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

Less is more: Fewer attract-and-kill sites improve the male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae)

The Male Annihilation Technique (also termed the Male Attraction Technique; "MAT") is often used to eradicate pestiferous tephritid fruit flies, such as Bactrocera dorsalis (Hendel). MAT involves the application of male-specific attractants combined with an insecticide in spots or stations across an area to reduce the male population to such a low level that suppression or eradication is achieved. Currently, implementations of MAT in California and Florida targeting B. dorsalis utilize the male attractant methyl eugenol (ME) accompanied with a toxicant, such as spinosad, mixed into a waxy, inert emulsion STATIC ME (termed here "SPLAT-MAT-ME"). While highly effective against ME-responding species, such applications are expensive owing largely to the high cost of the carrier matrix and labor for application. Until recently the accepted protocol called for the application of approximately 230 SPLAT-MAT-ME spots per km2; however, findings from Hawaii suggest a lower density may be more effective. The present study adopted the methods of that earlier work and estimated kill rates of released B. dorsalis under varying spot densities in areas of California and Florida that have had recent incursions of this invasive species. Specifically, we directly compared trap captures of sterilized marked B. dorsalis males released in different plots under three experimental SPLAT-MAT-ME densities (50, 110, and 230 per km2) in Huntington Beach, CA; Anaheim, CA; and Sarasota-Bradenton, FL. The plots with a density of 110 sites per km2 had a significantly higher recapture proportion than plots with 50 or 230 sites per km2. This result suggests that large amounts of male attractant may reduce the ability of males to locate the source of the odor, thus lowering kill rates and the effectiveness of eradication efforts. Eradication programs would directly benefit from reduced costs and improved eradication effectiveness by reducing the application density of SPLAT-MAT-ME.

Complementary use of visual and olfactory cues to assess capture of Bactrocera dorsalis (Hendel): Implementation and field verification via an IoT-based automatic monitoring system

This study examined the effect of combining visual and olfactory cues to attract oriental fruit flies (OFFs). Six different colored light-emitting diodes (LEDs) served as a visual attractant and methyl eugenol served as olfactory bait to lure male flies. An internet of things (IoT)-based pest monitoring system, consisting of sensor nodes, a gateway, and automatic counting traps, was deployed in the field to automatically collect environmental data and pest counts. The results of the calibrated experiments indicated that green, yellow, or red LEDs exhibited better performance in attracting flies than white, purple, or blue LEDs or no LEDs. With an accurate combination of visual and olfactory cues, the proposed IoT-based pest monitoring system may be an effective tool in agricultural pest management, given its advantages for efficiently capturing OFFs in a labor and time saving manner, providing accurate information regarding increases in pest populations, and enabling long-term, real-time data collection.

Simulation to investigate site-based monitoring of pest insect species for trade

Pest insect surveillance using lures is widely used to support market access requirements for traded articles that are hosts or carriers of quarantine pests. Modeling has been used extensively to guide the design of surveillance to support pest free area claims but is less commonly applied to provide confidence in pest freedom or low pest prevalence within sites registered for trade. Site-based surveillance typically needs to detect pests that are already present in the site or that may be entering the site from surrounding areas. We assessed the ability of site-based surveillance strategies to detect pests originating from within or outside the registered site using a probabilistic trapping network simulation model with random-walk insect movement and biologically realistic parameters. For a given release size, time-dependent detection probability was primarily determined by trap density and lure attractiveness, whereas mean step size (daily dispersal) had limited effect. Results were robust to site shape and size. For pests already within the site, detection was most sensitive using regularly spaced traps. Perimeter traps performed best for detecting pests moving into the site, although the importance of trap arrangement decreased with time from release, and random trap placement performed relatively well compared to regularly spaced traps. High detection probabilities were achievable within 7 days using realistic values for lure attractiveness and trap density. These findings, together with the modeling approach, can guide the development of internationally agreed principles for designing site-based surveillance of lure-attractant pests that is calibrated against the risk of non-detection.

