Reproduction of Diaeretiella rapae on Russian wheat aphid hosts at different temperatures

Diaeretiella rapae (M'Intosh), a polyphagous and cosmopolitan parasite of aphids, was imported from China to the USA for biological control of Diuraphis noxia (Mordwilko), a pest of small grains. We studied several aspects of its biology on D. noxia hosts in the laboratory at 3 constant temperatures, 10.0, 21.1, and 26.7 degrees C. Females lived significantly longer than males at all 3 temperatures, and longevity was greatest at 10 degrees C, followed by 21.1 and 26.7 degrees C. Fecundity (= number of mummies) did not differ significantly among the 3 temperatures studied. The ovarian egg-load was 129.1 +/- 9.3, and was significantly affected by the size of adult females. A pre-oviposition period (0.95 +/- 0.26 days) was detected at 10 degrees C, but not at the other temperatures. Pre-imaginal survivorship was similar among temperatures, while R(0) and T-c decreased with temperature, and r(m) increased with temperature. The offspring sex ratio (proportion females) was lowest at 26.7 degrees C, and similar between 10.0 and 21.1 degrees C. In addition, the offspring sex ratio significantly declined with the age of the female parent. The suitability of D. rapae for colonization against D. noxia in North America is discussed in relation to its responses to temperature and the climate of its home range.