No abstract

Ladybirds (Coccinellidae) defend themselves against attack by vertebrate predators by exuding a fluid from the femero-tibial joints. This fluid 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 weight), and the weight of the self-synthesized alkaloid can amount to several percent of the weight of the fluid. A study was carried out on these two defense characters and two other fitness characters (body weight and growth rate) to demonstrate a cost to defense in the form of genetic trade-offs between characters. The two sexes were analyzed separately, and a jackknife procedure was used to attach errors to the estimates of V and cov . All four characters were associated with high levels of V , but the cov values were mixed, some being negative and others positive. Principal-component analysis indicated the operation of factors constraining the cov values in males, and further possible reasons for the appearance of so many positive values are explored. A matrix analysis showed that the genetic variance/covariance matrices of the two sexes were significantly different from each other. Breeding values derived from sons plotted on breeding values from daughters had correlation coefficients significantly less than +1. This finding indicated that a substantial amount of sex-dependent gene expression was occurring.

A viable wingless 2spot ladybird Adalia bipunctata (L.) was found in the wild. Breeding through four generations revealed that the wingless trait was controlled by a recessive allele which displays variable levels of expression. The wingless ladybird is discussed in relation to its potential as a biocontrol agent. One ladybird also occurred in this stock which is suggestive of a supergene controlling the colour polymorphism in this species.

Abstract. The abdominal colour pattern of Eristalis arbustorum (L.) shows seasonal variation, with animals emerging in spring being darker than those emerging during summer. One of the most important environmental cues influencing the abdominal colour pattern is developmental temperature. An experiment was carried out to establish which period during the immature stages was important in determining final adult colour pattern. The results indicate a good relationship between the length of the pupal period and both the extent of the paler markings on the abdomen and the grey score of these markings. The length of the larval period did not have any effect on adult colour pattern.

The abdominal colour pattern of Eristalis arbustorum is a plastic character which is heavily influenced by developmental temperature. The present study investigated the form of the reaction norms of amount of abdominal yellow and intensity of the yellow (measured as grey value) on pupal development temperature. The slope of the reaction norm for amount of yellow was steeper in males than in females. The reaction norms for grey value on temperature were nonlinear. Family groups were reared to enable a consideration of the genetics to be made. There were significant family by environment interactions for both characters for both sexes indicating genetic variance for plasticity. Pupal development time is closely correlated with developmental temperature. The relationship between amount of yellow on the abdomen and log pupal development time was curvilinear and fitted a quadratic function well. There was significant among-family variation in the slopes of these lines for females, but not for males, again suggesting genetic variation for plasticity. The results are discussed in relation to the maintenance of genetic variation.