Moisture content gradient and ventilation in stored wheat affect movement and distribution of Oryzaephilus surinamensis and have implications for pest monitoring

This study was carried out primarily to ascertain whether the movement of Oryzaephilus surinamensis and Sitophilus granarius from low to high humidity zones occurs in bins of wheat and whether aeration of the grain (10 m³/h/t) affects this movement. The second aim was to ascertain the best placement of insect detection traps under the different conditions. Insects were introduced into the lower half of the grain in the bins and their movement was monitored using traps placed at various depths in the grain. Sitophilus granarius did not move through the grain into the top layer regardless of the moisture content, temperature or aeration status of the grain. More O. surinamensis were caught in unventilated bins than in ventilated bins. More insects were caught in the ventilated bins containing layers of both dry and wet grain than in the bins containing only dry grain. The spatio-temporal distribution of O. surinamensis varied significantly. The depth at which insects were trapped varied between treatments: in ventilated dry grain, most insects were trapped at the surface; in ventilated wet and dry grain, most insects were trapped at 10 cm and 0.75 m; in unventilated wet and dry grain, the vast majority of the insects were trapped at 0.75 m. Very few insects were trapped at 1.75 m regardless of the treatment. The proportions of the initial population of O. surinamensis which were recaptured in the top layer of grain varied between treatments. Most were recaptured in the unventilated bins containing wet and dry grain followed by ventilated bins containing wet and dry grain. The smallest proportion of the population was recaptured in the ventilated bins containing only dry grain. Immediate practical implications for pest monitoring based on physical control measures in use are discussed.     

Insect population dynamics in commercial grain elevators

Data were collected in 1998-2002 from wheat stored in commercial grain elevators in south-central Kansas. Bins at these elevators had concrete walls and were typically 6-9 m in diameter and 30-35 m tall. A vacuum-probe sampler was used to collect grain samples in the top 12 m of the wheat in each bin. The primary insect species found in the wheat samples were: Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum. In the top 3.7 m of grain, R. dominica, C. ferrugineus, T. castaneum and Sitophilus oryzae made up 44, 36, 19 and 1% of the insects found in the samples, respectively. From 3.8 to 12.2 m, R. dominica, C. ferrugineus, T. castaneum and S. oryzae were present at 84, 8, 8, and 1%, respectively. The most prevalent species also changed over time. In June, the start of wheat harvesting and storage in Kansas, insect density was low in the bins. At this time, C. ferrugineus was the most common insect, and it was found mostly in the top grain sample (0-1.2 m). In September through November, C. ferrugineus and R. dominica were at similar densities; however, from February to March, R. dominica was more common.Generally, insect density was greatest at the top and decreased with grain depth. Very few insects were found in samples collected from greater than 12 m (most of the bins contained grain to depths of 24-36 m). Insect density for all species increased rapidly from June through October. During this period less than 20% of the bins had economically significant insect densities (>2 insects/kg). From October until February, the average insect density remained fairly constant but it was greatly reduced in April, May, and June. Bins that had insect densities >2 insects/kg tended to be located adjacent to other heavily infested bins.     

Simulation model of Rhyzopertha dominica population dynamics in concrete grain bins

Rhyzopertha dominica is one of the most damaging insect pests in grain elevators and causes millions of dollars worth of stored grain losses annually in the USA. A simulation model was developed for predicting R. dominica population dynamics in concrete grain bins. The model used a two-dimensional representation of a cylindrical concrete bin (33 m tall×6.4 m wide), and used hourly weather data to predict changes in grain temperature. Output from the grain bin temperature and moisture module was used by the insect module to predict changes in insect density in 32 different bin regions. When compared to validation data from nine grain bins, the model accurately predicted insect vertical distribution and insect density. In December, the highest insect density was in the top center of the grain mass, and decreased steadily with increasing depth and towards the periphery of the grain mass. R. dominica attains this spatial distribution because immigration is primarily through the top of the bin, and higher populations occur in the interior of the grain mass because of warmer temperatures there. Initially, the model underestimated actual insect density in the grain bins. We increased the immigration rate by 50% and this resulted in a much better prediction of R. dominica density by the model. From 20 September to 14 December, populations of R. dominica increased from 0.1 to 3.5 insects per kg of wheat.     

