Frank H. Arthur

Grain protectants: Current status and prospects for the future

Abstract Since the 1960s grain protectants have been used as a primary means of insect pest management in bulk storages, especially in countries which store large amounts of grain for domestic food production and export trade. With the increasing costs of development and registration of insecticides, the number of available protectants has begun to decrease, a trend that will no doubt continue. Furthermore, there are several biological, economic and sociological influences that are causing a gradual shift from chemical-based pest management to integrated pest management utilizing computer-based decision support systems. This paper will discuss several factors in terms of their potential impact on the use of conventional grain protectants, including insecticide residues and consumer perceptions, resistance to protectants in major pest species, the direct and indirect costs of insecticides, development and registration of biopesticides, inert dusts, new technologies for fumigation and controlled atmosphere treatments, the expanded use of aeration in management programs, biological controls, and the development of expert systems. In this paper the term ‘grain protectants’ will be used to refer to only organophosphorus, pyrethroid, or carbamate insecticides that are applied directly to grain for residual control.

Effectiveness of Spinosad on Four Classes of Wheat Against Five Stored-Product Insects

Abstract Spinosad is a commercial reduced-risk pesticide that is naturally derived. Spinosad’s performance was evaluated on four classes of wheat (hard red winter, hard red spring, soft red winter, and durum wheats) against adults of the lesser grain borer, Rhyzopertha dominica (F.); rice weevil, Sitophilus oryzae (L.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); red flour beetle, Tribolium castaneum (Herbst); and larvae of the Indianmeal moth, Plodia interpunctella (Hübner). Beetle adults (25) or P. interpunctella eggs (50) were exposed to untreated wheat and wheat treated with spinosad at 0.1 and 1 mg (AI)/kg of grain. On all untreated wheat classes, adult beetle mortality ranged from 0 to 6%, and P. interpunctella larval mortality ranged from 10 to 19%. The effects of spinosad on R. dominica and P. interpunctella were consistent across all wheat classes. Spinosad killed all exposed R. dominica adults and significantly suppressed progeny production (84–100%) and kernel damage (66–100%) at both rates compared with untreated wheat. Spinosad was extremely effective against P. interpunctella on all wheat classes at 1 mg/kg, based on larval mortality (97.6–99.6%), suppression of egg-to-adult emergence (93–100%), and kernel damage (95–100%), relative to similar effects on untreated wheats. The effects of spinosad on S. oryzae varied among wheat classes and between spinosad rates. Spinosad was effective against S. oryzae, O. surinamensis and T. castaneum only on durum wheat at 1 mg/kg. Our results suggest spinosad to be a potential grain protectant for R. dominica and P. interpunctella management in stored wheat.

Toxicity of Diatomaceous Earth to Red Flour Beetles and Confused Flour Beetles (Coleoptera: Tenebrionidae): Effects of Temperature and Relative Humidity

Abstract Red flour beetles, Tribolium castaneum (Herbst), and confused flour beetles, Tribolium confusum (DuVal), were exposed for 8–72 h to diatomaceous earth (Protect-It) at 22, 27, and 32°C and 40, 57, and 75% RH (9 combinations). Insects were exposed to the diatomaceous earth at 0.5 mg/cm2 on filter paper inside plastic petri dishes. After exposure, beetles were held for 1 wk without food at the same conditions at which they were exposed. Mortality of both species after initial exposure was lowest at 22°C but increased as temperature and exposure interval increased, and within each temperature decreased as humidity increased. With 2 exceptions, all confused flour beetles were still alive after they were exposed at 22°C, 57 and 75% RH. Mortality of both species after they were held for 1 wk was greater than initial mortality for nearly all exposure intervals at each temperature–humidity combination, indicating delayed toxic effects from exposure to diatomaceous earth. For both species, the relationship between mortality and exposure interval for initial and 1-wk mortality was described by linear, nonlinear, quadratic, and sigmoidal regression. Mortality of confused flour beetles was lower than mortality of red flour beetles exposed for the same time intervals for 46.7% of the total comparisons at the various temperature–relative humidity combinations.

Long-Term Monitoring of Tribolium castaneum in Two Flour Mills: Seasonal Patterns and Impact of Fumigation

ABSTRACT Data from long-term Tribolium castaneum (Herbst) pheromone trapping programs in two flour mills was used to evaluate the impact of structural fumigations (n = 23) on pest populations. The two mills differed in mean number of beetles captured and proportion of traps with captures of one or more beetles, but in one of the mills the mean number of beetles captured was reduced after implementing a more intensive integrated pest management program. Mean number of beetles per trap and proportion of traps with captures increased by 52.7 ± 8.2 and 24.8 ± 4.7% from one monitoring period to the next but decreased by 84.6 ± 4.6 and 71.0 ± 5.1% when fumigation occurred between periods, respectively. Mean number of beetles per trap and proportion of traps with captures immediately after fumigation were both positively correlated with number captured per trap and proportion of traps with captures in the monitoring period immediately before fumigation. Mean daily air temperature inside the mill fluctuated with the season, and although always warmer than the outside temperature, the relative difference varied with season. Relationship between inside and outside temperature could be explained well by an exponential equation with the parameters a = 20.43, b = 2.25, and c = -15.24 (r2 = 0.6983, which is 94% of the maximum r2 obtainable). Although outside temperature differed between spring and fall fumigations, inside temperature and reduction in beetle captures was not affected by season. A better understanding of pest populations and the impact of structural treatments within commercial food facilities is critical for improving the management of pest populations and for the adoption of methyl bromide alternatives.

