Monitoring of Tribolium castaneum (Coleoptera: Tenebrionidae) in Rice Mills using Pheromone-Baited Traps.

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a common pest in rice mills. With limited information in the literature addressing T. castaneum in rice processing facilities, we examined the spatial and temporal distribution of T. castaneum inside and outside of three commercial rice milling facilities and one rice packaging plant from June 2012 to August 2014 using pheromone-baited dome traps. Each mill had very different population trends with fewer numbers collected in rough rice storage areas. T. castaneum were more commonly collected in processing areas. Beetle infestation at all the mills was evaluated using the threshold of mean beetle capture of 2.5 beetles per trap per 2 wk period. Trap captures were below threshold for all but one facility. Temperatures inside were ~1°C warmer than outside temperatures, with these temperature differences more noticeable during cool months (October-March). Higher numbers of T. castaneum were captured in 2012 in comparison to 2013, with higher beetle numbers observed during warmer (April-September) than cooler months. With variation in trap capture of T. castaneum occurring among all facilities, this study illustrates that having a monitoring program designed for each facility is important to help managers decide when and where to apply pest management tactics. The use of pheromone traps could provide information to mill managers to find locations within a mill that are most vulnerable to infestation by T. castaneum, and to assist with the timing of control interventions.

Evaluation of Pyrethroid Insecticides and Insect Growth Regulators Applied to Different Surfaces for Control of Trogoderma granarium (Coleoptera: Dermestidae) the Khapra Beetle.

The khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a serious pest of stored products and is the only stored product insect pest that triggers a quarantine response when it is found in the United States. The larvae of T. granarium feed on a wide range of dry food products of plant and animal origin, including cereals, dried fish, and museum specimens. In this study, we evaluated the residual efficacy of two pyrethroid insecticides, deltamethrin and cyfluthrin, applied on concrete, wood, painted wood, vinyl flooring tile, and metal surfaces using small and large T. granarium larvae. Residual efficacy of two insect growth regulators (IGRs), methoprene and pyriproxyfen was also evaluated on concrete, metal, and wood surfaces. In both studies, larvae were exposed with provision of a food source on the treated surfaces and residual assays were conducted at 0 months (1 d), 1, 2, and 3 months post treatment. In general, both of the pyrethroids provided a high level of control of T. granarium larvae, though small larvae were much more susceptible than large larvae. The IGRs were comparatively less effective, with more larval survival and adult emergence of exposed larvae compared with the pyrethroids. Residues of the pyrethroids and IGRs were most persistent on the metal surface. Results can be used to help to control and eradicate infestations of T. granarium when they are detected in the United States.

Contact Toxicity of Deltamethrin Against Tribolium castaneum (Coleoptera: Tenebrionidae), Sitophilus oryzae (Coleoptera: Curculionidae), and Rhyzopertha dominica (Coleoptera: Bostrichidae) Adults.

This study was conducted at Oklahoma State University, Stillwater, OK, to evaluate the response to deltamethrin concentrations for adults of three stored-product insects, Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Rhyzopertha dominica (F.). In insect toxicological studies, knockdown is the state of intoxication and partial paralysis as a result of exposure to an insecticide. Deltamethrin concentrations ranging from 0.48 to 140 mg/m(2) (1 to 3,000 ppm) were sprayed on glass Petri dishes. After the dishes dried, 20 adult insects of each species were placed on the treated dishes to determine the contact toxicity of deltamethrin. Assessments for knockdown were made at 15-min intervals for up to 8 h after initial exposure and then again after 24 or 48 h. Insects were then transferred to clean untreated Petri dishes with diet and observed from 0.5 to 72 h. Mortality was assessed 72 h after transfer to untreated dishes with food material. Deltamethrin was highly effective against all three species tested and achieved 99% knockdown of insects of all species within 4 h after exposure at concentrations ≥1.2 mg/m(2) Although some insects recovered from initial knockdown at concentrations ≤48 mg/m(2), nearly all the insects were killed at 140 mg/m(2) when exposed for 48 h. LC95 values for all species tested, for the 48-h exposure period, were <140 mg/m(2), the concentration of deltamethrin that could potentially be present in new ZeroFly Storage Bag fabric. ZeroFly bags are used for stored-product insect pest control.