Effect of low pressures on the survival of cocoa pests at 18°C

This study forms part of an effort to eliminate the need for fumigation with methyl bromide to control insect infestations in stored cocoa beans, through development of novel alternative vacuum-hermetic technology. In this communication, the effects of low pressures and exposure time were studied on the mortality of insects at a temperature of 18°C, chosen to simulate cocoa bean storage conditions in temperate climates.Three insect species were used, two of which are major pests of cocoa beans in producer countries, Ephestia cautella (Walker), and Tribolium castaneum (Herbst), while the third, Oryzaephilus surinamensis (L.), is a potential storage pest in temperate climates. For T. castaneum and E. cautella the egg stage was the most resistant to 55±10 mm Hg at 18°C, the times needed to obtain 99% egg mortality were 96 and 149 h, respectively. For O. surinamensis, the adult stage was the most resistant with 164 h being required to obtain 99% mortality.     

Low-temperature aeration to control Indianmeal moth, Plodia interpunctella (Hübner), in stored grain in twelve locations in the United States: a simulation study

Aeration management strategies were developed to control cold-acclimated and diapausing Indianmeal moth, Plodia interpunctella (Hübner), larvae in grain bins during winter in north- and east-central regions of the US. The application in this study focuses on corn because it is the dominant crop in these regions, but we believe that the analyses can be applied to other grains as well. Contour maps for hours below −10 °C for the months of December, January, and February were developed to help effective planning and management of aeration to control overwintering stored-grain insects. Two cumulative lethality index (CLI) models were developed to estimate mortality of laboratory-reared (diapausing without cold-acclimation) and field-collected (cold-acclimated, and diapausing with cold-acclimation) P. interpunctella larvae under changing temperature conditions. The CLI models were used for evaluating aeration management strategies. Simulation studies were conducted using 30 years of weather data for 12 locations in north- and east-central regions of the US to evaluate different aeration management strategies for controlling P. interpunctella larvae. For each strategy, temperatures of headspace air and grain in the top meter of the grain mass were simulated using an existing model for the period of December-February. The tested management strategies included no aeration, continuous aeration, and intermittent aeration by controlling fan operation. During aeration, air was pulled from the headspace downward through the grain with an airflow rate of 0.11 m³/min-t (0.1 cfm/bu). Simulation results indicated that a fan control strategy that turned the aeration fan on when the grain temperature at 0.4-m depth was greater than the headspace-air temperature was the best strategy for managing P. interpunctella larvae in all tested locations. For this strategy, the CLI model indicated that 100% mortality of P. interpunctella larvae could be achieved at a grain depth of 0.4 m from the top grain surface in all locations. For this strategy, the aeration fan operated about 10% of the time from December to February. The average cost of electrical energy required for aeration fan operation with this strategy for all locations was 1.3 ¢/t (0.033 ¢/bu) based on an electrical energy cost of 7 ¢/kWh.     

Feeding bioassay for stored-product insect pests using an encapsulated food source

A procedure that was developed to encapsulate liquid and semiliquid diets was used to encapsulate dry diet for use in a feeding bioassay for beetles that are pests of stored products. Vacuum was used to form Parafilm^® into numerous 6 mm diameter wells. The wells were filled with clean sand (control) or ground dry dog food (test), and the Parafilm^® sealed to produce individual pellets. A single pellet was then placed in the center of a 9 cm diameter Petri dish and feeding activity of groups of ten adults of Sitophilus oryzae (L.), the rice weevil; Oryzaephilus surinamensis (L.), the sawtoothed grain beetle; and Tribolium castaneum (Herbst), the red flour beetle, was tested. The number of insects on the encapsulated pellet and the amount of food or sand scattered were checked hourly for the first 8 h of the study and after 24 h. Few insects were observed on pellets containing sand and little or no sand was observed scattered outside of the pellet, so the presence of dog food in the pellet was needed for insects to feed on the pellet. In tests with encapsulated dog food, the amount of food scattered provided a better quantitative measure of feeding than the number of insects on the pellet. Insects that were starved for 48 h caused greater amounts of food scatter than insects starved for 24 h prior to the test. In direct comparisons among all three species, T. castaneum responded the most slowly and the bioassay may be improved by increasing the amount of time starved. Sitophilus oryzae responded very quickly and the entire pellet was essentially consumed within the first 4-5 h of the study. The encapsulated diets provide a promising method to evaluate feeding behavior of stored-product insect pests.     

