Evaluation of Solid Lure Plugs and Insecticide Dispensers on Capturing Dacine Fruit Flies and Non-target Insects

INTRODUCTION

The Dacini fruit flies within Tephritidae (Diptera: Tephritidae) are mainly florivorous or frugivorous and approximately 10 percent of the 932 recently recognized species are pests of various vegetables and fruits [1, 2]. The genus includes various highly invasive and/or serious polyphagous pest species viz., the melon fly, Zeugodacus cucurbitae (Coquillett), the pumpkin fruit fly, Zeugodacus tau (Walker), Bactrocera dorsalis sensustricto (Hendel), the oriental fruit fly, the peach fruit fly, Bactrocera zonata (Saunders) and many others. Ceratitis is also a genus of Tephritidae having around 65 species found in tropical and South Africa with many pest species. The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) which has spread to almost all warm temperate and tropical areas worldwide and captured using food baited traps in Hawaii and also traps baited with different amount of trimedlure (TML) [3, 4]. From an economic perspective, different fruit fly species of these genera: i. inflict direct and extensive damage to fleshy vegetables and fruits, ii. cause quarantine restrictions on infested areas, iii. need commercial fruits to undergo postharvest and protective treatment before export, and iv. provide a breeding reservoir for their introduction into other parts of the world [5]. Recently, the alarming invasion of these insects has been increased due to the increased human travel and global trade worldwide. These insects have been suppressed and even eradicated through the area-wide utilization of male lures. In addition to detection programs, the male lures also have been used to control or suppress through the male annihilation technique (MAT) [6-9]. The most commonly used Tephritids male lures for detection are TML (tert-butyl 4- and 5-chloro-cis- and trans-2-methylcyclohexane-1-carboxylate), raspberry ketone (RK) (4-(p-hydroxyphenyl)-2-butanone), Cue-lure (C-L) (4-(p-acetoxyphenyl)-2-butanone), and Methyl eugenol (ME) (4-allyl-1, 2-dimethoxybenzene-carboxylate). These are powerful male-specific lures. Males of above mentioned Bactrocera fruit flies are attracted to either C-L/RK or ME. TML is known to attract numerous male Ceratitis species (e.g., C. capitata and C. rosa Karsch) and is a mixture of eight isomers. ME is a widely distributed natural plant product and is found in >200 plant species in 32 families mainly found in the tropics. C-L has not been isolated as a natural product but it is rapidly hydrolyzed and forms RK, a very effective lure for Z. cucurbitae. An investigation recently reported that the CL hydrolysis is negligible and it remains intact in the atmosphere in the time-frame of the compound acting like a fruit fly lure [10]. Moreover, C-L was recently discovered in 2 daciniphilous flowers- Bulbophyllum hortorum [11, 12] and Passsiflora maliformis L. [13]. However, RK was isolated originally from Dendrobium superbum Rchb. F.  A novel fluorinated ana-log of raspberry ketone, raspberry ketone trifluoroacetate (RKTA) found to attract significantly more Q-flies, Bactrocera tryoni (Froggatt) than cuelure or melolure [14, 15]. However, of the 54 Dacini species (comprised of the 2 main genera Dacus F. and Bactrocera Macquart) that are agricultural pests, 16 respond to ME and 26 to C-L/RK.

