Consumption of Sugars by Anastrepha suspensa (Diptera ... - BioOne

ARTHROPOD BIOLOGY

Consumption of Sugars by Anastrepha suspensa (Diptera: Tephritidae) H. N. NIGG,1,2 R. A. SCHUMANN,1 R. J. STUART,1 E. ETXEBERRIA,3 J. J. YANG,1

AND

S. FRASER4

University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850

Ann. Entomol. Soc. Am. 99(6): 1139Ð1145 (2006)

ABSTRACT We were interested in determining the feeding response of the Caribbean fruit ßy, Anastrepha suspensa (Loew) (Diptera: Tephritidae), to various sugar concentrations to develop an improved bait for adults. We compared the consumption of 0.01Ð1.00 M concentrations of glucose, fructose, rafÞnose, and sucrose in no-choice tests for 24-h- and 6-d-old male and female ßies. Sucrose was the most consumed sugar or within the most consumed group of sugars at 0.02Ð 0.20 M concentrations. There were no differences in consumption among sugars at 0.01, 0.40, and 1.00 M. Consumption generally increased with increasing sugar concentration except that sucrose consumption peaked at 0.20 M. Twenty-four-hour-old females consumed less fructose than other sugars; 24-h-old males consumed more sucrose than fructose or rafÞnose with an intermediate response to glucose. Females in the 6-d-old group consumed more sucrose than the other three sugars, whereas 6-d-old males exhibited no difference in consumption among sugars. In choice tests, ßies consumed more sugar solution than water, but the difference between 0.20 M fructose and water was not signiÞcant for 24-h-old males or females. In choice tests between 0.20 M fructose and 0.20 M sucrose, both 24-h- and 6-d-old females showed a preference for fructose. Males of both age classes showed no preference. These results indicate that the responses of ßies to different sugars can vary by sugar, gender, and age. KEY WORDS bait design, bait station, Caribbean fruit ßy

The Tephritidae contains many economic pests worldwide (Hendrichs 1996, Mumford 2000). The Caribbean fruit ßy, Anastrepha suspensa (Lowe), is a pest of many tropical and subtropical fruits of central and southern Florida, with at least 84 hosts in 23 plant families (Swanson and Baranowski 1972). It was discovered in 1931 in Key West, FL, with a later introduction in 1965 into the Miami area where ⬎14,000 A. suspensa were trapped, and A. suspensa has been an economic problem for Florida ever since (Weems 1965, 1966). For Florida citrus, A. suspensa has been particularly costly (Nigg et al. 2004a). Current control technology uses a bait plus pesticide and trapping for ßy-free zones (Simpson 1993, Nigg et al. 2004a). An assumption of bait/pesticide technology is that ßies consume the pesticide-laden bait and subsequently die. To test this premise, we observed ⬇10,000 adult A. suspensa in the greenhouse with malathion/NuLure (Nu-Lure, an acid hydrolysate of corn, Zea mays L., protein was obtained from Miller Chemical and Fer1 Department of Entomology and Nematology, University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850. 2 Corresponding author, e-mail: hnn@uß.edu. 3 Department of Horticultural Sciences, University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850. 4 Florida Department Agricultural and Consumer Services, Division of Plant Industry, 1911 S.W. l34th St., Gainesville, FL 32608.

tilizer Corp., Hanover, PA) as the only presented food choice. Flies were neither attracted to nor fed upon the bait. We also knew that A. suspensa could be controlled by 2,000 times less malathion than the present bait/malathion mixture (Nigg et al. 1994, 2004c). We then postulated that by reducing pesticide quantity, we could optimize the malathion/NuLure combination, achieving management with reduced environmental risks. That is, we could reduce pesticide quantity, thus increasing intake and speciÞcity of the bait for A. suspensa (Nigg et al. 2004c). This hypothesis is based on the premise that these ßies would consume according to their nutritional needs (Lipke and Fraenkel 1956, Waldbauer 1968, Slansky 1982, Waldbauer and Friedman 1991) or maximum energy uptake (May 1985, Pivnic and McNeil 1985), or phenotypic plasticity (Nylin and Gotthard 1998, Grant 2001). That is, consumption might increase with decreasing sugar content or that sucrose might be preferred due to sucrose in the laboratory diet. Designing baits according to nutritional needs would seem to be a rational approach for insects in general. Tephritid ßies require carbohydrate minerals, amino acids (proteins), vitamins, and water (Friend 1958, House 1962, Scriber and Slansky 1981, Tsiropoulos 1992, Aluja 1994, Nigg et al. 1994). All insects require dietary sterols and some fatty acids (Canavoso et al. 2001). In particular, we know that A. suspensa

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adults require carbohydrate and water for survival and protein for egg development (Nigg et al. 1994, 2004c). Our initial studies developed a technique to measure individual ßy consumption (Nigg et al. 2004b) and suggested that glucose, fructose, sucrose, and rafÞnose would be candidates for further study to improve the consumption of A. suspensa baits (Nigg et al. 2004c). The purpose of these experiments was to determine A. suspensa’s preference for individual sugars and the maximally consumed concentration of glucose, fructose, rafÞnose, and sucrose.

