Nancy D. Epsky

Attraction of the redbay ambrosia beetle, Xyleborus glabratus, to avocado, lychee, and essential oil lures.

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is an exotic wood-boring insect that vectors the mycopathogen responsible for laurel wilt, a lethal vascular disease of trees in the Lauraceae. High mortality has occurred in native Persea species in the southeastern U.S., and the vector-pathogen complex poses an imminent threat to the production of commercial avocado, P. americana, in south Florida. There is a critical need for effective attractants to detect, monitor, and control this invasive pest. This study combined field tests and laboratory bioassays to evaluate the response of female X. glabratus to host-based volatiles from wood of avocado (cultivars of West Indian, Guatemalan, and Mexican races); from wood of lychee (Litchi chinensis, a presumed non-host that is high in the sesquiterpene α-copaene, a putative attractant); and to commercial lures containing manuka and phoebe oils, two reported attractive baits. Volatile collections and GC-MS analyses were performed to quantify the sesquiterpene content of test substrates. In the field, traps baited with lychee wood captured more beetles than those with wood from avocado cultivars; traps baited with phoebe oil lures captured more beetles than those with manuka oil lures (the current monitoring tool). In field and laboratory tests, X. glabratus did not show a preference among avocado races in either attraction or host acceptance (initiation of boring). In choice tests, lychee was more attractive than avocado initially, but a higher percentage of beetles bored into avocado, suggesting that lychee emits more powerful olfactory/visual cues, but that avocado contains more of the secondary cues necessary for host recognition. Emissions of α-copaene, β-caryophyllene, and α-humulene were correlated with field captures, and lychee wood may be a source of additional semiochemicals for X. glabratus.

Effect of Age on EAG Response and Attraction of Female Anastrepha suspensa (Diptera: Tephritidae) to Ammonia and Carbon Dioxide

Abstract Current ammonia-based lures vary considerably in their ability to attract Anastrepha fruit flies in the field. This report presents results from electroantennography (EAG) and behavioral bioassays that examined the effect of age on fly response to ammonia and carbon dioxide, two volatile chemicals released from commercial ammonium bicarbonate lures. EAG measurements from female Caribbean fruit flies, Anastrepha suspensa (Loew), showed that ammonia generated a greater EAG response in sexually immature females compared with mature females. Conversely, carbon dioxide elicited stronger EAG responses in sexually mature females. In flight tunnel bioassays, females from both age groups were captured in response to ammonia ranging from 60 to 3840 μg/h, but captures declined with increasing ammonia concentration. In bioassays with the two highest ammonia release rates, captures of immature females were significantly lower than captures of mature females. Carbon dioxide, ranging from 300 to 7200 μg/h, did not capture any flies when presented alone in the flight tunnel bioassay. However, for sexually mature flies, carbon dioxide in combination with ammonia was more attractive than ammonia alone. These age-related differences in response to ammonia and carbon dioxide may account for some of the variability observed in field tests with ammonium bicarbonate lures.

Attraction of 3-methyl-1-butanol and ammonia identified from Enterobacter agglomerans to Anastrepha suspensa

Tests demonstrated that volatile chemicals emitted from Enterobacter agglomerans, a bacterium that has been isolated from adults as well as fruit infested with larvae of the Caribbean fruit fly, Anastrepha suspensa (Loew) and other pest fruit flies, are attractive to female A. suspensa in laboratory bioassays. 3-Methyl-1-butanol and ammonia were identified as the two primary volatile chemicals released from active cultures of E. agglomerans. No 3-methyl-1-butanol and little ammonia (16.0 μg/hr) are released from sterile tryptic soy agar plates. E. agglomerans-inoculated tryptic soy agar plates, however, released an average of 1.5 ± 0.53 μg/hr 3-methyl-1-butanol and 332.9 ± 239.16 μg/hr ammonia after 24 hr of growth. 3-Methyl-1-butanol lures were formulated in a membrane-based system to provide a constant release rate of synthetic chemical. Release rates ranged from 0.046 ± 0.007 to 12.16 ± 2.76 μg/hr. In laboratory tests, equal numbers of females were captured in response to ammonium carbonate lures that released ammonia at the rate of 100 μg/hr and to 3-methyl-1-butanol lures that released 12.16 ± 2.756 μg/hr of synthetic material. The combination of the two lures was more attractive than ammonia alone. Availability of lures formulated for a range of 3-methyl-1-butanol release rates will facilitate field tests of this putative microbial attractant and may lead to a better understanding of the role of bacteria in the ecology of pest fruit flies.

