Temperature-dependent functional response of two aphid parasitoids, Aphidius colemani and Aphidius matricariae (Hymenoptera: Aphidiidae), on the cotton aphid

The functional response of two aphid parasitoids, Aphidius colemani Viereck and Aphidius matricariae (Haliday) (Hymenoptera: Aphidiidae), on the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), was examined. Five constant temperatures (10, 15, 20, 25, and 30 degrees C) and six host densities (2, 4, 8, 16, 32, and 64) were used during a 24-h period. At each temperature, 2-64 third-instar nymphs of A. gossypii were exposed to individual wasp mating pairs. A type II functional response model for both parasitoid wasps was fit separately for each temperature. The results showed that instantaneous attack rate (a) in A. colemani increased linearly as the temperature increases from 10 to 30 degrees C, but in A. matricariae, (a) increased almost linearly with temperature to reach a maximum at 25 degrees C, and then decreased at 30 degrees C, displaying an asymmetrical dome-shaped pattern. The highest instantaneous attack rate for A. colemani and A. matricariae were calculated 0.940 +/- 0.144 day(-1) at 30 degrees C and 0.687 +/- 0.157 day(-1) at 25 degrees C, respectively. Handling time (T-h) for A. colemani was inversely proportional to temperature and ranged from 0.093 +/- 0.026 day at 10 degrees C to 0.032 +/- 0.004 day at 30 degrees C, but in A. matricariae, (T-h) was between 0.078 +/- 0.015 day at 10 degrees C and 0.036 +/- 0.014 day at 20 degrees C. A. colemani achieved higher parasitism rate than A. matricariae at higher temperatures. This observation suggests that A. colemani maybe more effective for biological control of the cotton aphid during warmer periods.