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

Simple SummaryThe melon fly (Zeugodacus cucurbitae) is a pest that prefers to bore into and feed on cucurbitaceous crops and that pupates in the soil. The parasitoidSpalangia endiuscan burrow into the soil to attack melon fly pupae, but it only kills about 33% of them. Since insecticides are essential for controlling melon fly populations, we assessed how five commonly used insecticides affect the toxicity, survival, reproduction, choice-making behaviour, and parasitism ability ofS. endius. Our goal was to determine how to combine insecticides withS. endiusto more effectively control melon fly pupae. Through a series of laboratory and semi-field trials, we confirmed that abamectin is suitable for combined use withS. endius. However, we must be careful about the concentration and timing of abamectin application. The best approach is to spray abamectin on the soil surface before the melon flies pupate and then release the parasitoids.Spalangia endiusWalker, a pupal parasitoid of the alien invasive pestZeugodacus cucurbitae(Coquillett), causes 33% host mortality. This study assessed whether combiningS. endiuswith insecticides (abamectin, thiamethoxam, nitenpyram, emamectin benzoate, or beta-cypermethrin)—all effective againstZ. cucurbitae—could enhance control efficacy. Among these, abamectin was the least toxic to adultS. endius. Surface contact treatments with 12 and 15 mg a.i./kg of abamectin did not significantly increaseS. endiusmortality. However, mixing 12 mg a.i./kg of abamectin into a honey solution to encourage ingestion decreased the survival, parasitism, and fecundity ofS. endius. In olfactometer assays,S. endiusadults avoided abamectin-treated host pupae, though prior exposure to abamectin mitigated this avoidance. The timing of abamectin soil application relative to host pupation andS. endiusrelease affects host mortality. The most effective timing is spraying abamectin before host pupation (to exposeZ. cucurbitaelarvae) and then releasingS. endius. Field trials confirmed that combining abamectin (12 mg a.i./kg) withS. endiusincreased host mortality more than either treatment alone. In conclusion, abamectin (12 mg a.i./kg) is a suitable insecticide for combination withS. endiusto controlZ. cucurbitae.The application sequence should be spraying abamectin before hosts pupate and, only after that, releasing the parasitoid.