Growth, Development and Innate Capacity for Increase in Aphytis Chrysomphali Mercet and A. Melinus Debach, Parasites of California Red Scale, Aonidiella Aurantii (Mask.), In Relation to Temperature.

Abstract

A, melinus produced more female progeny and more than twice as many total progeny as A. chrysomphali; it also destroyed almost twice as many hosts through oviposition and mutiliation. A. chrysomphali had a longer post-oviposition period than A. melinus, especially at 30°C. The proportion of single progeny in a host was higher for A, chrysomphali than for A. melinus at all temperatures, and was related to temperature positively in A. chrysomphali and inversely in A. melinus. Large old female A. melinus produced only males at the end of their lives; they did not mate at that stage when offered males, not because they were aged but because they mate only once in their lives. As temperature decreased, female A. melznus ceased producing females earlier, probably because temperature affected either longevity of sperms or the mechanism controlling their release. Differential mortality, temperature, and age of mothers all influenced sex ratio. Pupal mortality was inversely related to temperature within the observed range 20-30°C; in female pupae of A. chrysomphali it was lower than that in either female or male pupae of A. melinus; it was higher in male than female pupae in A. melinus. A. melinus lived longer than A. chrysomphali at all temperatures. Duration of development was longer for A. chrysomphali than for A. melinus at 30°C, but shorter at 20 and 25°C. The threshold of development was 8.5C for A. chrysomphali and 11C for A. melinus. A. chrysomphali had a higher rm at 20 and 25°C than A. melinus, but much lower at 30°C. The highest rate of increase was at > 30°C for A. melinus, and at about 25°C for A. chrysomphali. The rm of the parasites was 3.1-5.0 times that of red scale, depending on parasite species and temperature. A. chrysomphali is smaller than A. melinus, and from the positive relationship between adaptation to cold and speed of development, and the negative relationship between speed of development and size, a negative relationship between size and adaptation to cold within Aphytis spp. may be postulated. A. chrysomphali is more adapted to cold and less to heat than A. melinus. This explains the seasonal and annual fluctuation in their relative abundance in southern Australia. The species would complement each other in controlling red scale; from the data presented here it is possible that Aphytis spp. in Australia may have evolved into more efficient control agents of red scale than elsewhere. Knowledge on the searching ability of Aphytis at different host densities is wanting.