A large-scale rearing method for Peristenus digoneutis (Hymenoptera: Braconidae), a biological control agent of Lygus lineolaris (Hemiptera: Miridae)

Releases of Peristenus digoneutis against Lygus spp. in North America have been conducted for many years; however, no published procedures for mass production of the biological control agent were available. A laboratory rearing method was developed using Lygus lineolaris as the host to enhance establishment efforts and provide large numbers of wasps for inundative releases into high value fruit crops. Experiments were conducted to determine optimum host:parasitoid density and rearing temperature. The effects of nymph:wasp ratios and temperature on parasitism and wasp survival showed a 20:1 ratio at 20°C provided high parasitism (256 parasitized nymphs/wasp over lifetime) and excellent wasp survival of 27 days. Experiments on diapause-inducing conditions for P. digoneutis demonstrated that fluctuating temperatures of 23°C (day) and <16°C (night) and corresponding photo phases of 16 h light, for rearing parasitized nymphs, produced 100% diapausing parasitoids whereas non-diapausing parasitoids were only produced at more than 16 h light. Furthermore, parasitized Lygus nymphs need to be transferred to short day conditions no later than 10 days after parasitism to produce diapausing parasitoids. Critical life stages for exposure to conditions inducing diapause, the egg, first and second instar parasitoid larva, occurred from 0 to 10 days at 24°C constant temperature. Increased time in cold storage reduced the number of days to first emergence of parasitoids from diapausing cocoons when transferred to warm temperatures. The optimum storage time for diapausing P. digoneutis is between 25 and 44 weeks, depending upon the length of time that cocoons remain at warm conditions prior to chilling.