Efficacy of 1,4-Diaminobutane (Putrescine) in a Food-Based Synthetic Attractant for Capture of Mediterranean and Mexican Fruit Flies (Diptera: Tephritidae)
Author(s): Robert R. Heath, Nancy D. Epsky, David Midgarden, and Byron I. Katsoyannos
ABSTRACT Field trials were conducted in Guatemala to evaluate the importance of 1,4 diami- nobutane (putrescine) in traps baited with ammonium acetate, trimethylamine, and putrescine. For the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), there were no differences in percentage of females captured in coffee and citrus or in percentage of males captured in citrus in traps with ammonium acetate and trimethylamine lures (females in coffee, 26.4 ± 6.27%; females incitrus, 35.7 ± 5.35%; males incitrus, 37.7 ± 7.48%) versus ammonium acetate, trimethylamine, and putrescine lures (females in coffee, 36.6 ± 9.64%; females in citrus, 41.1 ± 5.18%; males in citrus, 37.1 ± 6.09%). Percentage of males captured in coffee was reduced signiÞcantly when putrescine was not used with the ammonium acetate and trimethylamine (39.9 ± 4.34 versus 31.6 ± 5.29%). Lower percentages were captured in traps baited with ammonium acetate and putrescine, and the lowest percentages were captured in traps baited with putrescine and trimethylamine. When population level as indicated by capture in traps baited with ammonium acetate, trimethylamine, and putrescine was considered, a higher percentage of C. capitata males were captured in traps baited with all three components when one or more flies per trap per day were captured in coffee, and a higher percentage of females were captured when less than one fly per trap per day was captured in citrus. Percentage of the Mexican fruit fly, Anastrepha ludens (Loew), captured was signiÞcantly higher in traps baited with ammonium acetate and putrescine and signiÞcantly lower in traps baited putrescine and trimethylamine than in all other treatments. Results indicate that putrescine may be deleted when monitoring established populations of C. capitata but should be used in traps used to monitor A. ludens or to detect new infestations of C. capitata.
KEY WORDS Ceratitis capitata, Anastrepha ludens, trapping, ammonium acetate, putrescine
THE MEDITERRANEAN FRUIT FLY, Ceratitis capitata (Wiedemann), and the Mexican fruit fly, Anastrepha ludens (Loew), are of considerable economic impor- tance for fruit and vegetable production and export (White and Elson-Harris 1992, Aluja 1994). Because of the threat of introduction of C. capitata and A. ludens into areas of the world currently free from these pests, much emphasis has been placed on detection and eradication of these species. Surveys for C. capitata and A. ludens are included in state and federal exotic pest detection programs in at least nine southern and southwestern states in the United States (Lance and Gates 1994), and effective detection systems are es- sential for preventing the establishment of these species. California, Texas, and Florida deploy large num- bers of trimedlure-baited Jackson traps (Harris et al. 1971) for detection of male C. capitata and aqueous protein-baited McPhail traps (Newell 1936, McPhail 1939) for detectionof male and female C. capitata and
A. ludens (Gilbert et al. 1984).
Heath et al. (1995) reported that traps baited with a two-component synthetic attractant comprised of ammonium acetate and putrescine lures were effec- tive in capturing C. capitata and A. ludens in tests conducted in Guatemala. Subsequent work demon- strated that the addition of a third lure, trimethyl- amine, signiÞcantly improved trap capture of C. capi- tata and did not compromise capture of A. ludens compared with traps baited with the two lures alone (Heath et al. 1997). Field trials found similar results for
C. capitata when used in either dry traps or plastic McPhail traps (Epsky et al. 1999, Katsoyannos et al. 1999). Ammonia and acetic acid are important fruit fly attractants (Keiser et al. 1976, Bateman and Morton 1981, Mazor et al. 1987), and research on the devel- opment of the food-based attractants found that putrescine is a synergist to ammonium acetate (Heath et al. 1995) and that trimethylamine is a synergist to ammonium acetate and putrescine (Heath et al. 1997). Research related to other combinations of these at- tractants is lacking, and it was assumed that the release of ammonia, acetic acid, putrescine, and trimethyl- amine was needed for optimal attraction of C. capitata. Current management strategies to diminish the threat of invasion of C. capitata include release of sterile males in California and Florida (Hendrichs et al. 1995). Sterile insect technique (SIT) is a control method that has been used successfully for areawide population suppression (Gilmore 1989) and availabil- ity of genetic sexing strains of C. capitata enables single-sex release of males, which will further increase efÞcacy of SIT for C. capitata (Willhoeft et al. 1996). Efforts to eradicate C. capitata in areas of Mexico and Guatemala use both aerial bait sprays and release of sterile males (Hendrichs et al. 1995). Considerable resources are needed for monitoring systems that pro- vide program managers with information on popula- tions of sterile and wild flies. Use of a female-biased attractant for C. capitata affords a unique advantage to the SIT effort due to decreased labor associated with identiÞcation of sterile male flies captured. Because of the global use of the three component female-biased synthetic attractant in SIT and as a detection/delim- itation tool we reinvestigated the importance of am- monium acetate, putrescine, and trimethylamine as components required for trap capture of C. capitata and A. ludens and tested combinations of the components that have not been tested previously.
