Environmental impact of the locust control agents fenitrothion, fenitrothion-esfenvalerate and triflumuron on terrestrial arthropods in Madagascar

The held toxicity of three chemical locust control agents to terrestrial non-target arthropods was investigated in small- and large-scale held trails in the recession area of the migratory locust, Locusta migratoria capito (Sauss.) (Orthoptera: Acrididae), in Southwestern Madagascar. The insecticides were applied as full cover sprays on 16 ha (1994) and 400 ha (1995) plots, respectively. The relative abundance of more than 40 arthropod taxa (combined 1994 and 1995 trials) was monitored during 4 weeks before and at least 12 weeks after treatment. The organophosphate fenitrothion (F, 1994) caused significant medium to long-term population declines of > 75% in several epigeal non-target insect taxa (springtails, ants, Zophosis madagascariensis Deyrolle (Coleoptera: Tenebrionidae)) and was classified as a high risk product. Non-target grasshoppers were reduced by about 50-60%. Springtail relative abundance returned to pre-spray levels in the following season. Significant effects of the organophosphate-pyrethroid combination fenitrothion-esfenvalerate (FE, 1995) were usually < 75% (medium risk). However, springtails responded as sensitive to this product as to fenitrothion, and there were no indications of recovery over the 12 week post-treatment observation period. The insect growth regulator (IGR) triflumuron (TFM, 1994 and 1995) posed a low risk to ground-dwelling insects except for orthopterans (crickets and grasshoppers) and caterpillars which were significantly reduced for several weeks (moderate risk). Vegetation dwelling and flying insects were moderately affected by FE, Non-target butterfly densities increased towards the end of the trial which appeared to be related to a significant reduction in hymenopteran predators and parasitoids. TFM had a marked effect on butterflies (> 60%), but was harmless to the other insects. Spiders responded less sensitively to pesticide stress than insects, but orb web spiders were significantly reduced by fenitrothion-esfenvalerate. The breakdown of organic matter was not affected by any of the insecticides. The results suggest the following relative field toxicity ranking: TFM < FE < F. However, such a ranking system does not imply that the least hazardous product is the safest in all environmental settings. This study rather supports an integrated approach, where control strategies are adapted to the particular conservation priorities in the treated areas. (C) 2000 Elsevier Science Ltd. All rights reserved.