A novel disease affecting the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae): 2. disease transmission by adult females

Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of one of our laboratory populations (=NR-population), show the following set of symptoms: predators shrink several days after mating, cease egg production and die several days after shrinking, show a lower degree of attraction to herbivore-induced plant volatiles and a shorter choice time in olfactometer tests, have the tendency to leave a prey patch with ample food, may carry excretory crystals in the legs, may cease prey consumption, and have a lower excretion rate. We hypothesized earlier that this characteristic syndrome, called non-responding (=NR-) syndrome, is caused by a pathogen infecting P. persimilis. To further support this hypothesis we here study several transmission modes of the factor causing the NR-syndrome. In all tests we measured size, short-term fecundity, mortality, predator position, response to plant odors and crystal location, thus including 6 of the 9 symptoms known yet. No evidence was found for vertical transmission from parent to offspring. Eggs from symptomatic females of the NR-population mated by males of the NR-population gave rise to normal-sized, well performing predators, when they had been surface sterilized or transferred to a new leaf. However, such eggs gave rise to shrunken females (17%) when left on the leaf where they had been laid. In the latter case transmission via products deposited on the leaf by the mothers was possible. We therefore tested several modes of horizontal transmission by exposing females of a commercial population that never showed the NR-syndrome (=R1-population) to products related to the symptomatic NR-population. No evidence was found for transmission via food or via squashed adult females. However, symptoms were induced in adult females of the R1-population after a 3-day exposure to a live adult female of the NR-population (incubation period=3¿7 days, fraction shrunken females=53%) and after a 1-day exposure to feces and debris collected from such females (incubation period=2¿4 days, fraction shrunken females=65%). Contact with live females and feces of the R1-population did not induce the syndrome. These results clearly indicate that the NR-syndrome is a contagious phenomenon and that the factor inducing the syndrome is transmitted horizontally among and between generations via feces and debris deposited by symptomatic females. The results are discussed in the context of mite pathology and biological contro

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

Novel bacterial pathogen Acaricomes phytoseiuli causes severe disease symptoms and histopathological changes in the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae)

Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of a laboratory population show a set of characteristic symptoms, designated as non-responding (NR) syndrome. Mature predators shrink, cease oviposition and die. They show a lower degree of attraction to herbivore-induced plant volatiles and a greater tendency to leave prey patches carrying ample prey. Moreover, predators may carry excretory crystals in the legs, may cease prey consumption and have a low excretion rate. Here, we satisfy Koch¿s postulates for a strain of Acaricomes phytoseiuli (DSM 14247) that was isolated from symptomatic female P. persimilis of the NR-population. Adult female P. persimilis were either exposed to a bacterial inoculum suspension (treatment) or to sterile distilled water (control) for a period of 3 days. Control and treated predators were examined for the occurrence of six symptoms characteristic for the NR-syndrome and the presence of A. phytoseiuli after inoculation. The latter was done by re-isolation of A. phytoseiuli from individual predators and predator feces placed on nutrient agar, by PCR-based identification and by histopathological studies of individual predators. The NR-syndrome was clearly induced in those predators that had been exposed to the bacterial inoculum (incubation time = 2¿5 days, fraction shrunken females = 80%), whereas predators exposed to water did not show the NR-syndrome. A. phytoseiuli was never isolated from control predators whereas it could be re-isolated from 60% of the treated predators (N = 37) and from feces of 41% of treated predators (N = 17). Only one day after exposure A. phytoseiuli could not be re-isolated from treated predators and their feces. Light and electron microscope studies of predators exposed to A. phytoseiuli revealed striking bacterial accumulations in the lumen of the alimentary tract together with extreme degeneration of its epithelium. In addition, bacterial foci also occurred in the fat body. These phenomena were not observed in control predators that were exposed to sterile water. The present data prove that A. phytoseiuli can infect the predatory mite P. persimilis and induce the NR-syndrome and characteristic histopathological changes in adult female P. persimilis. This is the first record of a bacterial pathogen in a phytoseiid mite and the first description of pathogenic effects of a bacterial species in the genus Acaricomes