Matthew S. Siderhurst

Cucumber Volatile Blend Attractive to Female Melon Fly, Bactrocera cucurbitae (Coquillett)

The melon fly, Bactrocera cucurbitae (Coquillett), is a serious crop pest throughout the Asia Pacific sub-continent and Southeast Asia, causing damage to tree fruits, cucurbits, and related crops. Attractants for female melon flies are of particular interest as they could be used in control tactics to reduce pest levels. Previous work has shown that freshly sliced cucumbers are attractive to female melon flies, but the compounds responsible for this attraction were not identified. The objective of the present study was to create a synthetic lure for female B. cucurbitae based on its close association with Cucurbitaceae. Coupled gas chromatography-electroantennogram detection (GC-EAD) analysis of fresh and aged puréed cucumbers identified 31 compounds that were detected by females. Compounds that elicited EAD responses initially were screened as single components in glass McPhail traps in outdoor rotating olfactometer experiments. Four criteria were used to select compounds for testing in blends: a) strength of EAD response elicited; b) amount of compound present; c) relative attractiveness of a single compound; and d) compound novelty to Cucurbitaceae. Several synthetic blends attracted significant numbers of females in outdoor rotating olfactometer experiments; a nine-component blend (lure #7) was the most attractive. Field captures of female B. cucurbitae in traps baited with lure #7 were twice those in traps baited with Solulys protein bait. Besides having a female-biased attraction, this lure may have several advantages over protein baits: it can be used with a dry trap, is long lasting, and it captured low numbers of non-target species. Possible applications of this lure include trapping (for detection and/or monitoring/delimitation) and control/eradication (e.g., mass trapping, attract-and-kill, or as an attractant for existing protein insecticide bait sprays such as GF-120).

Alkylpyrazines: alarm pheromone components of the little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera, Formicidae).

The previous identification of 2,5-dimethyl-3-(3-methylbutyl)pyrazine as the mandibular alarm pheromone of the little fire ant Wasmannia auropunctata (Roger), has been found to be incorrect. Gas chromatography–mass spectrometry (GC/MS) of ant extracts suggested the correct structure to be the regioisomer 2,5-dimethyl-3-(2-methylbutyl)pyrazine, which was confirmed by comparison with the synthetic pyrazine. GC/MS analysis also revealed the presence of an additional disubstituted alkylpyrazine which was identified as 3-methyl-2-(2-methylbutyl)pyrazine. Headspace sampling of confined ants with SPME and Porapak Q followed by GC/MS analysis showed 2,5-dimethyl-3-(2-methylbutyl)pyrazine as the major volatile released by W. auropunctata workers while 3-methyl-2-(2-methylbutyl)pyrazine was only detected in trace amounts. In laboratory bioassays, W. auropunctata workers were attracted and arrested by both pyrazines, although the results were not always consistent. Synthetic pyrazines generally attracted as many W. auropunctata workers as were attracted to a single crushed ant. However, higher numbers of W. auropunctata were arrested by crushed ant treatments than by synthetic pyrazines in all bioassays but one.

Ring-Fluorinated Analog of Methyl Eugenol: Attractiveness to and Metabolism in the Oriental Fruit Fly, Bactrocera Dorsalis (Hendel)

Oriental fruit fly, Bactrocera dorsalis (Hendel), males are highly attracted to the natural phenylpropanoid methyl eugenol (ME). They compulsively feed on ME and metabolize it to ring and side-chain hydroxylated compounds that have both pheromonal and allomonal functions. Side-chain metabolic activation of ME leading to (E)-coniferyl alcohol has long been recognized as a primary reason for hepatocarcinogenicity of this compound in rodents. Earlier, we demonstrated that introduction of a fluorine atom at the terminal carbon of the ME side chain significantly depressed metabolism and specifically reduced formation of coniferyl alcohol but had little effect on field attractiveness to B. dorsalis. In the current paper, we demonstrate that fluorination of ME at the 4 position of the aromatic ring blocks metabolic ring-hydroxylation but overall enhances side-chain metabolism by increasing production of fluorinated (E)-coniferyl alcohol. In laboratory experiments, oriental fruit fly males were attracted to and readily consumed 1,2-dimethoxy-4-fluoro-5-(2-propenyl)benzene (I) at rates similar to ME but metabolized it faster. Flies that consumed the fluorine analog were as healthy post feeding as ones fed on methyl eugenol. In field trials, the fluorine analog I was ∼50% less attractive to male B. dorsalis than ME.