Efficacy of heat treatment for disinfestation of concrete grain silos.

Field experiments were conducted in 2007 and 2008 to evaluate heat treatment for disinfestations of empty concrete elevator silos. A Mobile Heat Treatment Unit was used to introduce heat into silos to attain target conditions of 50 degrees C for at least 6 h. Ventilated plastic containers with a capacity of 100 g of wheat, Triticum aestivum L., held Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Polyvinyl chloride containers with a capacity of 300 g of wheat held adults of Liposcelis corrodens (Heymons) (Psocoptera: Liposcelididae) and Liposcelis decolor (Pearman), which were contained in 35-mm Petri dishes within the grain. Containers were fastened to a rope suspended from the top of the silo at depths of 0 m (just under the top manhole), 10 m, 20 m, and 30 m (silo floor). When the highest temperature achieved was approximately 50 degrees C for 6 h, parental mortality ofR. dominica and T. castaneum, and both psocid species was 98-100%. Progeny production of R. dominica occurred when there was parental survival, but in general R. dominica seemed less impacted by the heat treatment than T. castaneum. There was 100% mortality of L. corrodens at all depths in the heat treatments but only 92.5% mortality for L. decolor, with most survivors located in the bioassay containers at the top of the silo. Results show wheat kernels may have an insulating effect and heat treatment might be more effective when used in conjunction with sanitation and cleaning procedures.

Use of a web-based model for aeration management in stored rough rice.

A web-based model was used to simulate the impact of aeration on population growth of the lesser grain borer, Rhyzopertha dominica (F.), and the rice weevil, Sitophilus oryzae (L.), in stored rough rice, Oryza sativa L., at Beaumont, TX. Simulations were run for each of 10 yr with 1 August as the start date; 31 December as the end date; beginning populations of 2.5 adults per metric ton (1000 kg); starting grain temperatures of 29.4, 32.2, and 35.0 degrees C; and aeration airflow rates of 0.27, 0.79, and 1.40 m3/min/metric ton of rice. In the absence of aeration, populations of both species increased exponentially, with maximum production of R. dominica and S. oryzae at starting grain temperatures of 35.0 and 32.2 degrees C, respectively. Final predicted populations of R. dominica on 31 December from grain starting temperatures of 29.4, 32.2, and 35.0 degrees C were 5465, 6848, and 11,855 per ton, respectively; final predicted populations of S. oryzae were 13,288, 21,252 and 4355, respectively. Aeration led to a reduction in grain temperature and a decrease in pest populations, regardless of starting grain temperature or aeration airflow rates. Predicted populations of R. dominica on 31 December ranged from 12 to 63 adults per ton at all grain starting temperatures and airflow rates; populations of S. oryzae on 31 December ranged from 108 to 193 adults per ton at all grain starting temperatures and airflow rates. The predicted population levels in aerated rice represented at least a 98% reduction compared with unaerated rice. Results show the utility of the web-based model and how the various model inputs can help define broader patterns of insect control in rice stored in the south central United States.

Monitoring Tribolium castaneum (Herbst) in pilot-scale warehouses treated with beta-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.

Methodology for assessing rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica.

Several physical and chemical attributes of rice were evaluated to determine which character would be best to use to assess multiple rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica (F.). Laboratory tests were conducted on single varieties of long-, short-, and medium grain-rice to develop procedures and methodologies that could be used for large-scale screening studies. Progeny production of R. dominica was positively correlated with the percentage of broken hulls. Although kernel hardness, amylose content, neonate preference for brown rice, and adult emergence from neonates varied among the three rice varieties tested they did not appear to be valid indicators of eventual progeny production, and may not be useful predictors of resistance or susceptibility. Soundness and integrity seem to be the best characters to use for varietal screening studies with R. dominica.

Susceptibility of eggs and adult fecundity of the lesser grain borer, Rhyzopertha dominca, exposed to methoprene.

