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Concentration of the Systemic Gametocide, TD-1123, in Cotton Nectar, and Honeybee Response¹

The production of hybrid cotton (Gossypium hirsutum L.) seed requires both a system of sterilizing one parent in the crossing block and the effective use of a pollen vector. This paper reports results from studies in which a systemic gametocide was used to produce male-sterile flowers and also reports behavioral responses of honeybees (Apis mellifera L.) to the gametocide. Field and greenhouse tests were conducted during 1984 and 1985 to determine the quantity of the foliar-applied systemic gametocide, TD-1123, that was translocated to the floral and bracteal nectar of cotton (G. hirsutum L. and G. barbadense L.). Field observations and a laboratory bioassay evaluated honeybee response to TD-II23 in nectar or to TD-1123- laced sucrose solutions. The gametocide was fonnd in floral nectar in the field (<1-542 mg L^-1) (bracteal nectar not collected) and in both floral and bracteal nectar (11-151 mg L^-1) in the greenhouse studies. The highest concentrations of TD-1123 were found in the floral nectar of upland cotton sampled 1 day after spraying (542 mg L^-1). Honeybee consumption of 0.84 M sucrose solutions that included TD-I123 was not significantly increased at 50 mg L^-1 but significantly increased at 75 mg L^-1 of the gametocide. Floral visitation by foraging honeybees as measured in the field was not affected by the gametocide. We concluded that although the gametocide occurs in the nectar of treated cotton plants, it should not pose a threat to adequate pollination activity by the honeybee.

Key Words: Hybrid cotton • Pollination • Nectar physiology

² G.M.L., research plant physiologist, R.L.B., agricultural research technician, USDA-ARS, Carl Hayden Bee Research Center, 2000 East Allen Road, Tucson, AZ 85719; and J.O., graduate associate, Univ. of Arizona, Cotton Research Center, 4201 East Broadway, Phoenix, AZ.

Received for publication March 3, 1986.