Pesticides Research, 91 – Biological Control of Weevils (Strophosoma Melangrammum and S. capitatum) in Greenery Plantations in Denmark

Biological Control of Weevils (Strophosoma melanogrammum and S. capitatum) in Greenery Plantations in Denmark

8 Perspectives

8.1 Biological control in Danish greenery and Christmas tree plantations
8.2 The status of insect pathogenic fungi in biological control
8.3 The grower's situation
8.4 Occupational health effects
8.5 Consumers' preferences
8.6 The final societal evaluation

8.1 Biological control in Danish greenery and Christmas tree plantations

Denmark has a long tradition for biological control. Approximately 50 organisms are commercially available for growers, especially for use in glasshouses (Eilenberg et al., 2000). Outdoor biological control is more limited and there is no long tradition for biological control in greenery and Christmas tree plantations. Since 1993, microorganisms for use as biological control agents must pass the approval in EU. Very few organisms have, however, passed so far due to the laborious work related to such an approval and not due to rejection because of detrimental effects. The most used microorganisms for biological control are thus still used by dispensation (A. Fjeldsted, pers.com.). M. anisopliae is commercially available in Europe against curculionid beetles from the genus Otiorhynchus, by dispensation. A development towards a product against Strophosoma spp. requires an approval from EU. The fungus is already used and much information on for example non-target effects and health effects is available in Europe and elsewhere. It is therefore reasonable to assume that it will be possible to have the fungus (or the other tested fungi) approved for commercial use.

It is, however, important that the application of a biocontrol agent is optimized in order to avoid significant non-target effects on other arthropods. In the case of microbial control of Strophosoma spp. larvae with M. anisopliae in greenery plantations, a precise targeting at the first instars larvae during the process of dropping to the ground would improve control leading to a lower effective dose and consequently a reduction of adverse side effects. Concerning control of adult Strophosoma spp. `fungal bands' placed on tree trunks should also be considered in the future control since such bands only expose arthropods on the tree trunks and not those on the ground. Furthermore, the fungal bands can be removed when they are not needed for control thus decreasing the exposure time for the non-target. However, for both strategies outlined here additional studies are needed with special attention to long-term non-target effects using the ecological host range as the measure.

8.2 The status of insect pathogenic fungi in biological control

The main insect pathogenic fungi in biological control are from the genera Metarhizium, Beauveria, Paecilomyces and Verticillium (Ingliss et al., 2001). They are used worldwide and for example M. anisopliae is widely used in United States (Anonymous, 2004), Africa (Ekesi and Maniania, 2003) and Latin America (Alves et al., 2003). M. anisopliae is used against a variety of pests from several insect orders. The potential broad target host range is needed, since many insect species are `local' and without sufficient economic importance for a full product development. The company Prophyta, who produced our M. anisopliae, agrees that the European `Strophosoma market' is too small to be immediately commercially interesting if a fungus product should be developed to target only Strophosoma species (P. Lüth, pers.com.). From a company point of view, M. anisopliae is nevertheless attractive because most technology needed for production is known and because of a potential big range of target species. We recommend that economic analysis on the costs for developing fungi for biological control in greeneries should be analysed in detail.

8.3 The grower's situation

The production of greenery and Christmas trees has both a high export value and a high national value. Also, there is a political intention to minimize the use of chemical pesticides. Growers will probably easily adopt biological control options, provided the methods work and provided that standard technology can be used or, at least that some easily adoptable new technology can be used. The main method for application of conidial suspension was based on a personal spray device, which is familiar to growers. The grower attitudes to new technologies are that they are willing to pay an additional cost of 10 – 25 % compared to the conventional (K. Østergaard, pers. com.). It is therefore assumed that a biocontrol product can be accepted even if it may cost more than conventional products. The growers' economic situation is, however, very severe and it is not to be expected that they can contribute economically significantly to the development of biocontrol products.

Also the strategy of application is important in considerations of adopting new control methods. In the case of Strophosoma spp., no immediate lethal effect on the pests occurs as with traditional chemical products; therefore the strategy must instead be prophylactic treatment leading to reduction of subsequent population levels.

8.4 Occupational health effects

A conference held November 27, 2003 under the auspices of `Danish Centre for Biological Control' (www.centre-biological-control.dk), paid attention to potential occupational health problems using microorganisms for biological control (Madsen et al., 2003). Growers can be exposed to large amounts of fungus spores when performing biological control with fungi, and in glasshouses this exposure is sometimes high, yet insignificant compared with the exposure to various naturally occurring fungi in the cropping system. It is assumed that the exposure to fungi for persons performing biological control outdoor is much less than in glasshouses. This project did not measure the exposure of the persons who applied M. anisopliae in our studies, but recommend such aspects are taken into consideration.

Personnal protection as recommended by the ministry shoul always be used when treating with biocontrol agents

8.5 Consumers' preferences

Not much is known about consumers' preferences and biological control. It is normally assumed that many consumers prefer crops without chemical agents. In Denmark many organic products are now sold at a higher price than conventionally grown food products and this documents that consumers are willing to pay a higher price in order to avoid product treated with chemicals. However, user preferences for organic food products are likely to differ from preferences for non-food products.. Nevertheless, in Denmark the sales of organically grown Christmas trees and greenery have increased over the years and may point towards a future demand for such products.

However, a preliminary study some years ago in Germany reflected that consumers in general do not regard Christmas trees and greenery as `ecological products'. They were therefore not immediately willing to pay a higher cost for pesticide free products (K. Østergaard, pers.com.).

We are not able to assess the consumers' reaction concerning biological control using fungi. Do they regard it as a nice and environmentally sustainable technology or do they regard it an unnecessary complex and `dangerous' biotechnological solution? A very recent study from USA (Jetter and Paine, 2004) showed that urban and suburban residents are willing to pay for biological control in the landscape. In general they preferred macroorganisms (exemplified by parasitoids) slightly to microorganisms (exemplified by Bacillus thuringiensis), while fungi were not included in the study. In this context, knowledge about adverse side effects on the environment, for example on non-target, may be an important element in user preferences. Studies on consumers' preferences for biological control should be initiated in Denmark, both with respect to non-food crops such as greenery and Christmas trees and with respect to food products.

It should also be noted that the perception of risk differs between scientific experts and the public (Sandøe, 2003). While the experts will evaluate the risk as `hazard X probability' the public perception is more complex. Studies on the public perception have only to a very limited extent so far been applied to biological control studies but will indeed be relevant for evaluating the potential for future use of biological control.

8.6 The final societal evaluation

As described above, the biological data obtained in this project, point towards a development for commercial use. However, some potential restrictions and conflicts occur, which basically can lead to three questions: Who pays? Who benefits? Are there any unacceptable risks? These questions are relevant at a societal level and are unavoidable in the development of future biological control.