Guthion™ is an effective alternative. With the recent development of Guthion-resistant codling moth populations after 20 years of use and restriction of the preharvest interval for Guthion by the California Department of Pesticide Regulation, growers have more incentive to adopt the virus-pheromone IPM program.
Application of baculovirus for control of beet armyworm, Spodoptera exigua (Hübner) has been well studied in greenhouse systems (Smits et al. 1987a). Such characteristics as dose-response curves, larval feeding behavior, application techniques (Smits et al. 1988), timing, and strain (Smits et al. 1987b) have been integrated into recommendations for operational use of virus with other control methods. On head lettuce in California, a beet armyworm NPV was field-tested for 3 years and compared with chemical insecticides (Gelernter et al. 1986); results indicated comparable control with methomyl and permethrin.
At the present stage in the development of baculovirus products, several limitations are associated with the viruses' use as insecticides. A major limitation in agricultural systems is the slow rate of kill, which results in feeding damage. Kill rate, however, is not as crucial in forest systems, where cosmetic damage is not as important. Reduction of kill time will rely on improvements in formulation and application in the immediate future. However, this limitation can be managed in the short term by using baculoviruses in combination with other insecticides through IPM.
Lower production costs are essential for both recombinant and wild-type baculoviruses to compete with classical insecticides. There are active research programs in both in vivo and in vitro production (Bonning 1996). Although viruses are less expensive to produce in vivo than in vitro, the cost still exceeds that of Bt. Viruses are formulated to be applied in the same fashion as Bt strains. However, for extensive use in IPM, dramatic improvements in formulation and application technology are needed. In formulation, knowledge of stability and shelf-life is required to optimize storage and distribution. In application, droplet size, density, dosage, and components in the tank mix (for example, stickers, and UV protectants) need to be optimized.
Another limitation of baculoviruses is their host specificity, which can reduce their commercial potential. However, the host specificity is viewed positively from the environmental and IPM standpoints. Two viruses with relatively broad host ranges are Autographa californica (alfalfa looper) NPV and Syngrapha falcifera (Kirby)(celery looper) NPV, each of which kills over 30 insect species. The celery looper virus is reported to have commercial potential in cotton IPM systems (Wood 1992). Host range can be broadened through molecular means or by mixing two viruses.
In the long term, the development of recombinant baculoviruses that