Simulation-based evaluation of two insect trapping grids for delimitation surveys

In the United States of America, delimitation trapping surveys with square grids have been used for decades for exotic insects without rigorous evaluation. We used simulations to investigate the effectiveness of two representative designs: an 8-km grid for Acrolepiopsis assectella (leek moth) and a 14.5-km grid for Ceratitis capitata (Mediterranean fruit fly, "Medfly"). We investigated grid compositions and design factors, measuring performance as the mean probability of pest capture over all traps, p(capture), and designed improved grids for both species. For the standard designs, p(capture) was 0.86 for leek moth and 0.71 for Medfly, with the latter performing better due to greater lure and trap attractiveness. For both designs, 86 percent or more of mean p(capture) came from core area captures. Egress testing indicated that both grids were oversized. An improved grid for leek moths would use 177 traps in a 4.8-km diameter circle, which had mean p(capture) = 0.73 and reduced the cost by 80 percent. The best Medfly grid was a 4.8-km diameter circle with 232 traps, which gave mean p(capture) of 0.66 and reduced the cost by 86 percent. Simulation may be used to improve trapping survey plans, often saving significantly on costs while maintaining survey performance.

Evaluating Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) Response to Methyl Eugenol: Comparison of Three Common Bioassay Methods

Insect responses to chemical attractants are often measured using olfactory bioassays prior to testing in field experiments. The attraction of sexually mature male Bactrocera dorsalis to methyl eugenol (ME) and the loss of attraction by ME pre-fed males have been demonstrated in laboratory bioassays and field trapping studies. It has been suggested that ME nonresponsiveness can be exploited to improve the effectiveness of B. dorsalis management programs by protecting sterile males from ME-based control measures. Currently, work is underway to identify alternatives that reduce or eliminate ME response. To support the development of compounds and evaluation of their effect on B. dorsalis attraction to ME, we compared the effectiveness of three common bioassay methods that have been used to measure lure response in Bactrocera flies under controlled conditions (choice assays using Y-tube [Y], small-cage arena [SC], and rotating carousel field-cage [RC]) to determine which bioassay method is efficient and reliable. A series of bioassays comparing ME-exposed and ME-naïve wild-type and genetic sexing strain males showed that the RC and SC were effective at both observing attraction to ME and detecting a significant reduction in ME response from ME-exposed males. However, the male attraction to ME and a significant decrease in response to ME after ME feeding was not observed in our Y-tube assays. These suggest that RC and SC are preferable options to evaluate ME non-responsiveness in B. dorsalis, and that Y-tube tests are difficult to administer correctly.

Potential of Fruit Extracts as Attractants of Female Oriental Fruit Flies

<b>Background and Objective:</b> The oriental fruit fly <i>Bactrocera dorsalis</i> (Hendel) is one of the most important insect pest species of fruit and vegetable crops in the tropical and subtropical regions. This study aimed to determine the attraction of female and male <i>B. dorsalis</i> fruit flies to the aroma of fruit juice from the host plants as well as their attraction to methanol extract, ethyl acetate extract and distillate water of selected host fruits. <b>Materials and Methods:</b> The attractiveness of the juice and extract/distillate water of the host fruits to <i>B. dorsalis</i> fruit flies was carried out in an experimental cage measuring 200×200×200 cm that was placed in the laboratory. The volatile compounds in the juice, methanol extract, ethyl acetate extract and distillate water of the selected fruits were analyzed using GCMS-Pyrolysis. <b>Results:</b> The results show that among the eight fruit juice aromas tested, the ones that significantly affected the number of trapped female <i>B. dorsalis</i> were the aromas of banana juice, papaya juice and chilli juice. The results of the analysis by GCMS-Pyrolysis showed that the methanol extract of banana fruit contains one volatile compound that was previously reported to have the ability to attract female <i>B. dorsalis</i> fruit flies. Two volatile compounds in the banana distillate water were also reported to have the ability to attract female <i>B. dorsalis</i> and other fruit flies. <b>Conclusion:</b> From the results of this study, it can be concluded that the methanol extract and distillate water of the green <i>Ambon lumut</i> banana fruit of <i>Musa acuminata</i> Colla has the potential to be developed as an attractant of female <i>B. dorsalis</i>.

