Neil W. Miller

Toxicity of Spinosad in Protein Bait to Three Economically Important Tephritid Fruit Fly Species (Diptera: Tephritidae) and Their Parasitoids (Hymenoptera: Braconidae)

Abstract The feeding toxicity of the natural insecticide spinosad in Provesta protein bait was evaluated for three economically important fruit fly species, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann); the melon fly, Bactrocera cucurbitae Coquillett; and the oriental fruit fly, Bactrocera dorsalis Hendel. Both females and males were evaluated. Spinosad was remarkably similar in toxicity to all three fruit fly species. Male C. capitata (24 h LC50 values and 95% fiducial limits = 2.8 [2.60–3.0] mg/liter spinosad) were significantly, although only slightly more susceptible to spinosad than females (4.2 [3.8–4.6] mg/liter). Male (5.5 [4.7–6.6] mg/liter) and female (4.3 [3.7–4.9] mg/liter) B. cucurbitae were equally susceptible to spinosad. Female (3.3 [3.1–3.6] mg/liter) and male (3.1 [2.9–3.3] mg/liter) B. dorsalis also were equally susceptible to spinosad. Provesta bait containing spinosad also was evaluated against two parasitoids of tephritid fruit flies, Fopius arisanus (Sonan) and Pysttalia fletcheri (Silvestri). These parasitoids did not feed on the bait, so a contact toxicity test was conducted. Significant amounts of mortality were found only after exposure of parasitoids to spinosad-coated glass vials with concentrations ≥500 mg/liter spinosad. Parasitoids were less susceptible than fruit flies to such a degree that use of spinosad in bait spray should be compatible with these parasitoid species. Because the fruit flies tested in this study were so susceptible to spinosad, this product seems to be promising as a bait spray additive and a replacement for malathion for control of these species.

Attraction and feeding responses of Mediterranean fruit fly and a natural enemy to protein baits laced with two novel toxins, phloxine B and spinosada

Studies were conducted to determine attraction and feeding propensity of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), to different protein bait mixtures with and without the insecticides malathion, spinosad, and phloxine B. Protein baits were more attractive to females than to males. Protein‐starved females responded more than protein‐fed females. The type of protein (USB® yeast hydrolysate enzymatic, Mazoferm®E802, Nu‐Lure®Insect Bait, or Provesta® 621 autolyzed yeast extract) in the bait had a major influence on C. capitata attraction, which was strongest to fresh Provesta. Aged baits (four day‐old) were not as attractive as fresh baits. In feeding propensity studies, highest response was observed for USB protein. On the basis of attraction and feeding responses Provesta (attraction and feeding) and USB (feeding) outperformed the standard Nu‐Lure. Protein‐starved flies were much more likely to feed on protein compared to protein‐fed flies. For protein‐starved flies, a mixture of Provesta and malathion repelled fruit flies, compared to a mixture of Provesta and spinosad or phloxine B. This was not the case with protein–fed flies. The wasp Fopius arisanus (Sonan), one of C. capitatas primary natural enemies in Hawaii, would not consume protein baits. Our studies suggest that spinosad or phloxine B, with low contact toxicity, mixed with protein baits offers a more environmentally friendly choice for control of C. capitata and conservation of F. arisanus, whereby the nontarget effects of broad spectrum contact poisons such as malathion can be avoided. Presumably, due to greater selectivity with spinosad and phloxine B bait treatments, the host would be killed, but not the natural enemy.

Feeding and Foraging of Wild and Sterile Mediterranean Fruit Flies (Diptera: Tephritidae) in the Presence of Spinosad Bait

The sterile insect technique (SIT) is used to control wild Mediterranean fruit fly introductions in California and Florida in the U.S. In the past, bait sprays containing malathion proved invaluable in treating new outbreaks or large populations before the use of SIT. Recently, a spinosad protein bait spray, GF-120, has been developed as a possible alternative to malathion, the standard insecticide in protein bait sprays. In this study, protein-deficient and protein-fed Vienna-7 (sterile, mass-reared, “male-only” strain) flies and wild males and females were evaluated to determine the effectiveness of the GF-120 protein bait containing spinosad with respect to bait attraction, feeding, and toxicology. There were no effects of diet or fly type on feeding duration in small laboratory cages. Wild flies, however, registered more feeding events than Vienna-7 males. Flies that fed longer on fresh bait died faster. Protein-deficient flies were more active and found the bait more often than protein-fed flies. Data suggest that adding protein to the diet of SIT flies may decrease their response to baits, therefore, reduce mortality, and thus, allow the concurrent use of SIT and bait sprays in a management or eradication program.

