Quality of augmentative biological control agents: a historical perspective and lessons learned from evaluating Trichogramma .

Abstract

AbstractAugmentative biological control involves one or more releases of a natural enemy in an attempt to suppress and maintain a pest population at subeconomic densities. The notion of releasing parasitoids augmentatively for pest suppression was initially proposed in the late 1800s. However, its first sustained use involved the suppression of the citrophilous mealybug, Pseudococcus calceolariae Fernald, a pest of citrus in southern California, which began sometime between 1913 and 1917. The biological control agent, the coccinellid Cryptolaemus montrouzieri Mulsant, initially introduced as a classical biological control agent, was unable to survive in sufficient numbers to affect control without augmentation. This coccinellid is still being used in citrus to suppress mealybug pests and it is still commercially available. The initial success of this tactic led to an expansion in its use against other pests, beginning with the most widely used augmentative biological control agents, Trichogramma species. Their use began in the late 1920s, when S.E. Flanders developed a mass-production system for them. In this chapter, we first summarize this historical origin and then illustrate the role of fundamental research and its interaction with theory in improving augmentative biological control's predictability, using Trichogramma species (Hymenoptera: Trichogrammatidae) as examples. Furthermore, we extend the notion of the quality of a biological control agent by defining it in terms of the attributes that make an agent successful against a particular pest under field conditions. We provide several examples in which Trichogramma species are assessed by using behavioural observations under laboratory conditions, employing a technique first used by European researchers. However, we frame this evaluation in the context of a parasitoid's reproductive success, defined in terms of its offspring's reproductive prospects - that is, the offspring's characteristics that allow them to maximize their reproduction in the field on the targeted pest. It is this field reproduction that provides biological control. We suggest that this behavioural approach provides a means of evaluating the likely prospects for augmentative biological control by a particular agent and the potential to manipulate the agent and its interaction with its host to enhance its success within an economic framework.