Orientation of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) adults at various distances to different concentrations of aggregation pheromone 4,8-dimethyldecanal

Tribolium castaneum is a serious pest of durable agricultural commodities during storage. The male T. castaneum adults release the aggregation pheromone 4,8-dimethyldecanal (4,8 DMD). The 4,8 DMD is produced commercially and available to be used in Dome traps along with their recommended kairomone but low trapping response is often reported. Concentration of 4,8 DMD influences the attraction of T. castaneum adults but its intensity may vary under different warehouse settings. Further, the orientation response of T. castaneum adults from different distances to the synthetic 4,8 DMD is still uncertain. Therefore, the objective of this research was to evaluate the effect of distance to the traps having different 4,8 DMD concentrations on the orientation response of T. castaneum adults. The dome trap having two pheromone septa and kairomone was placed inside the experimental arena. From pheromone, different concentrations were used. One-month-old T. castaneum adults were individually marked and released from different distances at the same time. The adults reached the trap were counted 4 h following release. Alternatively the experiment was repeated without having the kairomone inside the trap. One trap having neither the pheromone nor kairomone (empty trap alone) and one having hexane only were used as controls. For all the pheromone concentrations used, the maximum trapping percentage was found when the beetles were released at 30 cm or 60 cm from the pheromone. Further, the highest trapping percentage was given by 0.5 μL of 4,8 DMD. At a given distance, the traps having pheromone+kairomone better attract T. castaneum adults than those had only the pheromone. The study concludes that the degree of attraction of T. castaneum adults varies with the distance from the trap and the trap composition. Further studies are required to test the efficacy of 4,8 DMD and kairomones under real warehouse settings.     

Response of different population sizes to traps and effect of spinosad on the trap catch and progeny adult emergence in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Tribolium castaneum is a major pest in stored products throughout the world. Male T. castaneum adults produce aggregation pheromone 4,8-dimethyldecanal (4,8 DMD) which is synthetically developed and available for monitoring T. castaneum populations but low trapping by 4,8 DMD is reported. Effects of biorational insecticides on orienting to pheromone and progeny production is shown but such tests using spinosad has areas for further discovery. Therefore the objective of this research was to determine the effect of population size and spinosad exposure on the trap catch and progeny production in T. castaneum adults. In the first experiment, T. castaneum adults were released at different population sizes and the attraction to the pheromone traps was determined. The second experiment tested attraction of T. castaneum adults pre-exposed to spinosad to the pheromone traps. In the third experiment, progeny production of T. castaneum adults exposed to spinosad was assessed. The trapping of T. castaneum is increased at high population sizes and pre-exposure to spinosad while progeny was reduced on exposure to spinosad showing sex-based effects. This study concludes with management opportunities for different population levels of T. castaneum through effects of spinosad on pheromone perception and progeny production.     

Food oils as kairomones for trapping Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) adults

Insect infestation in the grain-based food in storage is often reported; Tribolium castaneum is a major pest. Determination of its population size using traps is entangled with the management attempts. Pheromone traps developed for T. castaneum often use kairomones with its aggregation pheromone 4,8-dimethyldecanal (4,8 DMD). However, low trapping efficacy is reported, and the information on promising kairomones is insufficient. The objective of this research was to evaluate the performance of some locally-available food oils as kairomones, alone and in combination with the pheromone for trapping T. castaneum adults. In the first experiment, the attraction of T. castaneum adults towards different food oils, the pheromone or the commercial kairomone was tested. In the second experiment, the attraction of T. castaneum to effective food oils + pheromone was determined under laboratory condition. In the third experiment, the attraction of T. castaneum by effective food oils + pheromone was evaluated under warehouse condition. Under laboratory condition, the highest attraction of T. castaneum adults was demonstrated by mee (Madhuca longifolia) and coconut (Cocos nucifera) oils. Either of these two oils when combined with the pheromone attracted more adults than the pheromone alone. Furthermore, attraction of T. castaneum adults by the two oils separately was similar to the commercially-available combination of pheromone and the kairomone. In contrast, under warehouse condition, the combination of mee oil and pheromone attracted T. castaneum adults similar to the commercially-available combination of pheromone and the kairomone. However, the attraction by the combination of coconut oil and pheromone was lower than that, and similar to the pheromone only. This study emphasizes the potential use of food oils as kairomones to trap T. castaneum adults, and augment the efficiency of pheromone traps available for this species.     

