Comparative performance of five hermetic bag brands during on-farm smallholder cowpea (Vigna unguiculata L.Walp) storage

Cowpea (Vigna unguiculata L. Walp) grain is an important source of protein for smallholder farmers in developing countries. However, cowpea grain is highly susceptible to bruchid attack, resulting in high quantitative and qualitative postharvest losses (PHLs). We evaluated the performance of five different hermetic bag brands for cowpea grain storage in two contrasting agro-ecological zones of Zimbabwe (Guruve and Mbire districts) for an 8-month storage period during the 2017/18 and 2018/19 storage seasons. The hermetic bag treatments evaluated included: GrainPro Super Grain bags (SGB) IVR™; PICS bags; AgroZ® Ordinary bags; AgroZ® Plus bags; ZeroFly® hermetic bags. These were compared to untreated grain in a polypropylene bag (negative control) and Actellic Gold Dust® (positive chemical control). All treatments were housed in farmers’ stores and were subjected to natural insect infestation. Hermetic bag treatments were significantly superior (p < 0.001) to non-hermetic storage in limiting grain damage, weight loss and insect population development during storage. However, rodent control is recommended, as rodent attack rendered some hermetic bags less effective. Actellic Gold Dust® was as effective as the hermetic bags. Callosobruchus rhodesianus (Pic.) populations increased within eight weeks of storage commencement, causing high damage and losses in both quality and quantity, with highest losses recorded in the untreated control. Cowpea grain stored in Mbire district sustained significantly higher insect population and damage than Guruve district which is ascribed to differences in environmental conditions. The parasitic wasp, Dinarmus basalis (Rondani) was suppressed by Actellic Gold Dust® and all hermetic treatments. All the hermetic bag brands tested are recommended for smallholder farmer use in reducing PHLs while enhancing environmental and worker safety, and food and nutrition security.     

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.     

Efficacy of d-tetramethrin and acetamiprid for control of Trogoderma granarium Everts (Coleoptera: Dermestidae) adults and larvae on concrete

The khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) is a dangerous insect of stored products that has currently expanded in Africa, Asia and Europe. Control of this species encounters difficulties when synthetic insecticides are applied either as surface treatments or as grain protectants. Therefore, new insecticidal formulations should be assessed as additional tools towards an effective management of T. granarium. In the current study, we tested the new insecticidal formulation Dobol, that contains the pyrethroid insecticide d-tetramethrin and the neonicotinoid insecticide acetamiprid, as treatments on concrete. Their direct and delayed mortality against adults and larvae of T. granarium were estimated under two label doses (min and max) and two temperature levels (30 and 35 °C) after 1, 2, 3, 4 and 7 d of exposure interval. Results revealed that Dobol caused direct mortality to T. granarium adults that ranged between 87.8 and 96.7%. Concerning larvae, direct mortality was generally much lower, being at most 84.4% at the max dose after 7 d of exposure. Temperature had significant impact on the direct mortality of T. granarium adults and larvae within the vast majority of the tested exposure intervals at both doses. However, when the surviving adults and larvae were transferred on untreated concrete surfaces, despite higher mortality at 35 than 30 °C, there was no significant impact of temperature on their mortalities within any exposure interval and dose. Our study revealed that Dobol is a promising insecticidal formulation that can be effectively used against adults and larvae of T. granarium on concrete surfaces.     

Effectiveness of hermetic containers in controlling paddy rice (Oryza sativa L.) storage insect pests

Naturally infested paddy rice was used to compare the effectiveness of polypropylene bags and hermetic storage containers over 12 months of storage in a warehouse. Insect pest identification as well as the infestation level, percentage of damaged grain, weight loss, and moisture content were evaluated. Five insect species associated with stored rice were identified during the storage period, namely lesser grain borer (Rhyzopertha dominica), red flour beetle (Tribolium castaneum), rice/maize weevil (Sitophilus spp.), angoumois grain moth (Sitotroga cerealella) and flat grain beetle (Cryptolestes ferrugineus). The lesser grain borer was the most predominant species with an average incidence above 70% after twelve months of storage, followed by the rice/maize weevil with an incidence of 17%. When compared to hermetic storage containers, polypropylene bag showed the highest mean infestation level with 233.3 individuals/kg after six months of storage, representing about 8-fold of the number of insects recorded in hermetic containers after six months of storage. In polypropylene container, the percentage of damaged grain and weight loss increased significantly achieving a maximum of 6.98% and 5.56% respectively, whereas using hermetic containers the highest percentage of damaged grain reached was 3.24% in polyethylene drum and the weight loss was 1.62% in GrainSafe bag. The results from the study show that the use of hermetic storage containers is a green alternative for safe storage of paddy rice, for 12 months without application of pesticides, bringing multiple advantages for smallholder farmers, lever food security and income generation for smallholder farmers and rice milling companies.     

