Mating success of differently sized onion flies Delia antiqua

In recent studies (Zurlini & Robinson, in litt.), it was demonstrated that reductions in pupal size (and hence adult size) in a laboratory strain of Delia antiqua resulted in reductions in fecundity, but mating success as measured by the percentage of mated females was not affected. However, these experiments were carried out with males and females descending from pupae within the same pupal length class, i.e. small males were allowed to mate with small females and large with large. In the present experiments important supplementary data have been added on the mating success among males and females of widely differing body sizes. The differences in adult size which could be produced were startling with, at the extreme range, a two-fold size difference between the sexes. In the literature there is an abundance of data on the effect of body size on many adult parameters for many insect species (David et al., 1971; Tsiropoulos & Manoukas, 1977; Miller & Thomas, 1958; Bar-Zeev, 1957 and Barbosa & Peters, 1970); but there appears to be little or no information regarding mating between adults of different sizes. If effective mating occurs between males and females of widely differing sizes then the maintenance of a particular pupal size during mass rearing is not of crucial importance. However, if flies have to be mass-reared for either sterile male release (Ticheler, 1978), where mating activity of the released male is crucial, or for control by the translocation method (Robinson, 1976), where both sexes participate in the mating process in the natural population, differences in size might become important. It is therefore important to know if differences in size could lead to some form of mating barrier. Using the technique of shortening of the larval feeding period (Chiang & Hodson, 1950; Bakker, 1959 and Zurlini & Robinson, 1978) pupae of different sizes were produced. The range of size of the pupae corresponded with the pupal length sizes which can occur in the field (Loosjes, 1976). Males and females from five pupal length classes were given the opportunity of mating in a majority of the possible combinations. Subsequently, various adult parameters were monitored.