Distance and height of attraction by walking and flying beetles to traps with simultaneous use of the aggregation pheromones from Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

Adults of Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) biosynthesize aggregation pheromones 4,8-dimethyldecanal and dominicalure-1/dominicalure-2, respectively. These pheromones are commonly used independently, and their simultaneous use has not been adequately studied. Furthermore, information on trapping flying R. dominica in pheromone traps is minimum. Therefore, the objectives were to evaluate distance of attraction of T. castaneum and R. dominica adults to traps having both pheromones, and height of R. dominica adult attraction to traps with its pheromone lure alone. In first experiment, both pheromones were deployed simultaneously inside a commercial pitfall trap. One-month-old 20 T. castaneum and R. dominica adults were released every 30 cm from the pheromone trap. The adults trapped were recorded at 4 and 24 h following their release. Adults of both species released were captured in higher percentages at 24 h than 4 h. At 30 cm distance, these values were 45.5% for T. castaneum and 10–12% for R. dominica for 24 h whereas they were 40.5% for T. castaneum and 5–7.5% for R. dominica following 4 h exposure. The maximum trap capture was at 30 cm for T. castaneum and 30–60 cm for R. dominica. In second experiment, a trap with two rubber septa containing dominicalure-1 and dominicalure-2 was placed at different heights inside cage, and R. dominica adults were released at the bottom. In each experiment, four replicates were tested. After 24 h, flying R. dominica adults were captured in progressively lower percentages as trap height increased up to 40 cm above the bottom of cage. Trap heights above 10 cm exhibited decreased trap capture of R. dominica compared to those at 3 cm. We conclude that simultaneous use of both aggregation pheromones better facilitates trapping of walking T. castaneum and R. dominica. Traps above 10 cm show decreased captures of flying R. dominica.     

Attraction of walking Tribolium castaneum adults to traps

The red flour beetle, Tribolium castaneum (Herbst), is a major pest of food processing facilities and can be monitored using pitfall type traps. To determine how beetles interact with these traps under field situations, the behavior of individual beetles released in the vicinity of traps was observed in a large arena. Specifically, the response of adults to traps baited with combinations of commercially available pheromone and kairomone attractants was measured, as was the influence of beetle sex and strain, airflow presence or absence, and distance from trap. The beetle's response to traps was strongest (e.g., more encountered trap, more remained in observation zone, more time was spent on treatment side, and decreased speed and increased turn angle) to pheromone/kairomone or pheromone baited traps when there was air movement, while kairomone alone and all attractants under still air conditions generated no significant response by the beetles. Even with the best combination of attractants and with airflow, average number encountering trap was only 40%. With airflow, beetles were successful at locating a pheromone/kairomone baited trap out to 90 cm, the maximum distance tested, but under still air conditions even at 10 cm there was no difference between traps with and without attractants. Since airflow at trap locations within commercial food facilities can vary considerably, these patterns of response to traps could significantly impact insect detection.     

Orientation of Tribolium castaneum (Coleoptera: Tenebrionidae) adults to 4,8-dimethyldecanal,kairomone and botanical oils following ambient,low, or high temperature exposure

The aggregation pheromone 4,8-dimethyldecanal (4,8 DMD) used alone or with kairomone-baited traps generally is used for monitoringTribolium castaneum (Herbst) but low efficiency is reported. Furthermore, insect orientation to pheromones and kairomones following low or high temperature exposure is not yet understood. This research evaluated the orientation of T. castaneum adults to 4,8 DMD and common kairomones following exposure to ambient, low or high temperatures. Fifty adults were introduced to the middle of rectangular glass chamber, and movement to the treatment or control was determined after 1 h. In experiment 1, insects reared at 30°C were used. Experiments 2 and 3 used insects exposed to 10°C for 4 days (cold temperature) and 42°C for 12 h (brief high temperature), respectively at 2–8 h following cold or heat exposure. The highest trapping occurred when 4,8DMD was combined with neem oil whereas the lowest was in coconut oil alone. Neem oil alone demonstrated repellent action. Prior exposure to cold or heat initially reduced taxis of T. castaneum adults to traps. The attraction for adults exposed to cold and heat was restored after 6–8 h when traps contained pheromone + neem or coconut oil. This study marks the first to experimentally test how exposure to high or low temperatures, two key IPM tactics in the post-harvest supply chain, affects the behavioral response of an important stored-product species to pheromone- and kairomones-baited traps.     

