Paul G. Fields

The control of stored-product insects and mites with extreme temperatures

Abstract Heating or cooling is used extensively to control stored-product insect and mite pests. For most stored-product insects 25–33°C is optimal for growth and reproduction, at 13–25 or at 33–35°C insects are able to complete their development and produce offspring, but 35°C insects eventually die. The more extreme the temperature the more quickly insects die, with death occurring in a few minutes at −20 or 55°C. Lethal temperatures vary considerably and depend on species, stage of development, acclimation, and relative humidity. Extensive tables listing the survival of the major stored-product insects and mites at extreme temperatures from over 50 papers is presented. There are many ways to cool the commodity: turning, aeration or refrigerated aeration, or to heat the commodity: infrared, microwaves, high frequency irradiation, or hot air in fluidized-bed. Some of these processes are available commercially, while others have been tested only in the laboratory. The proposed behavioral, physiological, and biochemical mechanisms that enable stored-product insects to survive extreme temperatures are reviewed. Possible synergists that might make stored-product insects more susceptible to extreme temperatures are suggested. One example is the use of ice-nucleating active bacteria to increase the supercooling points of insects, thereby making them less cold-hardy. The supercooling points of four beetles has been measured and compared to published data for other stored-product insects. A standard protocol for examining the survival of stored-product insects at extreme temperatures is outlined.

The effect of grain moisture content and temperature on the efficacy of diatomaceous earths from different geographical locations against stored-product beetles.

Abstract Source of diatomaceous earth (DE), insect species, grain moisture content, temperature, method of application and duration of exposure were all factors that influenced the mortality of stored-product insects. In all tests, regardless of the insect species, or source of DE, the lower the moisture content of grain, the greater the mortality. DEs from different geographical locations had different efficacies. The ranking of the different DEs remained similar at different moisture–temperature combinations. However, the mortality response with respect to moisture content did change among DEs from different sources for Sitophilus oryzae (L.), but not for Tribolium castaneum (Herbst). Of all the insects tested, Cryptolestes ferrugineus (Stephens) was the most sensitive to DE. Oryzaephilus surinamensis (L.) and S. oryzae were more tolerant than C. ferrugineus. Rhyzopertha dominica (F.) and T. castaneum were the most tolerant species tested. Applying DE as a dust was more effective than applying DE as an aqueous spray. For C. ferrugineus, lower temperatures reduced DE efficacy. The opposite was true for T. castaneum, as lower temperatures increased efficacy for most DEs tested. For S. oryzae some DEs had increased efficacy with lower temperatures and others had decreased efficacy with lower temperatures.

The effect of diatomaceous earth on grain quality

Abstract Protect-It is a newly developed diatomaceous earth (DE) based insecticide for stored-grain protection and structural treatment. It has proved effective at controlling stored-grain insects in laboratory tests at application rates well below other DE-based insecticides. This study examined the effect of Protect-It on quality, and physical and handling characteristics of cereals. Treatment of Hard Red Spring (HRS) wheat with either 50 or 300 ppm Protect-It had no significant effect on the milling, analytical, rheological or baking quality. The application of Protect-It on durum wheat did not affect the properties for high-quality pasta production at 50 ppm and 300 ppm, and treatment of barley at concentrations from 100 ppm to 900 ppm also showed no differences in malting quality characteristics. A different DE based insecticide, Insecto®, was used to examine the combined affect of DE and dockage on bulk density (test weight) on Hard Red Spring (HRS) wheat, durum wheat and barley. Both dockage and DE reduced bulk density. For HRS and durum wheat, the addition of 5%, 10%, or 15% dockage mitigated (less than 1 kg/hl) the reduction of bulk density when DE was applied. Protect-It treatment of HRS wheat, rye and barley gave 0.2% to 0.8% lower dielectric moisture values than before treatment, depending on the DE concentration and commodity. The effect was caused by physical effect of the dust on the grain, since wheat treated with DE had no actual loss of moisture. Protect-It did not affect the dielectric moisture content readings with oats and maize. In field tests, wheat treated with Protect-It at 75 ppm and 100 ppm, concentrations that controlled Cryptolestes ferrugineus (Stephens) and reduced Tribolium castaneum Herbst populations, did not cause a reduction in grain flow nor did it cause an increase in air-borne dust when grain was moved using a screw auger. Wheat treated with 300 ppm Protect-It had reduced grain-flow and caused an increase in air-borne dust. Bulk density of the wheat was measured before and after a spray (wet) application at 100 ppm or dust (dry) application at 75 and 100 ppm of Protect-It in both laboratory and field conditions. In the field, dry application of 75 ppm reduced bulk density by 1.6 to 2.5 kg/hl, 100 ppm by 2.0 to 2.8 kg/hl, and 300 ppm by 4.6 to 4.8 kg/hl. Protect-It reduced bulk density by 1.5 to 2.2 kg/hl at 100 ppm wet application.

