Host Searching by Trichogramma
and Its Implications for Quality
Control and Release Techniques
Franz Bigler, Bas P. Suverkropp, and Fabio Cerutti
A variety of Trichogramma species are mass reared and used for inundative releases in different agricultural crops and forest systems. Each crop is a distinct ecosystem that changes during growth. Thus, the wasps are faced with ecologically diverse situations. Crop architecture (size, shape, density) and plant morphology (veins, hairs, shape of organs) affect a wasp's searching behavior and success. These ecological differences become obvious if we compare, for example, a pine forest, a corn or sugar cane field, and a cabbage crop. Moreover, host eggs may be laid on specific plant parts depending on the pest species, plant variety, growth stage, and climatic conditions. Thus, the distribution of host eggs within the crop, on the plant, and between plant parts affects the probability of host encounters.
In addition to plant and host attributes, host searching is determined by the female's intrinsic capacity for dispersal within the crop and foraging on the plant. While dispersal of Trichogramma is mainly a function of flight abilities, foraging on the plant is affected primarily by walking and perceiving chemical and physical cues from the plant and the host guiding the female to the host egg. A number of behavioral attributes are needed to perform host searching successfully.
Mass rearing of Trichogramma for inundative releases tends to select for populations that perform well in the laboratory under optimal conditions but not necessarily in the field. It is therefore important to develop and implement quality control procedures to detect changes in attributes that affect host searching. Experiments based on female behavior must be designed to determine the value of quality traits that contribute to the overall performance. The aim of inundative release of Trichogramma is to bring the females as close as possible to the host egg in order to increase host encounters with the least possible waste of time and energy. This is not always easy to achieve. The development of an optimal release system must take into