Influence of temperature and application rate on efficacy of a diatomaceous earth formulation against Tribolium castaneum adults

Unsanitary storage bins can harbor grain-infesting insects, including the red flour beetle, Tribolium castaneum (Herbst). In a previous study involving heat treatment of empty bins, temperatures in the range of 50–55 °C for 2–4 h were effective in completely killing stored-product insects. Previous research in flour mills showed improved efficacy in killing stored-product insects by using diatomaceous earth (DE) dusts at temperatures below 50 °C. In the current study, the efficacy of a diatomaceous earth formulation (DiaFil^® 610) applied to concrete arenas, to simulate floor of empty bins, was examined at three application rates (0, 2.5 and 5.0 g/m²) to control T. castaneum adults at five constant temperatures (28, 36, 42, 44, and 46 °C). Ten adults of T. castaneum were placed on individual untreated and DE-treated concrete arenas for 4, 8, 12, and 24 h at each of the five temperatures. The efficacy of DE against T. castaneum adults increased with an increase in temperature and exposure time. Generally more adults died at 5.0 g/m² when compared with 2.5 g/m². In 2.5 and 5.0 g/m² DE treatments, exposure for 12 h at a temperature of 42 °C resulted in 73–77% mortality of adults with 100% mortality observed after 24 h. At 44 and 46 °C, 100% mortality of adults was observed after 24 h of exposure at both DE rates. At these two temperatures, the high mortality in untreated arenas (controls) at 8, 12, and 24 h exposures ranged from 27 to 100% confounding the true effects of DE. Our results suggest that combined use of DE and temperatures below 50 °C can be used as an integrated approach for controlling insects in empty bins prior to storage of newly-harvested grain.     

A simple technique to assess compounds that are repellent or attractive to stored-product insects

We have developed a simple and rapid technique that mimics storage conditions, and determines if products are repellent or attractive to stored-product insects. The technique determines the response of insects to potential repellents and attractants by measuring their movement from grain. The technique used a device consisting of a perforated cup (2 mm perforations) that holds 200 g of wheat. A Petri dish and cup collected the insects as they left the wheat. Several natural products were tested for repellency: diatomaceous earth (DE), ground peas (Pisum sativum), protein-rich pea flour, pea starch, and pea fibre. Adult insects of three species were tested: the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, and the rusty grain beetle, Cryptolestes ferrugineus. DE at 0.01% was repellent to all insects tested. Pea fibre, pea protein, and ground pea at 1% caused increased emigration of C. ferrugineus from the wheat. Pea starch did not affect movement out of the grain for all three insects. Only pea fibre and ground pea increased the movement of T. castaneum out of the grain. For S. oryzae, there were no differences after 1 h, but after 24 h both pea protein and ground pea increased movement out of the grain. Several potential attractants were placed outside the grain and the emigration out of the grain noted. For R. dominica, the commercial R. dominica pheromone increased the emigration of insects from the grain; R. dominica adults on broken grain enclosed in a ventilated vial in the collection jar also increased emigration, but not as much as the synthetic pheromone. The commercial Tribolium pheromone did increase movement out of the grain for T. castaneum, but the other treatments were no different from the control. None of the potential attractants increased the movement of S. oryzae from the grain. The implications of this work are discussed with reference to controlling and sampling stored-product insect pests.     