Efficacy of phosphine and insect penetration ability in ZeroFly® bags

The deltamethrin incorporated woven polypropylene ZeroFly® storage bag is a promising novel technology for grain storage. However, if grain stored in ZeroFly bags gets infested and has to be fumigated using phosphine (PH₃), data on the effectiveness of such treatments are needed. Additionally, obtaining field data on ability of stored-product insect pests to breach ZeroFly bags would facilitate insect management. Therefore, efficacy of PH₃ in immature and adult Sitophilus zeamais (Motschulsky), Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) in experimental cages in maize stored in 100-kg polypropylene (PP), jute and ZeroFly bags was investigated. Post-fumigation mortality of adults was recorded after 7 d, and after 7 wk for immatures. The ability of either S. zeamais or P. truncatus to penetrate fabric of PP, jute and ZeroFly bags was assessed. Phosphine efficacy was good in all the three types of bags and resulted in complete mortality of adults and immatures of the four species tested. Sitophilus zeamais and P. truncatus were more successful in penetrating the PP bag fabric and on average made 84 and 780 holes per bag over a 4 mo-period, respectively; this was followed by jute with 37 and 614 holes. The ZeroFly bag was harder to breach and ≤3 holes per bag were made for both species. This study shows that PH₃ is highly efficacious in insects that infest maize stored in ZeroFly bags, and that these bags are not easily penetrated by stored product insect pests. Hitherto, ZeroFly bags are a good technology for storing grain that is not infested, and fumigation using PH₃ can be effectively conducted if infestation occurs. Therefore, ZeroFly bags can be incorporated in integrated stored product insect management (IPM) programs for bagged grains.     

End-use quality characteristics of hermetically stored paddy

Four paddy varieties (Bg 352, Bg 300, Bg 358 and Bg 360) were stored in hermetic IRRI bags and common woven polyethylene bags (polybags) at room temperature either uninfested or infested with rice weevils (Sitophilus oryzae (L.)). After 9 months of storage, samples were tested for insect mortality, gas contents, moisture content (m.c.), thousand grain mass (TGM), porosity, hardness, whiteness, total milled rice yield (TMR), head rice yield (HRY), gelatinization temperature, amylose (AC), crude protein (CP), crude fat, free fatty acid (FFA), thiamine and niacin contents and sensory characteristics. These properties after storage were compared with their initial condition. The oxygen content dropped from 21% to 7% and 13.8% for infested and uninfested IRRI bag samples, respectively. The results showed that m.c., of the IRRI bag samples increased significantly (P < 0.05) by 5% when compared to the initial sample but it increased by 15% in polybag stored samples. After 9 months, dry matter loss (DM) was 65% higher in polybag than IRRI bag samples. Highest DM loss was observed in Bg 300 and the lowest DM loss was observed in Bg 358 and Bg 360. Paddy samples stored in IRRI bags showed reduced whiteness compared to polybag stored samples. Storage in IRRI bags significantly increased (P < 0.05) TMR, HRY, AC and sensory values compared to polybag samples. However, paddy samples stored in polybags significantly increased (P < 0.05) their CP and FFA contents while decreasing sensory values, thiamine and niacin contents. The FFA value of polybag samples was 2.5 times higher than IRRI bag samples. Hermetic storage of dry paddy improved overall paddy quality but different end-use quality parameters were observed in the two paddy grain types of short round (Bg 352 and Bg 300) or intermediate bold (Bg 358 and Bg 360).     

