Property rights and loss aversion in contests

We analyze the effects of property rights and the resulting loss aversion on contest outcomes. We study three situations: in “gain” two players start with no prize and make sunk bids to win a prize; in “loss” both the players start with prizes and whoever loses the contest loses their prize; and in “mixed” only one player starts with a prize that stays with him if he wins, but is transferred to the rival otherwise. Since the differences among the treatments arise only from framing, the expected utility and the standard loss aversion models predict no difference in bids across treatments. We introduce a loss aversion model in which the property rights are made salient, and as a result the reference point varies across treatments. This model predicts average bids in descending order in the loss, the mixed, and the gain treatment; and higher bids by the player with property rights in the mixed treatment. The results from a laboratory experiment broadly support these predictions. There is no significant difference in bids in the loss (gain) treatment and bids by property rights holder (nonholder) in the mixed treatment. A model incorporating both loss aversion and social preferences explains this result

Volatile chemical emission as a weapon of rearguard action: a game-theoretic model of contest behavior

We use a game-theoretic model to explore whether volatile chemical (spiroacetal) emissions can serve as a weapon of rearguard action. Our basic model explores whether such emissions serve as a means of temporary withdrawal, preventing the winner of the current round of a contest from translating its victory into permanent possession of a contested resource. A variant of this model explores an alternative possibility, namely, that such emissions serve as a means of permanent retreat, attempting to prevent a winner from inflicting costs on a fleeing loser. Our results confirm that the underlying logic of either interpretation of weapons of rearguard action is sound; however, empirical observations on parasitoid wasp contests suggest that the more likely function of chemical weapons is to serve as a means of temporary withdrawal. While our work is centered around the particular biology of contest behavior in parasitoid wasps, it also provides the first contest model to explicitly consider self-inflicted damage costs, and thus responds to a recent call by empiricists for theory in this area

Mutual interference reduces offspring production in a brood- guarding bethylid wasp

Parasitoids have the potential to suppress populations of their hosts and thus may play an 2 important role in influencing the temporal and spatial dynamics of pest arthropods. 3 Behavioural interactions between foraging females, collectively constituting ‘mutual 4 interference’, can reduce host suppression. We use laboratory microcosms to assess the 5 prevalence and consequences of mutual interference behaviour in a bethylid wasp, Goniozus 6 nephantidis (Muesebeck) (Hymenoptera: Bethylidae), which is known to brood guard and to 7 engage in agonistic contests for individual hosts and which is also an agent of biological pest 8 control. We hold host and parasitoid numbers constant and vary the degree of female-female 9 contact that can occur. Mutual interference is manifest in a considerable reduction in the 10 number of offspring produced when females are not fully isolated from each other, due to 11 effects operating at the early stages of offspring production. This mutual interference may 12 contribute towards the limited degree of host population suppression achieved when some 13 species of bethylids are deployed as agents of biological pest control and also has clear 14 potential to influence the efficiency of mass rearing of parasitoids prior to field release

Do resource value and ownership status affect intensity and resolution of contests in a parasitoid wasp?

International audienceBiological control of bruchid beetles, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), infesting cowpea seeds, Vigna unguiculata (L.)Walpers (Fabaceae), can be performed via augmentative releases of Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) parasitoid wasps. Females of the latter species are therefore likely to experience intense intraspecific competition: they should encounter numerous previously parasitized hosts but also conspecific competitors, with which they may fight to secure hosts on which to lay their eggs. Such contests might therefore disrupt biological control programs. Here, we studied aggressive behavior that D. basalis females show toward conspecific competitors and subsequent host exploitation strategies. We further investigated factors that classically affect contest intensity and outcomes in animals, such as the effect of ownership status, by manipulating the residency period before the intruder's arrival. In addition, we tested the effect of the size of female reproductive tissue (measured in terms of egg load) and the quality of the habitat previously experienced by females (either rich or poor in hosts). These two factors are expected to influence the value that females place on the host and therefore the costs they are willing to pay to win it. Finally, we discussed the consequences of agonistic behaviors on females' host exploitation strategies. Our results suggest that contest competition may actually enhance host control by favoring parasitoid dispersion, rather than disrupting it

The relative importance of RHP and resource quality in contests with ownership asymmetries

Ownership asymmetries lead to owners (residents) having substantial contest advantages over intruders, and this may overwhelm the fighting advantage of large body size. Why such an ownership advantage occurs, however, is not clear and requires further investigation. Here, we use a jumping spider, Phidippus clarus, to examine the role of ownership asymmetries and resource quality in determining contest outcomes and assessment strategies of both intruders and residents. Resident male P. clarus cohabit with and defend virgin females where reproductive potential increases with body size. Here, we show that ownership plays a significant role in contest outcomes, despite the previously demonstrated importance of body size when males encounter each other in the absence of a female. Owners have a substantial advantage over intruders with residency being more important than body size in determining contest outcomes. Intruders gave up more quickly when owners were larger, suggesting that owners follow a partial mutual assessment strategy. In contrast, contests won by intruders were "wars of attrition" where owners fought until resources were depleted as they were governed by the resource holding potential of the resident (loser). Finally, female size (reproductive potential) did not alter contest outcomes; however, it did affect how quickly contests were escalated. We highlight the importance of understanding the life history and reproductive biology along with the behavior and ecology of the species under study to truly understand the traits associated with fitness in contests. Copyright 2011, Oxford University Press.

Volatile chemical release by bethylid wasps: identity, phylogeny, anatomy and behaviour

International audienceThe structures of volatile chemicals released by parasitic wasps in the family Bethylidae are shown to correspond to the subfamily to which the species belong. Species in the Epyrinae release skatole (3-methylindole) and species in the Bethylinae release a spiroacetal (2-methyl-1,7-dioxaspiro [5.5]undecane): these compounds are chemically very different. The enantiomeric composition of the spiroacetal differs between congeneric species. Chemical release is a discrete event under the active control of both male and female wasps. Structural differences between the mandibular glands and intramandibular glands suggest the mandibular glands to be the source of released volatiles. Real-time mass spectrometry shows that the spiroacetal is released by Goniozus nephantidis females during dyadic resource contests, with release more common during more aggressive interactions. Chemical tagging with deuterium further shows that the volatile is released by the loser of an agonistic interaction and not the winner. The function of spiroacetal and skatole release by bethylids is discussed