Host propagation permits extreme local adaptation in a social parasite of ants

The Red Data Book hoverfly species Microdon mutabilis is an extreme specialist that parasitises ant societies. The flies are locally adapted to a single host, Formica lemani, more intimately than was thought possible in host-parasite systems. Microdon egg survival plummeted in F. lemani colonies > 3 km away from the natal nest, from c. 96% to 0% to < 50%, depending on the hoverfly population. This is reflected in the life-time dispersal of females, measured at < 2 m, resulting in oviposition back into the same ant nests for generation after generation. To counter destabilizing effects on the host, Microdon manipulates the social dynamics of F. lemani by feeding selectively on ant eggs and small larvae, which causes surviving larvae to switch development into queens. Infested colonies rear double the number of new queens, thus propagating the vulnerable local genotype and compensating for damage to the host colonies. The consequences of such extreme host specificity for insect conservation are discussed.

Parasitoid secretions provoke ant warfare

Insect social parasites are extreme specialists that typically use mimicry or stealth to enter ant colonies to exploit the rich, but fiercely protected, resources within their nests. Here we show how a parasitic wasp (parasitoid) contrives to reach its host, itself an endangered species of social parasite that lives inside the brood chambers of ant nests, by releasing semiochemicals to induce in-fighting between worker ants, locking the colony in combat and leaving it underprotected. Four of these chemicals are new to biology and have the potential to control pest species by inducing different agonistic behaviours in ants.

Visual responses of Musca domestica to pheromone impregnated targets in poultry units

Field trials investigating the effect of visual cues on catches of Musca domestica (Diptera: Muscidae) at toxic targets impregnated with the female sex pheromone (Z)-9-tricosene, were conducted in a caged-layer deep-pit poultry unit in southern England. Targets treated with azamethiphos and baited with 2.5 g of 40% (Z)-9-tricosene impregnated beads caught significantly greater numbers of M. domestica than control targets. The greater attractiveness of the pheromone impregnated targets persisted for at least 5 weeks. The addition of longitudinal black stripes, or a regularly spaced pattern of black spots, to the white targets had no effect on catch rates. However, a pattern of clustered black spots, designed to imitate groups of feeding M. domestica, significantly increased target catches; this effect was particularly pronounced in the targets impregnated with (Z)-9-tricosene. Trials comparing the attractiveness of white and fluorescent yellow pheromone-treated targets under two different lighting regimes indicated that M. domestica does not have a significant preference for either colour. The implications of these results in relation to the control of M. domestica populations in poultry units are discussed.

Evaluation of three (Z)-9-tricosene formulations for control of Musca domestica (Diptera: Muscidae) in caged-layer poultry units

A field trial comparing the effectiveness of toxic targets impregnated with different formulations of the Musca domestica L. female sex pheromone (Z)-9-tricosene was conducted in a caged-layer, deep-pit poultry unit in southern England. Targets baited with 5 g of technical grade (Z)-9-tricosene, or 5 g of a 40% polymer bead formulation, caught significantly greater numbers of M. domestica than control targets. This increase in attractiveness of the pheromone-impregnated targets persisted for at least 24 wk. However, mean daily catch rates of M. domestica at targets baited with 5 g of a 2% wettable powder formulation did not significantly differ from control levels. Technical grade and bead formulations of the pheromone attracted significantly more males than females. However, the catches of female M. domestica at these pheromone-impregnated targets were significantly greater than female catches at control targets. Monitoring with sticky cards indicated that the introduction of toxic targets successfully suppressed adult M. domestica population density for up to 13 wk. Possible hypotheses explaining the effect of (Z)-9-tricosene on female attraction are discussed.