Evaluation of Protein Bait Laced with Various Insecticides on the Queensland Fruit Fly (Diptera: Tephritidae): Attraction, Feeding, Mortality and Bait Persistence Kiran Mahat1,* and Richard A.I. Drew2 1 National Plant Protection Centre, Department of Agriculture, Thimphu, Bhutan 2 International Centre for the Management of Pest Fruit Flies, Griffith University, Australia *Corresponding author:
[email protected] Abstract The use of malathion in fruit fly protein bait sprays has raised serious concerns due to its adverse effects on non-target organisms. This has necessitated the evaluation of novel reduced-risk compounds. This study evaluated the effects of spinosad, fipronil, malathion and chlorpyrifos mixed with fruit fly protein bait (Mauri Pinnacle protein®) on attraction, feeding and mortality of the Queensland fruit fly, Bactrocera tryoni (Froggatt). The effects of outdoor weathering of these mixtures on fly mortality were also determined. In field-cage experiment, proteinstarved flies showed the same level of attraction to baits containing spinosad, fipronil, malathion, chlorpyrifos and protein alone used as control. Female proteinstarved flies were deterred from feeding on baits containing malathion and chlorpyrifos compared to baits containing spinosad, fipronil and protein alone. Baits containing malathion and chlorpyrifos caused higher fly mortality and rapid fly knock down than spinosad and fipronil. However, spinosad acted slowly and caused an increase in fly mortality over time, causing up to 90% fly mortality after 72-h. Baits containing malathion and chlorpyrifos, applied on citrus leaves and weathered outdoors, had longer residual effectiveness in killing flies than spinosad and fipronil. Residual effectiveness of the spinosad bait mixture waned significantly after 3 days of outdoor weathering. Results suggest that spinosad and fipronil can be potential alternatives for malathion in protein bait sprays. Keywords: Bactrocera tryoni, protein bait sprays, malathion INTRODUCTION Fruit flies require protein in their diet for development and to achieve sexual maturity. Food-based attractants based on protein have been successfully employed as olfactory attractants in controlling, monitoring and detecting a number of tephritid pest species (Jang and Light, 1996). From the late 1950’s malathion, an organophosphate insecticide, has been the most commonly used toxicant in protein bait spray formulations deployed in fruit fly control and eradication programs and still remains the most commonly used toxicant (Roessler, 1989). However, because of its widespread use in many fruit fly control and eradication programs the use of malathion in protein bait sprays has raised serious concerns mainly due to potential adverse effects on non-target organisms, human health and the environment. Several field and laboratory studies have documented the detrimental effects of malathion bait sprays on non-target or beneficial organisms (Troetschler, 1983; Gary and Mussen, 1984; Cohen et al., 1988; Daane et al., 1990; Hoelmer and Dahlsten, 1993; Messing et al., 1995). Use of malathion as cover sprays over large areas has also been attributed to the development of resistance in the Oriental fruit fly, Bactrocera dorsalis (Hendel) in Tawain (Hsu and Feng, 2000) and the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) in Spain (Magana et al., 2007). Concerns associated with the use of malathion in fruit fly control treatments have evoked numerous empirical studies evaluating various toxicants, with an objective to replace its use with reduced-risk insecticides. One such compound that has been evaluated several times for many tephritid pest species is spinosad. Spinosad is a bacterially derived insect control agent consisting Proc. XIIth Intl. Citrus Congress Eds.: B. Sabater-Muñoz et al. Acta Hort. 1065, ISHS 2015
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of two active compounds, spinosyns A and D which are fermentation products produced by the actinomycete Saccharopolyspora spinosa Mertz and Yao, a bacterial organism isolated from soil (Crouse et al., 2001; Cleveland et al., 2002). Spinosad has been reviewed as one of the most judicious insecticides available for use in pest management systems involving predator populations (Williams et al., 2003). In spite of the worldwide attention to evaluating and replacing reduced-risk compound for use in protein bait sprays, no such work has so far been documented for the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), classified as one of the most