Efficacy of 1,4-Diaminobutane (Putrescine) in a Food-Based Synthetic Attractant for Capture of Mediterranean and Mexican Fruit Flies (Diptera: Tephritidae)

Abstract Field trials were conducted in Guatemala to evaluate the importance of 1,4 diaminobutane (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 in citrus, 35.7 ± 5.35%; males in citrus, 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 significantly 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 significantly higher in traps baited with ammonium acetate and putrescine and significantly 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.

EXPLOITING THE INTERACTIONS OF CHEMICAL AND VISUAL CUES IN BEHAVIORAL CONTROL MEASURES FOR PEST TEPHRITID FRUIT FLIES

Traps for tropical pest tephritids have relied primarily on chemical cues while traps for temperate pest tephritids have relied primarily on visual cues. Here we review research on the interactions between chemical and visual cues that have been observed in the development of traps for the tropical Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and the temperate apple maggot, Rhagoletis pomonella (Walsh). By exploiting these interactions, it may be possible to produce efficacious trapping systems that could be used in a behavioral approach to fruit fly population control.

COMPARATIVE ANALYSIS OF TERPENOID EMISSIONS FROM FLORIDA HOST TREES OF THE REDBAY AMBROSIA BEETLE, XYLEBORUS GLABRATUS (COLEOPTERA: CURCULIONIDAE: SCOLYTINAE)

ABSTRACT The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an exotic wood-boring insect that vectors Raffaelea lauricola, the fungal pathogen responsible for laurel wilt, a lethal disease of trees in the Lauraceae. First detected in the U.S. near Savannah, GA in 2002, X. glabratus has since spread throughout the southeastern coastal plain causing high mortality in native Persea species, particularly redbay (P. borbonia) and swampbay (P. palustris). Currently, breeding populations of X. glabratus pose an imminent threat to the avocado (P. americana) industry in south Florida. There is a critical need for effective attractants to detect, monitor, and control the spread of this invasive pest. In an effort to identify host-based attractants for dispersing female X. glabratus, we conducted a comparative study of the volatile chemicals emitted from wood of six species of Lauraceae found in Florida: avocado (Persea americana), redbay (P. borbonia), swampbay (P. palustris), silkbay (P. humilis), camphor tree (Cinnamomum camphora), and lancewood (Ocotea coriacea). We compared chemical profiles to those obtained from wood of lychee, Litchi chinensis (Sapindaceae), a presumed non-host found to be highly attractive to X. glabratus in field tests. GC-MS analysis identified 11 terpenoid compounds common to all lauraceous species. Of these, 4 sesquiterpenes were also found in lychee: a-copaene, b-caryophyllene, a-humulene and cadinene. Future research will include field tests and laboratory bioassays to evaluate the roles of each of these potential kairomones.

A BIOASSAY SYSTEM FOR COLLECTING VOLATILES WHILE SIMULTANEOUSLY ATTRACTING TEPHRITID FRUIT FLIES

A bioassay system was developed that permits the testing of various substrates for biological activity in a flight tunnel, while simultaneously collecting a portion of the volatiles from the attractive source for subsequent chemical identification and quantification. Bioassays of the response of virgin female Caribbean fruit flies,Anastrepha suspensa (Loew) (Diptera: Tephritidae), to volatiles released by calling males were conducted in a greenhouse under natural light cycles and fluctuating environmental conditions, similar to those in the field. Using this system, the periodicity of response of the female flies between 1300 and 1845 hr (EST) was tested. Fifty to 75% response occurred between 1700 and 1845 hr. Male pheromone release was greatest between 1500 and 1800 hr. Videotaped records of insects, taken between 1700 and 1800 hr as flies approached and entered the traps, were analyzed to interpret the communicative role of the volatiles released. Significantly more flies landed on and entered the pheromone-emitting trap than the control trap. There was no difference in the amount of time spent on the trap face, an indication that volatiles were attractants. The system described should be of general utility in determination of the attraction of pest fruit flies to suspected attractants.