Evaluation of methoprene-treated packaging against Trogoderma granarium Everts and Trogoderma inclusum LeConte larval development and packaging penetration or invasion

Trogoderma granarium Everts, khapra beetle, and Trogoderma inclusum LeConte, larger cabinet beetle, are highly destructive insect species that can infest a variety of food sources. Methoprene is an insect growth regulator, IGR, and recently has been incorporated into packaging materials as a treatment option for packaged grain, food, birdseed, and feed products, and labeled for this use by the US Environmental Protection Agency. The objective of this research was to investigate the effect of continual exposure to this novel packaging technology on the development of T. inclusum and T. granarium larvae, and its potential use as a packaging treatment to prevent the penetration or invasion of T. inclusum and T. granarium into food packages. The methoprene-treated packaging incorporated into Kraft paper, woven bag material, polyethylene-polyethylene (PE-PE) material, and a polyethylene terephthalate-polyethylene (PET-PE) material, reduced normal adult emergence of exposed larvae. No normal adult emergence was observed on the inside surface of the PET-PE material. The polymer-based materials were the most effective at preventing penetration or invasion by Trogoderma spp. Only 2% of packages were invaded among all packaging treatment combinations compared to 16.7% invasion of untreated packages. The materials were ranked in effectiveness as Kraft < woven < PET-PE < PE-PE, however, all materials demonstrated significant positive results on Trogoderma spp. This novel packaging could easily be adopted as a packaging control strategy against these and other stored product insects in packaged products destined for commercial, international, and smallholder farm storage of cereal grains, feed, and other food products.     

Triple bag hermetic technology for post-harvest preservation of Bambara groundnut (Vigna subterranea (L.) Verdc.)

Experiments were conducted to evaluate the performance of hermetic triple bagging using Purdue Improved Crop Storage (PICS) bags for storage of Bambara groundnut (Vigna subterranea (L.) Verdc.). One set of experiments used grain heavily infested by Callosobruchus maculatus (F.) while a second set began with a low level infestation. Each experiment consisted of V. subterranea grain kept in four replicate 50 kg PICS bags or two replicate woven bags as controls. Two to five days after the beginning of the experiments, oxygen level inside the bags averaged about 21% (v/v) in the controls but decreased significantly in PICS bags, reaching 10% (v/v) with the heavily infested grain but falling only slightly in the lightly infested grain. After 7 months of storage, (i) the number of C. maculatus adults found between and within the grains, (ii) the 100 seed weight, (iii) the number of seed with holes, and (iv) the percentage germination of grain stored in PICS bags did not differ from what had been measured on the day that the experiment was set up. In woven bags, by contrast, there was a massive increase in C. maculatus numbers with means of 309 and 251 adults per 500 g in heavily and lightly infested grain, respectively. Grain weight losses in the woven bag controls ranged from 8 to 19% and the percentage of C. maculatus emergence holes per 100 seed increased from 51 to 135%.     

What does global warming mean for stored-grain protection? Options for Prostephanus truncatus (Horn) control at increased temperatures

Global climate change is expected to accelerate reproduction, development and activity of stored-product insect pests and degradation of grain protectants hence compromising efficacy of available storage pest management technologies. However, there is little information on these effects. The current laboratory study examined the effect of increasing temperatures on the efficacy of stored maize grain protectants and hermetic containers in controlling Prostephanus truncatus (Horn). In Experiment I, three commercial synthetic grain pesticides (cocktails of an organophosphate and a pyrethroid or a neonicotinoid) and two farmer-practices (neem leaf powder and wood ash) were tested on shelled maize grain. In Experiment II, four storage containers, viz Purdue Improved Crop Storage (PICS) bag, Super Grain bag (SGB), metal silo (MS) and polypropylene bag (PP) (all containing untreated maize) were tested. Both experiments were conducted for 12 weeks at 32 °C, 38 °C and mean ambient temperature of 26 °C; with three replicates per treatment. All treatments were artificially infested with laboratory-reared adult P. truncatus. Sampling was at baseline (0 weeks) and 4-weekly intervals. Overall, results showed significant differences in grain damage and weight losses between non-synthetic and synthetic grain protectants in all treatments at all tested conditions. The hermetic storage containers kept mean insect grain damage below 6.4% compared to 24.5% in the untreated control at all the experimental conditions. These results indicate that the use of synthetic grain protectants and hermetic storage containers (SGB, PICS and MS) in the management of P. truncatus may not be negatively affected by projected warmer temperatures of 32 °C or 38 °C; suggesting these storage technologies will remain efficacious under sub-Saharan Africa’s warming climates.     