In fruit fly suppression and detection programs, various types of traps were used baited with these male lures (plus a toxicant) usually in liquid form. Some of the common traps used for detection with C-L and ME are bucket, Champ, Jackson, and Steiner traps [16]. A surveillance reported on non-target insects captured in tephritid fruit fly traps in South Korea and also a novel dispensing system for male lures used to detect invasive fruit flies [17, 18]. MAT carriers including molded paper fiber, Min-U-Gel, cotton wicks, and fiberboard blocks are commonly used in different countries. For instance, fiberboard blocks impregnated with ME and different organophosphate insecticides including naled and malathion were utilized to eliminate B. dorsalis from Okinawa, and papaya fruit fly, Bactrocera papaya Drew and Hancock from Australia. Usually, the liquid lures have been a mixture of ME or C-L and liquid insecticides viz., nailed or malathion, placed on a cotton wick. These involve significant handling to measure and apply the liquids, and also potential health risks due to pesticide exposure [6, 19-21]. However, eventually, there is progressing toward replacement of liquid C-L and ME and insecticides with solid formulations (such as C-L plugs or Scentry ME cones, North Bend, WA, ME wafers, Farma Tech (FT), Boseman, MT) [3, 22, 23] and with solid lure/insecticide (such as DDVP) combinations [9], which proved convenience and safe for workers. Again, it was revealed that traps lacking an insecticide and containing a male lure generally captured fewer Z. cucurbitae or B. dorsalis males compared to those containing a naled plus lure or a separate DDVP strip [19]. It was also demonstrated that the presentation of a male lure plus spinosad, a low-risk pesticide, did not increase the effectiveness of the trap more than what was observed for traps with no insecticide. There is not any suitable alternative to organophosphate insecticides, and fruit fly surveillance programs continue to use them to retain insects in the traps [4, 17, 24, 25]. ‘Given this constraint, it was recommended that pre-packaged DDVP strips, which are safer and easier to handle than lure-naled solutions, can be as effective as these solutions in detecting infestations or monitoring Tephritids populations. The HAWPM (Hawaii Fruit Fly Area-Wide Pest Management Program) (2000-2009) program effectively-researched, developed, and registered novel fruit fly monitoring and control technologies (IPM package, i.e., (i) monitoring, (ii) field sanitation, (iii) protein bait sprays, (iv) MAT, (v) augmentative parasitoid releases, and (vi) sterile insect releases) [22]. The HAWPM has set one of the best examples of using traps baited with solid dispensers of male lures in MAT and monitoring of Bactrocera fruit flies. However, there has been much concern about the possible non-target effects of such lures on beneficial insects. The use of male lures for fruit fly control may impact non-target insects or risk possible extinction of small endemic populations in large-scale fruit fly eradication programs [26].

In Bangladesh, a new species and 33 new country records for Tephritid fruit flies were reported [27-30]. Four species in particular, B. zonata, B. dorsalis, Z. tau, and Z. cucurbitae - inflict serious damage to fruits and fleshy vegetables production in Bangladesh. Recently, the pheromone traps have gained popularity and become a vital tool for pest monitoring in a wide range of crops in Bangladesh. The design of the pheromone trap [31, 32], its placement, and the ratio of the chemical components are the factors influencing the number of insect capture [33]. The formulation of different lures, use of novel lures [34-41], combination of lures and traps [42, 43] are also considered as critical issues for the capture of pestiferous fruit flies. There was also scanty of literature on the use of solid formulation of male lures and the impact of these lure baited traps on non-target and beneficial insects in Bangladesh. The present study, therefore, has been undertaken to determine the efficiency of three solid single lure plugs (ME, C-L, and TML) in conjunction with insecticidal strips (DDVP) baited traps on the capture of four economically important Dacine fruit flies in Bangladesh. We also evaluated non-target attraction effects to traps baited with these lures.

MATERIALS AND METHODS

Study sites

In the present study the capture of two cucurbit pests Z. cucurbitae, Z. tau, and the fruit pests B. dorsalis and B. zonata were recorded at three green areas of Bangladesh during May-September, 2015. The experimental areas (Figures 1a and 1b) were: i. Atomic Energy Research Establishment (AERE) colony, Savar, Dhaka (8.64 ha) 23°57'35.60"N, 90°16'54.02"E, ii. AERE office campus, Savar, Dhaka (112.276 ha), 23°57'14.62"N, 90°16'44.79"E), and iii. Jahangirnagar University (JU) campus (214.62 ha) 23°52'8.85"N, 90°16'1.50"E) with mean monthly rainfall 394.5 mm, (minimum 185mm, maximum 623mm), mean monthly temperature 29.17 °C (minimum 25.7°C, maximum 31.8°C), and mean monthly relative humidity 77% (minimum 71%, maximum 81%). These areas mainly comprised of agricultural fields, backyard gardens, and mixed plantation with a diversity of vegetables and fruit trees planted, including jack fruit (Artocarpu sheterophyllus Lam.), guava (Psidium guajava L.), mango (Mangifera indica L.), and Oranges (Citrus), Star fruit (Carambola or Averrhoa), banana (Musa)  and also various vegetable hosts including melon (Cucumis), pumpkin (Cucurbita), Brinjal (Solanum melongena), chili peppers (Capsicum), etc. along with other non-host trees. The three experimental areas reflect typical of existence fruit and vegetable production and are commonly infested with Dacine fruit flies across much of Bangladesh.