Materials and Methods
Traps and Lures. Commercially available ammo- nium acetate, putrescine, and trimethylamine lures were used for all studies (Suterra LLC, Bend, OR). Traps were baited with one of the following four combinations of lures: 1) ammonium acetate and pu- trescine, 2) ammonium acetate and trimethylamine,
3) putrescine and trimethylamine, and 4) ammonium acetate, putrescine, and trimethylamine. Traps used in the study were plastic McPhail traps (≈17 cm in di- ameter at its widest point), each with a yellow base (≈ 7 cm in height) and a clear top (≈11 cm in height; Betterworld Manufacturing Inc., Miami, FL). Three hundred milliliters of an aqueous solution of pro- pylene glycol (5%) was added to the base of the trap to retaincaptured flies. Lures were replaced at the end of 6 wk, and propylene glycol solution was replaced as needed.
Field Studies. One Þeld site, Finca Retana, was located at the edge of the city limits of Antigua, Gua- temala, and was planted in coffee, Coffea arabica L. variety katourra, which was grownunder the shade of Gravilea robusta trees. The other Þeld site, Finca Can- delaria, was located ≈10 km outside of Ciudad Vieja, Guatemala, and was planted in citrus, Citrus sinensis (L.) variety Washington. The Þeld design was a ran- domized complete block using a four trap by seven row (block) trapping grid. The treatment of traps baited with the three component lure were used as the positive control for capture of C. capitata (Epsky et al. 1999), traps baited with ammonium acetate and pu- trescine were used as the positive control for capture of A. ludens (Thomas et al. 2001), and capture in these traps were used as a relative measure of fruit fly pop- ulationlevel. The citrus trees were ≈4 m inheight and were spaced ≈6 m apart. The coffee trees were ≈3.5 m in height and were planted in continuous rows. Traps were hung ≈18 m apart along a row of citrus trees (every third tree) and 10 m apart along a row of coffee trees. Treatment placement within a row was random, and there were two rows of trees without traps between each baited row. The experiment was begunon6 May 2002 incoffee, on9 May 2002 incitrus and ended on 18 July 2002 in both sites. Traps were checked every 3Ð 4 d, and the numbers of female and male C. capitata and A. ludens were recorded. Traps were rotated sequentially within a row at time of sampling.
Statistical Analysis. Numbers of flies per trap per day per treatment in each block were averaged over all of the 21 and 19 sample dates in coffee and citrus, re- spectively; the averages were converted to relative trapping efÞciencies per block to facilitate compari- sons among the range of population levels tested. Traps from Þve of the seven blocks were lost during the Þrst two sample dates inthe test incoffee, so data from only two blocks from those dates were used for subsequent analysis. Relative trapping efÞciency is the percentage of flies in each block that were captured in each treatment in that block over the entire sample period. This was calculated separately for males, fe- males, and total (males plus females) C. capitata in coffee and citrus, and A. ludens in citrus. Data were analyzed by one-way analysis of variance (ANOVA) using PROC GLM (SAS Institute 1985) on effect of treatment (four levels), with data from the blocks (seven) used as the replicate for a total of 28 degrees of freedom for each ANOVA. SigniÞcant ANOVAs were followed by least signiÞcant difference (LSD) test (P = 0.05) for mean separation. The BoxÐCox procedure, which is a power transformation that re- gresses log-transformed standard deviations (y + 1) against log-transformed means (x + 1), was used to determine the type of transformation necessary to stabilize the variance before analysis (Box et al. 1978). Separate analyses were run for data from each host type and species, and data were square-root trans- formed (x + 0.5) before ANOVA for all analyses. Nontransformed data are presented. For assessment of relative populationlevels, average number of total flies per trap per day per treatment was determined for each consecutive 3Ð 4-d sample period for each host and species.
