Abstract: 【Aim】 Despite the fact that coccinellids display inter- and intra-specific size variations, the question of whether size variations in coccinellid species modify their choice to eat well-defended prey (i.e., displaying various defence responses, including actively evading capture, fighting off predators or frequently using defensive chemicals) is still unclear. In present study, we hypothesized that irrespective of their size the coccinellid predators, i.e., Coccinella septempunctata (L.) (C7) and Menochilus sexmaculatus (Fab.) (Ms), would increase their consumption of a prey type ［i.e., the mustard aphid, Lipaphis erysimi (Kaltenbach)］ only when prey instars would be well-defended. This is because well-defended prey instars are large and more energetic. 【Methods】 We therefore, categorized the 4th nymphal instar of L. erysimi as well-defended and the 2nd nymphal instar as poorly-defended and assessed their preference by large and small variants of the two coccinellid species. 【Results】 The results revealed higher consumption of poorly-defended instar nymphs by both female variants of Ms, while large and small females of C7 consumed higher percentage of well-defended and poorly-defended instar nymphs, respectively, on an exclusive diet of well-defended/poorly-defended prey. On a mixed diet, female variants of C7 consumed similar fraction of both the prey instar nymphs, while variants of Ms consumed higher fraction of poorly-defended instar nymphs. While consumption of both prey instar nymphs increased with the increase in size of C7 females, but consumption of only well-defended instar nymphs increased with the increase in size of Ms females. 【Conclusion】 The results therefore oppose our hypothesis and illustrate that: (i) small coccinellids are more confined to poorly-defended prey instar nymphs while large coccinellids selectively consume well-defended prey instar nymphs; and (ii) within and between coccinellid species, preference for well-defended prey instars increases with the increase in size of predators. Results may be utilized for mass rearing of these coccinellids in laboratories for augmentative biocontrol of mustard aphids.

Key words: Coccinella septempunctata, Menochilus sexmaculatus, Lipaphis erysimi, coccinellids, aphids, biological control, aposematic signals