Insecticidal activity of photoactive dyes to American and migratory grasshoppers (Orthoptera : Acrididae)

Many photoactive dyes are relatively nontoxic to vertebrates despite their insecticidal properties. Several photoactive dyes known to be toric to some groups of insects were evaluated at various concentrations for toxicity to American and migratory grasshoppers in laboratory and field studies. Rose bengal and phloxine B were effective at inducing mortality of grasshoppers when applied at 2 and 5% to bran bait, though erythrosin B and uranine were ineffective. Partial replacement of phloxine with uranine in dye mixtures resulted in no significant loss of efficacy. Some indication of feeding inh ibition was observed at high dye concentrations, so minimum effective dosag es, probably 2%, are optimal. Phloxine B and rose bengal appeared to be sta ble upon exposure to sunlight, and able to withstand at least 24 h of sunli ght without significant degradation. Dyes such as phloxine B could be a via ble grasshopper control agent for small or medium-sized grasshopper species because mortality can be induced by consumption of a single flake dusted w ith 5% dye, and yet pose little hazard to vertebrates. Large species such a s American grasshopper must consume several flakes before mortality is indu ced.