Repellent effect of pea (Pisum sativum) fractions against stored-product insects

Peas (Pisum sativum) are toxic to some stored-product insects. The repellent effect of fractions of pea seed to stored-product insects was evaluated in multiple-choice tests in which wheat kernels were dusted with fractions rich in either protein, fibre or starch at 0.001 to 10% (wt:wt). There was a negative correlation between pea protein concentration and the number of adults found in grain for Cryptolestes ferrugineus and Sitophilus oryzae, but not for Tribolium castaneum. Pea fibre repelled C. ferrugineus adults but not S. oryzae and T. castaneum. Pea starch did not repel any of the insects. One-week old and 6-week old C. ferrugineus were equally repelled by pea protein. Repellency was detectable 1 h after exposure. Cryptolestes ferrugineus and S. oryzae did not become habituated to the repellent action of pea protein even after 4 weeks of exposure. Habituation was observed, however, when C. ferrugineus was exposed to pea fibre for 4 weeks. In a two-choice bioassay (0 vs. 0.1% and 0 vs. 1% pea protein), the pea-protein-treated grain had significantly fewer insects (C. ferrugineus, S. oryzae, Sitophilus zeamais, T. castaneum, and Tribolium confusum) than untreated grain. The properties of the pea protein fractions seem well suited for developing a natural stored grain protectant.     

History of an insect infestation in durum wheat during transport and storage in an inland terminal elevator in Canada

A bulk of 242 tonnes of infested durum wheat from a primary elevator was sampled when it was loaded into four boxcars in August 1974, when it was unloaded at the inland terminal elevator and when it was turned in the terminal elevator. During a storage period of 1 year, the wheat was cleaned once and turned 4 times. Grain temperature was recorded each time samples were taken. Three methods of collecting 1-kg samples were used; dip sampling during transfer of the grain at both elevators, vacuum probe sampling in the terminal elevator bin and drop sampling from the bottom of the terminal elevator bin. Samples were placed in Berlese-Tullgren funnels for 6 hr to remove insects. Adults and larvae of Cryptolestes ferrugineus (Stephens) and of Tribolium castaneum (Herbst) were found, with larvae of the former species being most prevalent. In insect traps placed in the loaded boxcars, an adult C. ferrugineus was caught in one, T. castaneum adults in three, and adult Lathridius minutus (L.) in all of the boxcars; no insects were found in traps placed in the grain in the terminal elevator bin in September and October. Cleaning the grain during storage was ineffective as a means of disinfestation. The number of insects in the samples decreased as the duration of storage increased and as grain temperature decreased. Only four insects were found after November, three of which were C. ferrugineus larvae (one third and two fourth instar) and one was a Trogoderma larva. The last insect found was a fourth instar larva of C. ferrugineus in February 1975. It had a starved desiccated appearance. Even after 1 year of storage, grain temperature did not exceed the 19°C recorded at the time the grain was placed in the elevator.     

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.     

Mortality of adult Cryptolestes ferrugineus (Stephens) exposed to changing CO2 concentrations

The concentration of carbon dioxide (CO₂) in a grain bin declines during a fumigation due to leakage, but mortalities of adult Cryptolestes ferrugineus (Stephens) have been obtained and reported at constant CO₂ concentrations. A procedure for predicting the mortality of adult C. ferrugineus exposed to conditions of changing CO₂ concentration was developed. Based on published data, a regression equation was obtained for mortality of adult C. ferrugineus exposed to elevated CO₂ concentrations at a temperature of 25°C. The regression equation was used to calculate a cumulative lethality index. Complete mortality should occur when the cumulative lethality index equals one. Agreement between the observed insect mortality and the corresponding cumulative lethality index was good in five experimental fumigations conducted in sealed, welded-steel hopper bins, but the cumulative lethality index over-predicted the insect mortality in the sixth experimental fumigation.     

Unbaited probe traps and grain trier: a comparison of the two methods for sampling Coleoptera in stored barley

Inside a Central Greece storeroom containing 80 metric tons of barley, 10 unbaited probe traps were placed at a depth of 80 cm from January 1997 to January 1998. The traps were inspected every 20 days. Additionally, during the same period, samples were taken every 20 days using a non-partitioned grain trier. More adults were found in the traps than in the grain trier, especially during the warm months. Twenty-one species were found. Cryptolestes ferrugineus, Alphitobius diaperinus, Oryzaephilus surinamensis, Ahasverus advena, Tribolium castaneum and Rhyzopertha dominica were the most abundant species in the traps, whereas Sitophius oryzae and Oryzaephilus surinamensis were the most abundant in the grain trier samples. Probe traps were more sensitive in detection of adults, with the exception of S. oryzae and S. granarius. Iwao’s regression analysis indicated repulsion among individuals in both techniques. Furthermore, all species (except for C. ferrugineus in grain trier samples) showed an aggregated distribution among sampling units. For Iwao’s model, the greatest r² values were those for the species C. ferrugineus and A. diaperinus in the traps, while the values for the same species in the grain trier samples were the lowest.     

