Michael D. Toews

Responses of Rhyzopertha dominica (Coleoptera: Bostrichidae) to Its Aggregation Pheromones as Influenced by Trap Design, Trap Height, and Habitat

Abstract Lindgren multiple funnel traps and Japanese beetle traps captured more lesser grain borers, Rhyzopertha dominica F. (Coleoptera: Bostrichidae), than did Pherocon II sticky traps or bucket traps when all were baited with the same aggregation pheromones. Bucket traps captured six-fold fewer beetles than Lindgren four-unit traps. Retentions of captured R. dominica were not significantly different in traps with soapy water or dry insecticide as killing agents for either trap design but were significantly higher than those retained in traps lacking a killing agent. Lindgren eight-unit funnel traps captured a similar number of R. dominica compared with the four-unit funnel traps. More beetles were captured near grain storage facilities than in forests or in open fields. Trap height (1, 2, or 4 m above the ground) had no detectable effect across habitat but significantly interacted with habitat. Traps placed 1 or 2 m high near grain elevators and in open fields captured similar numbers of beetles and yielded higher catches of R. dominica than traps placed 4 m high in these habitats. The reverse was true in forest habitats. Captured R. dominica were similarly female-biased in all trap designs, and the proportion of females to males did not differ among trap heights or habitats in which they were trapped.

Monitoring Tribolium castaneum (Coleoptera: Tenebrionidae) in Pilot-Scale Warehouses Treated with Residual Applications of (S)-Hydroprene and Cyfluthrin

Abstract Pilot-scale warehouses, artificially infested with all life stages of Tribolium castaneum (Herbst), were used to evaluate the efficacy of two contact insecticides, (S)-hydroprene and cyfluthrin, and to determine the effect of insecticide treatments on insect captures in food- and pheromone-baited pitfall traps. Two application strategies were compared; insecticides were applied at the labeled rate either around the inside perimeter of the warehouse or in a band around the base of shelf units containing discrete food patches (10 g of wheat flour) infested with T. castaneum. Insect populations were assessed weekly for 6 wk by recording number of dead adults on the warehouse floor; number of larvae and adults captured in pitfall traps; and number of larvae, pupae, and adults recovered from food patch samples. There were significantly more dead adults in warehouses treated with cyfluthrin than with (S)-hydroprene or water (control treatment). However, food patch samples showed no detectable differences in quantity of larvae, pupae, or adults among any treatments. Pitfall traps detected fewer larvae starting the fourth week of the study in the warehouses treated with cyfluthrin around the shelf perimeter. Rate of larval capture in traps increased overall with increasing larval populations, but it was more pronounced in traps located closer to the food patches. Number of adults captured in pitfall traps reflected adult mortality in cyfluthrin-treated warehouses. Capture of larvae and adults was greater near the source of the infestation than elsewhere in the warehouse, suggesting that trapping data should be considered when precision targeting insecticide applications in the field.

Role of Food and Structural Complexity on Capture of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in Simulated Warehouses

Abstract Tribolium castaneum (Herbst) is a cosmopolitan pest of stored products, grain processing, and food warehouses. This study was initiated to more fully characterize the role of structure, sanitation, and trap location on capture of T. castaneum in pheromone-baited pitfall traps commonly used in insect monitoring programs. Food patches, spatial structure, and trap position were manipulated in pilot scale warehouses with a known density of insects. Significantly greater quantities of insects were captured in traps placed in warehouses without food patches than those with food patches. Insects tended to be captured with greater frequency in the corners and underneath shelves than in the middle of warehouses. Correlation between actual density and trap captures was stronger in warehouses without food patches, suggesting that sanitation is an important part of pest monitoring. Finally, placement of concrete blocks in the middle of the warehouse did not increase the number of beetles captured in that area compared with warehouses without concrete blocks. Results from this study should be considered when developing guidelines for trap interpretation.

Monitoring Tribolium castaneum (Herbst) in pilot-scale warehouses treated with β-cyfluthrin: are residual insecticides and trapping compatible?