Efficacy of grain protectants against four psocid species on maize, rice and wheat.

BACKGROUND Psocids are emerging pests in stored products, particularly in amylaceous commodities such as grains. Currently, their control is based on the use of fumigants and contact insecticides; however, newer data indicate that psocids are tolerant to insecticides used to control other stored-grain species. This study evaluated the insecticides registered in the USA for use on stored maize, rice and wheat for control of the psocid species Lepinotus reticulatus, Liposcelis entomophila, L. bostrychophila and L. paeta. Mortality of exposed adult females was recorded after 7 and 14 days of exposure, while progeny production was assessed after 30 days of exposure. RESULTS On wheat and rice, chlorpyriphos-methyl + deltamethrin was generally more effective against exposed parental adults than spinosad or pyrethrin, while pirimiphos-methyl was more effective on maize than spinosad or pyrethrin. In most cases, progeny production was suppressed in the treated grains. Progeny production was consistently lowest on wheat and rice treated with chlorpyriphos-methyl + deltamethrin and maize treated with pirimiphos-methyl. CONCLUSIONS Chlorpyriphos-methyl + deltamethrin and pirimiphos-methyl were the most effective insecticides for all species and commodities. Conversely, efficacy of spinosad or pyrethrum was highly dependent on the psocid species and commodity.

Efficacy of Diatomaceous Earth to Control Internal Infestations of Rice Weevil and Maize Weevil (Coleoptera: Curculionidae)

Densities of 10, 20, and 30 hard red winter wheat kernels, Triticum aestivum L., were infested with different life stages of the rice weevil, Sitophilus oryzae (L.), mixed with 35 g of wheat treated with 300 ppm of the Protect-It (Mississauga, Ontario, Canada) formulation of diatomaceous earth (DE), and held at 22, 27, and 32 degrees C. A similar test was conducted by exposing densities of 6, 12, and 18 corn kernels infested with different life stages of the maize weevil, Sitophilus zeamais Motschulsky, mixed with 30 g of corn, Zea mays L., treated with 300 ppm of DE. Mortality of adults emerging from kernels in wheat treated with DE was always greater than controls, and ranged from 56 to 90% at 22 degrees C and was >90% at 27 and 32 degrees C. In most treatment combinations, exposure to DE suppressed F1 progeny by 60-90% relative to untreated controls. Mortality of adult maize weevils on treated corn held at 22 and 27 degrees C was lower than mortality of rice weevils on wheat, and ranged from 4 to 84%. F1 production was low in corn held at 22 degrees C, and no F1s were produced in either the controls or the treatments at 32 degrees C. In treated corn held at 27 degrees C, exposure to the DE suppressed F1 progeny by approximately 70-80% relative to the untreated controls. Results of this study show that rice weevils and maize weevils emerging from infested kernels as adults are susceptible to DE, and these results are comparable to other studies in which adult weevils were exposed directly on wheat or corn treated with DE. Although adult weevils will be killed by exposure to DE, some oviposition could still occur and progeny suppression may not be complete; however, application of DE to commodities already infested with internal feeders, such as the rice weevil and the maize weevil, could help eliminate or suppress the infestation.

Immediate and delayed mortality of Oryzaephilus surinamensis (L.) exposed on wheat treated with diatomaceous earth: effects of temperature, relative humidity, and exposure interval.

Adult Oryzaephilus surinamensis (L.), the sawtoothed grain beetle, were exposed for 4-72 h on wheat treated with diatomaceous earth (Protect-It(TM)), then removed and held for 1 week on untreated wheat. Beetles were exposed and held at 22, 27, and 32 degrees C, 40, 57, and 75% r.h. (nine combinations). Mortality after the initial exposures increased as exposure interval and temperature increased, but humidity effects were inconsistent with temperature. Mortality after the one-week holding period was greater than initial mortality, and also increased as the original exposure interval and the temperature increased. At 22 and 27 degrees C, mortality of beetles exposed from 4 to 24 h at 75% r.h. was significantly lower than mortality of beetles exposed for the same time intervals at 40 and 57% r.h. Nearly all of the beetles exposed for 72 h at all three relative humidities were dead after 1 week. The relationship between exposure interval and mortality was described by sigmoidal and linear regression for both the initial mortality and mortality 1 week after being transferred to untreated wheat. Results indicate that O. surinamensis is susceptible to the Protect-It(TM) formulation of diatomaceous earth, and will continue to suffer from the effects of exposure even after they are removed from the treated environment.

