NO EFFECTS OF A FOREST SPRAYING OF MALATHION ON BREEDING BLUE TIPS (PARUS-CAEREULEUS)

Ultra low volume (ULV) aerial spraying of the organophosphorus insecticide malathion is widely used in Spain to control Tortrix viridana, the most important lepidopteran pest of Spanish holm oak forests (Quercus ilex). A field study was carried out in spring 1988 to analyze the short-term effects of a standard application rate of malathion (1, 160 g a.i./ha) on the breeding success of the blue tit (Parus caeruleus). Several blue tit reproductive parameters and seasonal variation of arthropod densities in canopy trees (focusing on caterpillars, the main food resource for breeding blue tits) were compared between a malathion-treated plot and a control plot. None of the breeding parameters (nest abandonment, nest success, hatching success, nestling mortality, daily survival rate, and nestling weight) showed differences between the treated and the control plots. Malathion spraying caused nearly a 100% mortality of the target pest Tortrix viridana, but it did not reduce availability of another Tortricidae (Archips xylosteana), with the result that food supply was similar or higher in the treated plot than in the control plot. The main conclusion of this study is that a forest standard application of malathion did not cause adverse short-term effects on breeding blue tits. Moreover, this work focused on the indirect effects of insecticides via food depletion; its results suggest that in these kinds of studies it is more important to assess the abundance of arthropods remaining alive after treatment than the degree of arthropod mortality caused by the insecticide.