Developing sequential sampling plans for classifying Lasioderma serricorne (F.) (Coleoptera, Anobiidae) status in a cigarette factory

This paper presents sequential sampling plans for classifying the pest status of Lasioderma serricorne (F.) based on complete counts from insects caught in sex pheromone traps in a cigarette factory. The sampling plan used 26 pheromone traps. As the adult population follows the negative binomial distribution, a sequential sampling plan was developed using the sequential probability ratio test (SPRT). Iwao's confidence interval method was also employed to analyse results. The sampling plan was implemented to assist management decision-making based on the economic threshold of 5 insects/trap/week.The results show that, using SPRT or Iwao's methods, managers can make decisions using only seven and six traps, respectively, with a minimum risk of incorrect assessment.     

Biological activity of Cassia occidentalis L. against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

In developing countries, traditional control methods are commonly used against stored-product insects and mites. In Senegal, the leaves of Cassia occidentalis L. (Caesalpiniaceae) are used to protect cowpea seeds (Vigna unguiculata L. (Walpers)) against Callosobruchus maculatus (Coleoptera: Bruchidae). The biological activity of the leaves, the seeds and oil of C. occidentalis was evaluated in controlled conditions (28 ± 2°C, 45 ± 5% r.h.) against C. maculatus. At the rate of 10% (w/w), both fresh and dry leaves as well as whole and ground seeds had no contact toxicity on the cowpea beetle. In contrast, seed oil induced an increase in mortality of C. maculatus eggs and first larval instar at the concentration of 10 ml/kg cowpea. The basis of the ovicidal and larvicidal activities are discussed in this paper. Several trials using pure compounds have highlighted that several fatty acids (linoleic, oleic and stearic) are responsible for C. occidentalis toxicity. C. occidentalis seed oil did not reduce the oviposition of C. maculatus at 10 ml/kg seed.     

Wheat disinfestation using microwave energy

A pilot-scale industrial microwave system operating at 2.45 GHz was used to determine the mortality of three common species of stored-grain insects, namely Tribolium castaneum, Cryptolestes ferrugineus, and Sitophilus granarius. Wheat samples (50 g each) at 14%, 16%, and 18% moisture content (wet basis) were infested with 5, 10, or 15 insects. The infested samples were then exposed to microwave energy at four different power levels 250, 300, 400, and 500 W for two exposure times of 28 and 56 s. Complete kill of adults of all three species and of post-embryonic stages of T. castaneum was achieved at 500 W with an exposure time of 28 s. There was a significant difference in the mortality of T. castaneum and C. ferrugineus adults at 14% and 16% moisture content (m.c.) wheat but there was no significant difference in the mortality at 16% and 18% m.c. Mortality of insects increased with either power or exposure time or both. Germination of wheat kernels was lower after treatment with microwave energy. Milling and baking tests were done for the samples at which 100% mortality was obtained. There was no significant difference in the quality of grain protein, flour protein, flour yield, flour ash, and loaf volume of wheat treated with microwave energy.     

Thermal imaging to detect infestation by Cryptolestes ferrugineus inside wheat kernels

Canada's zero tolerance for live insects in grain received from farmers, and shipped to domestic and export buyers, has necessitated the development of an accurate insect detection method. An infrared thermal imaging system was developed to detect infestation by six developmental stages (four larval instars, pupae and adults) of Cryptolestes ferrugineus under the seed coat on the germ of the wheat kernels. The artificially infested wheat kernels were removed from the incubation room (30 °C), refrigerated (5 °C) for 60 s, maintained at ambient conditions for 20 s, and imaged using a thermal camera to identify each developmental stage (n=283). The means of the highest 5% and 10% of all temperature values on the surface of the grain were significantly higher (=0.05) for grains having young larvae inside and lower for grains having pupae inside. Temperature distribution on the surface of the infested kernels with different stages of C. ferrugineus was highly correlated with the respiration rate of each developmental stage (r=0.83–0.91). The overall classification accuracy for a quadratic function was 83.5% and 77.7% for infested and sound kernels, respectively, and for a linear function, it was 77.6% and 83.0% for infested and sound kernels, respectively, in pairwise discriminations. Thermal imaging has the potential to identify whether the grain is infested or not, but is less effective in identifying which developmental stage is present.     