A series of tests were conducted to determine the susceptibility of eggs and neonates of the lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae = Bostrychidae), exposed to the insect growth regulator, methoprene, on filter paper and on rough rice. In the first test, the hatch rate of eggs exposed on filter paper treated with methoprene at the label rate of 0.003 mg [AI]/cm(2) when used as a surface treatment in structures was 52.0 +/- 7.3% compared to 93.0 +/- 3.3% on untreated controls. In the second test, eggs were exposed to a dose-response series of 0.00003 to 0.03 mg[AI]/cm(2). Egg hatch was directly proportional to concentration and ranged from 85.0 +/- 2.0% on untreated controls to 26.7 +/- 8.3% at the highest concentration tested. In the third test, 1 ppm of methoprene was sprayed on long grain rough rice (paddy) (Cocodrie variety), and then individual kernels were cracked and an egg of R. dominica was placed directly on the kernel. On untreated rice kernels, 67.5 +/- 11.6% of the eggs hatched and were able to bore inside, and all of these larvae emerged as adults. In contrast, 40.0 +/- 5.3% of the eggs placed on treated cracked kernels were able to develop to where the larvae were visible through X-ray detection, but none emerged as adults. In the final test, newly-emerged adults were exposed on rough rice treated with 1 ppm methoprene. The number of eggs from adults on untreated rice was 52.1 +/- 4.3 eggs per female, and on treated rice the average egg production was 12.5 +/- 1.1 eggs per female. Methoprene applied on a surface or on rough rice affected development of egg hatch also reduced fecundity of parent adults exposed on the treated rough rice.

Cost and risk analysis of heat and chemical treatments.

An economic evaluation of newly developed methods for disinfesting empty grain storage bins by heat treatment will be a useful tool for decision-making by grain storage managers. An economic empirical model of heat treatment and chemical applications was developed using minimization of costs at a target risk level associated with the grain-damaging insects Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Rhyzopertha dominica (F.). Risk was measured as a deviation below a target mortality goal (Target MOTAD). Insect mortality and air temperature during heat treatment were evaluated for empty storage bins with a full drying floor, along with a similar evaluation of insect mortality for two application rates of a contact pyrethroid insecticide, cyfluthrin 20% active ingredient (AI) wettable powder. A high-output propane heater (29 kW) had the lowest cost and risk level of all heating systems and produced 100% mortality in 2 h for the three insect species at all test locations. An electric duct-heater system (18 kW) also produced 100% mortality at all test locations after 40 h, but it had significantly higher costs. The other heating system configurations in the study had significantly higher risk levels of insect mortality, and the electric systems were not cost-effective. Both chemical rates had low costs and risk levels, with high mortality results.

Hydroprene prolongs developmental time and increases mortality in wandering-phase Indianmeal moth (Lepidoptera: Pyralidae) larvae.

Wandering phase Indianmeal moth, Plodia interpunctella (Hübner), larvae were exposed to the label rate of hydroprene (1.9 x 10(-3) mg [AI] /cm2) sprayed on concreted petri dishes. Larvae were exposed for 1, 3, 6, 12, 18, 24, and 30 h and maintained at 16, 20, 24, 28, and 32 degrees C and 57% RH until adult emergence. Larval developmental time and mortality were significantly influenced by temperature and exposure intervals. Maximum developmental time (47.2 +/- 1.3 d) occurred at 16 degrees C, and the minimum developmental time (7.0 +/- 0.5 d) occurred at 32 degrees C. Larval mortality generally increased at all of the five tested temperatures as exposure period increased. The greatest mortality (82.0 +/- 0.1%) occurred when larvae were exposed for 30 h at 28 degrees C, and minimum mortality (0.0 +/- 0.5%) occurred at 16 degrees C when larvae were exposed for 1 h. The relationships between temperature, exposure period, and developmental time were described by polynomial models, based on lack-of-fit tests. Hydroprene has potential to be an effective alternative to conventional insecticides in surface treatments for Indianmeal moth management. Response-surface models derived from this study can be used in simulation models to estimate the potential consequences of hydroprene on Indianmeal moth population dynamics.