Raspberry Ketone Trifluoroacetate, a New Attractant for the Queensland Fruit Fly, Bactrocera Tryoni (Froggatt)

Queensland fruit fly, Bactrocera tryoni (Q-fly), is a major pest of horticultural crops in eastern Australia. Lures that attract male Q-fly are important for detection of incursions and outbreaks, monitoring of populations, and control by mass trapping and male annihilation. Cuelure, an analog of naturally occurring raspberry ketone, is the standard Q-fly lure, but it has limited efficacy compared with lures that are available for some other fruit flies such as methyl eugenol for B. dorsalis. Melolure is a more recently developed raspberry ketone analog that has shown better attraction than cuelure in some field studies but not in others. A novel fluorinated analog of raspberry ketone, raspberry ketone trifluoroacetate (RKTA), has been developed as a potential improvement on cuelure and melolure. RKTA placed on laboratory cages containing 2-week-old Q-flies elicited strong behavioral responses from males. Quantification of Q-fly responses in these cages, using digital images to estimate numbers of flies aggregated near different lures, showed RKTA attracted and arrested significantly more flies than did cuelure or melolure. RKTA shows good potential as a new lure for improved surveillance and control of Q-fly.

Di- and Tri-fluorinated Analogs of Methyl Eugenol: Attraction to and Metabolism in the Oriental Fruit Fly, Bactrocera Dorsalis (Hendel)

Oriental fruit fly, Bactrocera dorsalis (Hendel), males are attracted to the natural phenylpropanoid methyl eugenol (ME). They feed compulsively on ME and metabolize it to ring and side-chain hydroxylated compounds that have both pheromonal and allomonal properties. Previously, we demonstrated that mono-fluorination at the terminal carbon of the ME side-chain significantly reduced metabolic side-chain hydroxylation, while mono-fluorination of ME at position 4 of the aromatic ring blocked ring-hydroxylation but surprisingly enhanced side-chain hydroxylation. Here, we demonstrated that the introduction of fluorine atoms on both the ring and side-chain of ME blocks both positions that undergo enzymatic hydroxylation and, in particular, completely inhibits oxidative biotransformation of the allyl group. In laboratory experiments, B. dorsalis males initially were more attracted to both 1-fluoro-4,5-dimethoxy-2-(3,3-difluoro-2-propenyl)benzene (I) and 1-fluoro-4,5-dimethoxy-2-(3-fluoro-2-propenyl)benzene (II) than to ME. However, both I and II were taken up by flies at rates significantly less than that of ME. Flies fed with difluoroanalog II partially metabolized it to 5-fluoro-4-(3-fluoroprop-2-en-1-yl)-2-methoxyphenol (III), and flies fed with trifluoroanalog I produced 4-(3,3-difluoroprop-2-en-1-yl)-5-fluoro-2-methoxyphenol (V), but the rates of metabolism relative to rates of intakes were much lower compared to those of ME. Flies that consumed either the tri- or difluorinated analog showed higher post-feeding mortality than those that fed on methyl eugenol. In field trials, trifluoroanalog I was ∼90% less attractive to male B. dorsalis than ME, while difluoroanalog II was ∼50% less attractive. These results suggest that increasing fluorination can contribute to fly mortality, but the trade off with attractancy makes it unlikely that either a di or trifluorinated ME would be an improvement over ME for detection and/or eradication of this species.

Field Estimates of Attraction of Ceratitis capitata to Trimedlure and Bactrocera dorsalis (Diptera: Tephritidae) to Methyl Eugenol in Varying Environments

ABSTRACT Measuring and modeling the attractiveness of semiochemical-baited traps is of significant importance to detection, delimitation, and control of invasive pests. Here, we describe the results of field mark—release—recapture experiments with Ceratitis capitata (Wiedemann) and Bactrocera dorsalis (Hendel) to estimate the relationship between distance from a trap baited with trimedlure and methyl eugenol, respectively, and probability of capture for a receptive male insect. Experiments were conducted using a grid of traps with a central release point at two sites on Hawaii Island, a Macadamia orchard on the East side of the island and a lava field on theWest side.We found that for B. dorsalis and methyl eugenol there is a 65% probability of capture at ∼36m from a single trap, regardless of habitat. For C. capitata, we found a 65% probability of capture at a distance of ∼14m from a single trap in the orchard and 7 m in the lava field. We also present results on the spatial and temporal pattern of recaptures. The attraction data are analyzed via a hyperbolic secant-based capture probability model.

Raspberry Ketone Analogs: Vapour Pressure Measurements and Attractiveness to Queensland Fruit Fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

The Queensland fruit fly, Bactrocera tryoni (Froggatt) (Q-fly), is a major horticultural pest in Eastern Australia. Effective monitoring, male annihilation technique (MAT) and mass trapping (MT) are all important for control and require strong lures to attract flies to traps or toxicants. Lure strength is thought to be related in part to volatility, but little vapour pressure data are available for most Q-fly lures. Raspberry ketone (4-(4-hydroxyphenyl)-2-butanone) and analogs that had esters (acetyl, difluoroacetyl, trifluoroacetyl, formyl, propionyl) and ethers (methyl ether, trimethylsilyl ether) in replacement of the phenolic group, and in one case also had modification of the 2-butanone side chain, were measured for their vapour pressures by differential scanning calorimetry (DSC), and their attractiveness to Q-fly was assessed in small cage environmentally controlled laboratory bioassays. Maximum response of one category of compounds, containing both 2-butanone side chain and ester group was found to be higher than that of the other group of compounds, of which either of 2-butanone or ester functionality was modified. However, linear relationship between vapour pressure and maximum response was not significant. The results of this study indicate that, while volatility may be a factor in lure effectiveness, molecular structure is the dominating factor for the series of molecules investigated.