Insect populations in grain residues associated with commercial Kansas grain elevators

Grain residues in nine commercial elevators in Kansas were sampled monthly for insects in grain residues during 1999 and 2000. Five locations per elevator were observed; the boot pit, dump pit, headhouse, rail area, and tunnel. When a grain residue was found, the quantity was estimated and a sample taken. Adult grain pest insects and beneficial insects were removed and identified. Cryptolestes spp. and Sitophilus spp. comprised about 80% of the pest insects collected. The density of Cryptolestes spp. appeared to rapidly increase in spring but remained low at other times of the year. The density of Sitophilus spp. in the residues increased consistently through the warm months, peaked immediately after the warmest month, and declined gradually as ambient temperatures cooled. Pest insects were observed in 41.7% of the 1575 samples examined, and beneficial insects were collected from 5.1% of the samples. Residue samples taken from the elevator boot pit and tunnel areas contained a greater density of pest insects (all species combined) than other locations. About 42% of the residues were estimated to be smaller than 1.5 kg, and samples from these residues contained more insects per sample than did samples from larger residues. Anisopteromalus calandrae comprised 88.9% of the total number of beneficial insects found. Beneficial insects were observed infrequently, and mean populations exceeded 1 insect/kg of residue in any month at only two of the nine elevators. Results from our study showed that grain residues within the elevator often contain pest insects and could provide food and harborage when the bins are empty, serving as sources of insect infestation for new grain.     

Survival of Sitophilus oryzae (L.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on product efficacy

A series of experiments was conducted to evaluate the effects of temperature, relative humidity (r.h.), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It™ formulation of DE, and 10, 20, or 30 1-2 week-old mixed-sex adult weevils were exposed on 35 g of wheat for 1 week at combinations of 22°C, 27°C, or 32°C; 40%, 57%, or 75% r.h. No weevils survived when exposed at 40% or 57% r.h., but at 75% r.h. survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F₁s were produced at any r.h. on wheat held at 22°C. At 27°C and 32°C, the maximum number of F₁s was produced on wheat held at 75% r.h. In the second experiment, wheat was treated with 25%, 50%, 75%, or 100% of the label rate of 300 ppm, and 10 mixed-sex adult S. oryzae were exposed on 35 g of wheat for either 1, 2, or 3 weeks at 27°C, 57% and 75% r.h. Survival decreased with increasing exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75% versus 57% r.h. In the final experiment, wheat was treated with 300 ppm, held at 22°C and 27°C, 57% r.h., and bioassayed at monthly intervals for 3 months by exposing 20 adult mixed-sex S. oryzae on 35 g of wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22°C compared to 27°C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months. Results of these studies show that S. oryzae is susceptible to DE, but survival of exposed insects will depend in part on the temperature and r.h. humidity (or grain moisture content) at which they are exposed. Survival is directly related to temperature, and as r.h. increases either higher concentrations or longer exposure intervals will be necessary to maintain a certain level of mortality. There may also be a loss of efficacy with residual aging.     

Chemical composition and insecticidal properties of some aromatic herbs essential oils from Algeria

The biological effects on Sitophilus granarius were evaluated for three aromatic herbs essential oils: Foeniculum vulgare, Rosmarius officinalis and Lippia citriodora. Stored grain pests were currently controlled by chemical pesticides. This control method leads to pollution of the environment and intoxication of consumers. Essential oils of aromatic plants are more considered as good control alternative tools. Filter papers treated with 5, 50 and 500 μl of test oil were placed in the bottom cover of 1 l plastic bottle. The insects, 50 adults per bottle, were exposed for 1–5 days. Cumulative mortalities were determined 24 and 120 h after treatment. All treatments were replicated five times. The components of the essential oils were identified through GC and GC–MS. The identity of the constituents was confirmed and their relative proportions determined. The results indicate that these natural products may find potential application as useful, environmentally safe insect control and crop protectant agents.     