Integrated pest management strategies for cereal processing facilities often include both pheromone-baited pitfall traps and crack and crevice applications of a residual insecticide such as the pyrethroid cyfluthrin. In replicated pilot-scale warehouses, a 15-week-long experiment was conducted comparing population trends suggested by insect captures in pheromone-baited traps to direct estimates obtained by sampling the food patches in untreated and cyfluthrin-treated warehouses. Warehouses were treated, provisioned with food patches and then infested with all life stages of Tribolium castaneum (Herbst). Food patches, both those initially infested and additional uninfested, were surrounded by cyfluthrin bands to evaluate if insects would cross the bands. Results show that insect captures correlated with population trends determined by direct product samples in the untreated warehouses, but not the cyfluthrin-treated warehouses. However, dead insects recovered from the floor correlated with the insect densities observed with direct samples in the cyfluthrin-treated warehouses. Initially, uninfested food patches were exploited immediately and after six weeks harbored similar infestation densities to the initially infested food patches. These data show that pest management professionals relying on insect captures in pheromone-baited traps in cyfluthrin-treated structures could be deceived into believing that a residual insecticide application was suppressing population growth, when the population was actually increasing at the same rate as an untreated population.

Outdoor flight activity and immigration of Rhyzopertha dominica into seed wheat warehouses

The flight activity of lesser grain borer, Rhyzopertha dominica F. (Coleoptera: Bostrichidae), was monitored at two Foundation seed wheat warehouses during the 2003 and 2004 field seasons, using pheromone‐baited Lindgren funnel traps positioned indoors and outdoors. General stored‐product insect activity was also monitored using unbaited sticky traps positioned inside the warehouses around overhead doors. Pheromone‐baited traps were useful for monitoring R. dominica activity, however insect captures decreased when lures were not changed weekly. Flight peaks were documented in early May and again from September through October, and insect captures inside warehouses correlated with timing of outdoor captures. Multiple regression analyses showed that slightly more than half of the variability in R. dominica captures could be explained by mean ambient air temperature and wind speed during the 2 h preceding sunset. Stored‐product Coleoptera captured on unbaited glue boards around overhead doors included Ahasverus advena, Cryptolestes ferrugineus, R. dominica, Sitophilus oryzae, Tribolium castaneum, Trogoderma variabile, and Typhaea stercorea. Door gaskets significantly reduced the number of insect captures on glue boards placed around the overhead doors, and generally restricted their entry to ground level. These studies demonstrated that outdoor pheromone‐baited traps are effective monitoring tools for determining when grain‐handling facilities are most susceptible to infestation and that exclusion may be an effective component of a pest management program.

Susceptibility of Eight U.S. Wheat Cultivars to Infestation by Rhyzopertha dominica (Coleoptera: Bostrichidae)

Abstract Cultivars of wheat, Triticum aestivum L., were assessed to determine their respective level of resistance to lesser grain borers, Rhyzopertha dominica (F.), in postharvest storage. Cultivars were representative of hard red winter, soft red winter, white spring, and durum wheat classes currently grown in the United States. Samples of each cultivar were maintained at 30.0°C and 70% RH and infested with 2- to 3-wk-old adult beetles for 1 wk. Adult progeny were counted at the end of one life cycle. Two temperatures, 27.0 and 34.0°C, were studied to examine the role of temperature (calculated in degree-days) in development. This experiment was conducted three times under similar conditions. Cultivars harboring a large quantity of progeny were considered more susceptible than those cultivars in which fewer progeny completed their life cycle. Each cultivar was analyzed for single kernel properties such as hardness, protein, and diameter. Wheat cultivar had a significant influence on quantity of progeny in all experiments. There were no significant effects on survivorship of progeny as a result of temperature when calculated in degree-days. Cultivars with smaller kernels were more susceptible to development of larger generation sizes in experiment 1 but not in the other two experiments. A kernel size experiment using large and small kernels from the same cultivar suggested that larger quantities of progeny are produced on small kernels compared with large kernels. Individual beetle weights were not influenced by temperature or cultivar. These results imply that stored grain managers should be aware of potential differences in susceptibility, attributable to wheat cultivar, to lesser grain borer infestations.

Estimating Populations of Grain Beetles Using Probe Traps in Wheat-Filled Concrete Silos

Abstract Probe traps are sensitive tools for detecting populations of beetles in stored grain, but their use for estimating insect density in concrete silos has not been established. Populations of grain beetles infesting wheat in concrete silos at two commercial storage facilities in north central Oklahoma were sampled using probe traps and grain probe samples over a 17-wk period. Grain temperature and quality parameters were collected during the study. Thirteen insect species were detected using probe traps, whereas eight species were detected with the grain samples; Cryptolestes ferrugineus and Rhyzopertha dominca were the most common insects collected in the grain samples. Across dates, there were no differences in mean number of insects recovered by species near the grain surface and 1 m below in either probe traps or grain samples. Comparison of slopes (insects recovered in grain samples regressed on insects in probe traps) showed that there were significant differences by trap position for C. ferrugineus but not R. dominica. Multiple regression models, developed to predict insect population estimates using number of insects captured in probe traps and a temperature component, indicated that more variability in the data were explained using traps positioned 1 m below the grain surface (R2 = 0.70) than near the surface (R2 = 0.21) for C. ferrugineus. About one-half (R2 = 0.53) of the variability in insect density was described for R. dominca. These regression models show the potential for methodical use of grain probe traps in pest management decision-making.