Materials and Methods Anastrepha suspensa pupae were received weekly by overnight courier from the sterile ßy rearing facility in Gainesville, FL. Flies were fertile. Flies were held at 23.0 ⫾ 1.5⬚C under a photoperiod of 12:12 (L:D) h (0730 Ð1930 hours). Adults were allowed to emerge into a 30- by 30- by 30-cm cage (Bioquip, Rancho Dominguez, CA). Once emergence began, pupae were removed to an empty cage, emergence was allowed to continue for 12 h, and the remaining pupae were discarded. Before all experiments, active ßies with normal wings were grasped by one wing and placed into 950-ml translucent plastic containers (Þve males and Þve females per container). Adults were used for experiments at 1- to 2 d old (termed 24-h sexually immature) and 6- to 7 d old (termed 6-d reproductive). Flies were starved for 24 h before a J-tube presentation of solutions. Flies were allowed to feed from J-tubes for 45 min, the solution was removed from the J-tubes, the J-tubes were removed, and the ßies were placed in a ⫺17⬚C freezer for ⬇1 h. Consumption was quantiÞed according to Nigg et al. (2004c). Brießy, individual ßies were extracted in 1.5 ml of 0.1 M NaOH, the extracts were Þltered, and consumption was quantiÞed spectrophotometrically. Fluorescein (491 nm) and cresol red (573 nm) at 0.1% were used as the dyes for these experiments and were measured with a Shimadzu UV2401PC spectrophotometer (Shimadzu Corporation, Kyoto, Japan). A daily standard curve was used for quantiÞcation. DGlucose, D-fructose, sucrose, and rafÞnose were obtained from Sigma-Aldrich (St. Louis, MO) and were labeled as 99%⫹ pure. The mean quantity consumed by Þve males or the mean quantity consumed by Þve females was one replicate. There were Þve replicates of each experiment unless stated otherwise. A preliminary experiment was conducted to determine whether the dyes used to quantify consumption affected consumption. Flies were presented with two J-tubes both containing 0.20 M sucrose. One J-tube contained 0.1% ßuorescein, and the other J-tube contained 0.1% cresol red. Flies were removed and processed for consumption quantiÞcation at 45, 90, and 180 min. The assumption was that the consumption from the two tubes would be equal (not statistically different) if the dyes had no effect on consumption. There were 10 replicates of this experiment performed on the same day.

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We conducted a second preliminary experiment to determine whether the number of ßies per container affected consumption by an individual ßy. We used 1, 2, 4, 8, and 16 males and 1, 2, 4, 8, and 16 females in the same container. That is, containers held 2, 4, 8, 16, and 32 total ßies. Flies were presented with one J-tube containing 0.20 M sucrose ⫹ 0.1% ßuorescein. No-Choice Assessment. This experimental design presented a single J-tube to 24-h and 6-d ßies. Sugars were dissolved in glass-distilled, deionized water (DDI) at concentrations of 0.0, 0.01, 0.02, 0.04, 0.08, 0.1, 0.20, 0.4, and 1.0 M plus 0.1% ßuorescein. There were three replicates for each concentration level. Choice Assessments. We offered ßies a choice of water versus either 0.20 M fructose, 0.20 M glucose, 0.20 M sucrose, or 0.20 M rafÞnose solution. In a separate experiment, we gave ßies a choice of 0.20 M fructose versus 0.20 M sucrose, 0.20 M sucrose versus water, or 0.20 M fructose versus water. One solution contained 0.1% ßuorescein (generally water) and the other contained 0.1% cresol red (generally sugar). By analyzing each extract at 491 nm and also at 573 nm, we determined the quantity consumed from each solution by an individual ßy. For all experiments, only the ßies that fed were included in consumption calculations. Statistical Analyses. Preliminary analysis indicated signiÞcant differences among the week-to-week controls (i.e., water blank) run for each replicate (statistics not shown). Consequently, the amount consumed in the control was subtracted from the amount consumed at each concentration for each replicate with the provision that no amount was reduced below zero. The consumption values adjusted in this manner were then analyzed using Þve-factor analysis of variance (ANOVA) (PROC GLM, SAS Institute 2001) in which there were four levels for sugar (fructose, glucose, rafÞnose, and sucrose), two levels for sex (male and female), two levels for age (24 h and 6 d), eight levels for concentration (0.01, 0.02, 0.04, 0.08, 0.1, 0.20, 0.4, and 1.0 M), and three levels for replicate. Replicate was used as a blocking factor. Comparison of means used LSMEANS (SAS Institute 2001). Choice experiments were analyzed using three-factor ANOVA (PROC GLM, SAS Institute 2001) in which there were two levels for solution (variable among experiments), two levels for sex (male and female), and two levels for age (24 h and 6 d). Comparison of means used LSMEANS (SAS Institute 2001). Results In comparing consumption of 0.20 M sucrose with ßuorescein versus 0.20 M sucrose with cresol red, there were no statistical differences at 45 and 90 min. However, the 24-h males and females consumed more 0.20 M sucrose with ßuorescein than 0.20 M sucrose with cresol red at 180 min (data not shown). For the preliminary experiment on the number of ßies per container, the percentage of feeding ranged from 80 to 100, and the amount consumed per ßy ranged from 2.5

