Effects of aggregation pheromone concentration and distance on the trapping of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) adults

https://doi.org/10.1016/j.jspr.2020.101657Get rights and content

Highlights

  • Rhyzopertha dominica adults were released at various distances from traps.

  • Traps had pheromone (different concentrations) alone or together with kairomone.

  • Pheromone + kairomone attracts more R. dominica adults than pheromone alone.

  • Highest attraction of R. dominica occurs until 70 cm from pheromone.

  • Pheromone at 100 μL/1 m2 provides the maximum attraction of R. dominica adults.

Abstract

Rhyzopertha dominica male adults produce an aggregation pheromone that attracts both sexes. While many studies have tested the behavioral response of R. dominica adults to its aggregation pheromone, information on the distance of attraction and effective pheromone concentration are lacking. Therefore, the objectives of this study were to determine the recapture rate of R. dominica adults released at different distances from a pheromone-baited and pheromone + kairomone-baited trap, as well as the most effective pheromone concentration for R. dominica. Experiments were arranged as complete randomized design with four replicates. A commercial pitfall trap containing R. dominica pheromone alone or pheromone + kairomone was placed inside an experimental arena. Adult R. dominica were released at different distances from the trap and the adults captured were counted. A separate experiment was conducted using pitfall traps containing different concentrations of the aggregation pheromone placed inside the experimental arena. Adult R. dominica were released 60 cm away from the pitfall trap and the recaptured adults were recorded. The trapping efficiency was higher when the trap contained both the pheromone and kairomone than the pheromone alone. Trap capture was highest when the beetles were released at distances up to 70 cm and at a concentration of 100 μL/1 m2. Our findings suggest that food facility managers should take into account the effective pheromone concentration and distance of attraction, while also strongly consider including food kairomones in traps when developing monitoring programs for R. dominica.

Introduction

Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) has long been reported as a serious pest of stored food worldwide infesting fresh and processed food resources belonging to 53 plant species in 31 families (Potter, 1935; Crombie, 1941; Cotton, 1956; Aitken, 1975; Edde, 2012; Buonocore et al., 2017). It has been recorded on a variety of raw and processed food products, including cereals and pulses (Sinha and Watters, 1985), other crops such as legumes, tubers, bulbs (Rees, 2004), animal feed (Wijayaratne et al., 2019), products of medical importance, and in some woody and animal-based packaging materials (Riley, 1882; Winterbottom, 1922; Potter, 1935).

General management measures adopted for R. dominica and other stored-product insects include inspection of incoming raw materials on a regular basis, following sanitation practices in the maintenance of equipment and structure, chemical control methods (Larson et al., 2008; Martinazzo et al., 2000; Sakka et al., 2020), hermetic storage (Bailey, 1965; Donahaye et al., 1996; Carvalho et al., 2012a,b; Hasaranga et al., 2018). In addition, the management strategies for R. dominica may also include the use of aeration (Yang et al., 2017), modified atmosphere (Wijayaratne et al., 2009; Levy-De la Torre et al., 2019), application of ozone (Subramanyam et al., 2017; E et al., 2019), and extreme temperatures (Fields, 1992). However, there are some limitations in the currently-available control methods for R. dominica. Resistance to the conventional insecticides such as deltamethrin (Attia, 1984; Chen and Chen, 2013) and phosphine (Collins et al., 2017; Yang et al., 2018) as well as novel pest management agents such as spinosad (Chen and Chen, 2013; Yang et al., 2018) has been detected in R. dominica. In addition, many of these insecticides may cause deleterious effects on non-target species, human applicators, and the abiotic environment (Fields, 1992; Arthur, 1996; Hagstrum and Subramanyam, 2006; Phillips and Throne, 2010; Wijayaratne et al., 2018). Therefore, the adoption of reduced-risk or biorational methods in the protection of stored food commodities from insect pest infestation remains a high priority at present.

