Combination of the Parasitoid Spalangia endius Walker and Chemical Pesticides for the Control of Zeugodacus cucurbitae (Coquillett)

<i>Spalangia endius</i> Walker, a pupal parasitoid of the alien invasive pest <i>Zeugodacus cucurbitae</i> (Coquillett), causes 33% host mortality. This study assessed whether combining <i>S. endius</i> with insecticides (abamectin, thiamethoxam, nitenpyram, emamectin benzoate, or beta-cypermethrin)-all effective against <i>Z. cucurbitae</i>-could enhance control efficacy. Among these, abamectin was the least toxic to adult <i>S. endius</i>. Surface contact treatments with 12 and 15 mg a.i./kg of abamectin did not significantly increase <i>S. endius</i> mortality. However, mixing 12 mg a.i./kg of abamectin into a honey solution to encourage ingestion decreased the survival, parasitism, and fecundity of <i>S. endius</i>. In olfactometer assays, <i>S. endius</i> adults avoided abamectin-treated host pupae, though prior exposure to abamectin mitigated this avoidance. The timing of abamectin soil application relative to host pupation and <i>S. endius</i> release affects host mortality. The most effective timing is spraying abamectin before host pupation (to expose <i>Z. cucurbitae</i> larvae) and then releasing <i>S. endius</i>. Field trials confirmed that combining abamectin (12 mg a.i./kg) with <i>S. endius</i> increased host mortality more than either treatment alone. In conclusion, abamectin (12 mg a.i./kg) is a suitable insecticide for combination with <i>S. endius</i> to control <i>Z. cucurbitae.</i> The application sequence should be spraying abamectin before hosts pupate and, only after that, releasing the parasitoid.