A potential method for simultaneous,semiochemical-based monitoring of Cryptolestes ferrugineus and Tribolium castaneum (Coleoptera: Cucujidae and Tenebrionidae)

Capture and analysis by gas-liquid chromatography of volatiles from adult Cryptolestes ferrugineus (Stephens) infesting rolled oats disclosed that the naturally-produced ratio of the aggregation pheromones 4,8-dimethyl-(E,E)-4,8-decadienolide (I) and (3Z, 11S)-dodecen-11-olide (II) is 1.6:1.0. Approximately 990 and 640 pg/male beetle/h of the 2 pheromones, respectively, were produced in a culture with 76 beetles of mixed age and sex/g of oats. A newly designed trap, which confines beetles responding to attractive odors within an enclosed chamber, was very effective in recapturing released C. ferrugineus when baited with a 13:16 mixture of I and (±)-II released at 1.25 μg/24h, and also in recapturing released adult Tribolium castaneum (Herbst), in response to the aggregation pheromone, 4,8-dimethyldecanal, released at 0.08 μg/24h. Moreover, the capture of each species to traps baited with both species' pheromones was no different than to traps baited with its pheromone alone. Thus the pheromones of both species can be used together in the same trap in semiochemical-based, pest monitoring systems.     

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

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.     

Testing the consistency of spatio-temporal patterns of flight activity in the stored grain beetles Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.)

Many studies have been published on the flight activity of stored grain beetles in temperate regions, but few have focussed on tropical and sub-tropical regions. The spatio-temporal patterns of flight activity of Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) were quantified in a grain growing district on the Tropic of Capricorn in central Queensland, Australia. Nine traps baited with aggregation pheromone lures were monitored at 2-wk intervals (fortnightly) for 1 year along a 28.4 km linear transect that included sites at bulk grain depots and sites away from stored grain. Beetles of both species were trapped every fortnight during the study. The spatio-temporal patterns of flight activity differed greatly across the two species, as predicted from studies elsewhere. Rhyzopertha dominica was widespread across the landscape, as the mean trap catch of this species was equal in depot and non-depot traps. In contrast, T. castaneum was more frequently trapped in depot traps than non-depot traps during the colder months, but was much more widespread across the landscape during the summer months. Tribolium castaneum also showed a clear mid-summer peak in flight activity, whereas R. dominica flight activity was highly variable throughout the study. In general, our results reveal patterns that are consistent with those found for T. castaneum and R. dominica in southern Queensland. The contrasting spatio-temporal patterns of flight activity of R. dominica and T. castaneum show that species-specific approaches may be needed to manage these pests and that the spatio-temporal dynamics of resistance genes may differ across these species.     

Characterization of volatile organic compounds released by granivorous insects in stored wheat

Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by Tribolium castaneum (red flour beetle) and Cryptolestes ferrugineus (rusty grain beetle) by headspace analysis. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The amount of volatiles produced by T. castaneum adults increased with an increase in insect density. The concentration of methyl-1,4-benzoquinone; ethyl-1,4-benzoquinone; and 1-tridecene released by ten adult insects were: 8.5, 9.1 and 10.6 μg/100 μL compared to 7, 8 and 4.2 μg/100 μL for five adult insects. Extreme high or low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35 °C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition or at extreme cold or hot condition. The C. ferrugineus adults did not produce any detectable amount of volatiles even at very high insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile compounds as produced by T. castaneum insects alone.     

