Biological Studies of Amblyseius umbraticus (Acarina: Phytoseiidae)1

Abstract

A description and photographs of specimens of Amblyseius umbraticus Chant from New Jersey are presented, since they differ somewhat from the original species description. A. umbraticus was collected from 2 abandoned apple orchards but was not of widespread occurrence in this habitat. Laboratory studies were conducted at 25–26°C primarily on bean leaf discs with Tetranychus urticae Koch as the prey. The durations of the various developmental stages were similar for both sexes, averaging about 47 hours for eggs, 24 for larvae, and 43 for each of the 2 nymphal stages. Females which mated throughout their life had longer oviposition periods, laid more eggs, but did not live as long as females which mated only during the first few days of adulthood. Most aspects of the life history and habits of A. umbraticus are similar to other phytoseiids studied, but developmental times are longer, longevities greater, and oviposition rates lower than many other species. A. umbraticus was able to develop and reproduce on T. urticae, Panonychus ulmi (Koch), Calvolia lordi (Nesbitt), Aculus schlectendali (Nalepa), adults of Quadraspidiotus perniciosus (Comstock), and on apple pollen and cherry pollen. Adults of Agistemus fleschneri Summers and winter eggs of P. ulmi were not fed upon. Eggs, larvae, and protonymphs of T. urticae were the preferred prey for all stages of A. umbraticus . The optimum relative humidities for reproduction and development were high and narrow in range. Relative humidities of 75 and 85% caused desiccation and high mortality of larvae. A. umbraticus females overwintered primarily in cracks and crevices of small twigs. Winter mortality \estimates were 85–95%. Diapause was induced by exposure of the mites to a 12-hour photoperiod at 22°C during the complete developmental period. Diapausing females were less active, more cold hardy, and more resistant to starvation than females not in diapause.