How Efficient Is Apis cerana (Hymenoptera: Apidae) in Pollinating Cabbage, Brassica oleracea var. capitata? Pollination Behavior, Pollinator Effectiveness, Pollinator Requirement, and Impact of Pollination.

Cabbage is a cross-pollinated crop because of sporophytic self-incompatibility, and honey bees play an important role in its pollination. Though Asian honey bees, Apis cerana F., are used in pollination of cabbage, the rate of visitation, behavior, pollinator efficacy, and impact on seed-set are to be determined. Apis cerana occupy a share of 19.18% of all the flower visitors of cabbage in natural habitat of North Western Indian Himalayas. Pollination behavior in terms of peak activity, flowers processed per unit time, time spent per flower, and time spent in search of flowers are studied separately for both pollen and nectar foragers. Pollinator effectiveness as measured by seed set in flowers excluded from bee visitation, single bee visit, and unrestricted pollinator visits was 0.11. Studies on the impact of A. cerana bee pollination in cabbage seed production revealed an increase of 17.28% in siliqua per panicle, with 26.11% increase in seed yield. For assessing the requirement of A. cerana to pollinate one hectare of cabbage, flower availability and the speed with which the pollen and nectar foragers process the flowers are taken into consideration. A forager is estimated to pollinate 4,780 flowers a day, but cabbage flower requires 9.09 visits of A. cerana for optimum seed set. Thus, a maximum of 4,999 bee foragers or 8.33 colonies are needed to effectively pollinate 1 ha of cabbage. Though A. cerana is a good pollinator, our findings suggest that it is not an ideal pollinator of cabbage.

Evaluation of pesticide toxicity at their field recommended doses to honeybees, Apis cerana and A. mellifera through laboratory, semi-field and field studies.

A series of experiments were carried out to determine the acute toxicity of pesticides in the laboratory, toxicity through spray on flowering plants of mustard (Tier II evaluation) and field on both Apis cerana and A. mellifera bees. The overall mortality of honey bees through topical (direct contact) were found significantly higher than that of indirect filter paper contamination assays. Insecticides viz., chlorpyriphos, dichlorvos, malathion, profenofos, monocrotophos and deltamethrin when exposed directly or indirectly at their field recommended doses caused very high mortality up to 100% to both the bees at 48 HAT. The insecticides that caused less mortality through filter paper contamination viz., flubendiamide, methyl demeton, imidacloprid and thiamethoxam caused very high morality through direct exposure. Apart from all the fungicides tested, carbendazim, mancozeb, chlorothalonil and propiconazole, insecticides acetamiprid and endosulfan were found safer to both the bees either by direct or indirect exposures. Tier II evaluation by spray of pesticides at their field recommended doses on potted mustard plants showed monocrotophos as the highly toxic insecticide with 100% mortality even with 1h of exposure followed by thiamethoxam, dichlorvos, profenofos and chlorpyriphos which are not to be recommended for use in pollinator attractive flowering plants. Acetamiprid and endosulfan did not cause any repellent effect on honey bees in the field trials endorse the usage of acetamiprid against sucking pest in flowering plants.

Toxicity of diafenthiuron to honey bees in laboratory, semi-field and field conditions.

BACKGROUND: Cardamom, an important spice crop often attacked by many insect pests, is controlled mainly using synthetic insecticides. As honey bees play a vital role in pollination in cardamom, the impact of insecticides on honey bees needs to be explored to assess its safety. RESULTS: Risk assessment based on contact toxicity revealed diafenthiuron to be a non-selective insecticide to bees with a low selectivity ratio (the ratio between the LD(50) for beneficial and pest species). A dose of diafenthiuron that killed 90% of cardamom borer, Conogethes punctiferalis Guenee, was found to kill 100% of Indian bees. Based on the hazard ratio (the ratio between the field-recommended dose and the LD(50) for the beneficial), diafenthiuron was found to be slightly to moderately toxic to bees. Diafenthiuron, even at low concentrations of LC(1) (the concentration that killed 1% of bees), was found to affect the foraging and homing behaviour of Indian bees. Of bees fed with 30 microg mL(-1) of diafenthiuron, 40% were found missing on the third day after exposure. However, diafenthiuron did not affect bee visits to the cardamom fields. CONCLUSION: Diafenthiuron is more highly toxic to Apis cerana indica F. than to C. punctiferalis by contact, using selectivity ratio and probit substitution methods of risk assessment, but the hazard ratio revealed diafenthiuron to be a slightly to moderately toxic chemical. Diafenthiuron was found to affect the foraging and homing behaviour of bees at sublethal concentrations. Thus, sublethal effects are more relevant in risk assessment than lethal and acute effects.