Effects of Mediterranean Fruit Fly Malathion Bait Spray on the Longevity and Oviposition of Parasitoids of Linden and Tuliptree Aphids (Homoptera: Aphididae) KENT M. DAANE,' DONALD L. DAHLSTEN, ANDSTEVE H. DREIST ADT" Division of BiologicalControl, University of California, Berkeley, California 94720 Environ.Entomol. 19(4): 1130-1134 (1990) ABSTRACT The longevity of two primary aphid parasitoids, Aphidius liriodendrii Liu and Trioxys curvicaudus (MacKauer), was severely reduced when they were exposed in the laboratory to a malathion bait spray used to eradicate the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). The longevity of several hyperparasites of A. liriodendrii and T. curvicaudus also was reduced. Oviposition of A. liriodendrii was severely reduced on plants that received field applications of malathion bait spray. The parasitoids appeared neither attracted to nor repelled by the malathion bait. Pesticide contact occurred during apparently random searching by the parasitoids. As T. curvicaudus is reportedly responsible for the biological control of its aphid host, Eucallipterus tiliae (L.), malathion bait sprays used for Mediterranean fruit fly control may cause an increase in aphid populations by reducing the effectiveness of primary parasitoids. KEY WORDS Insecta, Aphidius liriodendrii, Trioxys curvicaudus, biological control NONTARGETIMPACTSTUDIESduring the 1980-198~~ Mediterranean fruit fly, Ceratitis capitata (Wiede- mann), eradication project in the San Francisco Bay area, California, substantially increased our knowledge of the ecological effects of malathion bait sprays (Dahlsten et al. 1985). Although it had been asserted that multiple aerial applications of 68.04 gm (2.4 oz) of 91% active ingredient mala·· thion per acre with 272.18 gm (9.6 oz) of Staley's protein bait "would not significantly affect non·· target insect populations" (USDA 1981), this was not the case. Malathion bait spray interference with natural enemy activity led to outbreaks of phytophagous insects in suburban gardens (Troetschler 1983). Saissetia oleae (Olivier) and other scales increased on citrus and olives (Ehler & Endicott 1984), and honeybee mortality increased (Gary & Mussen 1984). An endemic gall midge, Rhopalomyia cal.. ifornica Felt, normally occurring at low densities, increased to such an extent that its host plant, Bac .. charis pilularis DC, in some cases was defoliated (Ehler et al. 1984). Hymenopterous parasitoids of two scales on ornamental ice plants, Carpobrotus spp., were suppressed, as were in some instances the scales (Hagen et al. 1985). Although phytoph .. agous insects other than the Mediterranean fruit fly were killed, natural enemies were generally more severely affected (see review by Dreistadt & Dahl·· sten 1986). -------------------.- I Currentaddress:KearneyAgricultural Center, 9240 So.Riv· erbendAvenue,Parlier,Calif.93648. •Currentaddress:IPMEducationandPublications, University of California, Davis.Calif. 95616. Laboratory studies simulating the effects of the aerial spraying found that the malathion bait spray has severe adverse effects on the polyphagous pred- ators Hippodamia convergens Guerin-Mimeville (Granett & Horton 1982) and Chrysoperla carnea (Stephens) (M. A. Hoy, personal communication). Bait sprays had a lethal effect on the parasitoid Aphytis holoxanthus De Bach as an adult or when exposed before or during emergence to lethal levels present in the host scale cover (Cohen et al. 1987). Sublethal adverse effects also were reported on sev- eral other parasitic Hymenoptera after contact with bait sprays (Hoy & Dahlsten 1984). The studies reported here were part of an at- tempt to document any positive or negative effects associated with the aerial application of malathion bait sprays during the 1980-1982 Mediterranean fruit fly eradication efforts in the San Francisco Bay area. Effects on natural enemies, parasites, and predators of insects .on urban trees were the pri- mary focus. The laboratory studies presented in our paper investigated the effect of malathion bait spray on the parasitoids of aphids on two trees commonly planted along San Francisco Bay area streets. Materials and Methods Longevity Study. We evaluated the effect of malathion bait (68.04 gm [2.4 oz] 91% active in- gredient malathion with 272.18 gm [9.6 fluid oz] Staley's protein bait) on the longevity of the para- sitoid complex of two common street tree Aphid- idae: Illinoia liriodendri (Monell), a monophagous aphid of the tuliptree, Liriodendron tulipifera L.; 0046-225X/90/1130-1134$02.00/0 © 1990 Entomological Societyof America