Performance of triple bagging hermetic technology for postharvest storage of cowpea grain in Niger

Triple bagging technology for protecting postharvest cowpea grain from losses to the bruchid, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae) is currently being adopted on a fairly large scale in ten West and Central African countries, including Niger. The triple bag consists of two inner high-density polyethylene bags acting as oxygen barriers, which in turn are encased in an outer woven polypropylene bag that serves primarily for mechanical strength. These hermetic bags, available in either 50 or 100 kg capacity, are called Purdue Improved Cowpea Storage (PICS) bags. Adoption of PICS technology in West and Central Africa has been driven by its effectiveness, simplicity, low cost, durability, and manufacture within the region. From surveys on adoption we discovered that farmers have begun to re-use bags they had used the previous year or even the previous two years. In the present study, we compared the performance of three different types of PICS bags: (1) new 50 kg (2) new 100 kg bags and (3) once-used 50 kg bags, all filled with naturally infested untreated cowpeas. In these PICS bags the O₂ levels within the bags initially fell to about 3 percent (v/v) while the CO₂ rose to nearly 5 percent (v/v). After five months of storage, new and used 50 kg bags and new 100 kg bags preserved the grain equally well. There were greatly reduced numbers of adults and larvae in the PICS bags versus the controls, which consisted of grain stored in single layer woven bags. The proportion of grain having C. maculatus emergence holes after five months of storage in PICS bags was little changed from that found when the grain was first put into the bags. The PICS technology is practical and useful in Sahelian conditions and can contribute to improved farmers' incomes as well as increase availability of high quality, insecticide-free cowpea grain as food.     

Safe storage of maize in alternative hermetic containers

Purdue Improved Crop Storage (PICS) bags have been developed and extended as a way to address grain storage issues faced by smallholder farmers in developing nations. A hermetic technology, PICS bags reduce insect damage to grain significantly while maintaining its quality for many months or longer. Farmers with varying and often small volumes of grain at harvest, may still benefit from alternatives to PICS bags for storing their grain. We evaluated plastic bottles, which may be hermetically sealed, for storing maize grain. Clean maize grain was stored for eight months in sealed and unsealed plastic bottles with half of these bottles being infested by maize weevil (Sitophilus zemais, Motschulsky). Oxygen levels in the bottles were monitored throughout the trial and grain was assessed for moisture content, insect damage, germination rate and insect population size when the study was terminated. Sealed bottles preserved grain quality significantly better than unsealed, infested bottles and as well as non-infested unsealed containers. Plastic soda bottles can be used as hermetic containers for safely storing grain.     

Field evaluation of the long-lasting treated storage bag,deltamethrin incorporated, (ZeroFly® Storage Bag) as a barrier to insect pest infestation

The deltamethrin incorporated polypropylene (PP) bag, ZeroFly^® Storage Bag, is a new technology to reduce postharvest losses caused by stored-product insect pests. Maize was pre-fumigated and used for the following treatments: ZeroFly bags filled with untreated maize, PP bags filled with maize treated with Betallic Super (80 g pirimiphos-methyl and 15 g permethrin per liter as an emulsifiable concentrate (EC)), and PP bags filled with untreated maize (control). The experiment was conducted from February–August 2015, at four sites in different locations of the Middle Belt of Ghana. Moisture content (MC), number of live and dead insects, insect damaged kernels (IDK) and maize weight loss data were collected monthly. ZeroFly bags and Betallic treatment significantly reduced insect damage compared to the control treatment. ZeroFly bags were able to keep IDK levels below 5% for 4 months, but the levels increased to 5.2 and 10.2% by 5 and 6 months of storage, respectively. In the control, IDK increased significantly over time and reached 32% after 6 months. The ZeroFly bag was effective against Sitophilus, Tribolium and Cryptolestes species for 4 months. Mean weight loss of ≤3.68% was recorded in ZeroFly bags during 6 months of storage whereas 11.88% weight loss occurred in the PP bags by 6 months of storage. Based on our results, ZeroFly bags were found to have potential for use in the reduction of postharvest grain losses in bagged grains. Maize may still have been infested during bagging hence ZeroFly bags were effective for storage for only 4 months. However, greater benefits of using ZeroFly bags are realized if insect-free grains or legumes are stored in bags.     