Hydroprene prolongs developmental time and increases mortality of Indianmeal moth (Lepidoptera: Pyralidae) eggs.

Eggs of the Indianmeal moth, Plodia interpunctella (Hübner), were exposed to the labeled rate of hydroprene (1.9 x 10(-3) mg [AI]/cm2) sprayed on concreted petri dishes. These eggs were exposed for 1, 3, 6, 12, and 18 h and until hatching (continuous exposure) at temperatures of 16, 20, 24, 28, and 32 degrees C and 57% RH until the emergence of first instars. The developmental time and egg mortality were significantly influenced by temperature and exposure periods. At 16 degrees C, hydroprene did not cause differences in developmental time when eggs were exposed for different periods. At temperatures >16 degrees C, both exposure period and temperature influenced developmental time. The maximum developmental time (15.0 +/- 0.2 d) occurred at 16 degrees C, and the minimum developmental time (3.2 +/- 0.3 d) occurred at 32 degrees C. Mortality increased when eggs were exposed to hydroprene for longer periods at all of the five tested temperatures. The greatest mortality (81.6 +/- 2.1%) occurred when eggs were continuously exposed on treated surfaces at 32 degrees C. We used developmental time instead of rate (1/ developmental time) to fit simple linear or polynomial regression models to the development data. Appropriate models for developmental time and mortality were chosen based upon lack-of-fit tests. The regression models can be used in predictive simulation models for the population dynamics of Indianmeal moth to aid in optimizing use of hydroprene for insect management.

Effect of temperature, exposure interval, and depth of diatomaceous earth treatment on distribution, mortality, and progeny production of lesser grain borer (Coleoptera: Bostrichidae) in stored wheat.

Diatomaceous earth (DE) can be used as a surface treatment in stored wheat Triticum aestivum (L.) to control pest infestations. However, it is not known how the thickness of the DE-treated wheat layer or grain temperature impact effectiveness. Therefore, we conducted an experiment in growth chambers to assess the effect of different surface layers of hard winter wheat combined with DE on spatial distribution, adult survival, and progeny production of lesser grain borer, Rhyzopertha dominica (F.), and to determine whether temperature and exposure interval modified this effect. When adult lesser grain borers were released in experimental towers containing untreated wheat or wheat admixed with DE to a surface layer depth of 15.2, 22.9, or 30.5 cm, they were able to penetrate all DE layers and oviposit in the untreated wheat below. However, survival was significantly reduced in adults exposed to DE. Survival decreased both with increasing depth of the DE-treated wheat and with exposure interval. Temperature had no effect on adult survival, but significantly more progeny were produced at 32 than at 27 degrees C. Progeny production was inversely correlated with the depth of the DE-treated layer. Vertical distribution patterns of parental beetles were not significantly different among treatments or exposure intervals; however, more insects were found at greater depths at 32 than at 27 degrees C. The F1 production was reduced by 22% at the thickest DE-treated layer. However, we conclude that this level of survival could leave a residual population of lesser grain borers that would probably be above an allowable threshold for insect damage.

Comparison of aeration and spinosad for suppressing insects in stored wheat.

