Resistance of Pollen Beetle (Meligehes aeneus F.) in Poland

Pawel Wegorek, Aleksandra Obrepalska-Steplowska, Joanna Zamoyska, Katarzyna Nowaczyk
Institute of Plant Protection
Miczurina 20, 60-318 Poznan,
Poland

ABSTRACT Chemical plant protection is still an indispensable method in effective oilseed rape protection against the Pollen beetle -(PB) (Meligethes aeneus F) in Poland. This species had developed strong resistance in this country against active substances of pyrethroid insecticides used to control it. Therefore the objective of the study was to determine the present susceptibility level of Polish populations of PB to main groups of insecticides recommended in Poland for PB control. Another aim was to determine mechanisms that can be responsible for PB resistance in Poland.

KEYWORDS Meligethes aeneus, Pollen beetle, insecticide resistance, pyrethroids, organophosphorous, neonicotinoids, oilseed rape, resistance mechanisms.

Resistance of PB has been a severe problem in Poland for a number of years (Lakocy 1967, 1977). The dynamic and widespread of PB resistance in Poland to pyrethroids insecticides and increase in tolerance to neonicotinoids and organophosphorous has created a need for resistance monitoring and elaborating the strategies for the management of PB resistance to all synthetic insecticides recommended in Poland. Nowadays a lot of consideration is taken to neonicotinoids because the importance of these class of insecticides for PB control in Poland systematically increases. Researches concerning actual susceptibility level of PB to selected active substances were performed in the Institute of Plant Protection in Poznan and provided important information on PB resistance to insecticides applied currently in Poland.

In our research, populations from all areas demonstrated high levels of resistance to pyrethroid group and some level of resistance to neonicotinoid insecticide - acetamiprid. Survival at recommended concentrations in case of pyrethroids and neonicotinoids indicated occurrence of resistance to these active substances in examined populations. In laboratory studies (2003 - 2006) pyrethroid insecticides examinated in recommended doses were less effective in controlling PB. (Wegorek 2004, Wegorek and Zamoyska 2005). The results of insecticide susceptibility monitoring indicated that PB beetles do not show resistance to chlorpyrifos. The results concerning chlorpyrifos indicated that PB populations tolerant to pyrethroids and neonicotinoids were positive cross-resistant to this active substance. Resistance mechanisms were detected using piperonyl butoxid, tributylinacetate and carbaryl as synergists. High synergism of pyrethroid insecticides with piperonyl butoxid (oxidative metabolism) and low synergism with carbaryl (hydrolytic mechanism) and tributylinacetate (penetration factor) showed that within these three - the main mechanism of PB resistance can be oxidative metabolism. The analise of mitochondrial cytochrome oxidase (I and II subunits ) nucleotide sequence by using PCR and sequencing, as an example of an oxidative enzyme indicate occurrence of many substitution in mtCOI and mtCOII sequences when compared with sequences alredy deposited in GenBank. The existing substitutions in both subunits DNA sequences entail amino acid substitution that can change secondary structure of those peptides. However, those substitutions can result from variability in populations that are geographically isolated.

CONCLUSIONS PB is an example of insect species that can develop strong resistance mechanisms to most active substances used to control it in Europe (Hansen 2003, Heimbach at all.2006, Lakocy 1967, 1973, Wegorek 2005). In the case of studied pyrethroids and neonicotinoids, the survival of PB beetles in laboratory tests achieved very high level at doses higher than those commercially recommended. The decrease of PB susceptibility to examined active substances indicates the decline of chemical treatments efficiency under field conditions and points at selection of populations that metabolise high doses of insecticides faster and more effectively. Thus, continuous and widespread use of pyrethroids and neonicotinoids in Poland can lead to control failure. PB strains were still excellently controlled with organophosphorous (chloropirifos) insecticides. The resistance mechanism of surviving beetles using pyrethroids active substance and acetamiprid is caused mainly by enhanced oxidative metabolism (high synergism of pyrethroid insecticides with piperonyl butoxid and low with carbaryl and tributylin acetate - although some symptoms point at insensibility of nervous tissue in the place of biological activity of active substance. Positive cross resistance to chlorpyrifos is probably due to the creation of the very toxic metabolite of this active substance under the influence of oxidative enzyme action. The metabolite (oxidative analogue of chlorpyrifos) is very strong toxin for PB and other insects species (Rozanski 1992). However this conclusion requires further research.

Considering the possibility of high occurring PB resistance, it is necessary and advisable to control application of insecticides rationally, and to take into account their association with different chemical groups and mechanisms of resistance.

Only systematic monitoring of susceptibility of PB strains might ensure more effective protection of oilseed rape crops in Poland. Therefore one should take into consideration the necessity of PB susceptibility monitoring by regional plant protection services according to the method developed by the Institute of Plant Protection in Poznan in the year 2003.

Studies on mechanisms of PB resistance to active substances are very useful because they will allow to enterprise a better strategy for delaying PB resistance. Problems with PB resistance occur also in Germany, Sweden, Denmark and Estonia and France.

Presently the registration authorities must take into consideration the resistance risk analysis based on EPPO standards and recommendations (EPPO 2001). So during the registrative investigations, resistance phenomenon of agrophages must be seriously taken into consideration. Also chemical companies should take responsibility for constant control of efficacy of their products and update them if needed in accordance with new results from susceptibility monitoring. The future of chemical protection of rape plants against PB in Poland will be dependent on many factors, among which the resistance of this species will be one of the most important. The results suggest that at present the situation of PB resistance limitations in use of pyrethroid and neonicotinoid group is indispensable in Poland. Also, rational application of all recommended insecticides and their rotation including different modes of their molecular action is necessary. Oversensitiveness of PB to chlorpyrifos (Table 1.) should be used in recommendations and future practical strategies of rape protection in Poland.

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