Impact of Food Source on Survival of Red Flour Beetles and Confused Flour Beetles (Coleoptera: Tenebrionidae) Exposed to Diatomaceous Earth

Abstract A series of experiments was conducted to determine the effect of a flour food source on survival of red flour beetle, Tribolium castaneum (Herbst), and confused flour beetle, Tribolium confusum (DuVal), exposed to the labeled rate (0.5 mg/cm2) of Protect-It, a marine formulation of diatomaceous earth. Beetles were exposed at 27°C, and 40, 57, and 75% RH in 62-cm2 petri dishes. When beetles were exposed for 1 or 2 d in dishes with the labeled rate (0.5 mg/cm2, or 31 mg per dish) of diatomaceous earth or in dishes containing flour at varying levels from 0 to 200 mg mixed with the labeled rate of diatomaceous earth, survival of both species increased as the amount of flour increased, and quickly plateaued at levels approaching 100%. In a second set of experiments, beetles were transferred to dishes containing flour at varying levels from 0 to 200 mg after they were exposed for 1 or 2 d in dishes with the labeled rate of diatomaceous earth alone. There were no significant differences in beetle survival among the levels of flour, however, survival in dishes with flour was usually greater than survival in dishes with diatomaceous earth alone. In a third test, beetles were exposed for 1, 2, and 3 d in dishes with either the labeled rate of diatomaceous earth alone (clean dishes), dishes with diatomaceous earth and empty straws, or dishes with diatomaceous earth and ≈300 mg of flour packed in the straws. Survival was not significantly different between clean dishes or dishes with straws, but survival in dishes containing the straws with flour was usually 100%, regardless of exposure interval. In all experiments, confused flour beetles were less susceptible to diatomaceous earth than red flour beetles. In addition, survival was negatively related to exposure interval and positively related to relative humidity.

Evaluation of methoprene alone and in combination with diatomaceous earth to control Rhyzopertha dominica (Coleoptera: Bostrichidae) on stored wheat ☆

A series of experiments were conducted in which different formulations of the insect growth regulator methoprene were evaluated for control of Rhyzopertha dominica (F.), the lesser grain borer, a major internal insect pest of stored wheat. In the first test, application rates of 10-ppm R;S-methoprene (a racemic mixture of the R and S isomers of methoprene) and 1 and 5-ppm S-methoprene (S-isomer only) gave 100% suppression of F1 adult progeny of R. dominica for 24 weeks. In the second test, adult R. dominica were exposed at 27 � C and 32 � C, 57% and 75% relative humidity (r.h.) on untreated wheat and wheat treated with 1- to 10-ppm S-methoprene dust. Survival after a 3-week exposure decreased with increasing concentration of dust, and ranged from 69% to 99%, but no F1 adult progeny were produced in treated wheat. In the final test, concentrations of 0, 0.25, 0.50, 0.75, and 1.0 ppm S-methoprene EC were combined with concentrations of 0, 75, 150, 225, and 300 ppm of the commercial diatomaceous earth (DE) ProtectIt s . Within each methoprene concentration, survival generally decreased with increasing concentration of DE, and was generally greater at 75% than at 57% r.h. Only the wheat treated with 0-ppm methoprene contained an appreciable number of F1 adults. In summary, both the dust and EC formulations of Smethoprene gave 100% suppression of F1 adult progeny R. dominica at application rates of 1 ppm, and combination treatments involving reduced rates of methoprene and DE gave effective control of R. dominica.

Long-term monitoring of Tribolium castaneum populations in two flour mills: rebound after fumigation.

ABSTRACT Structural fumigations of food processing plants to manage stored-product insects has been a major component of pest management programs, but limited information on field efficacy is available. Efficacy, based on pheromone trapping data, consists of initial reduction in captures after treatment and rebound in trap captures over time. Pattern of Tribolium castaneum (Herbst) rebound was evaluated after 21 fumigations in two flour mills. Rebound in mean number of beetles captured and the probability of a trap capturing one or more beetles was evaluated. Rebound to a threshold mean beetle capture of 2.5 beetles per trap per 2-wk period took 174 ± 33 d and rebound took longer after fall (248 ± 50 d) than spring (104 ± 21 d) fumigations. Rebound to the probability of capture threshold of 0.50 was 120 ± 21 d, but there was no significant effect of season. Improvement in integrated pest management (IPM) practices in one of the mills was associated with an increase in time to reach mean beetle capture threshold (49 ± 15 d before and 246 ± 71 d after) but not in time to reach the probability of capture threshold (38 ± 14 d before and 165 ± 46 d after). There was a negative correlation between number captured after fumigation and time to rebound to threshold. After improved IPM there was a significant reduction in the number of beetles per trap immediately after fumigation. Above these two thresholds the degree of change in trap captures is significantly greater than below, which suggests they might be useful in evaluating risk in a pest management program.