Grain size and grain depth restrict oxygen movement in leaky hermetic containers and contribute to protective effect

Postharvest insect pests threaten the nutritional and financial security of smallholder farmers in the developing world. Hermetic storage, a technology that protects grain against insects by blocking their supply of oxygen, alleviates the problem of insect-caused losses. PICS (Purdue Improved Crop Storage) bags represent one hermetic technology that improves food availability and incomes of farmers. The polyethylene liners of PICS bags are sometime damaged during use, acquiring small holes or tears. Observations in the laboratory and field suggest that insect development remains localized around the point where the bag is damaged. We hypothesized that the grain within a hermetic container that has minimal localized damage (such as an insect hole), helps retard leakage of oxygen into the bag and contributes to limiting insect damage and to the overall protective effect. To test this hypothesis, we filled 4 cm dia. by 10 cm long PVC pipes with Callosobruchus maculatus (F.) infested cowpeas and sealed them with caps having a single, insect-sized hole in its center. A vertical tube positioned above the cowpea-filled PVC pipe was filled with one of three different grains (sesame, sorghum, and maize) to different depths (0, 5, 15, 30, 50 cm). Seed size and grain barrier depth significantly reduced the level of bruchid damage to the stored cowpea in the PVC container. Smaller sized grains used for the barriers retarded insect development more effectively than larger sized grains, while deeper grain depth was more effective than shallower barriers. The grain held in a hermetic container contributes in a small, but significant, way to the effectiveness of the containers.     

Impact of storage environment on the efficacy of hermetic storage bags

Small hermetic bags (50 and 100 kg capacities) used by smallholder farmers in several African countries have proven to be a low-cost solution for preventing storage losses due to insects. The complexity of postharvest practices and the need for ideal drying conditions, especially in the Sub-Sahara, has led to questions about the efficacy of the hermetic bags for controlling spoilage by fungi and the potential for mycotoxin accumulation. This study compared the effects of environmental temperature and relative humidity at two locations (Indiana and Arkansas) on dry maize (14% moisture content) in woven polypropylene bags and Purdue Improved Crop Storage (PICS) hermetic bags. Temperature and relative humidity data loggers placed in the middle of each bag provided profiles of environmental influences on stored grain at the two locations. The results indicated that the PICS bags prevented moisture penetration over the three-month storage period. In contrast, maize in the woven bags increased in moisture content. For both bag types, no evidence was obtained indicating the spread of Aspergillus flavus from colonized maize to adjacent non-colonized maize. However, other storage fungi did increase during storage. The number of infected kernels did not increase in the PICS bags, but the numbers in the woven bags increased significantly. The warmer environment in Arkansas resulted in significantly higher insect populations in the woven bags than in Indiana. Insects in the PICS bags remained low at both locations. This study demonstrates that the PICS hermetic bags are effective at blocking the effects of external humidity fluctuations as well as the spread of fungi to non-infected kernels.     

Triple bag hermetic technology for controlling a bruchid (Spermophagus sp.) (Coleoptera,Chrysomelidae) in stored Hibiscus sabdariffa grain

We assessed the performance of hermetic triple layer Purdue Improved Crop Storage (PICS) bags for protecting Hibiscus sabdariffa grain against storage insects. The major storage pest in the grain was a bruchid, Spermophagus sp.. When we stored infested H. sabdariffa grain for six months in the woven polypropylene bags typically used by farmers, the Spermophagus population increased 33-fold over that initially present. The mean number of emergence holes per 100 seeds increased from 3.3 holes to 35.4 holes during this time period, while grain held for the same length of time in PICS bags experienced no increase in the numbers of holes. Grain weight loss in the woven control bags was 8.6% while no weight loss was observed in the PICS bags. Seed germination rates of grain held in woven bags for six months dropped significantly while germination of grain held in PICS bags did not change from the initial value. PICS bags can be used to safely store Hibiscus grain after harvest to protect against a major insect pest.     

