Notes on the Variation of the Metrobates of Florida (Hemiptera, Gerridae)

Abstract

Inspection of numerous specimens of Metrobates collected by the junior author at various places in north-central Florida revealed to him an unexpected degree of variation in the brushlike hairs of the first antennal segment and in the extent of development of the curved hairs of the middle legs, both of which are secondary sexual characters limited to the males. This variation has led us to make a critical examination of the material at hand, with the result that we are able to recognize four distinct forms of Metrobates in this area. One of these has previously been described as Metrobates anomalus Hussey,' another is definitely a race of anomalus, while the remaining two, though differing from typical Metrobates hesperius Uhler, are unquestionably races of that wide-spread species. In the course of this study we have noted several points that do not seem to have been mentioned before in connection with this genus. In the females of the species here discussed the second and third antennal segments have a relatively small number of flattened scale-like hairs at their apices below, corresponding to rudiments of the swollen combs on the same segments of the males; and the first antennal segment has one or two hairs of moderate length arising from its under side where the males of most of these Metrobates have a brush of long hairs of various lengths. The females, but not the males, have four or five long, widely spaced hairs on the under side of the fore femora; and the female fore tarsus is roughly one-fourth longer than in the males, both absolutely and in proportion to the tibial length. On the ventral side of the middle leg in both sexes there is seen under high magnification a single row of extremely short oblique hairs, each one curving backward at its tip to meet the hair next behind it, forming a line scarcely more than 0.01 mm. in height along the apical half of the tibia, the entire length of the first tarsal segment, and at least the basal part of the second. This row of minute hooked hairs doubtless plays a role in the movements of the insect over the surface of the water. A similar band of hairs occurs on the hind legs of Trepobates (e.g., T.