Predicting insect density from probe trap catch in farm-stored wheat

Insect populations infesting wheat stored in four bins on two Kansas farms were monitored from early July 1996 through to the middle of January 1997. Estimates of adult insect density based upon the numbers of adult insects caught using probe traps differed from those based upon the number of insects found in grain samples. These differences were a result of differences in numbers of insects found and percentages of traps or grain samples with insects. Traps detected insects 15 to 37 d earlier than grain samples. The depth of traps below the grain surface tended to influence both the total number and species composition of the insects that were caught. Traps inserted with the top just below the grain surface collected an average of 1.9 times more Cryptolestes ferrugineus (Stephens), 1.2 times more Rhyzopertha dominica (F.), 4.1 times more Ahasverus advena (Waltl) and 77.4 times more Typhaea stercorea (L.) than traps inserted with the top 7.6 cm below the grain surface. However, trap depth did not have a significant effect on the number of R. dominica caught and on only 12 to 21% of sampling dates did trap depth have a significant effect on the number of insects of other species that were caught. Grain temperatures in three of the bins averaged 30°C during the first 70 d of storage and then decreased by 0.2°C/d. Grain in the other bin was initially more than 10°C warmer and grain temperature decreased by 0.2°C/d over the full storage period. The numbers of insects captured in traps decreased as grain temperature decreased even though grain samples indicated that insect populations were still growing. Thus, trap catches did not estimate insect population density consistently throughout the storage period. A method was developed in the current paper to adjust for the effect of seasonal changes in temperature on trap catch.     

A novel use of modified atmospheres: Storage insect population control

The research described here aimed to establish the feasibility of using modified atmospheres (MA) to protect commodities throughout their storage life by using oxygen (O₂) levels that disrupt the life cycles of the target beetle species. Rather than achieving complete mortality of all stages, the aim was to identify more easily obtainable MAs that would kill the most susceptible stage and prevent population growth. Simulated burner gas and nitrogen (N₂) atmospheres with O₂ contents between 3% and 6%, were tested, along with a N₂-based MA with elevated carbon dioxide (CO₂) (10–20%).

Laboratory tests were carried out on five species of stored-product beetles, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Sitophilus granarius, S. oryzae and Tribolium castaneum. After exposure to the MAs for 28 d an assessment was made of the mortality of adults, the number of adults from progeny produced under the MAs and, for the simulated burner gas, the number of adults from progeny produced in a 28-d period after exposure to the MA. The tests were carried out at 20 and 25 °C with 75% and 85% r.h. at each temperature.

The O₂ content preventing population growth varied with species and temperature. For simulated burner gas or N₂ it was about 4% for O. surinamensis, S. granarius and S. oryzae, and about 3% for C. ferrugineus and T. castaneum at 25 °C. At 20 °C it was about 3% for all species tested. When CO₂ was increased to 10% or 20%, reducing O₂ to 5% was sufficient to eliminate emergence of S. granarius at 20°C, but a few individuals emerged at 25 °C. For C. ferrugineus there was a 95% reduction with 5% O₂ plus 20% CO₂ at 20 °C, but not at 25 °C.     

Desiccation increases the efficacy of Beauveria bassiana for stored-grain pest insect control

The effect of desiccation stress on the efficacy of Beauveria bassiana for controlling stored-product insects was investigated in laboratory bioassays. The mortality of B. bassiana-treated Plodia interpunctella larvae was greater at a vapor pressure deficit (VPD) of 2.42 or 1.87 kPa than at 1.06 kPa. Moisture also had significant effects on the mortalities of adult rice weevils, Sitophilus oryzae and maize weevils, Sitophilus zeamais. Mortality of S. zeamais was higher at 2.42 and 1.87 kPa than at 1.06 kPa, while mortality of S. oryzae was higher at 1.87 kPa than at either 2.42 or 1.06 kPa. Higher control mortality at the higher two VPDs indicated that S. zeamais was less desiccation tolerant than S. oryzae. The mortalities of B. bassiana-treated adult Cryptolestes ferrugineus, larval Lasioderma serricorne and larval Oryzaephilus surinamensis were not significantly affected by VPD. These results demonstrate that dry stored-grain conditions are favorable for B. bassiana efficacy.     