HOW EFFECTIVE IS GF-120 FRUIT FLY BAIT SPRAY APPLIED TO BORDER AREA SORGHUM PLANTS FOR CONTROL OF MELON FLIES (DIPTERA: TEPHRITIDAE)?

Abstract Application of bait spray to non-host sorghum plants bordering host plants of melon flies, Bactrocera cucurbitae Coquillet, is a common practice for melon fly control in Hawaii. In a field study conducted in 2003 in Hawaii, we first asked whether GF-120 Fruit Fly bait spray applied to sorghum plants that bordered only two (opposite) sides of a patch of cucumbers was as effective in protecting cucumbers against melon flies as similar spray applied to sorghum plants that bordered all four sides of a cucumber patch. Second, we asked whether mature melon fly females carrying a high egg load but deprived of protein during the previous 24 h were more responsive to bait spray than mature females having continuous access to protein. Color-marked melon fly females were released outside of patches of sorghum-bordered cucumbers. We found no significant differences between two-sided and four-sided patches of sorghum or between protein-deprived (for 24 h) and protein-fed (continuously) mature females in percentages of released females that found cucumbers in bait-sprayed plots. Moreover, none of these percentages was significantly less than percentages of released females that found cucumbers in unsprayed plots, indicating an overall ineffectiveness of bait spray application. During the 24 h after alighting on cucumbers, released females that were captured alive on cucumbers and placed in cups with cucumbers laid on average almost as many eggs (insignificantly fewer) when taken from bait-sprayed plots as when taken from unsprayed plots. An overriding factor may have been the presence of just a narrow swath of sorghum (arising from a single row of plants), which may have permitted females easy access to cucumbers and masked potential differences among treatments. Bait spray applied to broader swaths of sorghum may be more effective.

Releases of Psyttalia fletcheri (Hymenoptera: Braconidae) and Sterile Flies to Suppress Melon Fly (Diptera: Tephritidae) in Hawaii

Abstract Ivy gourd, Coccinia grandis (L.) Voigt, patches throughout Kailua-Kona, Hawaii Island, HI, were identified as persistent sources of melon fly, Bactrocera cucurbitae (Coquillett). These patches had a low incidence of Psyttalia fletcheri (Silvestri), its major braconid parasitoid natural enemy in Hawaii, and were used to evaluate augmentative releases of P. fletcheri against melon fly. In field cage studies of releases, numbers of melon flies emerging from ivy gourd fruit placed inside treatment cages were reduced up to 21-fold, and numbers of parasitoids were increased 11-fold. In open field releases of P. fletcheri into ivy gourd patches, parasitization rates were increased 4.7 times in release plots compared with those in control plots. However, there was no significant reduction in emergence of melon flies from fruit. In subsequent cage tests with sterile melon flies and P. fletcheri, combinations of sterile flies and P. fletcheri produced the greatest reduction (9-fold) in melon fly emergence from zucchini, Cucurbita pepo L. Reductions obtained with sterile flies alone or in combination with parasitoids were significantly greater than those in the control, whereas those for parasitoids alone were not. Although these results suggest that the effects of sterile flies were greater than those for parasitoids, from a multitactic melon fly management strategy, sterile flies would complement the effects of P. fletcheri. Cost and sustainability of these nonchemical approaches will be examined further in an ongoing areawide pest management program for melon fly in Hawaii.

Effects of Aging and Dilution on Attraction and Toxicity of GF-120 Fruit Fly Bait Spray for Melon Fly Control in Hawaii

Abstract Attractiveness and toxicity of GF-120 Fruit Fly Bait (Dow AgroScience Indianapolis, IN) to melon flies, Bactrocera cucurbitae Coquillett, were examined to assess the effects of concentration and aging. We tested dilutions of 20, 40, and 80 ppm (AI) (spinosad) against water controls. The 80 and 40 ppm treatments were significantly more attractive than the 20 ppm and control treatments. Attraction was compared between baits aged for 2 and 24 h, fresh bait and water controls. Age had significant effects on both attractiveness and toxicity of GF-120. Baits aged for 2 h were 11 times less attractive to female melon flies than fresh bait. Mortality rates were reduced by 50% when GF-120 was subjected to rain. Our results suggest the need for frequent applications of Gf-120 to obtain maximum benefits, particularly in wet tropical climates.