Response of Tribolium castaneum and Tribolium confusum adults to vertical black shapes and its potential to improve trap capture

Tribolium castaneum and Tribolium confusum can be monitored in food processing facilities using traps baited with pheromones and kairomones, but beetle response to traps might be enhanced by adding visual cues. Against a white background, T. castaneum adults were more likely to visit black pillars than white pillars when presented with a choice (e.g., 73% of beetles visited black and 17% visiting white pillar), and visits to black pillars increased with pillar height. When tested against a black background, beetles did not show a significant preference for either color pillar regardless of height. When comparing beetle’s captures in pheromone/kairomone baited traps placed in front of a white or black panel in a white arena under high, low, or dark light conditions, more beetles were captured in traps in front of black panels under both high and low light conditions, but not under dark conditions. A similar pattern of capture under low light and dark conditions was also found for the closely related species T. confusum. In a larger scale choice test, the same pattern of greater T. castaneum captures in traps in front of black panels than white panels was obtained, whether traps were placed in corners or along walls. Our results suggest that captures in monitoring traps could be increased by adding dark vertical shapes behind trap locations or placing traps near dark structures.     

Male-produced sex pheromone in Tribolium confusum: Behaviour and investigation of pheromone production locations

It is generally accepted that mating in flour beetles of the genus Tribolium is mediated by a male-produced aggregation pheromone. The pheromone production site in T. castaneum is believed to be glands on the ventral side of the femur. Behavioural experiments with the confused flour beetle T. confusum were conducted using extracts of beetles and different body parts as well as live beetles to investigate the responses to the complete odour bouquet released from the beetles. In our experiments, females but not males were attracted to male-produced volatiles, corresponding to the definition of a sex pheromone rather than an aggregation pheromone. SEM pictures confirm the occurrence of glands on all three pairs of legs of male T. confusum, but behavioural experiments show that females are attracted not only to extracts of male legs but also to whole body extracts and extracts of bodies without legs. These data suggest that in this species attractive compounds are produced not only in the glands on the femurs but also at multiple locations. Thus the pheromone systems involved in mating of flour beetles may be more complex than previously reported and differ among closely related species.     

Comparative performance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) across populations,resource types and structural forms of those resources

The significance of Tribolium castaneum (Herbst) as a pest of stored grains will likely be influenced by the relative availability of different resources regionally and the beetles’ ability to utilize each of them. Therefore the performance across the life cycle of laboratory and field populations of T. castaneum on commonly available structural forms of wheat and sorghum, as conventional resources, was quantified and compared to that on cotton seed. The latter is not usually associated with T. castaneum, but large beetle infestations have been recorded commonly in cotton gins in Australia. The highest number of individuals of each stage (from a given number of eggs) developed on wheat and sorghum flour and kibbled seeds. Cotton seed did not support the development of laboratory population beetles and all neonate larvae died before pupation. In contrast, some of the field population larvae did develop on cotton flour, but their number was significantly lower in comparison to development on wheat and sorghum. Field population beetles produced significantly more eggs than did laboratory population beetles, on both the whole seed and flour. Field population females had a consistently higher fecundity (～78% more eggs) than the laboratory population females, at least over the first three weeks of adult life. These results suggest that field populations of T. castaneum should be used in experiments if we are to develop a more realistic understanding of the field ecology of this species. The relative rate at which these insects infest available resources in the field also warrants further investigation.     

Deployment of an attractive toxic sugar bait system (ATSB) with insecticide,for adult Tribolium castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum is a critical stored-grain pest of nuts and cereals. Insecticides have traditionally been used to control it; however, their overuse can result in the development of insecticide resistance. Effective bait pesticides could be useful tools for slowing down the rate of insecticide-resistance development and improving the management of stored grain pests. Attractive toxic sugar bait (ATSB) systems are used with mosquitoes and flies; they lure pests with liquid foods that contain sugars but also an oral toxin. It is unknown whether the ATSB system is applicable to T. castaneum adults who prefer dry food products with reduced water content. The objective of this study is to develop an optimal ATSB system for T. castaneum control. Thus far, it found that T. castaneum consumed a gypsum block. The dietary intake of T. castaneum adult beetles was facilitated with added mannitol into gypsum block. Combining insecticides that are oral toxins of the pests with these facilitating sugars results in the death of the pest. Spirotetramat causes a significant reduction in fatty acid biosynthesis by inhibiting acetyl-CoA carboxylase. In this investigation, we have demonstrated that spirotetramat, at low concentrations, was lethal to T. castaneum adults, when used with the ATSB system, combined with mannitol. The lethality of chlorfenapyr, an inhibitor of mitochondrial ATP synthesis, to adult T. castaneum did not increase when used in the ATSB system with mannitol. These results show that the active ingredient used in the ATSB system is integral for beetle control. Increasing the oral delivery rate of insecticides using carbohydrates leads to increased lethality rates of stored-grain pests.     