Laboratory evaluation of the juvenile hormone analogue fenoxycarb against some insecticide-susceptible and resistant stored products beetles

The juvenile hormone analogue fenozycarb, (ethyl[2-(phenoxy-phenoxy)ethyl] carbamate) was evaluated against a number of insecticide-susceptible and resistant strains of stored-product insects. The order of susceptibility to the compound was Tribolium castaneum > Cryptolestes ferrugineus > Oryzaephilus surinamensis > Rhyzopertha dominica. A malathion-specific resistant strain of T. castaneum (Kano-C) with > 260-fold resistance to malathion was found to be more susceptible to the compound than the insecticide-susceptible strain (FSS-II). Some degree of tolerance was evident in the non-specific malathion resistant strain of T. castaneum (CTC-12) compared with the susceptible strain. There was no evidence of cross-tolerance to fenoxycarb in insecticide-resistant strains of C. ferrugineus, O. surinamersis or R. dominica.     

The influence of relative humidity and thermal acclimation on the survival of adult grain beetles in cooled grain

The influence of humidity and thermal acclimation on the survival of Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus granarius, S. oryzae and Tribolium castaneum in cooled wheat or flour at 45 and 70% relative humidity was studied in the laboratory. Young adults were held continuously at 30 or 32°C; cooled gradually to 13.5°C and held at that temperature; cooled gradually to 9°C and held at that temperature; or transferred directly to 9°C.

Survival at low temperatures differed, often considerably, between species, being generally shortest in T. castaneum (0.7–16 weeks) and longest in S. granarius (5–40 weeks). There was considerable interaction between the effects of temperature and humidity, with survival being, to varying degrees, shorter in 45% r.h. than in 70% r.h. At 45% r.h., an equilibrium relative humidity common in Australian storages, all species survived when the grain was cooled to 13.5°C but only S. granarius survived 26 weeks in grain cooled to 9°C.

Chill-coma temperature and acclimation temperature were linearly related in all species at each humidity. Neither the slopes nor intercepts of the relationships were influenced by humidity. There was generally an inverse relationship between survival and chill-coma temperature.

At 45% r.h., the increase in survival at 9°C attributable to acclimation ranged from 2-fold in S. oryzae (0.9 weeks) to 3.5-fold in C. ferrugineus (3.8 weeks). Corresponding values for beetles at 70% r.h. ranged from 2.3-fold in R. dominica (2.4 weeks) to 7.9-fold in C. ferrugineus (6.9 weeks).     

Two-dimensional diffusion of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) populations in stored wheat under constant environmental conditions

Insect movement inside a stored-grain bulk increases the chance for the pests to find biologically suitable locations for their development and multiplication. The movement of rusty grain beetle, Cryptolestes ferrugineus, adults was determined in a 0.1×1×1 m wooden box filled with wheat. There were 12 combinations of temperature (20, 25, 30, or 35 °C), number of adults (125, 250, or 500), moisture content (12.5, 14.5, or 16.5%), and time periods (3, 6, 12, 24 or 72 h) over which movement could occur. The diffusivities in each set of environmental conditions were calculated using a developed procedure (program) and experimental data. The diffusivity at 14.5% m.c. and 20 °C in the 24 h movement period was 2.5±0.3×10⁻⁴ m²/h. The diffusivity increased with increasing temperature, decreasing moisture contents, decreasing movement periods, and increasing insect numbers. Adult numbers in each section of the wooden box were predicted using an analytical model and calculated diffusivities. There were no significant differences between measured and predicted adult numbers. This research suggests that distribution and dispersal of the C. ferrugineus adults in stored wheat follow a diffusion pattern under constant environmental conditions.     

Evaluation of sampling units and sampling plans for adults of Cryptolestes ferrugineus (Coleoptea: Laemophloeidae) in stored wheat under different temperatures, moisture contents, and adult densities

Development and evaluation of optimum size and number of sample units is required for cost-effective management of stored grain beetles. In this study, we evaluated the sampling parameters and accuracy of insect density detection and estimation, developed the optimum size and number of sample units, and conducted a feasibility study of the insect detection and density estimation. The measured insect densities in 92% of random samples were less than the introduced insect densities and 67.4 ± 10.8% of random samples did not contain adults when the introduced insect density was 0.1 A/kg (adult/kg). If the random sampling technique was used and 15% of the stored wheat bulk was sampled, 72% of determined means of insect densities of the sampling sets were lower than the introduced insect densities. Increasing the size of sample units did not improve the accuracy of the estimation of insect densities; however, it did considerably increase the probability of insect detection when insect densities were lower than 1.0 A/kg. We recommend at least 7 kg per sample unit for insect detection (especially when insect densities < 0.1 A/kg) and the optimum number of sample units with 15 kg grain per unit should be >24 for a fixed precision of 0.35 when insect densities < 0.1 A/kg. This might be a challenge for grain storage practice. Therefore, using sampling technique to estimate insect densities and detect insects at low insect densities (<0.1 A/kg) might not be practicable.     