State-Dependent Attractiveness of Protein Bait and Host Fruit Odor to Bactrocera cucurbitae (Diptera: Tephritidae) Females

Abstract We evaluated responses of protein-deprived and protein-fed mature (26–30-d-old) female melon flies, Bactrocera cucurbitae (Coquillett), to odor of host fruit and of proteinaceous baits by using 1 by 1 by 1-m cages containing nonhost plants. Protein-deprived and protein-fed females were attracted equally to odor of host fruit. For both types of females, odor of cucumber, Cucumis sativis L., and cantaloupe, Cucumis melo L., was more attractive than odor of tomato, Lycopersicon esculentum L. Odor of kabocha, Cucurbita maxima Duchesne, was more attractive than the odor of bittermelon, Momordica charantia L., but not more attractive than zucchini squash, Cucurbita pepo L. In choice tests, protein-fed females preferred cucumber odor over protein odor, whereas protein-deprived flies showed an almost identical response to the two odors. Our findings suggest that some feral host-seeking B. cucurbitae females that have fed recently on natural sources of protein and carry mature eggs might bypass proteinaceous baits, reducing the effectiveness of current approaches to melon fly management.

Oral and topical toxicity of fipronil to melon fly and oriental fruit fly (Diptera: Tephritidae).

The objective of this study was to develop oral and topical toxicity data for fipronil in Solulys protein bait to wild melon fly, Bactrocera Cucurbitae (Coquillett), and the oriental fruit fly, Bactrocera dorsalis (Hendel). For the oral study, both females and males were evaluated, whereas in the contact study only females were evaluated. The 24 h oral LC50 estimates for female B. Cucurbitae and B. dorsalis viere 113 and 108 mg ai/l, respectively. Female B. Cucurbitae were more susceptible than males, but female and male B. dorsalis were equally susceptible to fipronil after the oral route of exposure. Female B. Cucurbitae were significantly less susceptible to the fipronil-bait mixture after topical exposure compared with feeding exposure. However, female B. dorsalis were equally susceptible to either route of exposure. At the LC50, B. dorsalis was significantly more susceptible than B. Cucurbitae by the topical route of exposure. At the LC90, B. dorsalis was significantly more susceptible than B. Cucurbitae by both oral and topical routes of exposure. Results of this study indicate that there are differences in susceptibility between B. Cucurbitae and B. dorsalis to fipronil, especially at the LC90. Bactrocera dorsalis was more susceptible to fipronil than B. Cucurbitae by oral and topical routes of exposure. LC90 estimates were significantly lower than the 5,333 mg ai/l applied to Amulet Attract and Kill Stations for control of B. Cucurbitae and B. dorsalis.

Effect of Physiological State on Female Melon Fly (Diptera: Tephritidae) Attraction to Host and Food Odor in the Field

Abstract Foraging behavior of wild female melon fly, Bactrocera (Zeugodacus) cucurbitae Coquillett, a worldwide pest of economically important cucurbit crops, was examined through mark and recapture studies in both wild (Kona: dominated by the invasive weed ivy gourd, Coccinea grandis [L.] Voigt [Cucurbitaceae]), and cultivated (Kapoho: dominated by papaya, Carica papaya L. [Caricaceae] orchards) habitats on Hawaii Island. In particular, the extent to which wild melon flies and color-marked F2 females responded to cucumber odor and Solulys yeast hydrolysate laced with ammonium acetate (1%, wt/vol) according to sexual maturity stage and degree of protein hunger was documented. Kona results indicated that more wild and color-marked F2 females responded to cucumber (Cucumis sativus L. [Cucurbitaceae]) odor than to protein odor with the exception of captured wild flies without eggs, which responded similarly to protein bait and cucumber odor. Results with captured wild females and color-marked F2 females in Kapoho suggested a significant preference for cucumber odor over protein odor regardless of whether or not they had eggs in their ovaries with the exception of protein-deprived color-marked F2 females, which responded to both odors in equal numbers. Implications of these new findings based on wild melon flies in natural habitats are discussed with respect to integrated pest management control strategies with protein bait sprays used in Hawaii. The possibility of adding cucurbit volatiles to protein-based baits is discussed.