The effect of cold acclimation and deacclimation on cold tolerance, trehalose and free amino acid levels in Sitophilus granarius and Cryptolestes ferrugineus (Coleoptera)

Canadian and French laboratory strains of Sitophilus granarius (L.) and Cryptolestes ferrugineus (Stephens) were cold acclimated by placing adults at 15, 10 and 5 degrees C successively for 2wk at each temperature before deacclimating them for 1wk at 30 degrees C. Unacclimated S. granarius had an LT(50) (lethal time for 50% of the population) of 12days at 0 degrees C compared with 40days after the full cold acclimation. At -10 degrees C, unacclimated C. ferrugineus had an LT(50) of 1.4days compared with 24days after the full acclimation. Cold acclimation was lost within a week after returning insects to 30 degrees C. Trehalose, as well as the amino acids proline, asparagine, glutamic acid and lysine were higher in cold acclimated insects for both species. For S. granarius, glutamine was higher in cold acclimated insects and isoleucine, ethanolamine and phosphoethanolamine, a precursor of phospholipids, were lower in cold acclimated insects. For C. ferrugineus, alanine, aspartic acid, threonine, valine, isoleucine, leucine, phenylalanine and phosphoethanolamine were higher in cold acclimated insects. For both species tyrosine was lower in cold acclimated insects. There were small but significant differences between Canadian and French strains of S. granarius, with the Canadian strain being more cold hardy and having higher levels of trehalose. There were small but significant differences between male and female S. granarius, with males being more cold hardy and having higher levels of proline, asparagine and glutamic acid. In conclusion, high levels of trehalose and proline were correlated with cold tolerance, as seen in several other insects. However, correlation does not prove that these compounds are responsible for cold tolerance, and we outline further tests that could demonstrate a causal relationship between trehalose and proline and cold tolerance.

Mechanisms for tolerance to diatomaceous earth between strains of Tribolium castaneum

Fourteen strains of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) had mortalities ranging from 5 to 100% when exposed to diatomaceous earth at 600 ppm for seven days. The most tolerant strain had a lethal dose for 50% of the population (LD50) of 413 ppm and the most susceptible strain had a LD50 of 238 ppm. Adults of the tolerant strain were lighter (2.0 mg) than the susceptible strain (2.6 mg). Tolerant adults lost water at lower rate (6 μg h−1 than susceptible adults (12 μg h−1), when held in wheat treated with 600 ppm diatomaceous earth for 24 h, than held at 5% r.h. with no food. Tolerant adults that were not exposed to diatomaceous earth lost water at a lower rate (3 μg h−1) than susceptible adults (5 μg h−1). Both strains, exposed and not exposed to diatomaceous earth died when their water content was between 33 and 37% of their total weight. Insects taken directly from the cultures had 52% (tolerant) and 53% (susceptible) of their total weight as water. Tolerant adults moved slower through grain and across filter paper than susceptible adults. Tolerant adults avoided wheat treated with diatomaceous earth at concentrations as low as 75 ppm, whereas the adults from the susceptible strain did not avoid diatomaceous earth, even at 600 ppm. The consequences of a strain tolerant to diatomaceous earth is discussed with respect to the use of diatomaceous earth to control stored‐product insect infestations.

