Comparisons of Acoustic Courtship Signals in Wild and Laboratory Reared Mediterranean Fruit Fly Ceratitis capitata

Abstract

A major concern in rearing insects for sterile release is the production of males that are sexually competitive with wild rivals. A means of achieving quality control is to first quantify sexual signals in wild insects and then monitor these signals in laboratoryreared individuals (eg. Boller & Chambers 1977). Male acoustic signals are important components of courtship and territorial defense in lekking tephritids (Sivinski & Burk 1988). The sexual repertoire of the male Mediterranean fruit fly, Ceratitis capitata (Wied.), includes three distinct sounds: 1) the calling song, produced simultaneously with pheromone emission and often in the absence of other nearby flies, 2) the approach song, an intermittent series of buzzes made when other flies are nearby, and 3) the precopulatory song, a brief sound produced by males when they mount a prospective mate (Webb et al. 1983). Females in captivity make the equivalent of the first two songs although their function is presently obscure. We have on two occasions, April 1985 and 1987, recorded Mediterranean fruit flies in Guatemala City, Guatemala C.A. On the first of these occasions we obtained wild flies, reared from maggots in local coffee beans, and fertile laboratory-reared insects produced by the Moscamed Commission facility in San Miguel Petapa. On the second, both fertile laboratory-reared and irradiated sterile laboratory-reared flies from the above facility were recorded. With our data we can make three comparisons pertaining to the quality of the Guatemalan medfly product: 1) the acoustic signals of wild flies versus those of flies reared in the laboratory for several generations, 2) courtship sounds of sterile flies (irradiated at 17 kR 48 h before eclosion) versus fertile laboratory-reared flies, 3) flies reared in the laboratory in 1985 versus those of the same genetic stock still in the laboratory in 1987. The insects, when recorded, were held in either groups of 10 or less, in 10 cm x 7 cm wire screen cylinders or in large numbers (>100) in 30 cm x 30 cm x 30 cm plexiglass and wire screen cages. A condenser microphone (Sony MTL-96, Sony Corp., New York, NY) was held approximately 1-2 cm from the dorsal surfaces of calling males and the sounds were recorded on a Nakamichi 550 cassette recorder Sounds were later analyzed with a Nicolet 660A fast Fourier analyzer (Nicolt Instrument Corp., Madison, WI). The examined sound parameters were fundamental frequency (peak frequency in the first harmonic bandwidth), first harmonic bandwidth (total range of frequencies about the mode created by the fundamental frequency), and percent waveform distortion (the proportion of energy in a sound that is contained in the first harmonic band; for more details see Webb et al. 1984). Due to imperfect recordings or small sample sizes, not all of these features were measured for each category of fly. Statistical analysis is by Duncan's multiple range test and t-test. All results are in Table 1. There was a significant difference in the fundamental frequency of the calling song of wild males compared to those of both laboratory-reared males and females in 1985 (P<0.05). However, there were no differences among flies of the three groups in bandwidth or distortion of the song. The approach song of the wild male was also produced at a higher frequency than that of the laboratory-reared male (P<0.002). A possible contributing factor to the lower frequency of the reared flies was their notice-