Fertility of the polyembryonic parasite Copidosoma koehleri, effect of humidities on life length and relative abundance as compared with that of Apanteles subandinus in potato tuber moth

Abstract

SUMMARYMales and females of Copidosoma koehleri were kept separately in desiccators producing relative humidities of 20, 40 and 70% at 24 and 28°C and found to be very susceptible to low relative humidity. They lived less than 1 day at 20%, about 2 and 4 days at 40% and about six times longer than these respectively at 70% r.h. When kept at 26°C and 70% r.h. females of C. koehleri parasitised 98.8 hosts. The number of parasites that emerged from a male brood was 21.2 and from a female brood 33.2. Mated females produced 3026 progeny and unmated 2289. The sex ratio of broods produced by mated females was 1:1 and the female percentage among progeny was 59. It is known that C. koehleri is rare at the beginning of the potato‐growing season and becomes the predominant parasite later on. It is known also that in potato crops when the plants are small at the beginning of the season the air within the crop is less humid but as the canopy of foliage develops, relative humidity rises and becomes higher than at 1.2 m above ground. It is suggested that relative humidity in the potato crop is the major factor affecting the relative abundance of C. koehleri and Apanteles subandinus in South Africa.