Rhyzopertha dominica emits a male-produced aggregation pheromone that attracts both sexes (Khorramshahi and Burkholder, 1981; Williams et al., 1981; Cheskis et al., 1985; Liu and Lin, 1990; Razkin et al., 1996). In particular, the aggregation pheromone is a mixture of (S)-(+)-1-methylbutyl-(E)-2-methyl-2-pentenoate (dominicalure-1, or DL-1 hereafter) and (S)-(+)-1-methylbutyl-(E)-2,4-dimethyl-2-pentenoate (dominicalure-2, or DL-2 hereafter) (Williams et al., 1981) in a natural ratio of 1:2 (DL-1:DL-2),which serves as a lure in baited traps (Cogburn et al., 1984; Leos-Martinez et al., 1987; Fields et al., 1993; Fields and Phillips, 1994; Mills and White, 1994; Trece Inc., 2019). A substantial amount is already known about the basic chemical ecology of R. dominica. For example, this includes pheromone emission rates by adults (Edde and Phillips, 2010); effect of trap design (Leos-Martinez et al., 1987; Edde et al., 2005), age, sex, and female mating status (Dowdy et al., 1993), daily rhythm of pheromone release (Bashir et al., 2003a), as well as orientation differences of males and females (Cordeiro et al., 2019). However, the response of R. dominica adults when its pheromone components are used in commercial traps is limited.

The monitoring traps commercially available for certain other stored-product insect species such as Tribolium castaneum (Herbst) concurrently use kairomone with the pheromone (Campbell, 2012; Dissanayaka et al., 2020b). Similarly, the response of R. dominica to its pheromone when used in the traps either alone or in combination with kairomone under warehouse conditions needs to be determined to achieve the maximum benefit of using pheromone technology for monitoring of this species. Furthermore, deployment of correct trap density is required for accurate estimation of an insect population (Buckman and Campbell, 2013). Attraction of R. dominica adults located at various distances from the trap and the efficiency of adult attraction to different pheromone concentrations are two basic requisites for such determination of optimum trap density. However, the unavailability of these important information on R. dominica limits the potential use of aggregation pheromones in the monitoring programs for this pest within food facilities targeting its management and protection of stored food from its infestation. Therefore, the objectives of this study were to determine the distance of attraction to the traps baited with R. dominica pheromone, and to elucidate the effective pheromone concentration that maximizes attraction by R. dominica adults.

Section snippets

Insects

Rhyzopertha dominica were reared in the Entomology laboratory of Rajarata University of Sri Lanka since 2017 using routine culturing procedures (Wijayaratne et al., 2019). The colony was obtained from Anuradhapura, Sri Lanka at a commercial food facility. Cracked rice (var. Red Nadu) was used to rear the insects. One-month-old adults were used in the experiments below.

Pheromones, kairomones and traps

The two aggregation pheromone components of R. dominica, including(S)-(+)-1-methylbutyl-(E)-2-methyl-2-pentenoate (DL-1) and (S

Experiment 1: distance of attraction by Rhyzopertha dominica to pheromone-baited traps

Release distance of R. dominica affected recapture in traps baited with pheromone only (F20,63 = 21.21, P < 0.001). While recapture of R. dominica linearly declined with increasing distance of release from the trap, the percentage recaptured at 30 cm was not significantly different from recapture up to and including adults released 60 cm away from the trap (Fig. 3). The distance of attraction (e.g. recapture) by traps dropped off for adults released at 70 cm and 80 cm compared with those

Discussion

Capture of insects in pheromone-baited traps may be affected by a variety of factors, including trap design (Morrison et al., 2015), pheromone concentration (Morrison et al., 2016), presence of specific stimuli (Dissanayaka et al., 2018b), plume reach (Kirkpatrick et al., 2019), among other factors. Most notably, here we found that that attraction by R. dominica adults to traps quickly drops off with distance, and is significantly lowest once one moves 60 cm or 70 cm away from pheromone-baited

CRediT authorship contribution statement

D.M.S.K. Dissanayaka: Conceptualization, Investigation, Data curation, Formal analysis, Writing - original draft. A.M.P. Sammani: Investigation. L.K.W. Wijayaratne: Conceptualization, Methodology, Validation, Supervision, Writing - review & editing, Resources, Funding acquisition, Project administration. R.H.S. Rajapakse: Writing - review & editing. S. Hettiarachchi: Writing - review & editing. W.R. Morrison: Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors are thankful to the Sri Lanka Council for Agricultural Research Policy (NARP/16/RUSL/AG/01) for the financial assistance provided for this experiment. Mention of trade names is solely for the purposes of providing scientific information and does not constitute endorsement by the U.S. Department of Agriculture (USDA). The USDA is an equal opportunity employer.

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