Simulation-Based Investigation of the Performance of Delimiting Trapping Surveys for Insect Pests

Fully trapped survey designs are widely used to delimit adventive pests populations that can be detected using traps and lures. Delimitation includes verifying the presence of the pest and determining its spatial extent. The size and shape of the survey design and the density of traps can vary; however, resulting variation in detecting efficiency is often unknown. We used a trapping network simulation model with diffusion-based insect movement to investigate delimiting survey trapping design performance for fully trapped and some modified designs. Simulations included randomized outbreak locations in a core area and a duration of 30 d. We assessed impacts of insect dispersal ability, grid size and shape, and trap attractiveness and density on survey performance, measured as mean probability of capturing individual pests [p(capture)]. Most published grids are square, but circles performed equally well and are more efficient. Over different grid sizes, p(capture) increased for insects with greater dispersal ability but was generally unresponsive to size because most captures occurred in central areas. For low dispersing insects, the likelihood of egress was approximately zero with a 3.2-km square grid, whereas an 11.3-km grid was needed to contain highly vagile insects. Trap attractiveness affected p(capture) more strongly than density: lower densities of poorly attractive traps may underperform expectations. Variable density designs demonstrated potential for cost savings but highlighted that resource-intensive outer bands are critical to boundary determination. Results suggesting that many grids are oversized need empirical verification, whereas other principles, such as using circular shapes, are readily adoptable now.

Non-linear physiological responses to climate change: the case of Ceratitis capitata distribution and abundance in Europe

Understanding how climate change might influence the distribution and abundance of crop pests is fundamental for the development and the implementation of pest management strategies. Here we present and apply a modelling framework assessing the non-linear physiological responses of the life-history strategies of the Mediterranean fruit fly (Ceratitis capitata, Wiedemann) to temperature. The model is used to explore how climate change might influence the distribution and abundance of this pest in Europe. We estimated the change in the distribution, abundance and activity of this species under current (year 2020) and future (years 2030 and 2050) climatic scenarios. The effects of climate change on the distribution, abundance and activity of C. capitata are heterogeneous both in time and in space. A northward expansion of the species, an increase in the altitudinal limit marking the presence of the species, and an overall increase in population abundance is expected in areas that might become more suitable under a changing climate. On the contrary, stable or reduced population abundances can be expected in areas where climate change leads to equally suitable or less suitable conditions. This heterogeneity reflects the contribution of both spatial variability in the predicted climatic patterns and non-linearity in the responses of the species’ life-history strategies to temperature.

Does Ammonia Released from Protein-Based Attractants Modulate the Capture of Anastrepha obliqua (Diptera: Tephritidae)?

Simple Summary

The West Indian fruit fly, Anastrepha obliqua (family Tephritidae), is an important pest of mango and guava in the Neotropical region. Previous studies have indicated that ammonia is involved in fruit fly attraction to sources of food, particularly if protein is present. In laboratory experiments, flies were attracted to ammonia solutions of increasing concentration. In contrast, fly captures by different protein-based attractants were not related to the quantity of ammonia released by the attractant. Flies also responded differently to yeast suspensions of different alkalinity that released different amounts of ammonia. In field experiments, flies were strongly attracted to yeast in ammonia solutions after 24 h, but this effect did not persist when measured over a 7-day period. We conclude that A. obliqua flies are attracted to ammonia solutions in the absence of other stimuli, but attraction to protein-based attractants or alkaline yeast suspensions is not correlated with the quantity of ammonia released by these substances. Ammonia is an important component in fruit fly attraction, which also seems to depend on the presence of other compounds derived from protein food sources in different stages of decomposition.