On-farm comparison of different postharvest storage technologies in a maize farming system of Tanzania Central Corridor

Seven methods for storing maize were tested and compared with traditional storage of maize in polypropylene bags. Twenty farmers managed the experiment under their prevailing conditions for 30 weeks. Stored grain was assessed for damage every six weeks. The dominant storage insect pests identified were the Maize weevil (Sitophilus zeamais) and the Red flour beetle (Tribolium castaneum). The moisture content of grain in hermetic conditions increased from 12.5 ± 0.2% at the start of storage to a range of 13.0 ± 0.2–13.5 ± 0.2% at 30 weeks. There was no significant difference (F = 87.09; P < 0.0001) regarding insect control and grain damage between hermetic storage and fumigation with insecticides. However, the insecticide treatment of polypropylene yarn (ZeroFly^®) did not control the insect populations for the experimental period under farmers' management. Grain damage was significantly lower in hermetic storage and fumigated grain than ZeroFly^® and polypropylene bags without fumigation. No significant difference in grain damage was found between airtight treatment alone and when combined with the use of insecticides. During storage, S. zeamais was predominant and could be of more economic importance than T. castaneum as far as maize damage is concerned. At 30 weeks, the germination rate of grain stored with insecticides or in hermetic storage (68.5 ± 3.6% to 81.4 ± 4.0%) had not significantly reduced from the rate before storage (F = 15.55; P < 0.0001) except in ZeroFly^®, also in polypropylene bags without treatment. Even though such bags did not control storage pests, farmers still liked this cheap technology. Hermetic storage techniques can be recommended to farmers without the use of insecticides provided they are inexpensive, and the proper application of technologies is ensured.     

Comparative effects of hermetic and traditional storage devices on maize grain: Mycotoxin development,insect infestation and grain quality

A large-scale study was conducted to assess which of the five most accessible hermetic storage devices on the Kenyan market fulfill the needs of smallholder farmers by positively impacting three major areas of concern: insect infestation, grain quality, and mycotoxin (aflatoxin and fumonisin) contamination. Efficacy of two hermetic silos (plastic and metal) and three hermetic bags (PICS, GrainPro's GrainSafe™, and Super Grain) was directly compared to current maize storage in polypropylene (PP) bags under local environmental conditions using representative storage volumes during a 6-month storage period. Impact of maize grain stored at typical (∼15%) and recommended (<13.5%) moisture levels and potential efficacy losses through frequent interruption of the underlying hermetic principals was assessed. Hermetic storage significantly reduced the increase in aflatoxin compared to PP bags regardless of the moisture level of the grain. An <5% per month aflatoxin increase was achieved by three of the five devices tested: Metal silo, PICS and GrainSafe™ bag. A strong correlation between grain moisture, storage time and aflatoxin development was found in PP bags, but not in any of the hermetic devices. The same result was not obtained for fumonisin development in stored maize. The rate of Fumonisin increase was similar in all tested devices, including the polypropylene bags, and conditions. The periodic opening of the hermetic devices had no significant effect on the efficacy of the hermetic devices but the repeated disturbance of the PP bags led to a significant increase in aflatoxin levels. The maize weevil Sitophilus spp. was most commonly found with a total incidence of 72%. Grain storage under hermetic conditions reduced insect infestation, grain weight loss and discoloration. However, maize storage above recommended moisture levels led to a distinct odor development in all hermetic devices but not the PP bags. Hence, proper grain drying is a prerequisite for maize storage in airtight conditions.     

