Changes in behaviour, flight tone and wing shape in nematode-infestedChironomus (Insecta, Diptera)

Abstract

The flight tones generated by wing beat frequencies of adult female and male non-biting midges,Chironomus anthracinus, infested by a species ofLimnomermis are very similar (mean values 219.9 and 228.9 Hz respectively), intermediate between normal females (205.1) and males (363.1), but closer to that of the uninfested females. Similarly, the wing shape of parasitized individuals appears intermediate resembling the female more than the male. Statistically wing width and surface area in the parasitized adults resemble those of females and differ significantly from those of normal males. The wing length of the parasitized midges, however, is more like that of males, but there is no statistically significant difference between the groups. Malnutrition of the larvae caused by competition with the parasite seems to result in wing shortening superimposed on sexual differences. All parameters of wing shape are negatively correlated with flight tones. Weight and musculature of the parasitized individuals have also been investigated, but only where worms were present in the thorax was a change found in the flight tones. The flight tone changes served no apparent biological function for the parasitized midges, but the worms apparently benefit from behavioural changes of the infected host, thereby reaching habitats where fresh hosts for its larvae may be available.