Abstract

Tephritid fly responses to food-based attractants involve a complex range of food-derived semiochemicals, including ammonia. We performed laboratory and field experiments to compare the attraction of Anastrepha obliqua (Macquart) to ammonia with the attraction to commercial food attractants and torula yeast at a range of pHs. A positive correlation was established between the concentration of ammonia in solution (1.5–150 mM ammonium solution) and gaseous ammonia released by bottle-type traps. This resulted in an asymptotic response in captures of A. obliqua flies in traps that released 99–295 µg ammonia/h. Pairwise comparisons in laboratory cages revealed that traps baited with 150 mM ammonia solution captured similar numbers of A. obliqua as traps baited with Biolure 2C, CeraTrap, and hydrolyzed protein products (Captor, Winner, and Flyral) plus borax, despite the low quantities of ammonia (11–56 µg/h) released from these attractants. Subsequent choice experiment captures in traps containing ammonia solution were similar or higher than those of commercial attractants, with the exception of Winner + borax, but were not correlated with the ammonia released from attractants. Captures of flies in traps containing ammonia solution were increased by the addition of 1% torula yeast or torula yeast alkalized with sodium hydroxide or borax despite differences in the quantities of ammonia released. Fly captures generally increased with increasing alkalization of torula yeast (pH 7.5–9.5). In the field, torula yeast in ammonia solution captured similar numbers of A. obliqua flies as Captor + borax when traps were evaluated after 24 h but not after a 7-day trapping period. Traps baited with ammonia solution or Winner + borax were significantly less attractive than Captor + borax in both field experiments. We conclude that A. obliqua flies are attracted to ammonia solutions of increasing concentration, up to 150 mM, in the absence of other stimuli, whereas attraction to commercial attractants or alkalized torula yeast is not correlated with the release of ammonia.

Vapor Pressures and Thermodynamic Properties of Phenylpropanoid and Phenylbutanoid Attractants of Male Bactrocera, Dacus, and Zeugodacus Fruit Flies at Ambient Temperatures

We report on the vapor pressures at ambient temperatures of seven attractants of Bactrocera, Dacus, and Zeugodacus fruit flies-raspberry ketone, cuelure, raspberry ketone trifluoroacetate, methyl eugenol, methyl isoeugenol, dihydroeugenol, and zingerone-by a vapor saturation method. Dry nitrogen was passed over each compound at well-controlled temperatures. Entrained vapor from the compounds was trapped on Tenax GR tubes and analyzed by thermal desorption-gas chromatography-mass spectrometry. The measured attractant amounts on the traps were converted to vapor pressures. Data were subsequently fitted by the Antoine equation. From the Antoine equation parameters, thermodynamic properties for each compound were calculated at 298 K. The calculated vapor pressures were used to compare the volatility of the fruit fly attractants and to infer implications for field applications. Using ambient temperature readings yields far better estimates of vapor pressure values at temperatures relevant for insect control than do Antoine equation parameters derived from high-temperature readings.

Recaptures of feral Bactrocera dorsalis and B. umbrosa (Diptera: Tephritidae) males after feeding on methyl eugenol

Two major fruit fly pest species, Bactrocera dorsalis and B. umbrosa, are strongly attracted to methyl eugenol (ME) found in >450 plant species. They are, however, exclusive pollinators of certain daciniphilous (attracting Dacini fruit flies) Bulbophyllum orchids. A comparison between the recaptures of feral males after feeding ad libitum on 0.6 mg ME (simulating an average floral quantity of an orchid flower - Trial 1) and 480 mg in Trial 2 was investigated using the non-invasive capture-mark-release-recapture (CMRR) technique. Based on daily CMRR over a 16-day period, using a different colour enamel paint each day, percentages of B. dorsalis males recaptured in Trial 1 were significantly higher than those in Trial 2. However, for B. umbrosa, percentages of recaptures for different day-specific colours were highly variable due to low fly numbers captured/day. In Trial 1, of 756 B. dorsalis males released, 36.4% were recaptured once, 7.7 twice, 2.4 three times and 0.4 four times. While in Trial 2 of 1157 released males, 6% were recaptured once and 0.3% twice. Of 67 B. umbrosa males released, 28.4% were recaptured once and none more than once in Trial 1. Nevertheless, of 119 flies released in Trial 2, 25.2% were recaptured once and 3.3% twice. Overall, many marked males did return to a single ME-source to 'refuel' ME (a sex pheromone precursor). The results also show that a relatively high number of flies paid multi-visitations to a single 0.6 mg ME-source and indicate that the presence of natural ME-sources may impact area-wide IPM programmes.