Influence of grain and relative humidity on the mortality of Sitophilus oryzae (L.) adults exposed to ethyl formate vapour

Ethyl formate (EF) is being investigated as an alternative to phosphine and methyl bromide, for the fumigation of stored products. The compound has been found to have a rapid action against stored-product insects and shows promise as a fast-acting disinfestant.The response of Sitophilus oryzae adults to EF in a sealed system was studied. Insects were exposed to a range of EF doses for 24 h at 25 °C, with a range of grain quantities and relative humidities (r.h.). It was found that rapid mortality of S. oryzae adults in a sealed system was obtained, with a range of applied concentrations required to achieve 99% mortality. Concentrations as low as 11.2 mg L⁻¹, for the exposures without wheat at 97% r.h., achieved 99% mortality, whereas 81.2 mg L⁻¹ EF was required for the exposures carried out on 1500 g wheat in 2.7 L at 60% r.h. Modelling studies of the mortality data revealed that, in general, the presence or absence of grain had the largest influence on mortality, where the larger the grain quantity, the higher the required EF dose to achieve 99% mortality. To a lesser degree, the r.h. also influenced the observed mortality, where the higher the r.h., the lower the required EF dose to achieve 99% mortality. In this experimental system, the factors that determined the level of mortality were a complex interaction of the initial dosage concentration (C₀), concentration×time product (Ct), grain quantity and r.h.     

Efficacy of powder and essential oil from Chenopodium ambrosioides leaves as post-harvest grain protectants against six-stored product beetles

Powder and essential oil obtained from dry ground leaves of Chenopodium ambrosioides were tested under laboratory conditions (25±1°C, 70-75% r.h.) for their ability to protect grains from damage by six insect pests, Callosobruchus chinensis, C. maculatus, Acanthoscelides obtectus, Sitophilus granarius, S. zeamais and Prostephanus truncatus. The insects were reared and tested on whole maize grain for S. zeamais and P. truncatus, whole wheat for S. granarius, green peas for C. chinensis, mung bean for C. maculatus and white bean for A. obtectus. The powder prepared from dry leaves of C. ambrosioides was mixed with grains at different dosages ranging from 0.05-0.80% (wt/wt) for C. chinensis, C. maculatus and A. obtectus and from 0.8-6.4% (wt/wt) for S. granarius, S. zeamais and P. truncatus. The dosage of 0.4% killed more than 60% of all the bruchids 2 days after treatment, while a dosage of 6.4% induced total mortality of S. granarius and S. zeamais within the same exposure time. All levels of the dry ground leaf concentrations inhibited F1 progeny production and adult emergence of the tested insects. The dosage of 0.2 μl/cm² of the essential oil killed 80-100% of the beetles within 24 h except C. maculatus and S. zeamais, where this dosage induced only 20% and 5% mortality, respectively. These results indicate a scientific rationale for the use of this plant in grain protection by local communities in the western highlands of Cameroon.     

Effectiveness of products from four locally grown plants for the management of Acanthoscelides obtectus (Say) and Zabrotes subfasciatus (Boheman) (both Coleoptera: Bruchidae) in stored beans under laboratory and farm conditions in Northern Tanzania

The effectiveness of whole or powdered leaves (botanicals) from four locally grown plant species applied at a rate of 1.5 kg per 100 kg beans (Phaseolus vulgaris) against Acanthoscelides obtectus and Zabrotes subfasciatus was compared under laboratory and farm conditions. In the laboratory, Chenopodium ambrosioides, applied as powder or as whole leaves, was the most effective, with 100% mortality of adult insects in less than three days and no progeny. Less C. ambrosioides (about 200 g per 100 kg beans) still resulted in 100% mortality within 24 h. Tagetes minuta applied as powder also increased mortality and reduced oviposition and progeny production significantly. The other treatments - T. minuta applied as leaves, and Azadirachta indica or Cupressus lusitanica applied as powder or as whole leaves - had no significant effects upon mortalities, oviposition rate, or progeny production compared with control treatments. When the rate of application was increased to about 8.3 kg per 100 kg beans, there was a slight increase in mortality using T. minuta and A. indica, but not with C. lusitanica. An additional trial with C. ambrosioides from different collections and with plants at different stages of development revealed considerable variations in the efficacy of the treatment.In the on-farm trials, A. indica-seed powder was the most effective treatment, followed respectively by leaf powders of C. ambrosioides, C. lusitanica and T. minuta. All treatments were significantly more effective than the control in reducing the numbers of live insects; they also reduced numbers of damaged beans and maintained germination rates after 5 months of storage. The results of evaluations of the treatments made by farmers just after the trials and five years later are reported.     

