[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

MITE PATHOGENS IN IPM
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on the twospotted spider mite, but the preparation did show a toxic effect on M.
occidentalis. Eggs were not affected, but if juveniles were treated, only 65% reached
the adult stage. This toxic effect could be enhanced by starving the mites: the
authors assumed that starvation may lead to a higher uptake of the material, or that
the mites were more exposed to the preparation as starving mites tend to move
faster. It is also possible that starvation acts as a stress factor. The authors have no
explanation for the toxic effect on the predatory mite: the preparation did not contain
the β-exotoxin (thuringiensin) known to be toxic for mites.
In more recent years, isolates of B. thuringiensis have been found that do show
toxicity towards spider mites and house dust mites (Payne, Cannon, & Bagley, 1993;
Payne, Cannon, & Ralph, 1994). It has been suggested to isolate the δ-endotoxin of these
isolates and to formulate it as an acaricide. One may also transfer the gene, encoding for
this specific δ-endotoxin into a crop plant in order to protect the crop against spider mite
infestations.
An interesting discovery is the isolation of a B. thuringiensis strain from dead
twospotted spider mites, T. urticae (Jung, Mizuki, Akao, & Côte, 2007). In
sporulating cultures of the bacterium, roughly spherical parasporal inclusion bodies
are formed. This crystalline body is composed of at least two polypeptides of 86 and
79 KDa. The crystal is not toxic to the twospotted spider mite, but after cleavage
with trypsin, it is cytocidal to some human cancer cells.
In Table 1, a list is given of bacteria that have been isolated from mites. We realize
that this list may not be complete, but we have tried to limit the list to bacteria that show
pathogenicity towards mites. Many species of bacteria may be isolated from mites (and
other organisms): in many instances, these may not appear to be pathogenic.
Aksoy, Ozman-Sullival, Ocal, Celik, and Sullivan (2008) studied the effect of
Pseudomonas putida biotype B on the twospotted spider mite T. urticae. The
bacterium had been isolated from greenhouse soil in Turkey and was tested on newly
emerged, copulated females. The authors observed a strongly reduced egg production
and no hatching of the eggs was noted. The results showed that the bacterium may be
very effective in causing mortality in T. urticae populations. Further research is
required to find out whether this organism may be developed to a microbial miticide.
The predatory mite Phytoseiulus persimilis has been mass cultured for several
decades for the biological control of spider mites in various field and glasshouse crops.
This predator species is very important in integrated pest control programs and has
stimulated research on predator-prey interactions and foraging behavior. It has been
shown in several instances that adult female predatory mites are attracted to volatiles that
are emitted by plants infested by prey. This emission of volatiles by the plant after
herbivore attack is apparently a defense mechanism against herbivorous mites. Schütte
(2006) noticed a change in response to prey-induced plant volatiles in a laboratory
colony of P. persimilis. This population showed a lower attraction to these volatiles than
other populations of the predator. It could be demonstrated that the change in behavior is
caused by the involvement of a bacterium. Transmission of the bacterium occurs through
feces and debris. There is no evidence that vertical transmission (from one generation to
the next) occurs. The bacterium could be isolated and was described as Acaricomes
phytoseiuli (Pukall, Schumann, Schütte, Gols, & Dicke, 2006). Comparative analysis of
the 16S rDNA sequence revealed that it belongs to the Micrococcaceae, and that it is