Laboratory studies evaluating the efficacy of diatomaceous earths, on treated surfaces, against stored-product insect and mite pests

The efficacy of dry dust and slurry applications of Silico-sec^® and Diasecticide™, applied to glass and plastic surfaces, was assessed in the laboratory against the beetles Tribolium castaneum, Sitophilus granarius and Oryzaephilus surinamensis, the mites Acarus siro and Lepidoglyphus destructor, and against larvae of the moth Ephestia kuehniella. For the insects, doses of 5, 10 and 20 g/m² were evaluated for all preparations, while for the mites 0.5, 1 and 2 g/m² of the dry dusts, and 2.5, 5 and 10 g/m² of the slurries were assessed. Mortality was evaluated after 7 days and 24 h for the insects and mites, respectively, in conditions of 15 °C and 80% r.h., chosen to represent typical UK conditions immediately after harvest. The Silico-sec^® dry dust was the most effective treatment with mean mortalities ranging from 93-100% for all the pest species at all doses. The Diasecticide™ dry dust was ineffective against T. castaneum and S. granarius with mean mortalities ranging from 86-98% for the other species at the highest dose. With both DEs the slurry applications were generally less effective than the dry dusts at equivalent doses. Oryzaephilus surinamensis was the least tolerant insect species and S. granarius and T. castaneum the most tolerant. The mite A. siro was less tolerant than L. destructor.     

Efficacy and adherence ratio of diatomaceous earth and spinosad in three wheat varieties against three stored-product insect pests

Laboratory tests were carried out in order to evaluate the efficacy of three diatomaceous earth (DE) formulations; Protector, SilicoSec, and Insecto, and one spinosad dust formulation in three commercially available wheat (Triticum durum) varieties, Athos, Pontos, Sifnos, originating from Greek cultures. The efficacy of the above formulations was assessed against adults of Rhyzopertha dominica, Sitophilus oryzae and Tribolium confusum. The DE formulations were applied at three dose levels; 250, 500 and 1000 ppm, while spinosad was applied at 100, 500 and 1000 ppm of the formulation, corresponding to 0.125, 0.625 and 1.25 ppm active ingredient (a.i.), respectively. The adherence ratio of the DE and spinosad formulations to the kernels of the wheat varieties was assessed. Bioassays were carried out at 30°C and 60% r.h. Mortality was recorded after 7 and 14 d in the case of R. dominica and S. oryzae, and after 7 d, 14 d and 21 d of exposure in the case of T. confusum, on the treated varieties. Progeny production of the individuals exposed on the treated varieties was also assessed. Even the lowest dose of spinosad was highly effective (>90%) against R. dominica and S. oryzae. In the case of T. confusum a combination of longer exposures with higher doses was required for each formulation to be effective. Generally, the performance of all formulations was greater in Athos or Sifnos compared to the Pontos. Progeny production of S. oryzae and R. dominica was significantly higher in untreated Pontos than in the other varieties. Progeny production was always greater in untreated than treated substrates. Although adherence ratios for the tested DE and spinosad formulations were generally high (>90%), significant variations in adherence levels among the wheat varieties were recorded.     

Mortality and progeny production of four stored-product insect species on three grain commodities treated with Beauveria bassiana and diatomaceous earths

Laboratory bioassays were conducted to estimate the effectiveness of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) at 1.5 × 10⁸ and 1.5 × 10¹⁰ conidia/kg grain alone or mixed with the diatomaceous earths (DEs) Protect-It at 150 ppm and DEBBM at 50 ppm against adults of the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The adult insects were exposed to treated grains for 7, 14 and 21 days. For progeny emergence data, the treated units were remained under the same conditions for 62 days for all beetles and 30 days for psocids. The results revealed significant differences in mortalities of insect species among treatments and grains. The combined use of B. bassiana, at the highest dose, and DE increased adult mortalities of all species. In general, the treatments were least effective against T. castaneum and most effective against L. paeta. More numbers of dead insects were found on wheat than on rice or maize. The emergence of progeny was considerably reduced on grains treated with B. bassiana, at the highest dose, plus DE. The results of the present study suggest that the effectiveness of B. bassiana is fortified by the addition of DEs, but it varies among exposed insect species and commodities.     

Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests

The insecticidal effectiveness of two natural zeolite formulations (Minazel plus and Minazel), applied to wheat at selected rates of 0.25, 0.50 and 0.75 g/kg, and a diatomaceous earth formulation (DE) (Protect-It™), applied at the recommended rates of 0.15 g/kg for Sitophilus oryzae, 0.20 g/kg for Rhyzopertha dominica and 0.30 g/kg for Tribolium castaneum, were tested under laboratory conditions (24 ± 1 °C temperature and 45 ± 5% relative humidity). The highest adult mortality was observed after the longest exposure period of 21 days and 7 days of recovery, when all three zeolite dosage rates and the recommended DE dosage caused 97-100% mortality of S. oryzae and 94-100% of T. castaneum. On the other hand, 100% mortality was not achieved in any test variant involving R. dominica; the highest (about 92%) was detected for DE, while 52% and 79% mortality was achieved with the zeolites at the highest rate of 0.75 g/kg. Progeny reduction by >90% was achieved after 21 days of contact of all three beetle pests with DE-treated wheat, while the same level of reduction was achieved for S. oryzae and T. castaenum only after contact with the highest rate of the zeolite product, Minazel. Thus the two zeolite formulations are comparable to diatomaceous earth in controlling adult S. oryzae, R. dominica and T. castaneum, but only the Minazel formulation could effectively protect wheat from attack by S. oryzae or T. castaneum, and only with a higher rate of application than for the DE formulation.     

