Effect of Temperature on the Production of Males and Sexual Mosaics in a Uniparental Race of Trichogramma semifumatum (Hymenoptera: Trichogrammatidae)12

Abstract

Trichogramma semifumatum (Perkins) parasitizes a wide variety of insect eggs. Like most Hymenoptera this species usually exhibits a type of parthenogenetic reproduction known as arrhenotoky, i.e., fertilized eggs produce females and unfertilized eggs produce males. In 1961, a uniparental race of T. semifumatum was discovered near Bishop, Calif. When this race is continually reared below 78°F, the progeny are almost entirely females but on a very rare occasion a male is produced. As the temperature is increased to 78°F and above, males are produced in higher ratios. At 90°F the progeny consists of about 97% sterile males and 3% sexual mosaics. Sex of the offspring is determined by the temperature at which the mother is reared and not by the temperature at which the progeny are reared. There is a critical period during development of the mother in which temperature and its duration drastically affect the sex of her offspring. This period occurs in the pupal stage when reproductive cell division and egg maturation take place. Exposure to heat (78°–90°F) before or after this critical period does not change the sex of the offspring from females to males and sexual mosaics. The ability to reproduce is retained by sexual mosaic females, even though they possess extreme degrees of male characters in the structure of the antennae. Males produced at 80°F were found to be sterile. Probably all males produced by this uniparental race are sterile.