Field studies were conducted from July 2002 to January 2003 for evaluating the effects of controlled aeration and a commercial biological insecticide, spinosad, in suppressing insect populations in stored wheat. Six cylindrical steel bins were filled with newly harvested (2002 crop year) hard red winter wheat on 9 and 10 July 2002. Each bin contained 30.7 metric tons (1,100 bu) of wheat. Wheat in two bins was left untreated (control), whereas wheat in two bins was treated with spinosad, and in another two bins was subjected to aeration by using aeration controllers. Spinosad was applied to wheat at the time of bin filling to obtain a rate of 1 mg ([AI])/kg. Aeration controllers were set to run the fans when ambient air temperature fell below 23.9, 18.3, and 7.2 degrees C for the first, second, and third cooling cycles, respectively. We added 400 adults each of the rusty grain beetle, Cryptolestes ferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); and red flour beetle, Tribolium castaneum (Herbst), to the grain at monthly intervals between July and October 2002. Insect density in the bins was estimated monthly by taking 3-kg grain samples from 21 locations within each bin by using a pneumatic grain sampler. No live T. castaneum or C. ferrugineus and very low densities of R. dominica (<0.008 adults per kilogram) were found in wheat treated with spinosad during the 6-mo sampling period. Density of C. ferrugineus and T. castaneum in aerated bins did not exceed two adults per kilogram (the Federal Grain Inspection Service standard for infested wheat), whereas R. dominica increased to 12 adults per kilogram in November 2002, which subsequently decreased to three adults per kilogram in January 2003. In the untreated (control) bins, R. dominica density increased faster than that of C. ferrugineus or T. castaneum. Density of R. dominica peaked at 58 adults per kilogram in October 2002 and decreased subsequently, whereas T. castaneum density was 10 adults per kilogram in October 2002 but increased to 78 adults per kilogram in January 2003. Density of C. ferrugineus increased steadily during the 6-mo study period and was highest (six adults per kilogram) in January 2003. This is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins. Our results suggest that spinosad is very effective in suppressing R. dominica, C. ferrugineus, and T. castaneum populations in stored wheat.

Susceptibility of last instar red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) to hydroprene.

Last instar larvae of the red flour beetle, Tribolium castaneum (Herbst), and the confused flour beetle, Tribolium confusum Jacquelin du Val, were either exposed for 8-144 h on concrete treated with 1.9 x 10(-3) mg(AI)/per cm2 hydroprene, or continually exposed on concrete treated with 9.8 x 10(-4) to 1.9 x 10(-3) mg[AI]/per cm2 hydroprene. In both tests, larvae were exposed and held at 27 or 32 degrees C and 40, 57, or 75% RH. When larvae were exposed with no food to hydroprene for different time intervals, then transferred to untreated concrete containing flour, consistent effects were produced only at 144 h. At this exposure interval, the percentage of beetles arrested in the larval stage after 3-4 wk was generally greater at 75% RH compared with 40 and 57% RH, but there were no differences between species or temperature. The percentages of dead adult red flour beetles and live adults with morphological deformities were also greatest at 75% RH, and defects were more prevalent in red flour beetles than in confused flour beetles. When larvae were continually exposed to different concentrations of hydroprene on concrete that contained flour, the percentage of arrested larvae, dead adults, and live adults of both species generally increased with concentration. There were more deleterious effects at 75% RH compared with either 40 or 57% RH, and effects were more pronounced in the red flour beetle compared with the confused flour beetle. In both experiments, temperature effects were variable and inconclusive. Results indicate that continual exposure of last instar red flour beetle and confused flour beetle to hydroprene can limit population development, but exposure intervals of >6 d may be required for maximum effectiveness.

Impact of food source on survival of red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) exposed to diatomaceous earth.

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 degrees 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 approximately 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.

Aeration management for stored hard red winter wheat: simulated impact on rusty grain beetle (Coleoptera: Cucujidae) populations.

Simulation studies were conducted to determine temperature accumulations below defined thresholds and to show the impact of controlled aeration on populations of the rusty grain beetle, Cryptolestes ferrigineus (Stephens), a major secondary pest of stored wheat, Triticum aestivum (L.). Recorded data from weather stations in Texas, Oklahoma, Kansas, eastern New Mexico, and eastern Colorado (356 total) were used to determine hours of temperature accumulation below 23.9 degrees C in June and July, 15.6 degrees C in September and October, and 7.2 degrees C in December. At an airflow rate of 0.0013 m3/s/m3 (0.1 cubic ft3/min/bu), which requires 120 h of temperatures below the specified threshold to complete an aeration cycle, summer cooling at 23.9 degrees C in bulk-stored wheat could be completed throughout the hard red winter wheat zone except for extreme southern Texas. An early-autumn cooling cycle at 15.6 degrees C could not be completed throughout most of Texas and Oklahoma before the end of September. The late-autumn cooling cycle could be completed in all states except Texas by the end of November. Five geographic regions were delineated and the times required for completion of the summer, early-autumn, and late-autumn cooling cycles within each region were estimated. Population growth of the rusty grain beetle was modeled for San Antonio, TX; Abilene, TX; Tulsa, OK; Topeka KS; and Goodland, KS, by predicting the numbers of adults in the top, outer middle, outer periphery, and the center of the bin during a 1-yr storage season. Populations of C. ferrugineus in San Antonio and Austin were predicted to exceed the Federal Grain Inspection Service (FGIS) threshold of two beetles per kilogram of wheat in all four levels of the bin during late autumn, decline during the winter, and increase the following spring. In Midland, TX, and Oklahoma City, OK, populations were predicted to exceed the threshold only in the top and outer middle of the bin, whereas populations in the Kansas locations were not predicted to exceed the threshold at any time.