Isofuranodiene-based nanoemulsion: larvicidal and adulticidal activity against tenebrionid beetles attacking stored wheat

The resistance of insect populations to the existing insecticides grows fast due to their continuous use. Thus, the need for new and effective formulations is increasing. Isolated compounds of botanical origin may represent a promising solution for green pest management strategies. In this study, isofuranodiene derived from Smyrnium olusatrum L. (Apiales: Apiaceae) essential oil (EO), was nanoemulsified (3% w/w) to treat wheat kernels with two concentrations (500 and 1000 ppm) against adults and larvae of three tenebrionid beetles attacking stored products, the red flour beetle, Tribolium castaneum (Herbst), the confused flour beetle Tribolium confusum Jacquelin du Val, and the yellow mealworm beetle, Tenebrio molitor L. Mortality rates were calculated after 4, 8 and 16 h and 1, 2, 3, 4, 5, 6 and 7 days. The isofuranodiene-based nanoemulsion (NE) exhibited high adulticidal effects against T. molitor, and larvicidal activity against T. castaneum and T. confusum, reaching 98.6, 97.4 and 93.5% at 1000 ppm after 7 days of exposure, respectively. On the other hand, the NE caused low mortality rates on adults of T. castaneum and T. confusum, as well as on larvae of T. molitor, not exceeding 26.2, 10.0 and 15.6% at 1000 ppm, 7 days post-exposure, respectively. Overall, the 3% (w/w) isofuranodiene-based NE developed here has a significant potential to protect stored wheat from tenebrionid beetle infestations.     

Monitoring flight activity of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in outdoor environments using a commercial pheromone lure and the kairomone 1-octen-3-ol

Effective trapping techniques for Cryptolestes ferrugineus are essential for developing an understanding of the ecology of this beetle outside the storage environment, and will assist in monitoring the spread of fumigant resistance in field populations. We evaluated ten different volatile compounds associated with stored grains or fungi as potential attractants for C. ferrugineus using Lindgren funnel traps fitted with glass dispenser tubes. Only two compounds, 1-octen-3-ol and 3-octanone, were effective attractants in outdoor environments. Beetle captures increased with increasing release rates of both compounds. 1-octen-3-ol was the most effective attractant, and we evaluated it in conjunction with a commercial rubber septum lure containing the two macrocyclic lactones that constitute the C. ferrugineus aggregation pheromone. In parallel trials the commercial lure performed poorly, catching only 2% of the wild beetles recovered. 1-octen-3-ol deployed alone caught 26% of beetles, however a combination treatment (pheromone lure + 1-octen-3-ol) accounted for 72% of C. ferrugineus captures, suggesting a synergistic interaction. Evaluation of rubber septa impregnated with 1-octen-3-ol demonstrated that these were just as effective as glass release tubes when deployed with the pheromone lure over a five day period. A comparison of different trap types using the pheromone lure/1-octen-3-ol combined attractants showed that significantly more C. ferrugineus were captured with a panel trap than with either 4-unit or 9-unit Lindgren funnel traps, correlating to the much higher rate of 1-octen-3-ol volatilisation from the panel trap. A funnel trap fitted with a 1-octen-3-ol dispenser was used to continuously monitor C. ferrugineus flight activity for a three year period and captured 4335 individuals, demonstrating that although optimum catches are obtained using the pheromone/1-octen-3-ol combination, 1-octen-3-ol can be used alone to monitor the seasonal flight activity of C. ferrugineus.     

