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

Summary

The aim of the project was to describe to which extend beneficial predatory arthropods are risk factors for development of allergy, asthma, and other airway diseases among employees in greenhouses culturing ornamental plants.

Beneficial predatory arthropods are widely used in Danish greenhouses. The most frequently used are parasitoids, predatory bugs, mites, and nematodes. The mite Amblyseius cucumeris used for the control of thrips and Phytoseiulus persimilis used for the control of spider mites have in studies caused sensitization in about 25 % of the persons exposed. No direct information of the predatory wasps in study is available but some other wasps have caused asthma in the persons breeding them. European studies have shown a high prevalence of asthma among greenhouse workers, almost on level with that in farmers.

The investigation has been based on data and biologic material from an epidemiological follow-up study of employees at 31 different greenhouse firms (the BIOGART study). The primary goal of this study was to investigate the health effects of microbiological pest management on allergic and inflammatory airway diseases.

In the study 579 persons participated of who 256 were followed during three years with annual examinations while 400 were followed for at least a year. At each examination an interview was done including the use of predators, microbiological pest management, and pesticides. Besides, the persons were asked about symptoms from the lungs, nose, eyes, and skin. Finally, lung function tests, a test of the bronchial reactivity, prick tests for common allergens were made and blood samples were taken.

The actual project included an evaluation of the exposure to predatory mites and wasps. This evaluation was based on the information from the participants in the annual examinations combined with the results of a survey conducted in the participating greenhouses in 2004.

Eighty percent of the participants worked in greenhouses where the beneficial arthropods were applied while 4-10 % handled the products themselves during the observation period. Two predatory insects, Aphidius colemani and Encarsia formosa and three mites Amblyseius cucumeris, Phytoseiulus persimilis, and Hypoaspis miles were included as well as the spider mite Tetranychus urticae, which is naturally occurring in the greenhouses and used as prey for the beneficial species.

Screening for IgE antibodies against A. colemani, A. cucumeris, P. persimilis, and H. miles in the last two blood samples of the persons detected antibodies against all the species. For A. colemani 4 % showed positive values while A. cucumeris, P. persimilis, and H. miles showed sensitization rates of 8, 3, and 3 %, respectively. Only antibodies against A. cucumeris were to some extend, related to the measures of exposure while no relation was seen in the other species. Particularly the persons with the highest exposure, those who had handled the animals themselves, had the lowest rate of sensitization to all the animals.

A histamine liberation test against the two mites A. cucumeris and P. persimilis and the wasp A. colemani was carried out on a sample of the persons. The principle in this is that basophile leucocytes from the persons blood reacts with the antigen in the extract by liberating histamine depending on the degree of sensitization. In the actual setup an indirect method was used as donor blood cells were incubated with the person’s serum and then reacted with the antigen. The 70 persons tested were those who had reacted with a positive IgE to one of the arthropods and 30 persons without a positive IgE. For each person all samples, three or four were analyzed. Besides, test was carried out on 138 persons without relation to agriculture or the greenhouse trade. These persons were participants in a population study of asthma.

The histamine reaction was considerably more sensitive than the IgE. Among the persons exposed to A. cucumeris the rate of positive reactions during the study increased from 13 % to 22 % during the observation period while the unexposed showed a rate of 5 %. Eight persons showed signs of sensitization during the study defined by two levels increase in the reaction. Seven of these persons were exposed in the greenhouse.

The rate of sensitization against P. persimilis was somewhat higher than for A. cucumeris from 30 % to 35 % among the exposed compared to 15 % to 32 % among the unexposed. Seven persons showed signs of sensitization during the study, four of these were exposed to P. persimilis.

For A. colemani the sensitization rate was 30 % without relation to the exposure. Five persons were sensitized, four exposed and one non-exposed.

Based on the histamine reaction a pilot study of exposure measurements was conducted in a large greenhouse firm using A. cucumeris. During three workdays airborne antigen was sampled in dust filters of personal samplers in three different departments, A. cucumeris being used in two. Samples were taken before, during, and the day after the application of mites. Dust samples from 25 filters were eluated and tested against five different sera from persons with a strong reaction against A. cucumeris.

In four of the 25 filters antigen could be quantified. They were sampled in the departments where the mites were used and the concentration varied from 0.2 to 70 μg/m³. The method, however, is not optimized and needs improvements to achieve a satisfactory recovery of antigen from the filters.

The statistical association between the prevalence of symptoms on one side and the estimates of exposure and sensitization on the other side was analyzed. The prevalence of symptoms at the first examination of the 579 persons was tested in a logistic regression with sex, status of atopy, and smoking habits as additional variables. Similar analyses were made on the last samples on the persons participating in the two last examination rounds (338 persons). In this group the relation between symptoms and the sensitization to each of the four beneficial species and T. urticae was tested, too. Besides, the incidence of symptoms, the decline in lung function, and the variation in bronchial reactivity were tested against the exposure variables.

There was some correlation between exposure variables and some of the vast number of prevalent symptoms, although not systematically. There were some significant relations between sensitization to the mites and lung symptoms while sensitization to the wasp A. colemani was correlated with nasal and eye symptoms. There was no effect of exposure on either asthma score or the different measures of lung function.

Consistently, the persons actually handling the animals generally had fewer symptoms than the rest. This may either be attributed to “healthy worker selection” or the exposure may not be specially related to the actual handling of the predators.

Five persons showed both signs of developing sensitization to one of the mites and a change in symptoms during the observation period. Symptoms from eyes and nose seemed to develop concomitantly with sensitization while no sign of asthma was seen. Most of the persons also had or developed other common allergies.

The study showed that occupational exposure to the two mites A. cucumeris and P. persimilis give rise to allergic sensitization and possibly eye and upper airway symptoms. The picture of the insect A. colemani with no sign of sensitization but some exposure related symptoms is more unclear. The group of predators are then one among a number of allergens in the greenhouses i.e. certain plants and naturally occurring fungi.

As the study shows possible health effects of the predatory animals guidelines and preventive measures when handling at least the mites are suggested. More information about the exposure is needed before these measures can be planned in more details.

Further studies are needed to evaluate the exposure to antigen both directly during handling of the products and by indirect exposure when handling the plants. The dose needed to sensitize or cause symptoms has to be characterized as well as the persons at risk. Finally, the possibility of the beneficial arthropods to cause the more serious disease asthma will have a great impact on the need for regulation of the use of the beneficial arthropods.