Ecological Interactions and Biological Control

that host eggs are not evenly distributed over the plant, e.g., located on the upper part of a tree canopy or laid on the lower side of maize leaves, it will be advantageous to use specific techniques for placing the parasitized eggs as close as possible to the host eggs. Short walking distances will increase host finding and thus prevent wasps from wasting their time searching plant parts where no host eggs are available.

Host-searching requirements of inundatively released Trichogramma depend mainly on the crop, the distribution of host eggs, and the release technique. The specific interactions of each tritrophic system must be known in order to determine traits that are important for host-searching success. Quality attributes like flight, initiation, short-range flights, and walking velocity seem to be important in all systems. Dispersal and emigration are governed mainly by temperature, wind, and density of the canopy. Dispersal within the crop is random, and a significant proportion of adult parasitoids leave the release fields. Searching on the plant is partly directed by plant structures, though the efficacy compared to random search is not increased. The impact of semiochemicals on host searching in the field remains unclear. The release technique determines to a large extent how close to their hosts the wasps emerge, hosts and thus locomotor requirements of female wasps depend on release technique. The development of a quality control program must rely on thorough knowledge of the crop system, host factors, and the specific host-searching requirements, because traits involved in host-searching are considered of prime importance for the field performance of Trichogramma. Quality control must include quantitative assessments of attributes that determine searching efficacy, such as flight initiation and walking activity. A number of traits, considered important for host searching, are presented for different crops and related to behavior and release techniques.

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