A novel disease affecting the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae): evidence for the involvement of bacteria

Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of a laboratory population show drastic changes in foraging behavior, anatomy and life history compared to typical laboratory populations. We demonstrated earlier that the set of characteristic symptoms, called non-responding (NR) syndrome, is transmitted horizontally between and among predator generations via feces and debris deposited by symptomatic females. Here, we prove that bacteria present in feces and debris deposited by symptomatic females are involved in the induction of the NR-syndrome. The potential of predator products to induce the NR-syndrome was assayed by keeping healthy adult female predators during a period of 3 days on prey-infested bean leaves, which had previously been sprayed with an aqueous suspension of feces and debris. The NR-syndrome was clearly induced in those predators that had been exposed to a suspension collected from symptomatic females (incubation time 4-6 days, 93% shrunken females), whereas predators exposed to a suspension collected from non-symptomatic females did not show the NR-syndrome. Moreover, predators from the first group transmitted infectious products themselves already 5 days after the initial exposure, whereas this was not the case for the second predator group. The bioassay used in the present study is important for laboratories and companies as it can be applied for testing the presence of the novel disease in populations of P. persimilis. To investigate the involvement of bacteria in syndrome induction we (1) eliminated bacteria from a feces-and-debris suspension of symptomatic females by passing the suspension through a bacterial microfilter and (2) added the antibiotic tetracycline to a suspension of feces and debris from symptomatic females. A suspension of feces and debris collected from symptomatic females did not induce the NR-symptom after bacteria had been eliminated, whereas an untreated portion of the same suspension did so. Moreover, the NR-syndrome was induced in predators exposed to an aqueous suspension of the residues that had not passed the bacterial filter. A suspension of feces and debris collected from symptomatic females, to which the antibiotic tetracycline had been added, did not induce the NR-syndrome whereas the same suspension did induce all symptoms when no tetracycline was added. These findings prove that bacteria are involved in the induction of the NR-syndrome. The results are discussed in the context of mite pathology and biological control