Efficacy of Insecticide Incorporated Bags against Major Insect Pests of Stored Paddy in Sri Lanka

A study was conducted to evaluate the efficacy of an insecticide (deltamethrin) incorporated bags (Zerofly®) against the insect attacks during paddy storage under Sri Lankan conditions. The study was conducted at Institute of Post Harvest Technology (IPHT), Anuradhapura andat the warehouse of Paddy Marketing Board (PMB), Anuradhapura. Paddy sample in Zerofly® sacks were stacked at both locations and for controls, untreated polysack bags were used. Paddy samples that were collected before storage and at monthly intervals during the storage period were analysed for moisture content, weight loss due to insect damages, Thousand Grain Mass (TGM), germination percentage, Total Milling Yield (TMY) and Head Rice Yield (HRY). Data was analyzed using Analysis of Variance (ANOVA) by Statistical Analysis System (SAS). The moisture content of paddy grains fluctuated between 13.3 – 14.3% during storage period but any significant difference was not observed among bag types. The level of insect damages in control was increased with storage time while the initial level of insect damage of treated bags remained unchanged. The mass loss due to insect damagesof grains was significantly higher (p=0.05) in untreated bags than treated bags. The insect damage was reduced by 3.5-4.a% using Zerofly® bags during paddy storage. In addition, dead insect bodies were found onouter surface of the insecticide incorporated bags but no live or dead insects were found on untreated bag surface during storage. Mainly rice weevil (Sitophils oryza) and lesser grain borer (Rhysoperthadominica) were found in paddy samples of untreated bags and number of insects increased with time. The germination percentage of grains in untreated bags was significantly higher than to thecontrol. It was reduced from 93% to 60-64% and 93% to 82-83% in control and treated bags respectively. During the six months of storage, TGM did not show any significant difference (p=0.05) among different treatments. TMY and HRY resulted significantly (p=0.05) lower values of paddy stored in untreated bags than Zerofly® bags. Use of insecticide incorporated bags can reduce the loss of TMY and HRY of paddy during storage. The study revealed that insecticide treated bags are an appropriate packaging material to protect stored paddy from insect infestations under Sri Lankan conditions.     

Susceptibility of Trogoderma granarium Everts and Trogoderma inclusum LeConte (Coleoptera: Dermestidae) to residual contact insecticides

Commercial formulations of the pyrethroid insecticides β-cyfluthrin and deltamethrin were evaluated for delayed mortality of Trogoderma granarium (Everts), the khapra beetle, and T. inclusum (LeConte), the larger cabinet beetle. Ten 3-4 week-old larvae of either species were exposed on treated concrete arenas for 1, 2, 3, and 7 d then transferred into 175 ml diet cups containing 5 g of untreated rearing media for 30 d to evaluate delayed mortality. In a subsequent study, residual efficacy of β-cyfluthrin, deltamethrin, and chlorfenapyr was evaluated at 0–12 wks post-treatment against adults and larvae of a laboratory and a field strain of T. granarium. Ten adults or larvae of either strain were exposed on treated arenas at selected wks post-treatment and mortality was assessed after 4 and 30 d of exposure for adults and larvae, respectively. In the first study, delayed morality of T. granarium and T. inclusum larvae was <26% when exposed on arenas treated with the two pyrethroids, and T. inclusum larvae were less susceptible than T. granarium. Adult mortality was 90–100% for both strains of T. granarium across post-treatment assays regardless of insecticide treatment and there was no difference between strains. All three insecticides produced 100% mortality for the laboratory strain of T. granarium larvae in initial post-treatment assays, but then efficacy declined. Field strain larvae were more tolerant to the insecticides than laboratory strain larvae, and larvae of both T. granarium strains were more tolerant than adults. Longer exposure times were required to produce complete mortality of larvae compared to adults. All three insecticides provided residual efficacy of adults for up to three months.     

Chlorine dioxide fumigation to control stored product insects in rice stored in a room

Gaseous chlorine dioxide (ClO₂) was applied to fumigate larvae and adult stages of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) and Sitophilus zeamais (Motschulsky) in rice grain bags stored in a grain storage room. It was confirmed that the fumigation efficiency varied depending on the storage position and insect life stage and species. The fumigation effect was the highest on the surface of the grain bag and lowest on the middle of the outer position on the grain storage bag. The mortality of adult P. interpunctella, 5 days after ClO₂ fumigation, reached 100% regardless of their position, whereas that of the larva P. interpunctella and adult S. zeamais varied depending on their positions. The mortalities in the outer portions of the grain bag were the highest, followed by that at the top of the grain bag. The ClO₂ residue of treated rice were lower than that accepted by international standards. To achieve fumigation effectiveness which similar with lab scale experiment, more researches which are related to infiltration or circulation of gaseous ClO₂ are needed.