Rapid Assessment of Insect Fragments in Flour Milled from Wheat Infested with Known Densities of Immature and Adult Sitophilus oryzae (Coleoptera: Curculionidae)

Abstract Milling wheat, Triticum aestivum L., infested with low densities of internal feeding insects can result in flour containing insect fragments. The Food and Drug Administration (FDA) enforces a standard or defect action level stating that a maximum of 75 insect fragments per 50 g of flour is allowed. However, the relationship between level of infestation and number of resulting fragments is not well documented, and a more rapid method for enumerating insect fragments is needed. We characterized the number of insect fragments produced from milling small lots of wheat spiked with known densities and life stages of Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Insect fragments were enumerated with near-infrared spectroscopy (NIRS), a quick nondestructive procedure, and with the industry standard flotation method. Results showed that an individual small larva, large larva, pupa, or adult produced 0.4, 0.7, 1.5, and 27.0 fragments, respectively. NIRS-predicted counts of ≤51 (from small larvae), ≤53 (from large larvae), ≤43 (from pupae), or 0 (from adults) indicated that there were <75 actual fragments in that sample, because the upper bound of associated 95% inverse prediction confidence intervals was less than the standard; NIRS-predicted counts of ≥98, ≥117, ≥108, or ≥225 fragments (same life stages as above) signaled that these flour samples contained >75 actual fragments. These data suggest that NIRS could be adopted for rapid assessment of insect fragments resulting from relatively low levels of infestation with immature life states, but that it was not accurate enough for enumerating insect fragments, relevant to FDA standards, resulting from adults.

Electronic and manual monitoring of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat

Trapping studies were conducted with field populations of Cryptolestes ferrugineus in small steel bins filled with stored wheat. Traps tested in a comparison experiment included two types of commercially available probe-pitfall trap and the trapping body of the electronic grain probe insect counter (EGPIC) system. Quantities of insects captured were compared among the three traps. Insect captures in PC pitfall traps, whether at the grain surface or 17 cm below the surface, exceeded those found in WB II probe and EGPIC probe bodies. The number of adult C. ferrugineus captured was similar between the EGPIC probe bodies and WB II probe traps. With probes positioned near the grain surface, insect counts generated by the EGPIC system were analyzed for changes in rate of capture after inserting the probe, changes within a single 24-h period, and variation with temperature. EGPIC counts varied from 0.5 counts per hour to 5.9 counts per hour throughout the study. Cryptolestes ferrugineus counts increased with increasing daily mean air temperature and decreased when air temperature decreased. There was a consistent increase in the rate of counts during the early evening hours. Increased activity of C. ferrugineus in the early evening hours may have been due to insect response to higher air temperatures near the grain surface late in the day, although grain temperature near the trap varied little throughout the day. Alternatively, diel periodicity in C. ferrugineus may be due to an independent circadian rhythm as evidenced in other grain insects. Variation in counts among days after the probe was inserted was not consistent.

Survival of Stored-Product Insect Natural Enemies in Spinosad-Treated Wheat

Abstract The survival of stored product insect natural enemies in wheat treated with spinosad was investigated in laboratory and pilot scale experiments. The predator Xylocoris flavipes (Reuter), the warehouse pirate bug, and the parasitoids Habrobracon hebetor (Say), Theocolax elegans (Westwood), and Anisopteromalus calandrae (Howard) were exposed to wheat treated with aliquots of water or spinosad at 0.05–1 mg ([AI])/kg. X. flavipes was the only species that survived (92% survival) in spinosad-treated wheat at 1 mg/kg. X. flavipes suppressed populations of immature Tribolium castaneum (Herbst), the red flour beetle, by nearly 90% compared with a water-treated control, but 100% suppression of immatures was achieved in wheat receiving spinosad or spinosad + X. flavipes treatments. A 3-mo pilot scale experiment to evaluate T. castaneum suppression in drums holding 163.3 kg of wheat showed that the pest populations increased throughout the study in the control treatment, but peaked after 1 mo in the X. flavipes-treated drums. By comparison, better T. castaneum population suppression was achieved in spinosad or spinosad + X. flavipes treatments. Although X. flavipes can survive and reproduce in spinosad-treated wheat, under our test conditions spinosad alone provided adequate suppression of T. castaneum populations in stored wheat.