THE GENETICS AND COST OF CHEMICAL DEFENSE IN THE 2-SPOT LADYBIRD (ADALIA-BIPUNCTATA L)

Ladybirds (Coccinellidae) defend themselves against attack by vertebra te predators by exuding a fluid from the femero-tibial joints. This fl uid carries a noxious or toxic alkaloid. The amount of fluid produced during a single attack can be very high (up to 20% of fresh body weigh t), and the weight of the self-synthesized alkaloid can amount to seve ral percent of the weight of the fluid. A study was carried out on the se two defense characters and two other fitness characters (body weigh t and growth rate) to demonstrate a cost to defense in the form of gen etic trade-offs between characters. The two sexes were analyzed separa tely, and a jackknife procedure was used to attach errors to the estim ates of V-a and cov(a). All four characters were associated with high levels of V-a, but the cov(a) values were mixed, some being negative a nd others positive. Principal-component analysis indicated the operati on of factors constraining the cov(a) values in males, and further pos sible reasons for the appearance of so many positive values are explor ed. A matrix analysis showed that the genetic variance/covariance matr ices of the two sexes were significantly different from each other. Br eeding values derived from sons plotted on breeding values from daught ers had correlation coefficients significantly less than +1. This find ing indicated that a substantial amount of sex-dependent gene expressi on was occurring.