THE IMPACT OF AERIAL FENITROTHION SPRAYING UPON THE POPULATION BIOLOGY OF BUMBLE BEES (BOMBUS LATR.: HYM.) IN SOUTH-WESTERN NEW BRUNSWICK

Abstract

Aerially sprayed fenitrothion (0.21 kg/ha) caused mortalities from 100% among experimentally caged bees in exposed habitats to 47% in cages placed under dense forest canopy. Bumble bees found foraging in sprayed areas during the days immediately following the spray suffered significantly higher subsequent mortality than those in unsprayed areas. Long-term effects were investigated by comparing late summer Bombus population densities among sites representing various spray histories. For all species combined, abundances in unsprayed areas averaged 3 times higher than in fenitrothion treated areas. Population recovery appeared to be complete within a few years after discontinuation of spraying. Foraging performance by laboratory reared colonies was significantly higher in sprayed areas with reduced bee populations than in a control area, possibly because of relaxation of competitive stress. The diversity of plant species used for pollen collection was nearly twice as great in the control as compared with sprayed areas, suggesting that the effect of fenitrothion spraying on cross-pollination may be greatest for plants which are subdominant in the hierarchy of bee preference In one such plant, red clover, reduced seed-set was demonstrated.