The Melon Leaf Miner Liriomyza Pictella (Thomson) (Diptera: Agromyzidae) II. Ecological Studies1

Abstract

The optimum temperature for development of the immature stages was in the range from 23.0° to 27.8° C. The developmental time from egg to adult was shortest (12.1 days) at 32.2° and longest (65.3 days) at 12.8°. Mature third-instar larvae experienced difficulty in pupating, and pupal mortality was 100%, at temperatures both above 35° and below 10°; the time required for pupation was greatly and abruptly increased below 18°. Mature pupating larvae are negatively phototactic and positively thigmotactie. They pupated in shorter time under semidark conditions than in natural light, and tended to crawl beneath some object or to burrow in soil for pupation. Under natural light they moved as much as 40 mm., and at a rate of 30 mm. per hour, before pupating. Relative humidity had no appreciable effect on length of pupal period, but the time required for pupation was nearly doubled and pupal mortality was much higher at 5% and at 96% R.H. as compared with 67% R.H. The optimum range was between 30% and 70% R.H. Screened topsoil provided the most nearly optimum substrate for pupation and pupal development. Pupal mortality was highest under natural light conditions, regardless of substrate, and lowest on a soil substrate in semidark conditions. When adults were kept without food or moisture, several lived for 16 days at 7.2° C. constant temperature, but there was 100% mortality in 8 to 12 hours at 32.2°. No adults died when exposed for 24 hours to constant temperatures of 0° or −2.78°, but there was 38% average mortality at −7.78° C ; females were more resistant than males. Adults lived an average of 12.3 days on a diet of honey, 1.5 days on a protein hydrolysate, and 1.1 on water alone, and females in all instances lived longer than males.