Sex attractant for the banana moth, Opogona sacchari Bojer (Lepidoptera: Tineidae): provisional identification and field evaluation.

BACKGROUND The banana moth, Opogona sacchari Bojer, is a polyphagous agricultural pest in many tropical areas of the world. The identification of an attractant for male O. sacchari could offer new methods for detection, study and control. RESULTS A compound extracted from female O. sacchari elicited responses from antennae of male moths. This compound was identified as a 2/3,(Z)13-octadecadienal by gas chromatography-mass spectrometry. An analog, 2/3,(Z)13-octadecadienol, was also detected in some extracts at roughly a 1:20 ratio (alcohol:aldehyde) but did not elicit responses from antennae of male moths. Electroantennograms of synthetic candidate dienals found the strongest responses from (Z, Z)-2,13-octadecadienal and (E, Z)-2,13-octadecadienal. In field trials, (E, Z)-2,13-octadecadienal attracted more male O. sacchari than (Z, Z)-2,13-octadecadienal. Attraction was not improved for either of these compounds when the corresponding stereoisomeric alcohol was added at ratios of 1:1, 1:10 or 1:100 (alcohol:aldehyde). Jackson sticky traps containing 250 microg lures of (E, Z)-2,13-octadecadienal caught as many males as did traps holding virgin females. CONCLUSION (E, Z)-2,13-octadecadienal has been identified as an attractant for O. sacchari males and can be used as a monitoring lure of populations of this moth.

Judas Beetles: Discovering Cryptic Breeding Sites by Radio-Tracking Coconut Rhinoceros Beetles, Oryctes rhinoceros (Coleoptera: Scarabaeidae)

Abstract The coconut rhinoceros beetle, Oryctes rhinoceros L., is a serious pest of coconut and other palms throughout Southeast Asia and on several Pacific Islands. Adults damage and sometimes kill palms when they bore into the crown to feed. In contrast, larvae feed only on dead plant material at breeding sites. Typically, coconut rhinoceros beetle populations are controlled with a combination of biocontrol, pheromone traps, and breeding site removal. A field trial was performed at two locations on Guam to test the feasibility of using the Judas technique, releasing radio-tagged adults to discover cryptic breeding sites, for potential coconut rhinoceros beetle control. Of 33 radio-tagged beetles that were released, 19 were successfully tracked to landing sites, 11 of which were considered to be active or potential breeding sites, in five different microhabitats. The remaining 14 beetles were lost when they flew beyond the range of receivers. Only one of the radio-tagged beetles was caught in the numerous pheromone traps present at the release sites. Percent emergence weight (%EW, ratio of current/ emergence weight) varied significantly by the microhabitat to which coconut rhinoceros beetles were tracked. When microhabitats were further grouped, the difference in mean %EW between the arboreal (74 ± 2%) and the soil-associated (82 ± 3%) groups were found to be highly significant. The %EW for coconut rhinoceros beetles that were successfully located (78 ± 2%) and those that were lost (72 ± 2%) also differed significantly. Radio-tracking coconut rhinoceros beetles shows promise as a method to identify cryptic breeding sites, which could then be treated, removed, or destroyed.

Hydrolysis of Queensland Fruit Fly, Bactrocera tryoni (Froggatt), Attractants: Kinetics and Implications for Biological Activity

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is a major insect pest of horticultural crops in Australia. Cuelure is the most commonly used attractant for monitoring as well as for management of Q-fly populations through the male annihilation technique and mass trapping. There has been some concern that cuelure is susceptible to hydrolysis, which would limit its usefulness under conditions of high humidity and give rise to inconsistent fly population monitoring. To give some insight into the hydrolysis of cuelure and two closely related compounds, melolure and a newly developed lure, 4-(4-(2,2,2-trifluoroacetoxy)phenyl)-2-butanone (RKTA), the kinetics of hydrolysis of these compounds were quantitatively investigated by gas chromatography–flame ionization detection. From the experimental data, we found the hydrolysis half-lives of cuelure, melolure, and RKTA, at a water concentration of 25 mol L–1, to be ~20 days, 22 h, and 1.2 min respectively. When extrapolated to a water concentration of 1.3 mmol L–1, corresponding to atmospheric conditions of 100 % relative humidity at 25°C, the half-lives are ~1660, ~51, and ~1.4 years respectively.