Prospects of monosodium glutamate use for enhancement of spinosad toxicity against codling moth neonates

Abstract

It was demonstrated that neonates of the codling moth,Cydia pomonella (L.), feed on ‘Red Delicious’ apple leaves and successfully molt to the second instar. Next, using a non-choice bioassay, we targeted codling moth neonates feeding on apple leaves, with standard concentrations of a culinary taste enhancer, monosodium glutamate (MSG), and Success®, which contains 22.8% spinosad as its active ingredient. The addition of 25 ppm MSG increased feeding by 20–30%. Stimulatory properties of MSG were preserved in the presence of 12.5 ppm Success, and mortality from a 12.5 ppm Success + 25 ppm MSG combination increased by factors of 3.1–1.6 compared with Success alone. In a field experiment without rain, MSG maintained its stimulatory properties for 24 h, increasing feeding by 37%. Consistently, without rain, MSG increased the toxicity of Success in the field by a factor of × 3.5. However, the stimulatory properties of MSG dropped to 19% with 4.3 mm of rain, and to zero with 9.6 mm of rain. Increased Success toxicity by MSG was reduced to × 1.6 with 4.3 mm of rain, and dropped to zero after 9.6 mm of rain. It is concluded that MSG seems to be a promising feeding stimulant, enhancing the toxic properties of Success which itself is a good candidate for codling moth control. However, field persistence of MSG needs to be improved, either by formulating the Success + MSG combination into some field-stable matrix, or by employing a sparingly water-soluble substance mimicking MSG’s action as a feeding stimulant in codling moth neonates.