Thermal reaction of the intrinsic rate of population increase in Habrobracon hebetor (Say)

The intrinsic rate of population increase (r) is one of the most important biological attributes of insects which is highly influenced by ambient temperature. In the present research, the response of Habrobracon hebetor (Say) (Hym.: Braconidae) intrinsic rate of population increase reared on Galleria mellonella L. (Lep.: Pyralidae) larvae was evaluated at 6 different temperatures (20, 22.5, 25, 27.5, 30, 32.5 ℃), 65±5% RH and 16:8 h L:D. For each temperature 80 to 250 fresh eggs of the wasp were reared as a cohort. The r was calculated using TWOSEX-MSChart software and obtained values were fitted to Briere-2 and Lactin-2 thermal models. Results showed that r was 0.0387 day-1 at 20 ℃ and increased to 0.0899 day-1 at 22.5, almost 2.3 folds higher. However, it was 0.1120 day-1 at 25 ℃ which only elevated 1.3 folds compared to that at 22.5 ℃. Nevertheless, the intrinsic rate of population increase of H. hebetor reached to its maximum value at 27.5 ℃ (0.2001 day-1), though, it decreased about 7.5 and 10% at 30 and 32.5 ℃, respectively. Thermal modelling proved that calculated values of r were almost identical to estimated ones only at low temperatures (20 and 22.5 ℃). In contrast, both models estimated H. hebetor intrinsic rate of population increase significantly lower compared with calculated ones at higher temperatures. Despite what was observed by calculations, Briere-2 and Lactin-2 models recorded the maximum r at 30 ℃ to be 0.1918 and 0.1922 day-1, respectively. It is recommended to consider insects’ life parameters estimations of thermal models along with real values.