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Fig. 1. Results of the no-choice experiment indicating the two-way interaction between sugar and concentration in determining the amount consumed (mean ⫹ SE) by ßies and showing comparisons among sugars within concentrations (A) and comparisons among concentrations within sugars (B). Analysis involved a Þve-factor ANOVA with mean separation by using LSMEANS. Bars with common letters were not signiÞcantly different at the P ⫽ 0.05 level within their respective groups.

to 3.5 ␮l for males and from 2.0 to 5.5 ␮l for females. There were no differences in amount consumed per ßy by age, sex, or number of ßies per cage, except that with one female per cage there was less consumption by that female. No-Choice Experiments. The ANOVA indicated a highly signiÞcant result (F ⫽ 2.45; df ⫽ 129, 380; P ⬍ 0.0001). The main effects for age, sugar, and concentration were highly signiÞcant (age, F ⫽ 24.47; df ⫽ 1, 380; P ⬍ 0.0001; sugar, F ⫽ 13.60; df ⫽ 3, 380; P ⬍ 0.0001; and concentration, F ⫽ 11.08; df ⫽ 7, 380; P ⬍ 0.0001), but the main effects for sex and block were not (sex, F ⫽ 2.26; df ⫽ 1, 380; P ⫽ 0.1339; and block, F ⫽ 2.26; df ⫽ 2, 380; P ⫽ 0.1064). The two-way interactions between sugar and sex, and between sugar and concentration were signiÞcant (sugar ⫻ sex, F ⫽ 3.25; df ⫽ 3, 380; P ⫽ 0.0224; and sugar ⫻ concentration, F ⫽ 1.98; df ⫽ 21, 380; P ⫽ 0.0078), and the three-way interaction between sugar, sex, and age was highly signiÞcant (F ⫽ 9.28; df ⫽ 3, 380; P ⬍ 0.0001). None of the other interactions was signiÞcant. The two-way interaction between sugar and concentration is illustrated in Fig. 1 and shows signiÞcant differences in the feeding responses of ßies to various sugars at all concentrations between 0.02 and 0.20 M (Fig. 1A). No preference was observed at 0.01, 0.40, or 1.00 M. The preference of ßies varied among concentrations of each sugar and generally increased with

increasing concentration except for sucrose, where the amount consumed peaked at 0.20 M and was signiÞcantly lower at concentrations above and below this level (Fig. 1B). Sucrose was either the most preferred sugar or within the most preferred group of sugars at all of these concentrations (Fig. 1A). The three-way interaction between sugar, sex, and age is illustrated in Fig. 2. Similar to our previous data (Nigg et al. 1995), 24-h males responded more strongly to sucrose than 6-d males. There was no difference in the response of 24-h and 6-d males to any of the other sugars (Fig. 2A). Six-day females showed a stronger response to sucrose; 24-h females responded more to the other three sugars (Fig. 2A). Twenty-four-hour females consumed more rafÞnose than 24-h males, but 24-h males and females did not differ in their responses to the other three sugars (Fig. 2A). Six-day males and females differed in their responses to every sugar except rafÞnose. Six-day males consumed more fructose and glucose; females consumed more sucrose (Fig. 2A). Six-day females showed a clear preference for sucrose over glucose, fructose, and rafÞnose (Fig. 2B). Six-day males exhibited no preference among sugars (Fig. 2B). Twenty-four-hour females preferred all other sugars over fructose, but they showed no preference among the other sugars. Twenty-four-hour males preferred sucrose over fructose and rafÞnose (Fig. 2B).

