Search

Social aggression arises from conflicts of interest over reproduction in animal societies. Aggression is often highly variable between individuals in a group, may be correlated with dominance, and is often integral to the establishment of dominance hierarchies that in turn determine reproductive opportunities. However, reproductive dominance is not always linked with social dominance: 'queens' are not always the most aggressive individuals in a group. Furthermore, in some animals social rank is determined without aggression, and derived through another means, such as gerontocracy. In such instances, what is the role of aggression, and what underlies the variation between individuals? Here, we investigate the relationship between inheritance rank and aggression in the hover wasp Liostenogaster flavolineata, which has an age-based inheritance queue. All females in this study were of known age and, thus, rank could be determined independently of behaviour. Observations of intra-colony aggression indicated that aggression increased with inheritance rank and occurred among non-breeding subordinates. This cannot be explained by models that do not account for aggression between non-breeders. It is likely that contests over inheritance rank and the higher future fitness anticipated by high-ranking individuals account for this pattern.

Nesting tactics of individually marked female solitary wasps, Ammophila sabulosa (L.) (Sphecidae), were studied over two seasons at a Norfolk heathland site. Females provision unicellular nests with 1-5 paralysed caterpillars. The entire nesting cycle requires approximately 8-10 hours of activity and there is no evidence that nesting success depends on female size. Prey are obtained by hunting or are stolen from other females' nests, which are found by searching in the nesting area. Females search on the nesting area and open other females' nests at significantly later times of day and lower temperatures than those at which they are absent from the nesting area (presumably hunting) and provision hunted prey. This may reflect thermal constraints or changes in prey availability or availability of detectable nests. Hunting and searching are mutually exclusive alternatives, but because females frequently switch between them it is difficult to estimate the time costs of either. Brood parasitism is an alternative way in which an A. sabulosa female can provide her larva with food and shelter. After completing her previous nest she must find a new digging site. While searching in the nesting area she may come across another female's nest, which she opens and usually brood parasitizes if it contains prey. It is again difficult to compare the time costs of non-parasitic nesting and parasitism, this time because alternative behaviours are not mutually exclusive - finding digging sites and finding other females' nests both involve searching on the nesting area. Females might find other females' nests opportunistically, or spend time searching for them. My methods and interpretation are compared with those of BROCKMANN et al., who analysed alternative nesting strategies in Sphex ichneumoneus. The alternative behaviours in Sphex are 'digging' and 'entering', two ways of acquiring a burrow. BROCKMANN et al. included nights and periods of poor weather in their time cost measurements, decreasing the likelihood of detecting differences between the net benefits of digging and entering. They also assumed that eggs laid after digging and entering had equal chances of survival, and that a female decides unconditionally to either dig or enter immediately after closing her previous nest. A major problem in both studies is that of pin-pointing when decisions are made and hence defining the strategy set. This is particularly difficult when alternative behaviours are not mutually exclusive.

The nesting behaviour of marked female solitary wasps, Ammophila sabulosa (L.) (Sphecidae), was studied over two seasons at a Norfolk heathland site. Females mass provisioned unicellular nests with 1-5 paralysed caterpillars. Intraspecific parasitism was the major mortality factor before the egg hatched - approximately 28% of eggs were destroyed by parasites. Parasites stole caterpillars to provision their own nests, replaced host eggs with their own eggs (brood parasitism), or simply discarded prey from host nests. Hosts were ineffective at preventing parasitism. Individual females both provisioned their own nests and parasitized those of other females. Parasitism usually occurred soon after the previous activity at the host nest. Parasitism events were clumped at certain nests, which were parasitized up to five times each. Once a nest had been brood parasitized, the prey were significantly more likely to be stolen or discarded than were prey in unparasitized nests, and only 17 % of eggs laid by brood parasites survived. Circumstantial evidence suggests that chemical stimuli are important in detection of host nests by parasites. High levels of intraspecific parasitism have rarely been reported in solitary wasps and bees, and parasitic behaviour is rare and unspecialized in some other Ammophila species. Parasitism by miltogrammine flies was of relatively minor importance in A. sabulosa as in other Ammophila species, probably because provisioning events, during which flies larviposit, are few and well separated in time.