TRILLING FIELD CRICKETS IN A ZONE OF OVERLAP (ORTHOPTERA, GRYLLIDAE, GRYLLUS)

A bimodal distribution of pulse rates in field recordings of calling s ongs suggests that the ranges of the morphologically similar field cri ckets Gryllus rubens Scudder and G. nr. integer Scudder (=''integer'') overlap for at least 300 km in western Florida. When sons were reared from 42 females collected at 5 sites on 7 trips to this region during 1977-1978, those within a sibship had similar modal pulse rates. At M ilton, the westernmost site, 28 of 31 females produced sons with mean modal pulse rates typical of G. rubens; the other 3 were among 6 femal es collected 1 October 197; and 30 September 1978 and had modal pulse rates in or near the ''integer'' range. None of the 11 females from ot her sites had sons with a mean modal pulse rate indicative of ''intege r.'' Most progenies of females collected at Milton on 25 September 198 2 were reared as 2 cohorts of contrasting initial density, and each so n was recorded on 2 dates. The mean, temperature-adjusted modal pulse rates of the 39 recorded cohorts, from 22 females, showed no effect of initial density but fell nearly evenly into 2 discrete groups: 46-60 pulses s(-1) with a mean of 52 (G. rubens) and 64-78 pulses s(-1) with a mean of 71 (''integer''). Lack of intermediate sibships indicates t hat G. rubens and ''integer'' remain distinct in their zone of overlap . A spring-adult generation of ''integer'' in western Florida is postu lated but not confirmed. Reared under the same conditions, G. rubens m ales from fail females had a significantly lower mean modal pulse rate than males from spring females (52 versus 55), indicating a parental effect. G. rubens males reared from fall females had a significantly h igher mean modal pulse rate than captured spring-adult males (52 versu s 49), and males reared from spring females had a significantly lower modal pulse rate than captured fall-adult males (55 versus 59). Becaus e G. rubens is bivoltine, both of these comparisons indicate that deve lopmental conditions affect calling-song pulse rate. Fall males of ''i nteger'' had a significantly higher mean modal pulse rate than males r eared from fall females (79 versus 70), indicating one or both effects . These are the Ist parental and developmental effects on pulse rates reported for crickets.