RESEARCH TO DEVELOP AN INTEGRATED METHOD OF REDUCING POPULATIONS OF COCKCHAFERS MELOLONTHA SPP. Cezary BYSTROWSKI, Barbara GŁOWACKA, Andrzej KOLK, Monika MAŁECKA, Marzena NIEMCZYK, Zbigniew SIEROTA, Alicja SIERPIŃSKA, Iwona SKRZECZ, Alicja SOWIŃSKA, Lidia SUKOVATA, Danuta WORETA In the protection of nurseries and plantations alike, an important issue is the damage caused by grubs of cockchafer beetles Melolontha spp. In the wake of the European Commis- sion ban on soil applications of insecticides there remained no effective plant protection methods by which populations of the grubs might be reduced. For this reason, a decade of research by the IBL Departments of Forest Protection and of Silviculture and Genetics of Forest Trees has focused on an integrated forest-protection method which would allow for reductions in populations of cockchafers at both the grub and adult stages. The scope of the research has taken in preventive (silvicultural), mechanical and biological methods, as well as chemical methods to be resorted to in the case of a threat to the sustainability of a forest. Some of the results of the work are described briefly in the following sections: 1. Preventive silvicultural measures. Chafers were found to be most frequent in broadleaved stands growing in fertile hab- itats, especially where open areas are present just nearby. The best conditions for the development of grubs are therefore found in stands with moderate (20-35%) light pene- tration, since these foster the growth of herbs on whose roots grubs at stages L1 and L2 feed particularly intensively. Black alder is found to be the forest-forming species least favouring growth in the European cockchafer. 2. Strengthening soil resilience. The use of sawdust in soil enhances its colonisation by microorganisms whose me- tabolites generate a repellent effect that results in reduced densities of grub populations. 3. Monitoring the European cockchafer population. To determine the onset and culmination of swarming by cockchafers (with a view to the date on which protective measures are to be taken being decided upon), it is possi- ble to use traps of the IBL-5 type featuring the Melolodor attractant developed by Z.D. Chemipan. An average rate of capture of cockchafers exceeding 3 specimens/trap/day is now shown to mean that at least 80% of the beetle’s population is concentrated in the topsoil (down to a depth of 10 cm), with this in turn signalling the start of the intensive swarming period. 4. Agricultural methods. To reduce populations of grubs cultivation of mustard greens (Brassica juncea) is recommended, with these being cut after flowering, shredded as much as possible and immediately tilled over, preferably when the soil is wet. In areas where grubs occur at stage L1 only, buckwheat (Fagopyrum esculentum) can also be sown. 5. Biological methods. It proved possible to raise two parasitoid fly species of the family Tachinidae (i.e. Dexia rustica and Microphthalma europea) from European cockchafer grubs, with a determination that up to 3% of the grub population was parasitized in this way. The fungus Beauveria brongniartii is another parasite, whose rates of infection of grubs are highest in soils with a neutral or alkaline reaction. Application of this form of biological control method is therefore possible where soil pH is higher than is usual for forest soils (for example in long-used nurseries, cultivated sites or ex-agricultural land). Research into the impacts of plant chemicals (quercetin or an extract from the leaves of black alder) on growth in cockchafers was able to demonstrated enhanced mortality, lower fertility and a reduced intensity of feeding where oaks were sprayed with a rutin solution. 6. Chemical method. Registration-related research was carried out to allow the insecticide Mospilan 20 SP (20% acetamipride) to be applied in reducing populations of cockchafer imagines. The preparation is used at a dose of 0.4 kg/ha in aerial and ground control measures applied using ODW-1 tractor sprayers. The research was financed by: the General Directorate of the State Forests (Project BLP-335, BLP-394), the National Centre for Research and Development (No. N R12 0096 10) and the Ministry of Science and Higher Education (No. 4299/B/P01/2010/38)..