Description and Bionomics of Frankliniella insularis Franklin (Thysanoptera)

Abstract

(1) Frankliniella insularis (Franklin) is found on various food-plants, including tomatos, in the Adelaide area.(2) The life-history and bionomics of the species have been investigated, particularly on tomato plants under glasshouse conditions. The various stages of the insect have been described.(3) The eggs are laid in the tissues of the tomato leaf, and the larvae feed on the leaves or in the flowers; when mature they leave the plants and pupate in the débris on the surface of the soil or penetrate into the upper layers of the soil. Sometimes they pupate on the plant in rolled leaves, depressions in the stem or other similar situations; this habit has been also observed on tomato plants growing in the open during the summer. In carnation flowers eggs were laid in the tissues of the sepals and petals.(4) The duration of the egg stage for 64 examples varied from 9–14 days when the mean daily temperature was 64·5° F. In a number of other observations it was found to vary from 3 days, when the mean temperature was 100° F., to 15 days, when the mean temperature was 63·1°F. The rate of oviposition is markedly affected by temperature: with a mean temperature of 77·5° F., one female laid an average of 3·9 eggs daily; two other females laid an average of 1·2 and 1·7 eggs daily when the mean temperature was 68·2°F.; and another female laid an average of 1·3 eggs when the mean temperature was 67·7° F. Below 60° F. the rate of oviposition is greatly retarded, but egg-laying may extend over a long period: one female continued oviposition over a period of 157 days. The largest number of eggs laid by a single female was 92 over a period of 70 days.(5) The duration of the larval stages for 32 individuals varied from 9 to 13 days when the mean temperature of the periods varied from 66·6° F. to 65·7° F. In a number of observations on other individuals at various times the period varied from 7 to 14 days when the mean temperature varied from 74·9° F. to 63·4° F.(6) The duration of the pupal stages obtained from 19 individuals varied from 7 to 14 days when the mean temperature of the periods varied from 72·8° F. to 66·7° F.(7) The complete life-cycle under glasshouse conditions occupied 36–39 days when the mean temperature of the period was about 66° F. Observations made on a number of individuals at various periods gave a variation in the period of the complete life-cycle from 13 to 41 days with mean temperatures varying from 89·5° F. to 64·1° F.(8) The chief distribution of Frankliniella insularis appears to be the region of Central America. It is common in the Adelaide area during the warmer period of the year (approximately November to April), and rare or absent during the remaining months. Its seasonal occurrence appears to be due to temperature, since it was readily reared at all periods of the year on tomato plants in the glasshouse.(9) The economic importance of the species is due to the fact that G. Samuel and J. G. Bald have shown experimentally that it can transmit the virus of spotted wilt disease of tomatos.