Results
The relative populationdensity of C. capitata inthe coffee was high, and over the 481 trapping days (two traps per treatment times 6 d plus seven traps per treatment times 67 d), with an average (±SD) of
Fig. 1. Percentage of C. capitata males, females, and total (males plus females) captured inplastic McPhail traps baited with putrescine and trimethylamine (open bar), ammonium acetate and putrescine (large grid), ammonium acetate and trimethylamine (small grid), or ammonium acetate, pu- trescine, and trimethylamine (solid bar) in Þeld trials con- ducted in coffee near Antigua, Guatemala. Bars headed by the same letter within a group are not signiÞcantly different (LSD means separation test on square-root [x + 0.5] trans- formed data, P = 0.05; nontransformed means presented).
10.3 ± 16.70 total (females plus males) C. capitata captured per trap per day in traps containing ammo- nium acetate, putrescine, and trimethylamine, the standard lure for this fruit fly. Treatment affected the percentage of female, male and total C. capitata cap- tured (F = 72.98; df = 3, 24; P < 0.0001; F = 139.26; df = 3, 24; P < 0.0001; and F = 94.24; df = 3, 24; P < 0.0001, respectively) (Fig. 1). The highest percentage of fe- male and total C. capitata were captured in traps baited with ammonium acetate and trimethylamine, or ammonium acetate, putrescine, and trimethyl- amine; and there was no difference in capture be- tween these two treatments. The lowest capture was in traps baited with putrescine and trimethylamine, and this was signiÞcantly lower than all other treat- ments. There was no difference in capture of females between traps baited with ammonium acetate and putrescine versus ammonium acetate and trimethyl- amine, although capture of total flies was signiÞcantly lower. Capture of male C. capitata followed the same trend of highest capture in traps baited with all three lures and lowest capture in traps baited with pu- trescine and trimethylamine, but there were signiÞ- cant differences found among all treatments.
The relative population density of C. capitata was approximately 10 times lower in citrus than in coffee over the 490 trapping days (seven traps per treatment times 70 d of trapping), with an average (±SD) of
1.3 ± 1.70 total flies per trap per day captured intraps containing ammonium acetate, putrescine, and tri- methylamine. Treatment affected percentage of fe- male, male, and total C. capitata in citrus (F = 151.55; df = 3, 24; P < 0.0001; F = 80.48; df = 3, 24; P < 0.0001; and F = 140.83; df = 3, 24; P < 0.0001, respectively). Capture of female and total C. capitata followed the same patterns as those obtained in coffee (Fig. 2). However, unlike results obtained in coffee, there was no difference in capture of male C. capitata between traps baited with ammonium acetate and trimethyl- amine, or ammonium acetate, putrescine, and tri-methylamine. Capture of all groups was lowest in traps baited with putrescine and trimethylamine and inter- mediate in traps baited with ammonium acetate and putrescine.
The population density of A. ludens was similar to levels of C. capitata in citrus, with an average (±SD) of 1.1 ± 1.09 total flies per trap per day captured in traps baited with ammonium acetate and putrescine, the standard synthetic lure for A. ludens. Treatment affected percentage of female, male and total A. ludens captured in traps placed in citrus (F = 78.66; df = 3, 24; P < 0.0001; F = 56.84; df = 3, 24; P < 0.0001; and
F = 119.64; df = 3, 24; P < 0.0001). Response was the same for female, male, and total A. ludens, with capture in traps baited with ammonium acetate and putrescine signiÞcantly higher than capture in all other treat- ments (Fig. 3). As was observed with C. capitata, percentage captured in traps baited with putrescine and trimethylamine was signiÞcantly lower than all other treatments. There was no difference in capture in traps baited with ammonium acetate, putrescine, and trimethylamine versus ammonium acetate and trimethylamine, and captures in these traps was in- termediate to the other two treatments.
Field trials were initiated toward the end of the dry season in Guatemala, when populations of fruit flies (as indicated by capture of C. capitata or A. ludens in treatments with all three lures or ammonium acetate and putrescine, respectively) were declining (Fig. 4). Relative population of C. capitata was ≈10 times higher in coffee than in citrus, but all populations showed a large decrease by the sixth sample period,
≈3 wk into the study. Due to the degree of change in populationlevel over the course of the study, the data from the samples were divided into three population level groups of >10, between 1 and 10, and <1 total (female plus male) C. capitata per trap per day cap- tured in traps baited with ammonium acetate, pu- trescine, and trimethylamine. Relative trapping efÞ-
Fig. 3. Percentage of A. ludens males, females, and total (males plus females) captured inplastic McPhail traps baited with putrescine and trimethylamine (open bar), ammonium acetate and putrescine (large grid), ammonium acetate and trimethylamine (small grid), or ammonium acetate, pu- trescine, and trimethylamine (solid bar) in Þeld trials con- ducted incoffee near Ciudad Viejo, Guatemala. Bars headed by the same letter within a group are not signiÞcantly dif- ferent (LSD means separation test on square-root [x + 0.5] transformed data, P = 0.05; nontransformed means pre- sented).