destructive and costly horticultural pests in Australia (Sutherst et al., 2000). Identification of alternative material and integration of new generation insecticides into protein-bait technology for B. tryoni have been pointed out to be areas requiring urgent research (Clarke et al., 2011). In addition, recent reviews carried out by the Australian Pesticides and Veterinary Medicines Authority pose a possible restriction on the use of two important organophosphorus insecticides, fenthion and dimethoate, commonly used in fruit fly control (PHA, 2008). This necessitates the need to test and identify alternative toxicant for controlling B. tryoni. This study investigates the effects of malathion, chlorpyrifos, fipronil and spinosad mixed in fruit fly protein bait on attraction, feeding and mortality of the Queensland fruit fly. In addition, it evaluates the effects of weathering of these protein bait-insecticide mixtures on the mortality of B. tryoni. MATERIALS AND METHODS Adult Flies and Protein Bait Insecticides Mixtures New generations of adult B. tryoni, to be used for the experiments, were produced from a laboratory colony maintained for 20 generations at Griffith University (Nathan campus, Brisbane, Australia). The rearing techniques were adopted from those described by Heather and Corcoran (1985). Fruit fly colonies were held in the laboratory at 25±2°C, with a relative humidity of 65±5%, and a photoperiod of 12:12 (L:D). Flies tested in the experiments were all deprived of protein and were tested when they were between 10 to 12 days after eclosion from the puparia. Malathion (Amgrow, 500 g/L EC), Chlorpyrifos (Superway, 50 g/L EC) Fipronil (Reagent, 800WP) Spinosad (Success, 10 g/L EC) insecticides were mixed into Pinnacle Protein Insect Lure (420 g/L protein) (Mauri Yeast Australia Pty Limited, Toowoomba, Australia) at 0.2, 0.2, 0.005, 0.02% active ingredient respectively. Each insecticide: Pinnacle protein mixture was diluted at a rate of 50 ml per 1 L water. Protein alone was used as the control. Experiment 1: Field Cage Attraction The study was carried out in a lychee (Litchi chinensis Sonn.) orchard in Shailer Park (Logan city, Queensland, Australia). Four evenly spaced nylon screen field cages (4×4×2.5 m) enclosing one non-fruiting lychee tree were used. In each cage, five Steiner traps each with a different test solution (30 ml of each mixture or the control in a 100 ml glass beaker), were randomly suspended in one of the five positions around the perimeter of the canopy with a flexible copper wire. To prevent the escape of attracted flies, the openings of the traps were fitted with cones made from 110 mm filter paper. When all traps were in place around the tree, approximately 3000 protein deprived 10-12 d-old adult B. tryoni were released into the field cage. The traps were rotated in a clockwise direction every 30 min to avoid any positional effect. One experiment lasted for two and half hours and ended when each trap occupied all five positions around the tree. The flies were collected at the end of the experiment and the number of flies attracted to each treatment recorded for each experiment day. In one experimental day four replicates were run for each treatment, and after four separate experimental days a total of sixteen replicates were carried out for each of the five treatments. The experiment was carried out between 0900 and 1130 h. The total numbers of B. tryoni captured in the Steiner type fruit fly traps for each field experiment day was log (x+1) transformed and were subjected
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to a repeated-measures analysis of variance. Sampling days were taken as repeated measures. Experiment 2: Laboratory Feeding Study A no choice feeding test was conducted in the laboratory under controlled conditions (24±2°C) in single aluminium framed, nylon screened cages (30×30×30 cm). In order to avoid mixing of chemicals cues, the feeding test for each treatment was conducted in a separate isolated cage. From each pre-mixed treatments solution, 0.5 ml was placed on a 1.5×0.5 cm sponge (Wettex®, Freudenberg household products, Victoria, Australia). A single female fly was gently placed within 2cm of the sponge. Each fly was allowed for 300 seconds to feed on the insecticide mixture. Feeding was defined as actual contact of the labellum with the test solution and when feeding commenced the total amount of time spent feeding was recorded with a stopwatch. Each fly was tested only once and discarded. Flies landing on the sponge and staying for
