Effective Augmentative Biological Control – Importance of Natural Enemy Dispersal, Host Location, and Post-release Assessment

Augmentative biological control in outdoor cropping systems is often considered to be ineffective. High release rates are often needed for effective control and may be so frequently required that they become prohibitively expensive, especially when natural enemies are purchased from commercial suppliers. Natural enemies released argumentatively may provide control levels that are considered too low to be economically viable. Other germane issues are the selection of appropriate natural enemy species or strains for specific crops, and protocols related to timing and density of releases relative to crop phenology and other pest management strategies. There are indeed cases where effective augmentative programs have been implemented in outdoor crops. This paper addresses grounds for the effectiveness of these programs, with special reference to the use of Trichogramma ostriniae in sweet corn and field corn, where low-density inoculative releases can be highly effective. The importance of understanding dispersal capacity and host location behavior of the biological control agents is examined. Host-seeking behavior of parasitoids in different crop habitats is considered and expanded upon as an aspect of central importance in ensuring effectiveness of augmentative biological control. This is compared to less successful efforts at developing augmentative biological control in other crops with other parasitoid species (Trichogrammatidae and Scelionidae), in an attempt to identify key characteristics of a potential augmentative agent that are likely to result in success or failure.