Movement and distribution of adult Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat in response to temperature gradients, dockage, and moisture differences

The movement and distribution of adult Cryptolestes ferrugineus were determined in 100×100×1000 mm wheat columns with or without 5 °C/m temperature gradients (from 27.5±0.2 to 32.5±0.2 °C or at 27.5±0.2 °C) under: (1) 5% and 10% uniform dockage (14.5±0.2% moisture content (m.c.), wet basis); (2) half of the columns with 5% or 10% dockage and the other half without dockage; (3) 12.5%, 14.5% or 16.5% m.c. wheat without dockage; and (4) half of the columns with 12.5% or 14.5% m.c. wheat and the other half with 16.5% m.c. wheat.Adults introduced in the middle of the horizontal wheat columns with or without uniform dockage showed no bias in the direction of net displacement, with the distribution pattern gradually becoming more uniform when time increased from 1 to 144 h. In vertical columns with 0%, 5% and 10% uniform dockage, the adults preferred to move down in the first 24 h; however, they moved up after 24 h. Grain with a high percentage of dockage (10%) decreased beetle movement speed. A low percentage of dockage (5%) did not influence insect movement and distribution. Positive geotaxis was more important than the attraction of dockage.Adults responded to both temperature gradients and moisture differences in columns of wheat with temperature gradients and moisture content differences. The response was different at different moisture conditions. Adults were more sensitive to moisture differences and moved faster in 12.5% m.c. wheat than in 14.5% m.c. wheat. Adults stayed in warmer sections in both high and low moisture grain. At different moisture conditions, adults changed their preference (e.g., preferred high moisture grain in dry grain, and preferred warmer temperature in damp grain).     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

Effect of wood ash and conidia of Beauveria bassiana (Balsamo) Vuillemin on mortality of Prostephanus truncatus (Horn)

A series of experiments was carried out to investigate the effect of treating maize with wood ash and entomopathogenic fungus on the mortality of the larger grain borer Prostephanus truncatus. Jars of maize were treated with ash and/or conidia of Beauveria bassiana at doses of 0.0005, 0.005, 0.05 and 0.2 g conidia/g ash/100 g maize. Adult P. truncatus were placed on the maize and numbers of live and dead insects were assessed weekly.Ninety-five per cent mortality of P. truncatus was observed after 1 week and 100% mortality after 2 weeks in maize treated with the highest dose of conidia with ash (0.2 g/g). Mortality of P. truncatus in all ash with conidia treatments was significantly higher than untreated controls over a 4-week period, except the lowest dose of conidia at week 4. The three highest concentrations of conidia per gram of ash resulted in significantly (1% level) higher mortality of P. truncatus than ash alone.In an experiment to investigate the possible synergy of ash and conidia, there were no significant differences in mortality of P. truncatus between treatments with the same concentration of conidia regardless of whether the conidia were mixed with ash or applied alone. Larval populations of P. truncatus were observed in all treatments without ash, but only one larva was observed in one replicate of a treatment containing ash suggesting that ash has an important effect in preventing the establishment of a second generation of insects.     

