HOW DOES INSECTICIDAL CONTROL OF GRASSHOPPERS AFFECT NON-TARGET ARTHROPODS?

摘要

Outbreaks of Calliptamus italicus L. and grasshoppers cause significant yield losses due to the recent extension of vast unmanaged agricultural lands in Russia. The problem of a choice of adequate insecticides to control grasshopper outbreaks as well as the lack of knowledge on non-target effect of anti-grasshopper insecticides in Russia inspired the present research. To evaluate the side-effect of treatments against grasshoppers the new insecticide, fipronil, was chosen. Chlorpyrifos served as a standard control. Field trials were done near Ust-Ordynsky, 70 km to the north-east of Irkutsk in Baikal region, Siberia. Four groups of plots were set up. The first (blanket treatment) was sprayed with chlorpyrifos (205 g a.i./ha), the second and the third (one blanket and one barrier treatment) were sprayed with fipronil (4 g a.i./ha), and the fourth plot was control (without treatments). Each plot occupied ~ 30 ha. Trials were conducted in pastures and fallows with a perennial grass Bromopsis inermis, to control grasshopper adults, particularly Aeropus sibiricus L., Stauroderus scalaris F.d.W., Chorthippus albomarginatus DeG., Pararcyptera microptera F.d.W., and Arcyptera fusca Pall. Arthropods were collected with sweep-nets or with pitfall traps on the following sampling dates: one day before treatment and on the 1st, 3d, 5th, 7th, 14th, and 21st day after treatment. The analysis of the response of non-target arthropods to the fipronil application showed the following results. (1) Taxa living in the grass layer or regularly visiting it are most at risk (Chrysomelidae, Curculionidae, Miridae, Lygaeidae, Cicadellidae, Aphididae, Psyllidae, Agromyzidae, Pyralidae, Chalcidoidea, Ichneumonoidea, Thomisidae). (2) Within these groups the maximum hazards occur in herbivorous insects possessing mandibulate mouthparts (Chrysomelidae, Curculionidae); in herbivorous insects possessing sucking mouthparts and high grass-dwelling activity (Miridae, Lygaeidae); in predators (Thomisidae) and parasitoids (Chalcidoidea, Ichneumonoidea) inhabiting the upper part of the grass stratum. (3) Insects possessing sucking mouthparts and low grass-dwelling activity, or with grass-flying activity, are at less risk (Cicadellidae, Aphididae, Psyllidae). (4) The risk to ground-dwelling arthropods is less, and correlated with their ability to hide in litter, soil etc. (Cydnidae, Carabidae, Lycosidae). (5) Treated sites attract species which use dead organic material for feeding and development (Silphidae). A comparison of the side-effects of fipronil and chlorpyrifos proved that fipronil was much more hazardous than chlorpyrifos. At the same time fipronil was more selective due to the reduced mortality of non-target arthropods with "cryptic" modes of life (Cydnidae, Cicadellidae, Lycosidae). An effective way to diminish the negative impact of grasshopper control treatments on non-target fauna appeared to be the method of barrier spray applications, which allows a quick recovery of parasitoids, predators and herbivores with sucking mouthparts (Chalcidoidea, Ichneumonoidea, Thomisidae, Miridae, Lygaeidae, Cicadellidae). On the contrary, even in barrier treatments we did not observe a recovery of chrysomelid beetles (with mandibulate mouthparts), as in the target Acrididae. As a result of conducted research, the use of fipronil for grasshopper control in Russia is proposed.