Chemical Composition of the Rectal Gland and Volatiles Released by Female Queensland Fruit Fly, Bactrocera tryoni (Diptera: Tephritidae)

The composition of the rectal gland secretion and volatiles emitted by female Queensland fruit fly, Bactrocera tryoni was investigated. Esters were found to be the main compounds in the gland extracts and headspace, while amides were the minor compounds in the gland extracts and headspace. Ethyl dodecanoate, ethyl tetradecanoate, ethyl (Z9)-hexadecenoate and ethyl palmitate were the main esters in the gland extracts, while ethyl dodecanoate and ethyl tetradecanoate were the main esters in the headspace. Four amides (N-(3-methylbutyl)acetamide), N-(2-methylbutyl)propanamide, N-(3-methylbutyl)propanamide, and N-(3-methylbutyl)-2-methylpropanamide were found in the gland extracts and the headspace. Among the amides, N-(3-methylbutyl)acetamide and N-(3-methylbutyl)propanamide were the main amides in the gland extracts and the headspace. Traces of three spiroacetals were found both in the gland extracts and in the headspace. (E,E)-2,8-Dimethyl-1,7-dioxaspiro[5.5]undecane, (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane, (E,E)-2-propyl-8-methyl-1,7-dioxaspiro[5.5]undecane. All compounds found in the headspace were present in the extract of the rectal gland suggesting that the rectal gland is the main source of the headspace volatiles, whose function remains to be elucidated. This is the first comprehensive chemical analysis of the rectal gland secretions and volatiles of female B. tryoni, and further laboratory and field bioassays are required to determine the function of compounds identified in this study. Discovery of the same amides previously identified in the male rectal gland in the female rectal gland raises questions about the pheromonal role previously suggested for these compounds.

A field test on the effectiveness of male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae) at varying application densities

Male Annihilation Technique (MAT) is a key tool to suppress or eradicate pestiferous tephritid fruit flies for which there exist powerful male lures. In the case of Bactrocera dorsalis (Hendel), a highly invasive and destructive species, current implementations of MAT utilize a combination of the male attractant methyl eugenol (ME) and a toxicant such as spinosad ("SPLAT-MAT-ME") applied at a high density with the goal of attracting and killing an extremely high proportion of males. We conducted direct comparisons of trap captures of marked B. dorsalis males released under three experimental SPLAT-MAT-ME site densities (110, 220, and 440 per km2) near Hilo, Hawaii using both fresh and aged traps to evaluate the effectiveness of varying densities and how weathering of the SPLAT-MAT-ME formulation influenced any density effects observed. Counterintuitively, we observed decreasing effectiveness (percent kill) with increasing application density. We also estimated slightly higher average kill for any given density for weathered grids compared with fresh. Spatial analysis of the recapture patterns of the first trap service per replicate x treatment reveals similar positional effects for all grid densities despite differences in overall percent kill. This study suggests that benefits for control and eradication programs would result from reducing the application density of MAT against B. dorsalis through reduced material use, labor costs, and higher effectiveness. Additional research in areas where MAT programs are currently undertaken would be helpful to corroborate this study's findings.

Terminalia Larval Host Fruit Reduces the Response of Bactrocera dorsalis (Diptera: Tephritidae) Adults to the Male Lure Methyl Eugenol

Methyl eugenol (ME) is a powerful semiochemical attractant to males of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), and is the keystone of detection, control, and eradication programs against this polyphagous and highly invasive tephritid pest. Despite its status as a model lure against B. dorsalis, variation among individuals in their attraction is known, independent of the generally increasing attraction with age and decreases with previous exposure. Here we report that adult male B. dorsalis that fed on Terminalia catappa L. (Myrtales: Combretaceae) (tropical almond) fruit as larvae have a significantly lower behavioral response to ME compared with wild males from Psidium guajava L. (Myrtales: Myrtaceae) or colony-reared males raised on artificial larval diet. F1 males from the tropical almond stock reared on artificial larval diet did not show reduced attraction to ME, suggesting that the lowered response of parental males (sires) results from the host fruit itself, perhaps its relatively high amount of ME. Experiments with ME added to artificial diet lend some support to this interpretation. In addition to the results above, we report on quantities of ME in three different host fruits (T. catappa, P. guajava, and Carica papaya L. (Brassicales: Caricaceae)) of B. dorsalis. This study indicates the need for further research on the effect of host fruit on adult response to lures in economically important tephritids.