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Research conducted using only honey bees as the indicator species may not adequately reflect the risk posed by insecticides to wild bees because of their differential susceptibility and unique biology.

C.D. Scott-Dupree, L. Conroy, and C.R. Harris

ABSTRACT Pest management practices may be contributing to a decline in wild bee populations in or near canola (Brassica napus L.) agroecosystems. The objective of this study was to investigate the direct contact toxicity of five technical grade insecticides - imidacloprid, clothianidin, deltamethrin, spinosad, and novaluron - currently used, or with potential for use in canola integrated pest management on bees that may forage in canola: common eastern bumble bees [Bombus impatiens (Cresson); hereafter bumble bees], alfalfa leafcutting bees [Megachile rotundata (F.)], and Osmia lignaria Cresson. Clothianidin and to a lesser extent imidacloprid were highly toxic to all three species, deltamethrin and spinosad were intermediate in toxicity, and novaluron was nontoxic. Bumble bees were generally more tolerant to the direct contact applications > O. lignaria > leafcutting bees.
However, differences in relative toxicities between the three species were not consistent, e.g., whereas clothianidin was only 4.9 and 1.3x more toxic, deltamethrin was 53 and 68x more toxic to leafcutting bees than to bumble bees and O. lignaria, respectively. Laboratory assessment of direct contact toxicity, although useful, is only one measure of potential impact, and mortality under Þeld conditions may differ greatly depending on management practices. Research conducted using only honey bees as the indicator species may not adequately reßect the risk posed by insecticides to wild bees because of their unique biology and differential susceptibility. Research programs focused on determining nontarget impact on pollinators should be expanded to include not only the honey bee but also wild bee species representative of the agricultural system under investigation.

The main findings of this study include:

The descending order of contact toxicity to bumble bees was:
clothianidin > imidacloprid > deltamethrin > spinosad > novaluron;

to alfalfa leafcutting bees was
clothianidin > deltamethrin > imidacloprid > spinosad > novaluron;

and to O. lignaria bees was
imidacloprid > clothianidin > spinosad > deltamethrin

The neonicotinoid insecticides clothianidin and to a lesser extent imidacloprid were highly toxic to the three bee species. For example, clothianidin was about 23, 16, and 47x more toxic to bumble bees, alfalfa leafcutting
bees, and O. lignaria bees, respectively, than was the microbial bioinsecticide spinosad.

Pesticide impacts on social (e.g., honey and bumble bees) and solitary (e.g., alfalfa leafcutting bees and O. lignaria) bee pollinators may vary substantially depending on foraging patterns, nesting behavior, seasonal activity, and diurnal flight activity; all need to be considered in future research.

Protecting wild bees from exposure to insecticides is essential, particularly given their increasing importance in pollination as honey bee populations are compromised. To this end, it is important to establish globally accepted laboratory and field study protocols for comparative assessment, before registration, of lethal and sublethal pollinator responses to novel insecticides and other control products.

Source: J. Econ. Entomol. 102(1): 177-182 (2009)