ciencies of traps baited with ammonium acetate and trimethylamine with and without the addition of pu- trescine were compared directly with separate t-test comparisons for each site and for each population level (Table 1). There were Þve, seven, and nine samples of the three population levels for the trials in coffee, and zero, six, and 13 samples for the trials in citrus. Higher percentages of males were captured in traps baited with all three lures when populations were higher than one fly per trap per day in tests conducted in coffee. This was also observed for female and total capture in the tests conducted in citrus when the population was less than one fly per trap per day.
Fig. 4. Average number of fruit flies captured per trap per day (FTD) captured in traps baited with standard syn- thetic lures (ammonium acetate and putrescine for A. ludens; ammonium acetate, putrescine, and trimethylamine for C. capitata) in Þeld trials conducted in coffee near Antigua, Guatemala (C. capitata, solid square, solid line) and in citrus near Ciudad Viejo, Guatemala (C. capitata, solid triangle, dashed line; A. ludens, open triangle, dotted line). Samples were collected every 3Ð4 d from 6 May 2002 to 18 July 2002.
There was no such effect of population level on cap- ture of A. ludens because capture of this species was always highest intraps baited with ammonium acetate and putrescine.
Discussion
The importance of ammonia in traps for C. capitata and for A. ludens was againdemonstrated inthat traps baited with putrescine and trimethylamine lures cap- tured a lower percentage of flies than any of the traps baited with ammonium acetate plus another lure. Sim- ilarly, the importance of trimethylamine as an attract- ant for C. capitata was demonstrated in that the traps baited with ammonium acetate, putrescine, and trim- ethylamine captured more of this species than traps baited with ammonium acetate and putrescine alone. However, it was found that there was no difference in percentage capture of female and total C. capitata in traps baited with ammonium acetate, putrescine and trimethylamine versus traps baited with ammonium acetate and trimethylamine alone. Capture in traps with all three lures tended to be slightly higher, how- ever, and in tests conducted in citrus when fruit fly populations were very low, capture in traps baited with the three lures was higher than in traps baited with ammonium acetate and trimethylamine alone. This environment may more closely reflect conditions of concernwhentraps are used for detectionof initial infestation in areas that are threatened by invasion and establishment of C. capitata populations. Therefore, for monitoring established populations, traps baited with ammonium acetate and trimethylamine may pro- vide sufÞcient efÞcacy. However, it may be better to use traps baited with ammonium acetate, trimethyl- amine and putrescine when monitoring for new in- festations.
Higher capture in traps baited with ammonium ac- etate, trimethylamine, and putrescine than in traps baited with ammonium acetate and trimethylamine was also observed for male C. capitata traps in tests conducted in coffee with populations of one fly per trap per day or higher. This suggests that there may be an advantage in SIT programs to monitor C. capitata populations with traps baited with ammonium acetate and trimethylamine, especially if the same response is obtained in studies with sterile flies. Use of traps baited with ammonium acetate and trimethylamine may cap- ture fewer sterile male flies without compromising capture of wild female flies.
