Assessing what attracts the predatory mites Neoseiulus californicus and Phytoseiulus persimilis based on the presence and density of their prey, Tetranychus urticae, to optimise biocontrol on bean.

Tetranychus urticae is one of the most common pest mites in agriculture. Its biocontrol by predatory mites such as Neoseiulus californicus (generalist predator) or Phytoseiulus persimilis (specific predator) is a promising option for its regulation. However, the reason why predators are attracted to prey remains poorly understood. To answer this question, we set up an experiment to study what caused the predator to move. By placing the predators on a leaf of a mint (companion plant) and observing whether they crossed to an infected bean leaf, we sought to evaluate what caused the strongest tropism: the HIPVs (herbivorous induced plants volatiles) produced by the plant or the smell of the prey itself. Our results did not show any real tropism of the predators for the HIPVs produced by the plant following infection, regardless of density. The predators do not forage away from their companion plant. As for the presence of the prey themselves, a slight tendency seems to emerge in N. californicus when prey density is high. For the other conditions and treatments, no results stand out, which leaves room for further studies on the subject to determine whether a prey-density threshold of attraction exists.