Grain bulk density as affected by diatomaceous earth and application method

Abstract The effect of the enhanced diatomaceous earth (EDE) insecticide Protect-It ™ was studied at different concentrations on the bulk density of wheat, corn, barley, rye and oats at three moisture contents (12, 14 and 15% m.c., dry basis). The greatest changes in bulk density occurred when the concentration of EDE ranged from 50 to 200 parts per million (ppm). At concentrations greater than 500 ppm, bulk density decreased little with increased EDE concentrations. The bulk density reductions in all five grains tested were significantly higher for the grain at a dry basis moisture content of 15% than at 12%. The reduction in bulk density as a result of the EDE application was described mathematically using empirical equations. The bulk density of wheat was measured before and after the wet (suspension) or dry (dust) application at 100 and 300 ppm of EDE under laboratory conditions. The dry application caused a significantly greater reduction in wheat bulk density than did the wet application. Application of only 10 ppm of either marine or fresh-water DE significantly reduced the bulk density (about 1.3–1.8%, w/w, respectively) of 13.9% m.c. wheat without dockage. Twenty five various DE obtained from different regions of the world were tested for bulk density changes when applied to wheat at various concentrations. All DE decreased wheat bulk density, though there were significant differences between DE. The most active DE formulations against stored grain insects, such as Protect-It ™ , Dryacide ® , Insecto ® , Dicalite, DE Eu and DiaFil, also had the greatest effect on the bulk density.

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 1h 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.

The effect of repellents on penetration into packaging by stored-product insects

Abstract Two known repellents of stored-product insects, DEET and neem, were compared to protein-enriched pea flour, defatted protein-enriched pea flour, and pea protein extract for their efficacy at reducing penetration and invasion by several common stored-product insects: Sitophilus oryzae (L.), Tribolium castaneum (Herbst) , Cryptolestes ferrugineus (Stephens), and Oryzaephilus surinamensis (L.). The methods of preparation of pea extract affected the penetration of S. oryzae . Protein-enriched pea flour, DEET and neem reduced the penetration of S. oryzae, but defatted protein-enriched pea flour and pea protein extract did not. The number of S. oryzae, T. castaneum, C. ferrugineus and O. surinamensis entering pierced paper envelopes that contained wheat and were treated with DEET was reduced by 99%, 86%, 97% and 91%, respectively. Neem was less effective than DEET in reducing penetration and invasion of insects. Protein-enriched pea flour did not prevent insects entering pierced envelopes.

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.

Insecticidal activity of Melia toosendan extracts and toosendanin against three stored-product insects

Abstract Repellency, toxicity, and fecundity-reducing effects of bark extracts of Melia toosendan on three stored-product beetles, the rusty grain beetle, Cryptolestes ferrugineus (Stephens), the rice weevil, Sitophilus oryzae (L.), and the red flour beetle, Tribolium castaneum (Herbst), were investigated in the laboratory. Wheat kernels treated with extracts containing 75 and 3% toosendanin at concentrations from 0.05 to 0.4% (375-3000 ppm toosendanin), and from 0.5 to 2.5% (150–750 ppm toosendanin), respectively, repelled beetles by 50–98%, compared with controls. The test materials were more toxic to S. oryzae than C. ferrugineus and were not toxic to T. castaneum . The LC 50 values for the extract containing 75% toosendanin for S. oryzae and C. ferrugineus after 6 weeks exposure were 675 and 1875 ppm toosendanin, respectively. Both extracts significantly reduced F 1 adults of all three insect species in most treatments. Pure (98%) toosendanin caused only 4% mortality of C. ferrugineus and S. oryzae at a concentration of 0.15% (1470 ppm toosendanin) after 2 weeks, but significantly reduced the F 1 adults compared with controls. This study indicates that a natural grain protectant based on M. toosendan extracts may be feasible.