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Fig. 2. Results of the no-choice experiment indicating the three-way interaction between sugar, sex, and age in determining the amount consumed (mean ⫹ SE) by ßies and showing comparisons among sex and age groups within sugars (A) and comparisons among sugars within sex and age groups (B). Analysis involved a Þve-factor ANOVA with mean separation by using LSMEANS. Bars with common letters were not signiÞcantly different at the P ⫽ 0.05 level within their respective groups.

Choice Experiments. There were two J-tubes presented to each cage (replicate) in these experiments, each containing a different dye. Again, this allowed us to quantify individual ßy consumption from two sources in the same cage. Flies that did not feed (generally ⬍10% of the ßies observed) were not included in these analyses. The ANOVA for fructose and water produced a highly signiÞcant result (F ⫽ 6.87; df ⫽ 7, 35; P ⬍ 0.0001). The main effects for sex and age were not signiÞcant (sex, F ⫽ 2.90; df ⫽ 1, 35; P ⫽ 0.0997; and age, F ⫽ 1.54; df ⫽ 1, 35; P ⫽ 0.2249), but the main effect of solution was signiÞcant (F ⫽ 35.92; df ⫽ 1, 35; P ⬍ 0.0001). None of the interactions was signiÞcant. All categories of ßies showed some degree of preference for fructose over water, 24-h males and females and 6-d males in particular (Fig. 3A). The ANOVA for sucrose and water produced a highly signiÞcant result (F ⫽ 10.18; df ⫽ 7, 35; P ⬍ 0.0001). The main effect for sex was not signiÞcant (F ⫽ 0.14; df ⫽ 1, 35; P ⫽ 0.7075), but the main effects for age and solution were signiÞcant (age, F ⫽ 17.57; df ⫽ 1, 35; P ⫽ 0.0003; and solution, F ⫽ 40.14; df ⫽ 1, 35; P ⬍ 0.0001), and there were signiÞcant interactions between solution and sex (F ⫽ 5.68; df ⫽ 1, 35; P ⫽ 0.0242) and between solution, sex, and age (F ⫽ 6.74; df ⫽ 1, 35; P ⫽ 0.0148). A preference for sucrose over water was exhibited by 24-h males and 6-d females, but there was no signiÞcant difference for 6-d males and

Fig. 3. Summary of the results of choice experiments that compared the preference of ßies for various sugars versus water as indicated by amount consumed (mean ⫹ SE). Statistical comparisons were by ANOVA and LSMEANS: ns, P ⬎ 0.05; *, P ⬍ 0.05; **, P ⬍ 0.01; and ***, P ⬍ 0.001.

24-h females (Fig. 3B). These results were similar to previous data (Nigg et al. 1995). The overall ANOVA for glucose and water was highly signiÞcant (F ⫽ 3.92; df ⫽ 7, 39; P ⫽ 0.0034). The main effects for sex and age were not signiÞcant (sex, F ⫽ 0.65; df ⫽ 1, 39; P ⫽ 0.4260; and age, F ⫽ 1.41; df ⫽ 1, 39; P ⫽ 0.2430), but the main effect for solution was signiÞcant (F ⫽ 16.89; df ⫽ 1, 39; P ⫽ 0.0003); none of the interactions was signiÞcant. All categories of ßies showed some degree of preference for glucose over water (Fig. 3C). The ANOVA for rafÞnose and water produced a highly signiÞcant result (F ⫽ 5.72; df ⫽ 7, 37; P ⫽ 0.0003). The main effects for sex and age were not signiÞcant (sex, F ⫽ 0.46; df ⫽ 1, 37; P ⫽ 0.5019; and age, F ⫽ 0.79; df ⫽ 1, 37; P ⫽ 0.3822), but the main effect for solution was signiÞcant (F ⫽ 35.24; df ⫽ 1, 37; P ⬍ 0.0001). None of the interactions was significant. All categories of ßies showed some degree of preference for rafÞnose over water (Fig. 3D).

