Ecological and economic evaluation of augmentative biological control in concert with other non-insecticidal tactics as an alternative to chemical management of squash bugs, Anasa tristis (DeGeer), on pumpkins

Studies were undertaken to determine whether biological suppression tactics for the squash bug, Anasa tristis (De Geer), have the potential of being both effective and economical for commercial pumpkin production. In 1991, releases of the egg parasitoid, Gryon pennsylvanicum (Ashmead), had a measurable impact on squash bug population densities. However, these densities were consistently higher throughout the season than those treated with insecticide. Yields of a squash bug-susceptible cultivar also were significantly lower when biological control was used as an alternative to chemical control. The difference in mean seasonal densities of squash bugs where parasitoids were released and insecticide-treated plants decreased by more than two-fold when G. pennsylvanicum was released on a resistant pumpkin cultivar. Yields and fruit quality also increased when biological control was integrated with host plant resistance. In 1992, under wet, cool conditions, squash bug densities were uniformly higher on insecticide-treated plants, and uniformly lower on plants treated with biological control compared to those found in 1991. In all experimental treatments, the quality of pumpkins in 1992 was reduced substantially for both cultivars. Weather conditions in 1992 appeared to have less of an effect on squash bugs and yields for resistant pumpkins than for susceptible pumpkins. The projected revenues from pumpkin yields were higher in 1991 when insecticide was used than those estimated when biological control was applied. When biological control was integrated with host plant resistance, costs were reduced substantially relative to revenues. However, only a small percentage of the consumers surveyed would pay a high enough price for pumpkins to make this integrated pest management approach economically feasible. Costs of using biological pest suppression were reduced substantially during 1992 as compared to those in 1991. The premium price that consumers would pay may be sufficient for growers to make a profit when using biological control plus host plant resistance during wet, cool seasons. Experiments showed that extrafloral nectaries of squash leaves are an adequate source of nutrients for adult G. pennsylvanicum. These findings have two important benefits for an augmentation program involving G. pennsylvanicum. First, adult food should not limit the population and therefore the impact of this parasitoid on squash bugs. Second, additional costs for artificial food supplements can be avoided.