The Genetics and Cost of Chemical Defense in the Two-Spot Ladybird (Adalia bipunctata L.)

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 a • All four characters were associated with high levels of Va> but the cov a values were mixed, some being negative and others positive. Principal-component analysis indicated the operation offactors constraining the cOV a 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 + I. This finding indicated that a substantial amount of sexdependent gene expression was occurring.

Effects of a larval antipredator response and larval diet on adult phenotype in an aposematic ladybird beetle

“…Our results show that life history traits are in¯uenced by use of re¯ex bleeding, but only if food quality is above some minimum threshold. Detailed quanti®cation of the characters underlying re¯ex bleeding (e.g., Holloway et al 1991Holloway et al , 1993 under dierent environmental conditions would be valuable.…”

“…There was, however, a moderately strong eect of re¯ex bleeding on H. axyridis life history. More work is needed on the role of food quality in mediating the eects of re¯ex bleeding with an emphasis placed on re¯ex bleeding as a trait, rather than an imposed treatment (e.g., Holloway et al 1991Holloway et al , 1993.…”

“…This response, known as re¯ex bleeding, occurs both in adults and larvae of H. axyridis; we examine eects of larval bleeding in this study. As in other ladybird species, re¯ex bleeding in H. axyridis is thought to be defensive (Komai 1956;Holloway et al 1991Holloway et al , 1993 though the exact nature of the physiology and biochemistry underlying the response is poorly understood. Previous studies of other ladybird species have shown that re¯ex bleeding, in combination with aposematic coloration, is associated with reduced rates of attack, increased survival of prey animals after an attack (Wiklund and Jarvi 1982;Marples et al 1994), and even death of potential predators (Marples et al 1989).…”

Coccinellids and Semiochemicals

“…Adults bleed from the tibiofemoral joints and larvae from dorsal glands. The amount of refl ex fl uid emitted by ladybirds in response to an attack can be very high (up to 20% of body fresh weight), and the alkaloid component can constitute several per cent of the weight of the fl uid (Holloway et al 1991(Holloway et al , 1993. The exudates are yellowish/orange and are mostly toxic to other organisms and sometimes also distasteful with a strong fl avour.…”

Why does the larval integument of some sawfly species disrupt so easily? The harmful hemolymph hypothesis

“…In the definition, the "body" excludes the head capsule. Easy bleeding is different from reflex bleeding known from a series of insect orders, and where hemolymph is only released from a few given weak points of the integument, for instance, at the junction of leg segments (CuØnot 1896;Hollande 1911;Happ and Eisner 1961;Wallace and Blum 1971;Benfield 1974;Blum and Sannasi 1974;Holloway et al 1993).…”