Two new species of the genus Microstigmus Ducke (Hymenoptera: Sphecoidea)

Summary

Five species of tettigoniid of the Decticine genus, Platycleis (sensu stricto), are found in the environs of Montpellier, Hérault, S. France. P. intermedia, P. sabulosa and P. albopunctata are essentially early-evening singers. There is a nycthemeral cycle of vertical migration in these three species—they sing from a greater height than that at which they rest during the daytime. P. affinis and P. falx sing both during the day and during the evening. As the syllables of the songs of the five species are similar, and since these insects sing at the same time of year and at least during the evening, interspecific acoustic interference would seem likely. However, such interference appears to be avoided by spatial separation of singing individuals (the males only). The difference in habitat preferences may be so distinct that two species do not occur in the same locality (e.g. P. falx and P. albopunctata). Where two species do occur in one local area, one of them is generally confined to one type of vegetation (e.g. P. intermedia in the bushes) and the other to another type (e.g. P. affinis on the open ground). Differences in chirp types, and in the specific response to particular song patterns, mean that ethological barriers as well as ecological ones would appear to prevent heterospecific matings. However, prevention of acoustic interference between allospecific males seems to be brought about mainly by habitat-preference differences. In one species pair, P. falx and P. affinis, the habitat-preference difference is very slight, and their songs are similar. These facts, coupled with the impression that the range and abundance of P. affinis are increasing, while those of P. falx are decreasing, suggest that P. affinis is supplanting P. falx in the open areas of wasteland in the Montpellier area.