Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/24/2011
Publication Date: 4/11/2011
Citation: Wang, X., Johnson, M.W., Opp, S.B., Krugner, R., Daane, K.M. 2011. Honeydew and insecticide-bait as competing food resources for a fruit fly and common parasitoids. Entomologia Experimentalis et Applicata. p.128-137. Interpretive Summary: Several pest and beneficial insect species may feed on both honeydew (excreta) from scale insects and insecticidal baits used to control pests. In California olive orchards, the efficacy of insecticidal baits to control olive fruit fly may be reduced if flies prefer to feed on black scale honeydew than on its insecticidal-based bait (GF-120). The food searching behavior and survival of olive fruit fly and two parasitoids were evaluated in choice testes between black scale honeydew and GF-120, a spinosad-based bait. In food choice tests, honeydew and GF-120 bait were equally attractive to female flies, but male flies and parasitoids were more attracted to honeydew than GF-120 bait. Adults of the three insect species readily fed on honeydew, but the parasitoids rarely fed on GF-120 bait. A single meal of honeydew increased longevities for all insects tested. The results suggest that the presence of honeydew would benefit all three insects and may reduce the efficacy of GF-120 for fly control due to competition between honeydew and the fruit fly bait as the preferred food resource. Because black scale honeydew is the predominant natural source of sugars for flies in California’s olive orchards, control of black scale may help control olive fruit fly using GF-120.
Technical Abstract: Honeydew from phloem-feeding insects and fruit fly insecticidal baits may both serve as adult food resources for some insect species. In California olive orchards the black scale, Saissetia oleae (Olivier), is a common honeydew-producer, while spinosad-based fruit fly bait (GF-120) is used to control the olive fruit fly, Bactrocera oleae (Rossi). The adult foraging and survival of the olive fruit fly and two parasitoids in the olive agroecosystem: Scutellista caerulea (Fonscolombe), a parasitoid of black scale, and Psyttalia humilis (Silvestri), a larval parasitoid of the fruit fly, were evaluated using black scale honeydew and GF-120 as food resources. In food choice tests, female flies did not show a preference between GF-120 bait and honeydew, while male flies and both parasitoids preferred honeydew. Adults of the three insect species readily fed on honeydew, but the parasitoids never (P. humilis) or rarely (S. caerulea) fed on GF-120 bait (without spinosad). Olfactometer tests further confirmed that the tested parasitoids were not attracted to GF-120 bait. The presence of honeydew significantly reduced the fly’s mortality when both honeydew and GF-120 were provided, compared with GF-120 only. A single meal of honeydew increased longevities for all insects tested. The longevities of honeydew-fed insects were not significantly different from those feeding on clover honey, a more carbohydrate-rich food resource. The results suggest that the presence of honeydew would benefit all three insects and may reduce the efficacy of GF-120 for fly control due to competition between honeydew and the fruit fly bait as the preferred food resource.