Insecticidal effect of three diatomaceous earth formulations, applied alone or in combination, against three stored-product beetle species on wheat and maize

Laboratory tests were carried out to examine the insecticidal effect of three commercially available diatomaceous earth (DE) formulations on wheat and maize against three major stored-grain beetle species: Rhyzopertha dominica, Sitophilus oryzae, and Tribolium confusum. The three DEs tested were Insecto^®, PyriSec^®, and Protect-It^®. These DEs were applied alone or in all possible combinations (Insecto^®+PyriSec^®, Insecto^®+Protect-It^®, PyriSec^®+Protect-It^®, and all three DEs together), at three (total) dose rates: 0.25, 0.5, and 0.75 g/kg of each commodity. Adults of the above species were exposed to the treated commodities for 7 d at 26 °C, and 65% r.h., and after this interval the mortality was measured. For each species, adult mortality was significantly affected by the type of DE, the commodity, and the dose rate. All DEs were less effective against T. confusum, where mortality did not exceed 67%, in comparison with the other two species, where 100% mortality was achieved in some combinations. For all species tested, all DEs were more effective on wheat than on maize. Generally, the mix of two or three DEs was more effective than the application of one DE, for all species and commodities. The results of the present work clearly indicate that a blending of several DEs together may produce a new DE formulation that is highly effective at low dose rates.     

Performance of diatomaceous earth and imidacloprid as wheat,rice and maize protectants against four stored-grain insect pests

Laboratory experiments were conducted in Pakistan to investigate the effectiveness of the diatomaceous earth (DE) formulation, Protect-It, at 150 ppm and imidacloprid, at 1.25, 2.5 and 5.0 ppm, alone or in combination, against the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The bioassays were conducted at 25 °C, 65% relative humidity (r.h.) and continuous darkness by using adults of each insect pest that were exposed on treated or untreated wheat, rice and maize. Adult mortality counts were performed 1, 2, 4 and 7 days post-exposure. Progeny production was also evaluated 62 and 30 days after the last mortality count for beetles and psocid respectively. Results showed that mortality was increased with the increase of dose and exposure interval. Imidacloprid was more effective at the highest dose than the DE alone. The combination of DE plus imidacloprid resulted to higher mortalities than DE or imidacloprid alone at almost all exposure intervals. There was higher mortality on wheat than on rice or maize. In general, T. castaneum was the most tolerant insect species to any treatment while L. paeta was the least tolerant. The highest progeny production was observed for T. castaneum (i.e., 33.1 individuals per vial) while the lowest for L. paeta (i.e., 11.1 individuals per vial) on maize treated with Protect-It alone. The findings of the current study indicate that the combined use of DE and imidacloprid, as wheat, rice and maize protectants, may provide adequate level of management to several important stored-product insects.     

Effectiveness of grain storage facilities and protectants in controlling stored-maize insect pests in a climate-risk prone area of Shire Valley,Southern Malawi

Shire Valley is one of Malawi's most vulnerable areas to climate change (CC). In addition to other impacts, CC is expected to affect storage insect pest status, and the efficacy of grain storage facilities and protectants. On-farm grain storage trials were therefore conducted in Shire Valley to assess the performance of storage facilities and grain protectants against storage insect pests. Eight smallholder farmers hosted the trials in Thyolo and Chikwawa districts. Seven grain storage treatments were evaluated for 32 weeks during two storage seasons: Neem leaf powder (NM), Actellic Super dust (ASD), ZeroFly^® bag (ZFB), Purdue Improved Crop Storage bag (PICS), Super Grain Bag (SGB), hermetic metal silo (MS) and untreated grain in a polypropylene bag (PP). Insect pest populations and grain damage increased with storage duration and differed significantly between treatments (p < 0.05). Grain stored in hermetic bags (PICS, SGB) sustained significantly lower (p < 0.05) insect damage and weight loss compared to other treatments across sites and seasons. The hermetic bags also outperformed the other treatments in suppressing insect numbers. However, germination rates of undamaged grains stored in the hermetic storage facilities (MS, PICS, SGB) for 40 weeks were extremely low (<15%) compared to that of undamaged grains from NM treatment (53–58%) and the other treatments (>75%) at both sites. The hermetic MS, ZFB bags, ASD and NM treatments did not effectively protect grain from insect damage. High in-store mean temperature (35.6 °C) and high initial grain moisture content (13.7%) may have negatively affected efficacy of some treatments and seed germination. Tribolium castaneum survival in the MS requires further investigation. The hermetic storage bags (PICS, SGB) can be recommended for long-term maize grain storage (≥32 weeks) by smallholder farmers in Shire Valley and other similar climate change-prone areas in sub-Saharan Africa.