Comparing injection, feeding and topical application methods for treatment of honeybees with octopamine

Entomologists have used a range of techniques to treat insects with neuroactive compounds, but it is not always clear whether different treatment methods are equally effective in delivering a compound to a target organ. Here, we used five different techniques to treat honeybees with H-3-octopamine (H-3-OA), and analysed the distribution of the H-3 radiolabelled compound within different tissues and how it changed over time. All treatment methods, including injection of the median ocellus, resulted in H-3-OA detection in all parts of the honeybee. Injection through the median ocellus was the most effective method for delivering H-3-OA to the brain. Topical application of H-3-OA dissolved in dimethylformamide (dMF) to the thorax was as effective as thoracic injections of H-3-OA in delivering H-3-OA to the brain, but topical applications to the abdomen were less so. Most of the H-3-OA applied topically remained associated with the cuticle and the tissues of the body segment to which it had been applied. For all treatment methods, H-3-OA was rapidly lost from the brain and head capsule, and accumulated in the abdomen. Our findings demonstrate the value of thoracic topical treatment with compounds dissolved in dMF as an effective non-invasive method for short-term, systemic pharmacological treatments. (c) 2007 Elsevier Ltd. All rights reserved.