigh mortality from more frequently studied predators, notably birds. The gut analyses from the herpetological literature used in this study, suggest that in studying predation of insects, entomologists should consider specialized literature on other animal groups.
Highlights
Ladybird beetles have a prodigious array of natural enemies
If coccinellids are taken as prey by frogs and toads in proportion to their occurrence in the habitat, low ladybird numbers in anuran diets probably only indicate their relatively minor faunistic contribution to the potential prey in the habitats of the predators, rather than avoidance related to their chemical defense
The results suggest that ladybirds would gain little protection from anurans/amphibians with the warning signals they possess, because of their behavior
Summary
Ladybird (coccinellid) beetles have a prodigious array of natural enemies. In the last two decades there has been intense interest in the parasites and pathogens of ladybirds [1±4] and in intraguild predation by and of ladybirds [5±8]. A possible reason for the limited amount of attention devoted to such predation might be the formidable chemical defenses of ladybirds, which are often assumed to deter generalist predators. These are based on interspecifically variable distasteful or toxic alkaloids that are present throughout all ladybird life history stages [9±12]. Methylalkylpyrazines provide ladybirds with an unpleasant smell, which serves as an olfactory equivalent of warning coloration [13] These chemical defenses clearly do provide ladybirds with a degree of protection from predation, as might be expected (e.g., [9,14±17]), this is by no means universal. I conclude by considering why amphibians eat ladybirds and why they are not more strongly affected by ladybird chemical defenses when they do
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