Thermal Requirements for Development of the Polyphagous PredatorMacrolophus pygmaeus(Hemiptera: Miridae)

Abstract

The effect of temperature on the duration of embryonic and nymphal development as well as on the preoviposition period of the polyphagous predator Macrolophus pygmaeus Rambur was studied in the presence and in the absence of prey on eggplant, pepper-plant, and tomato at 15, 20, 25, 27.5, 30, and 35°C, with 65 ± 5% RH and photoperiod of 16:8 (L:D) h. The aphid Myzus persicae (Sulzer) was used as prey on eggplant and pepper-plant and the whitefly Trialeurodes vaporariorum (Westwood) on tomato. The data obtained were used for the estimation of the thermal requirements of this predator. The temperature threshold for egg development was found as 7.61 and 6.92°C, for nymphal development in the presence 8.74 and 9.19°C and in the absence of prey 8.21 and 9.29°C, for preimaginal development 8.68 and 8.79°C, for preoviposition 7.58 and 6.96°C, and finally for egg-to-egg development 8.48 and 8.51°C on eggplant with M. persicae and on tomato with T. vaporariorum, respectively. On pepper-plant the temperature threshold for nymphal development was 8.26 and 8.23°C in the presence and in the absence of prey, respectively. The values of temperature threshold for development of the various nymphal stages were similar. It was also found that the slopes of the linear regressions between the rate of nymphal development and temperature were not significantly different among the different host plants in the presence and in the absence of prey. Also, the slopes of the linear regressions concerning the development of each nymphal stage with temperature were not found to differ significantly among the host plants in the presence and in the absence of prey. The thermal constant for egg development was estimated as 177 and 182, that for nymphal development in the presence 269 and 253 and in the absence of prey 332 and 306, for preimaginal development 439 and 431, for preoviposition 100 and 98 and finally that of egg-to-egg development 541 and 533 degree-days when fed on M. persicae on eggplant and on T. vaporariorum on tomato, respectively. On pepper-plant the degree-days for nymphal development was 280 and 361, in the presence and in the absence of prey, respectively. The temperature threshold for development was not found to differ among the host plants in the presence and in the absence of prey. However, the degree-days were significantly different between the presence and absence of prey on each host plant; the thermal constant in the absence of prey was estimated as an average of 1.21 times of that in the presence of prey. The results show that M. pygmaeus can establish, develop, and oviposit even in the absence of prey in relatively low temperatures and hence it can be released early in the season for an earlier and more effective control of whiteflies and aphids on vegetables.