Evaluation of kaolinite-based particle films to control Tribolium species (Coleoptera: Tenebrionidae)

Adults of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed to kaolinite-based particle film dusts. When beetles were continuously exposed to the hydrophobic particle film M-96-018 at the rate of 0.1-0.5 mg/cm², all the T. castaneum at 0.1 mg/cm² were dead after 3 days, but 40±13.8% of the exposed T. confusum were still alive after 7 days. At higher concentrations, all the T. castaneum were dead after 2 days, but 5-6 days of exposure were needed to kill all T. confusum. In a subsequent test, adults of both species were exposed for 8-72 h to 0.5 mg/cm² of the particle film M-96-018, removed, then held without food for 1 week. No T. castaneum survived, while survival of the T. confusum ranged from 0 to 55±17.3%, depending on the exposure interval. In a test conducted at controlled conditions of 40%, 57% and 75% r.h., 27°C, T. confusum were exposed for 8-72 h to the particle film M-96-018 and a hydrophilic particle film M-97-009 at the rate of 0.5 mg/cm², then removed and held either with or without wheat flour for 1 week. All the T. confusum exposed to the particle film M-97-009 usually survived, while survival of the T. confusum exposed to the particle film M-97-018 after the 1-week holding period increased with increasing relative humidity and with the presence of food. The particle film M-96-018 was effective against both the Tribolium species, and appears to have a potential for use in management programs to control beetles within storage facilities.     

From immobilization to recovery: Towards the development of a rapid diagnostic indicator for phosphine resistance

The aim of this work was to evaluate the insect mobility patterns of phosphine-resistant and -susceptible adults of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) after exposure to phosphine. Exposure bioassays were carried out at two concentrations, 1000 and 3000 ppm, while adults were observed every 15 min, for a total period of 90 min. During this observation interval, adults were visually classified as active (able to walk normally), partially immobilized (not able to walk, but showing a minimal movement), or completely immobilized (no visible movement). After the observation period, all adults were placed in a phosphine-free environment, and they again were classified as active, partially immobilized or completely immobilized. At 1000 ppm, the majority of adults of the susceptible T. castaneum population were quickly immobilized after a 15 min observation period, while in contrast, the majority of adults of the resistant T. castaneum population were still active after the termination of the 90 min interval. At 3000 ppm, the percentage of immobilized susceptible adults was increased at the 15 min observation period, while the majority of resistant adults were immobilized only after 90 min. In the post-exposure period, the vast majority of the susceptible adults were dead. In contrast, most resistant adults recovered, regardless of the concentration that had been exposed. The results of this study delineate major differences in movement in phosphine-resistant and -susceptible T. castaneum strains, and can be applied as a quick diagnostic bioassay for the evaluation of resistance to phosphine in stored product insects.     

Toxicity and repellent action of Coffea arabica against Tribolium castaneum (Herbst) adults under laboratory conditions

Coffea arabica parchment extracts and caffeine isolated from the plant were evaluated randomly against 1-week-old adults of red flour beetle, Tribolium castaneum for fumigant toxicity and repellent action under laboratory conditions. The effects on detoxification enzymes and neuroenzyme was also determined. Among the various extracts prepared sequentially using hexane, dichloromethane, ethyl acetate and methanol as solvents, the dichloromethane extract did repel insects on contact (EC₅₀ = 4380.65 ppm). The repellence was more prominent when an olfactory response was measured (EC₅₀ = 2571 ppm). The active ingredient isolated from dichloromethane extract was identified as caffeine which showed very strong repellency as compared to the extract. In terms of toxicity of this extract, a significant mortality was recorded in fumigation assay (LC₅₀ = 5555 and 791 ppm, 24 and 48 h post-treatment, respectively). However, caffeine did not induce similar toxicity as the dichloromethane extract. The studies on the impact on detoxification enzymes of T. castaneum showed that dichloromethane extract inhibited carboxyl esterase activity, which possibly led to high toxicity. However, caffeine inhibited glutathione-s-transferase and induced carboxylesterase enzymes. It was, therefore, obvious that C. arabica parchment crude extracts have dual effects against T. castaneum adults, i,e, fumigant toxicity and repellent effects. However, the active compounds responsible for the two activities are surely different as caffeine could only induce repellent action against the beetles and the toxic compound needs to be identified, which is presently being investigated.