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

Abstract

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 NRsyndrome 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 4Á6 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.

Verified and potential pathogens of predatory mites (Acari: Phytoseiidae)

“…This effect vanished totally when the suspension was treated with the antibiotic tetracycline. Moreover did the bacterial fraction of feces and debris suspension collected from symptomatic predators induce the NR-syndrome whereas the viral fraction of the same suspension did not (Schütte et al 2008a). These findings proved that bacteria are involved in the induction of the NR-syndrome.…”

“…With knowledge about the main reservoir of the infectious agent it could be determined to which group the pathogen in question belongs (Schütte et al 2008a). A reliable bioassay for testing the infectiousness of predator feces and debris fractions was developed, 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.…”

“…Screening of populations on a regular basis for an infection with A. phytoseiuli should therefore be executed, as in this case a reliable detection method has been developed. Possible methods of curing infected populations consist of antibiotic treatment (Schütte et al 2008a) and washing of eggs with bleech (Schütte et al 2006b). …”