Temperature-dependent development of immature stages of predatory ladybird beetle Stethorus vagans (Coleoptera: Coccinellidae) at constant and fluctuating temperatures

Abstract

Influence of temperature on the development of the predatory ladybird, Stethorus vagans Blackburn, fed on Tetranychus urticae Koch was assessed at seven constant (10, 12, 15, 20, 25, 30 and 35 °C) and fluctuating (12.7–32.1 °C) temperatures. There was a strong positive correlation (r = 0.99) between rate of development and temperature. The development times from egg to adult emergence were 65.2±2.3 and 9.2±0.3 days at 12 and 30 °C constant, respectively and 15.4±0.3 days at fluctuating temperature. Average egg incubation period decreased from 16.5±0.8 to 2.18±0.2 days with increasing temperatures from 12 to 30 °C, respectively and was 4.1±0.3 days at the fluctuating temperature. Eggs did not develop at 10 °C; however, they could survive a long period of exposure to this temperature. None of two hundred eggs that were placed at a constant temperature of 10 °C for 60 days hatched; but when they were subsequently exposed to ≥ 15 °C, more than 120 of them hatched. Eggs appeared to develop normally at 35 °C, however, larvae died before or immediately after emergence. The lower development threshold temperature for egg, 1st, 2nd, 3rd, 4th larval instars, pupal and all these stages combined was 10.1, 9.5, 9.5, 9.1, 8.2, 8.0, and 9.1 °C, respectively. Degree-day (DD) accumulation was also calculated for each stage as well as for all stages combined. It was estimated to be 189.2±4.8 DD at 12 °C and 207.8±6.9 DD at 30 °C constant, respectively, and 189.1±5.0 DD at fluctuating temperatures.