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niÞcant. Sucrose was preferred over water, and females showed a stronger sucrose preference than males (Fig. 4B). The ANOVA for fructose and sucrose produced a signiÞcant result (F ⫽ 2.40; df ⫽ 7, 37; P ⫽ 0.0450). The main effects for sex and age were not signiÞcant (sex, F ⫽ 1.48; df ⫽ 1, 37; P ⫽ 0.2327; and age, F ⫽ 1.94; df ⫽ 1, 37; P ⫽ 0.1740), but the main effect for solution was signiÞcant (F ⫽ 6.02; df ⫽ 1, 37; P ⫽ 0.0202) and the interaction between sugar and sex was signiÞcant (F ⫽ 7.37; df ⫽ 1, 37; P ⫽ 0.0109). Females preferred fructose over sucrose, whereas males showed no preference (Fig. 4C). Discussion

Fig. 4. Summary of the results of choice experiments that compared the preference of ßies for fructose or sucrose, either versus water (A and B) or when both were presented (C) as indicated by amount consumed (mean ⫹ SE). Statistical comparisons were by ANOVA and LSMEANS: ns, P ⬎ 0.05; *, P ⬍ 0.05; **, P ⬍ 0.01; and ***, P ⬍ 0.001.

In the choice experiments that examined the response of ßies to fructose versus water and sucrose versus water only, one or two ßies did not feed, and only a few ßies fed only on fructose or only on sucrose. For the fructose versus sucrose choice comparison, 92% of 24-h males and 60% of 24-h females fed on both sucrose and fructose. For 6-d ßies, 100% of males and 72% of females fed on both sucrose and fructose; 20% of 6-d females fed on sucrose only. The ANOVA for fructose and water produced a highly signiÞcant result (F ⫽ 6.10; df ⫽ 7, 37; P ⫽ 0.0002). The main effects for sex and age were not signiÞcant (sex, F ⫽ 1.21; df ⫽ 1, 37; P ⫽ 0.2809; and age, F ⫽ 1.27; df ⫽ 1; 37; P ⫽ 0.2679), but the main effect for solution was signiÞcant (F ⫽ 1510; df ⫽ 1, 37; P ⫽ 0.0005) and the interaction between solution and age was signiÞcant (F ⫽ 23.69; df ⫽ 1, 37; P ⬍ 0.0001). Fructose was preferred over water by 6-d ßies, but there was no signiÞcant difference for 24-h ßies (Fig. 4A). The ANOVA for sucrose and water produced a highly signiÞcant result (F ⫽ 10.89; df ⫽ 7, 39; P ⬍ 0.0001). The main effect for age was not signiÞcant (age, F ⫽ 1.32; df ⫽ 1, 39; P ⫽ 0.2598), but the main effects for sex and solution were signiÞcant (sex, F ⫽ 4.82; df ⫽ 1, 39; P ⫽ 0.0354; and solution, F ⫽ 65.66; df ⫽ 1, 39; P ⬍ 0.0001). None of the interactions was sig-

The objective of the choice and no-choice experiments presented here was to determine the maximally consumed concentration of the preferred sugar for A. suspensa. The complexity of the responses of male and female ßies at 24 h and 6 d of age suggests that relatively high concentrations of any of the four sugars tested could enhance adult baits. On the basis of nochoice tests, 0.20 M sucrose might be considered especially suitable for baits, but 0.20 M fructose was preferred over 0.20 M sucrose by female ßies in choice tests. Further study of the feeding dynamics of ßies under both experimental and natural conditions is warranted. To compare consumption of solutions containing the same number of molecules, we used molar solutions at the same molarity. For the future, fruit ßy consumption research should be conducted with solutions of equal molarity so that an equal number of molecules is compared. The same concentration (percentage) of different chemical compounds compares unequal numbers of molecules. There was no trend toward increased consumption with decreasing sugar molar concentration. Indeed, the opposite trend was observed. It seems that our hypothesis that ßies would consume more solution as the sugar concentration was lowered was incorrect for the range of concentrations examined. Figure 4 presents the mean total consumption of ßies offered a choice of 0.20 M fructose or water, 0.20 M sucrose or water, and 0.20 M sucrose, or 0.20 M fructose. Flies consumed more sugar solution compared with water except for fructose (Fig. 4A, 24-h ßies). When fructose and sucrose solutions were presented to the same cage, the females chose fructose; males did not show a preference (Fig. 4C). Males moved between solutions; 92% (24 h) and 100% (6 d) fed on both sucrose and fructose. For females, 60% (24 h) and 72% (6 d) fed on both solutions. For the consumption of each sugar solution, females showed a preference for fructose (Fig. 4C). This Þnding could be interpreted to indicate that fructose is more phagostimulatory to 24-h and 6-d females. However, 6-d females that fed only on fructose only consumed 0.13 ␮l per ßy, and 72% of 6-d females consumed both sucrose and fructose. These data show that fructose was not so powerful a phagostimulant that ßies re-

