Pesticides Research Nr. 110 2007 – Health effects of predatory beneficial mites and wasps in greenhouses

Health effects of predatory beneficial mites and wasps in greenhouses

10 Conclusions

The use of beneficial arthropods is a well consolidated technology in Danish greenhouses. In contrast to the chemical pesticides and to some extend the microbiological control agents there are no regulations of the use.

The present study showed development of sensitization to the predatory mites and description of cases with exposure related symptoms.

Amblyseius cucumeris caused sensitization in about 7% of the exposed persons and development of new sensitization was seeen in several persons during the observation period. A number of persons developed allergic symptoms in the eyes, nose and throat in parallel with the sensitization.

Phytoseiulus persimilis gave rise to a higher sensitization rate than A. cucumeris. The sensitization seems to be less specific due to a relatively high sensitization rate in the unexposed group. Development of sensitization and symptoms were seen in a small number of persons during the observation period.

There were signs of sensitization against the wasp Aphidius colemani but both in those exposed and those not exposed. A number of symptoms, mainly from the upper airways, may be related to exposure to A. colemani.

Two different measures of sensitization were used. We were able to show reliable antibody response to the above mentioned arthropods, while IgE antibodies against the mite Hypoaspis miles were not reproducible. On the other hand the specific IgE levels were low and no relation to exposure was seen. In contrast, histamine release test seems to be a more sensitive and reliable measure of sensitization, although considerably more expensive.

Exposure to the predators seems to give rise to some symptoms from eyes, nose and throat. On the other hand there was no indication of that any of the beneficial animals may cause asthma or other imflammatory lung diseases.

The study has been limited by the possibility of good individual exposure estimates, but a limited pilot study has shown that antigen from A. cucumeris can be traced in the work room air. Better individual exposure estimates may improve the results but they will still be influenced by the selection of workers (“healthy worker effect”).

The study shows that in workers exposed to the beneficial mites and possibly wasps give rise to health effects. The effects are clearly more pronounced than those of the microbiological control agents Bacillus thuringiensis, Trichoderma harzianum, and Vertilcillium lecanii, but several other factors in the greenhouses, i.e. plants and naturally occurring microbial fauna have comparable effects.