Differences between the 7‐spot and 2‐spot ladybird beetles (Coccinellidae) in their toxic effects on a bird predator

Abstract

Abstract. 1. Experiments with nestling blue tits Parus caeruleus L. examined the effects of feeding them 7‐spot ladybird Coccinella septempunctata (L.), 2‐spot ladybird Adalia bipunctata (L.) or controls Tenebrio sp. 2. A feeding rate of 51/3 7‐spot ladybirds per day ‘killed’ nestlings within 2 days. Three of six nestlings fed at half this rate survived 4 days. In contrast, all experimental birds survived sixty‐four 2‐spot ladybirds fed over 4 days (equivalent by weight to the high 7‐spot diet). 3. Nestlings fed 7‐spot ladybirds also grew more slowly than birds fed 2‐spot ladybirds. The latter birds showed no difference in weight gain from the controls although they begged more strongly for food. 4. Cadavers of birds fed 7‐spot ladybirds showed evidence of severe liver damage. 5. The results indicate a substantial difference between the ladybird species in their toxicity to nestling blue tits. They support the hypothesis that 2‐spot ladybirds are largely‐edible, polymorphic Batesian mimics of well‐protected, monomorphic species such as the 7‐spot ladybird.