Toxicity of diatomaceous earth to red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae): effects of temperature and relative humidity.

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 degrees 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 degrees 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 degrees 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.

Susceptibility of northern fowl mites in North Carolina to five acaricides.

The susceptibilities (dosage-response regression curves) of northern fowl mites collected from six poultry farms in North Carolina were determined for five acaricides by exposure of the mites for 24 hr to acaricide residues inside glass pipettes. The residue concentrations were expressed as parts per million on a weight-volume basis of the acaricide-acetone solution in which the pipettes were immersed prior to testing. All of the acaricides, except malathion, were highly toxic to the northern fowl mites. The mean LD50 values (ppm) were: permethrin, .53; tetrachlorvinphos, 4.06; carbaryl, 4.11; and coumaphos, 5.04. For malathion, the mean LD50 for mites from three caged layer flocks was 119.35 ppm while concentrations as high as 500 ppm gave only low mortalities (20% or less) of mites from the other flocks and LD50 values could not be calculated. These data show that northern fowl mites are highly resistant to malathion in North Carolina, as has been reported elsewhere, but there is no evidence of resistance to the other acaricides tested. The effect of temperature on the toxicity to northern fowl mites of the newest acaricide, permethrin, was determined. Permethrin was significantly more toxic at 20 C than at 25, 30, or 35 C.

Northern fowl mite population development on laying hens caged at three colony sizes.

Beginning 5 weeks after being experimentally infested with known numbers of northern fowl mites, Ornithonyssus sylviarum (Canestrini and Fanzago), White Leghorn pullets caged alone supported a significantly higher mite population than did pullets housed two and three per cage. During the following 6 weeks, mite populations remained high on the birds caged singly whereas mite populations drastically declined on the birds housed two or three per cage. Eleven weeks after the experiment was initiated, all hens caged alone were infested with northern fowl mites, whereas 22% of the birds housed two per cage and 43% of the birds housed three per cage were free of mites. These data support the hypothesis that social stress in birds influences the development of northern fowl mites (more stress, higher resistance to mites).

Comparisons of permethrin formulations and application methods for northern fowl mite control on caged laying hens.

Formulations of permethrin (Ectiban), a synthetic pyrethroid, as an emulsifiable concentrate (EC), wettable powder (WP), and dust were nearly equally effective for 9 or more weeks for control of the northern fowl mite, Ornithonyssus sylviarum (Canestrini and Fanzago), on caged laying hens under environmentally controlled conditions. The permethrin was applied to the vent area as .05% active ingredient (AI) spray of the diluted EC or WP at 40 ml per bird, .1% AI mist of the diluted EC at 20 ml per bird, and 4.5 g per bird of the .25% AI dust. Dilute sprays of .05% permethrin prepared from the EC and WP and applied at 40 ml per bird were more effective in a commercial caged-laying hen house for northern fowl mite control than were .5% sprays of tetrachlorvinphos (Rabon), Ravap, and carbaryl (Sevin). Satisfactory mite control was obtained with .6% permethrin prepared from the EC and misted at the rate of 2.5 ml per bird. Low volume, high concentration misting of permethrin was a promising method for mite control with satisfactory control achieved with .2% AI at 5 ml per bird and .6% AI at 2.5 ml per bird.