North American Lauraceae: Terpenoid Emissions, Relative Attraction and Boring Preferences of Redbay Ambrosia Beetle, Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae)

The invasive redbay ambrosia beetle, Xyleborus glabratus, is the primary vector of Raffaelea lauricola, a symbiotic fungus and the etiologic agent of laurel wilt. This lethal disease has caused severe mortality of redbay (Persea borbonia) and swampbay (P. palustris) trees in the southeastern USA, threatens avocado (P. americana) production in Florida, and has potential to impact additional New World species. To date, all North American hosts of X. glabratus and suscepts of laurel wilt are members of the family Lauraceae. This comparative study combined field tests and laboratory bioassays to evaluate attraction and boring preferences of female X. glabratus using freshly-cut bolts from nine species of Lauraceae: avocado (one cultivar of each botanical race), redbay, swampbay, silkbay (Persea humilis), California bay laurel (Umbellularia californica), sassafras (Sassafras albidum), northern spicebush (Lindera benzoin), camphor tree (Cinnamomum camphora), and lancewood (Nectandra coriacea). In addition, volatile collections and gas chromatography-mass spectroscopy (GC-MS) were conducted to quantify terpenoid emissions from test bolts, and electroantennography (EAG) was performed to measure olfactory responses of X. glabratus to terpenoids identified by GC-MS. Significant differences were observed among treatments in both field and laboratory tests. Silkbay and camphor tree attracted the highest numbers of the beetle in the field, and lancewood and spicebush the lowest, whereas boring activity was greatest on silkbay, bay laurel, swampbay, and redbay, and lowest on lancewood, spicebush, and camphor tree. The Guatemalan cultivar of avocado was more attractive than those of the other races, but boring response among the three was equivalent. The results suggest that camphor tree may contain a chemical deterrent to boring, and that different cues are associated with host location and host acceptance. Emissions of α-cubebene, α-copaene, α-humulene, and calamenene were positively correlated with attraction, and EAG analyses confirmed chemoreception of terpenoids by antennal receptors of X. glabratus.

Evaluation of protein bait formulations for the Caribbean fruit fly (Diptera: Tephritidae).

Laboratory and field trials were conducted to determine the preference of the Caribbean fruit fly, Anastrepha suspensa (Loew), for aqueous formulations of the protein bait NuLure@? and standard torula yeast plus sodium borate (HTY-borax) pellets. Addition of 1-10% borax to 10% NuLure solution increased bait pH, and this increase was directly correlated with increase in number of female flies trapped in two-choice laboratory bioassays and in field trials conducted in three locations in south Florida during the spring of 1992. Overall, significantly more flies were attracted to volatiles from HTY-borax solution than to volatiles from any of the NuLure solutions. There was variation in the response of flies to baits observed among the three test locations. Age structures of the populations at the different locations were compared by determining the percentage of females mated among the trapped females. There were significant differences in the percentage of mated females at the 3 locations, which ranged from 26-65% mated. In the locations with a high percentage of unmated female flies, the flies were less discriminating, at least among the protein baits offered in this study. Thus, age structure of the target population may alter response to bait. There was also variation in the pH of the baits at different locations due to the pH of the water used to prepare the solutions. Bait pH may be a significant factor that has been overlooked in field tests conducted at different locations or at different times as changes in water pH, as well as bait protein pH, may strongly affect trap efficacy.

Temporal Analysis of Sesquiterpene Emissions From Manuka and Phoebe Oil Lures and Efficacy for Attraction of Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae)

ABSTRACT Redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is an exotic wood-borer that vectors the fungal agent (Raffaelea lauricola) responsible for laurel wilt. Laurel wilt has had severe impact on forest ecosystems in the southeastern United States, killing a large proportion of native Persea trees, particularly redbay (P. borbonia) and swampbay (P. palustris), and currently poses an economic threat to avocado (P. americana) in Florida. To control the spread of this lethal disease, effective attractants are needed for early detection of the vector. Two 12-wk field tests were conducted in Florida to evaluate efficacy and longevity of manuka and phoebe oil lures, and to relate captures of X. glabratus to release rates of putative sesquiterpene attractants. Two trap types were also evaluated, Lindgren funnel traps and sticky panel traps. To document lure emissions over time, a separate set of lures was aged outdoors for 12 wk and sampled periodically to quantify volatile sesquiterpenes using super-Q adsorbant and gas chromatography-mass spectroscopy analysis. Phoebe lures captured significantly more X. glabratus than manuka lures, and sticky traps captured more beetles than funnel traps. Phoebe lures captured X. glabratus for 10–12 wk, but field life of manuka lures was 2–3 wk. Emissions of &agr;-copaene, &agr;-humulene, and cadinene were consistently higher from phoebe lures, particularly during the 2–3 wk window when manuka lures lost efficacy, suggesting that these sesquiterpenes are primary kairomones used by host-seeking females. Results indicate that the current monitoring system is suboptimal for early detection of X. glabratus because of rapid depletion of sesquiterpenes from manuka lures.