Pieris rapae (cabbage white butterfly)

Insecticides have been used to control Pieris rapae since crucifers have been cultivated. Generally, insecticides have to be applied every one or two weeks to achieve good crop quality and this has led to numerous instances of insecticide resistance in P. rapae (Chou et al., 1984; Han et al., 1987). Pesticide applications should begin when the P. rapae population reachs a threshold of one larva per plant. Spraying should be repeated every 5-7 days as needed.In recent years, good control has been achieved using managed spray or IPM programmes (Leibee et al., 1984; Theunissen, 1984; Stewart and Sears, 1988; Ferguson and Barratt, 1993). These generally combine close monitoring of pest and natural enemy populations with judicious applications of selective pesticides (Jackson and Hartley, 1982; Endersby et al., 1992; Forster and Hommes, 1992; Dornan et al., 1994). Thresholds for chemical and/or biological control of P. rapae have been developed in a number of countries. In Canada, timing of an insecticide treatment based on an action threshold of one larva/plant (57% infestation), produced quality cabbage heads for storage or the fresh market. Treatment when an average of three larvae per plant (87% infestation) occurred, resulted in cabbages suitable for processing (Mailloux and Belloncik, 1995).

Some attempts have been made to breed varieties of crucifers resistant to P. rapae with only limited success (Dickson and Eckenrode, 1978; Shelton et al., 1988). Resistant varieties include Mammoth, Red Rock, Chieftan, Savoy, Savoy Perfection and Drumhead.

New plantings should be as far as possible from those of the previous season. At the end of the season crops should be harvested without delay and plant residues should be ploughed under or destroyed. Intercropping and trap crops have had limited success as methods of controlling P. rapae (Kenny and Chapman, 1988; Luther et al., 1996; Wiech, 1996). Both strategies are likely to have some value in IPM systems based on pesticides or natural enemies.

Biever et al. (1994) developed a biological control system for P. rapae based on natural enemies for 53 hectares of cabbage in Texas. In Bermuda, a parasitic wasp, Pteromallus puparum, was introduced for control in 1987.Much use has been made of bacterial (primarily Bacillus thuringiensis) and viral preparations against P. rapae. These formulations are usually compatible with natural enemies and form the basis of many IPM systems for P. rapae (Goral et al., 1984; Su, 1986, 1989, 1991; Webb and Shelton, 1991).Classical biological control has been carried out in a number of countries using Cotesia glomerata, Cotesia rubecula, Pteromalus puparum, Compsilura concinnata or Phryxe vulgaris. In Australia (Wilson, 1960) partial control was achieve. In New Zealand (Cameron et al., 1989, 1995) and in the USA (Clausen 1978) substantial control was achieved. In Canada, parasitoids have beeen established (Corrigan, 1983).