Capture of A. ludens was signiÞcantly greater in traps baited with ammonium acetate and putrescine than the other combinations tested. Previous experi- ments indicated that addition of trimethylamine to traps baited with ammonium acetate and putrescine did not signiÞcantly reduce capture of A. ludens (Heath et al. 1997). In the earlier study, capture of A. ludens ranged from 0 to 23 total flies per trap per day. Inthe study reported herein, A. ludens capture ranged from 0 to 10 total flies per trap per day but dropped to below one fly per trap per day for most of the study. These tests were conducted later in the season than
Table 1. Comparisons of relative trapping efficiency (mean percentage ± SD) for C. capitata captured in McPhail traps baited with ammonium acetate and trimethylamine alone or with putrescine in field tests conducted in coffee and citrus in Guatemala
Population level Ammonium acetate, trimethylamine
>10 flies per trap per day, coffee Ammonium acetate, t P
putrescine, trimethylamine
Males 30.9 ± 6.39 39.7 ± 5.34 2.81 0.0157
Females 32.0 ± 7.57 38.3 ± 13.51 1.07 NS
Total 31.7 ± 7.15 39.6 ± 8.16 1.91 NS
1Ð10 flies per trap per day, coffee
Males 30.9 ± 8.59 42.7 ± 8.58 2.58 0.0239
Females 32.9 ± 8.93 35.9 ± 6.84 0.71 NS
Total 32.0 ± 8.08 39.3 ± 6.10 1.90 NS
1Ð10 flies per trap per day, citrus
Males 39.9 ± 6.52 35.3 ± 6.07 1.36 NS
Females 38.0 ± 4.28 39.0 ± 6.35 0.35 NS
Total 38.7 ± 4.61 37.9 ± 5.05 0.33 NS
<1 fly per trap per day, coffee
Males 35.6 ± 15.00 27.4 ± 8.46 1.25 NS
Females 41.3 ± 7.27 30.4 ± 14.60 1.76 NS
Total 39.3 ± 7.13 29.1 ± 11.18 2.02 NS
<1 fly per trap per day, citrus
Males 31.4 ± 19.23 43.4 ± 17.04 1.24 NS
Females 30.0 ± 8.45 48.0 ± 8.78 3.94 0.0020
Total 31.3 ± 9.14 45.7 ± 8.56 3.05 0.0102
NS, not signiÞcant.
The other treatments included traps baited with ammonium acetate and putrescine, and traps baited with putrescine and trimethylamine, which always captured a lower percentage of flies and were not included in the analyses. There were 21 3-4-d sample periods in coffee and 18 3-4-d sample periods in citrus that were subdivided by number of flies (males plus females) captured in the traps baited with ammonium acetate, putrescine and trimethylamine, the standard three-component synthetic attractant for C. capitata.
the previous study; thus, fly populations were not only very low but also host availability was minimal during these tests. There were also differences in the vege- tation between the two studies. The previous study was conducted in a Þeld in which citrus was inter- planted with coffee. In the current study, citrus was a monoculture with areas between the trees mowed.
There are several salient points regarding the reason for targeting detection systems for female C. capitata. When an introduction occurs, the Þrst flies captured are often female C. capitata captured in traps baited with food-based attractants (Dowell and Penrose 1995). When fly population density is low, such as at the start of the season, these traps tend to outcapture traps baited with the male-targeted parapheromone trimedlure (Katsoyannos et al. 1999). More recent studies in Greece (Papadopoulos et al. 2001) found that capture of C. capitata in trimedlure-baited traps typically occurs 2Ð 4 wk after flies were detected with the synthetic food-based lure. Considerable resources are required to service parapheromone traps during SIT release because of the capture of large number of sterile male flies. When SIT with sterile male-only strains are used, as occurs in many countries such as Madeira, Portugal, resources are minimized by using female-biased traps containing food-based attractants. The food-based attractant is highly attractive for the wild female C. capitata and weakly attractive to the sterile and wild male flies, and the eradication efforts are monitored by capture of wild female flies and detection of fruit infested with larvae.
Actionprograms require optimum trapping systems for the detection and delimitation of economically important pests. The ability to ensure that invasive species of exotic fruit flies are detected in an expedi-
tious manner mandates the availability of effective detectionsystems. Delay indetectionof exotic insects results in population increase and dispersal, which obligates an increase of resources needed for eradi- cation. Areawide eradication of pest insects requires that managers of these programs have detection sys- tems that enable them to monitor the eradication effort. Recent advances in the chemistry of the at- traction of female tephritid flies compared with tra- ditional liquid protein traps resulted in a synthetic attractant and a new frontier for fruit fly detection systems. Traps baited with ammonia (as ammonium acetate or ammonium bicarbonate) and putrescine are highly attractive to A. ludens and to the Caribbean fruit fly, A. suspensa (Loew) (Robacker and WarÞeld 1993, Thomas et al. 2001). The addition of trimethyl- amine signiÞcantly improves the attraction of C. capi- tata to traps (Heath et al. 1997, Epsky et al. 1999, Gazit et al. 1998, Katsoyannos et al. 1999). In this study, we provided further deÞnition of the chemical compo- nents used in the synthetic attractant for detection of
C. capitata and A. ludens. Putrescine may be deleted when monitoring moderate or high populations of C. capitata in areas where the pest is established, but it should be used in traps to monitor Anastrepha spp. fruit flies or to detect new infestations of C. capitata.
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