Comparison of the desiccation effects of marine and freshwater diatomaceous earths on insects

The desiccating effects of two different types of diatomaceous earths (DEs), of freshwater and marine origin, applied by two different methods, were compared on four species of insects, Cryptolestes ferrugineus, Rhyzopertha dominica, Sitophilus oryzae and Sitophilus granarius. The purpose was to investigate the performance of DEs, including their abrasive and absorptive effects through the accumulation of silica dusts on the insect cuticle, resulting in death of the insects by desiccation. The data obtained showed that similar insects treated with the same type of diatom, but applied either by spraying or dusting, did not have the same initial mortality rate.

After examining and comparing the data obtained, it appeared that weight loss at death of insects subjected to the action of sprayed DEs was slightly less than for insects subjected to dust application, while mortality was slightly more rapid during the observation period. The extra weight of dusted insects was ascribed to greater adherence of dust particles to the treated insects.     

PCR assay for differentiating between Group I (proteolytic) and Group II (nonproteolytic) strains of Clostridium botulinum

Groups I (proteolytic) and II (nonproteolytic) C. botulinum are genetically and physiologically distinct groups of organisms, with both groups being involved with human botulism. Due to differences in spore heat resistance and growth characteristics, the two groups possess different types of human health risks through foods, drink, and the environment. The epidemiology of human botulism due to Groups I and II C. botulinum is poorly understood, largely due to insufficient characterization of disease isolates, and warrants thorough outbreak investigation with a particular attention to discrimination between the different physiological groups of C. botulinum. In this study, a PCR assay was developed to discriminate between Group I and Group II C. botulinum. The assay is based on the fldB associated with phenylalanine metabolism in proteolytic clostridia, and employs an internal amplification control targeted to conservative regions of 16S rrn in Groups I and II C. botulinum. The assay correctly identified all 36 Group I and 24 Group II C. botulinum strains, possessing a 100% exclusivity and inclusivity. The assay provides a substantial improvement in discriminating between the Groups I and II C. botulinum, which traditionally is based on a time-consuming and error-prone culture method. Differentiation between the physiological groups of C. botulinum is an essential step in investigation of human botulism outbreaks, and should be considered as a diagnostic corner-stone in order to improve our epidemiological understanding of human botulism.     

Stored products pests and remote moisture sensors

It was found that moisture sensors, containing insecticide-treated grain and implanted into an experimental bulk of wheat, acted as ready-made insect traps. The presence of dead insects in the sensors gave a clear indication of the insect distribution in the bulk.

Laboratory tests have shown that the number and proportion of Tribolium castaneum, Oryzaephilus surinamensis, Cryptolestes ferrugineus and Sitophilus oryzae entering the sensors depends upon both the filler and the surrounding medium. Paddy proved to be a medium in which wheat or brown rice filler would attract particularly large numbers of insects but, in general, brown rice was found to be the more attractive.

It was shown that the filler must be treated with insecticide. Fillers to which only fungicide was admixed subsequently became heavily infested, giving rise to much lower moisture meter readings than the controls. In contrast, insecticide-treated fillers killed those insects in contact with them and gave readings that were higher than the control, although by not more than 0.8% moisture content. The reason for, and possible significance of, the slight increase in readings is discussed.

It was concluded that for very accurate moisture measurements it would be best to choose the least attractive filler and treat it with an insecticide and insect repellent. In situations where slight inaccuracy in readings can be tolerated, the efficiency of the sensors as insect traps could be increased by loading them with the most attractive filler, treated with an insecticide. The sensors could supplement data obtained from routine insect sampling and could be used in circumstances where conventional methods cannot be employed.     

Ultrasonic communication in Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae)

Male Corcyra cephalonica (Stainton) produce trains of 125 kHz sound pulses with a striated tymbal located on each tegula. There are nine striae on each tymbal making possible 36 sound pulses during each pulse train. The tymbals are activated by downward pressure of the forewings against the tegular-wing coupler. The sound is produced in two temporal patterns—a slow phase and a buzz phase. The sound produced by a calling male affects the behavior of both male and female C. cephalonica. It may also play a defensive role against other moth species competing with C. cephalonica for the same food resource. C. cephalonica infestations can be discovered and located by detecting male sound. Males can be accurately separated from females either by the presence of sound in living specimens or the presence of striated tymbals on dead specimens.