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mained to feed on fructose only. Instead, they moved between the sucrose and fructose sources. We suggest that 0.20 M sucrose and 0.20 M fructose would be effective in maximizing bait consumption by A. suspensa and the inclusion of both sugars might ensure maximum consumption by all ages. However, the response of ßies to mixtures of sugars remains to be tested. In previous research, the consumption of sugar seemed to be a sexually immature phenomenon in both A. suspensa (Nigg et al. 1995) and Rhagoletis pomonella (Walsh) (Webster et al. 1979). Sexually mature ßies seemed to be less interested in sugar compared with immature ßies, but other studies disagreed with this interpretation (Gelperin and Dethier 1967, Landolt and Davis-Hernandez 1993). Our present results indicate that the inßuence of ßy age on sugar consumption varies depending on gender and the sugar solution being tested. For example, in nochoice comparisons, the 24-h male consumed more sucrose compared with fructose and rafÞnose; there were no differences for the 6-d male (Fig. 2B). Six-day females consumed more sucrose; 24-h females consumed less fructose (Fig. 2B). Six-day females generally consumed less fructose, glucose, and rafÞnose, and more sucrose compared with the other ages and sexes (Fig. 2A). Previous studies of ßy consumption were quantiÞed by weighing coverslips of food (Webster et al. 1979), by observing ßies arriving and/or remaining at a food source (Landolt and Davis-Hernandez 1993, Nigg et al. 1995) with a J-tube (Sharp and Chambers 1984, Sharp and Landolt 1984, Galun et al. 1985, Landolt and Davis-Hernandez 1993), by weighing individual ßies (Yee 2003), and by dissecting and weighing crops (Dethier 1961, Gelperin and Dethier 1967). Previous studies measured intake over days and averaged the data (Webster et al. 1979, Sharp and Chambers 1984, Sharp and Landolt 1984, Landolt and Davis-Hernandez 1993, Galun et al. 1985). We used a consumption technique with a lower limit of ⬇300 nl per ßy (Nigg et al. 2004b). The 0.20 M concentration of sucrose consumed heavily in this study is 6.8% sucrose (wt: vol). Sharp and Chambers (1984) found that 8% sucrose was consumed more by A. suspensa than lower or higher percentages, and Galun et al. (1985) found that 4% sucrose was consumed ⬎16% sucrose by male and female Certitis capitata (Wiedemann). Our data indicated reduced consumption for high molarity sucrose solution. NuLure, the present commercial bait for A. suspensa, contains 1% sucrose equivalents and spinosad, another bait used for A. suspensa, contains 14% sucrose equivalents (Nigg et al. 2004c), most likely incorrect sugar concentrations for A. suspensa. Our experiments were conducted with laboratoryreared ßies, and these ßies can differ in their behavior compared with feral ßies (Leppla et al. 1976, Webster et al. 1979, Galun et al. 1985, Lawrence 1989). Our laboratory ßies were reared on sucrose. In addition, sucrose is one of the major products of photosynthesis and a major form of plant carbohydrate storage (Pontis 1977, Etxeberria 2004). Our ßies might be expected

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to be selected for sucrose consumption through natural selection or phenotypic plasticity (Grant 2001). However, the experimental ßies used here seem not to be adapted to sucrose because there was no difference between fructose and sucrose for males when given a choice and females preferred to consume fructose (Fig. 4C). We note that the sugar receptor in Drosophila melanogaster (Meigen) responds to fructose (Hallem et al. 2006). Although this receptor is not known in A. suspensa, the readily consumed sugars by A. suspensa, fructose, rafÞnose, and sucrose have the fructose molecule in common. Based on these data, we suggest that bait consumption by male and female A. suspensa might be enhanced by supplementing with a maximally consumed concentration of any of the four sugars tested here. Sucrose and fructose seem to be especially good candidates, and the possible effects of mixing them in A. suspensa baits deserve further study. Acknowledgments This research was supported by the Florida Agricultural Experiment Station and a grant from the Florida Citrus Production Research Advisory Council. We thank the Florida citrus growers for support of this research.

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