A Novel Disease Affecting the Predatory Mite Phytoseiulus persimilis (Acari, Phytoseiidae): 2. Disease Transmission by Adult Females

Abstract

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 nonresponding (=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 NRpopulation (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 control.

Incidence of the endosymbionts Wolbachia, Cardinium and Spiroplasma in phytoseiid mites and associated prey

“…faeces (e.g. Schütte et al 2006) and symbionts could increase resistance of their hosts to environmental conditions like high temperatures or pathogens (e.g. Scarborough et al 2005, Montllor et al 2002.…”

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

“…transmission from parent to offspring directly via the egg, (2) interspecific horizontal transmission between the prey T. urticae and adult female P. persimilis, (3) horizontal transmission via body fluids, i.e. from squashed female predators to female P. persimilis (Schütte et al 2006b). Instead there was clear evidence for horizontal transmission between and among generations via feces and debris released by diseased adult female P. persimilis (Schütte et al 2006b).…”

“…from squashed female predators to female P. persimilis (Schütte et al 2006b). Instead there was clear evidence for horizontal transmission between and among generations via feces and debris released by diseased adult female P. persimilis (Schütte et al 2006b). After contact with feces and debris deposited by diseased females during only 1 day, the majority of healthy female P. persimilis (65%) became dorso-ventrally flattened after only 3 days.…”

“…From eggs laid by diseased mothers a minority of the offspring became dorso-ventrally flattened (17%) when adult. This was only the case, when the eggs were left on the place where the mother had laid them (Schütte et al 2006b).…”

“…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). …”