Fumigation trials on the application of ethyl formate to wheat, split faba beans and sorghum in small metal bins

Field trials were carried out in Australia with ethyl formate for insect control in wheat (Harden, NSW), split faba beans (Vicia faba) (Two Wells, SA) and sorghum (milo) (Warwick, Qld) in unsealed metal bins normally used to store grain on farms. Liquid ethyl formate was applied as a split dose (a first dose of 85 g t⁻¹ and after 4 h another dose of 85 g t⁻¹) to the top of the grain through a PVC probe (4 cm i.d.×1.2 m). This method of application was chosen to maintain ethyl formate concentrations below the flammability level, reduce vaporisation, maintain an effective concentration of ethyl formate for >10 h and to avoid liquid ethyl formate accumulating at the bottom of the bin. With wheat, the concentration of ethyl formate was maintained at effective levels for about 2 days, all insects at all stages were killed rapidly, and in 5-7 days the residues were reduced to natural levels without aeration. Split faba beans sorbed ethyl formate strongly, the residues persisted longer and complete insect control was achieved. Control was high but not 100% in the sorghum trials. Residues in the sorghum at 10 °C persisted significantly longer than at 20 °C. During application and fumigation, the levels of ethyl formate in the working environment did not exceed a threshold limit value (TLV) of 100 ppm. The field trials have shown that ethyl formate has good potential as a fumigant in unsealed small metal bins as it kills insects rapidly. Residues decreased to natural levels even without aeration after 7 days for wheat and sorghum and 26 days for split faba beans.     

Insecticidal activity of asarones identified in Acorus gramineus rhizome against three coleopteran stored-product insects

The insecticidal activities of Acorus gramineus rhizome-derived materials against adults of Sitophilus oryzae (L.), Callosobruchus chinensis (L.) and Lasioderma serricorne (F.) were examined using direct contact application and fumigation methods. The biologically active constituents of the Acorus rhizome were characterized as the phenylpropenes (Z)- and (E)-asarones by spectroscopic analysis. Responses varied with insect species, compound and exposure time rather than dose. In a filter paper diffusion test, (Z)-asarone caused 70% and 90% mortality against S. oryzae adults at 0.064 and 0.255 mg/cm² at 4 days after treatment, respectively, with 100% mortality at 7 days after treatment. (E)-Asarone at 0.255 mg/cm² was almost ineffective against S. oryzae adults at 7 days after treatment. Against C. chinensis adults at 0.064 mg/cm², (Z)- and (E)-asarones gave 100% mortality at 3 and 7 days after treatment, respectively. Against L. serricorne adults, (Z)-asarone gave 90% and 83% mortality at 0.255 and 0.064 mg/cm² at 7 days after treatment, respectively, whereas (E)-asarone at 0.255 mg/cm² was almost ineffective at 7 days after treatment. These results indicate that the toxicity of asarones might be due to the cis configuration rather than to the position of the double bond. In a fumigation test, (Z)-asarone at 0.577 mg/cm² was much more effective against adults of all three insect species in sealed containers than in open ones, indicating that the insecticidal activity of the compound was largely attributable to fumigant action.     

Heat combined with diatomaceous earth to control the confused flour beetle (Coleoptera: Tenebrionidae) in a flour mill

An alternative to methyl bromide fumigation for controlling stored-product insects in food processing facilities is to heat part or all of a facility to 50-60°C for 20-30 h. However, some equipment or structures cannot tolerate these conditions, or it is difficult or expensive to attain these high temperatures. It may be possible to reduce the temperature requirements necessary for effective control by using a desiccating dust, such as diatomaceous earth (DE), in combination with the heat treatment. The objectives of this study were to examine the combined impact of high temperature and DE on the mortality of Tribolium confusum (du Val) in a flour mill environment and to evaluate the effects of DE application rate on insect mortality in a mill environment during heat treatment. In areas of the mill where temperatures were in excess of 47°C, DE applications of 0.3 g/m² in combination with heat were no more effective than the heat treatment alone. At higher application rates, the DE was more effective. In cooler areas, adult beetles exposed to DE died sooner than insects not exposed to the insecticidal dust. These results indicate that application of DE in areas that cannot be heated to 47°C is effective for controlling T. confusum in a flour mill. A comparison is made with a parallel study conducted in Canada.