Household grain storage continues to be of paramount importance in improving food security in sub-Saharan Africa (SSA) where maize post-harvest losses of 10-20 % are reported. On-farm trials to compare alternative solutions for reducing household maize storage losses were conducted in the 2014/15 and 2015/16 storage seasons in two contrasting agro-ecological zones in the Hwedza district of Zimbabwe. A wide range of treatments including a commercial synthetic pesticide composed of fenitrothion 1 % and deltamethrin 0.13 % 1 , unregistered but commonly used botanical pesticides (Aloe ash, Colophospermum mopane leaves, Eleusine coracana (rapoko) chaff, and Ocimum gratissimum), hermetic storage facilities (metal silos, GrainPro Super Grain Bags (SGB) IVR ™ , Purdue Improved Crop Storage (PICS) bags), and storage bags with deltamethrin incorporated into their fabric, were evaluated. The results demonstrated the superiority of hermetic storage facilities (PICS bags, SGBs, and metal silos) in suppressing insect pest build-up, insect grain damage and weight loss in stored maize grain. A newly introduced synthetic pesticide on the Zimbabwean market which has pirimiphos-methyl 1.6 % and thiamethoxam 0.36 % was also evaluated in the 2015/16 season and was found to be highly effective. The following grain storage technologies: hermetic metal silos, SGB bags, PICS bags, and the pesticide formulation of pirimiphosmethyl 1.6 % and thiamethoxam 0.36 % are therefore recommended for smallholder farmer use to reduce stored grain losses due to insect pests. 1 Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the University of Zimbabwe or Natural Resources Institute and does not imply its approval to the exclusion of other products that may also be suitable.

Grain storage trials were conducted in two districts of Zimbabwe with contrasting agro-climatic conditions (mean annual temperature of 18-30 °C and 28-42 °C; total rainfall of 750-1000 mm per annum and < 450 mm per annum; respectively) to determine the comparative efficacy of commercially-available grain storage synthetic pesticides under contrasting climatic conditions. The five grain protectants, namely Shumba super dust ® (fenitrothion 1 % + deltamethrin 0.13 %), Actellic gold dust ® (pirimiphos-methyl 1.6 % + thiamethoxam 0.36 %), Super guard ® (pirimiphos-methyl 1.6 % + permethrin 0.4 %), Chikwapuro ® (pirimiphos-methyl 2.5 % + deltamethrin 0.1 %) and Ngwena yedura ® (pirimiphos-methyl 2.5 % + deltamethrin 0.2 %) were evaluated at label rates on stored shelled maize. The trials were conducted for a 40 week-long storage season in 2014/15 and again in 2015/16. Samples were analysed for insect grain damage, total insects per kilogram, grain weight loss, insect feeding chaff and grain moisture content. Temperature and relative humidity within stores were recorded using data loggers. The results highlighted the generally poor efficacy of the synthetic pesticides under both cooler and hotter climatic test conditions. The pesticides failed to prevent insect grain damage or suppress insect pest numbers. Only Actellic gold dust ® , introduced in the 2015/16 storage season was effective under both the agro-climatic conditions. The current study suggests that only Actellic gold dust ® can be recommended for smallholder farm grain protection under both cooler and hotter climatic conditions. The findings confirm the frequent claims of smallholder farmers in east and southern Africa regarding poor storage pesticide performance, and emphasize the need to develop alternative effective storage insect pest control options.

Many smallholder farmers in sub-Saharan Africa rely on synthetic pesticides for protecting stored-grain. Recommendations on use of these grain protectants are typically based on "blanket" application rates which are fixed rates that are not varied according to grain type, pest range or agro-climatic regions. There are numerous anecdotal reports of storage pesticide failure or reduced efficacy from farmers. Might rising global temperatures be a contributory factor? Smallholder farmers are responding by over-applying pesticides, increasing the application frequency or switching to non-recommended pesticides; leading to a pesticide treadmill. Trials to determine the efficacy and persistence of five commercially-available synthetic pesticides applied at manufacturer's recommended rates on stored sorghum grain under contrasting climatic conditions were conducted in Mbire (mean temperatures of 32-42 o C and 30-50 % rh) and Harare (18-32 o C; 42-75 % rh) districts in Zimbabwe. Grain samples were collected at 8-*Manuscript Click here to view linked References week intervals throughout a 10 month period in the 2014/15 and 2015/16 storage seasons. The samples were analyzed for insect grain damage, weight loss, total number of storage insects by species) and grain moisture content. Results showed significant differences in the performance of treatments (p < 0.001). Grain damage was consistently higher in Harare than in Mbire. Tribolium castaneum was the dominant pest in Mbire, while Sitotroga cerealella and Sitophilus oryzae were dominant in Harare. Tribolium castaneum populations were high in the Shumba Super dust ® (fenitrothion 1% + deltamethrin 0.13%) treatment in Mbire, while S. cerealella was dominant in Super guard ® (pirimiphos-methyl 1.6% + permethrin 0.4%) and Actellic Gold dust ® (pirimiphos-methyl 1.6% + thiamethoxam 0.36%) treated grain in Harare. Grain moisture content varied with ambient conditions, and was high in treatments with high insect pest levels. The results show that differences in climatic conditions influence insect pest species dynamics and response to pesticide treatments. Storage pesticides are not equally effective across different climatic conditions; thus more context-specific application recommendations are required.

Field evaluation of six grain storage technologies under hot and arid conditions (32–42 °C; rainfall < 450 mm/year) in two locations in Zimbabwe were conducted over two storage seasons. The treatments included three hermetic technologies (Purdue Improved Crop Storage bags, GrainPro Super Grainbags, metal silos); three synthetic pesticide-based treatments; and an untreated control, all using threshed sorghum grain. Sampling was at eight-week intervals for 32 weeks. Highly significant differences (p < 0.01) occurred between hermetic and non-hermetic treatments regarding grain damage, weight loss, insect pest populations, and grain moisture content; with the hermetic containers exhibiting superior grain protection. Weight losses were low (< 3%) in hermetic treatments compared to pesticide-based treatments (3.7 to 14.2%). Tribolium castaneum developed in metal silos, deltamethrin-incorporated polypropylene bags and a pesticide treatment containing deltamethrin 0.13% and fenitrothion 1% while Sitotroga cerealella developed in a pesticide treatment containing pirimiphos-methyl 0.16% + thiamethoxam 0.036%. Mechanisms of survival and development of these pests in the tested treatments and under similar climatic conditions need further elucidation. These hermetic technologies can be successfully used by smallholder farmers in developing countries as alternatives to synthetic pesticides for protecting stored-sorghum grain under hot and arid climatic conditions to attain household food security. To our knowledge, this is the first published study on modern hermetic storage of sorghum grain under typical smallholder storage conditions and involving stakeholders.

Prostephanus truncatus is a notorious pest of stored-maize grain and its spread throughout sub-Saharan Africa has led to increased levels of grain storage losses. The current study developed models to predict the level of P. truncatus infestation and associated damage of maize grain in smallholder farmer stores.Data were gathered from grain storage trials conducted in Hwedza and Mbire districts of Zimbabwe and collated with weather data for each of the sites. Insect counts of P. truncatus and other common stored grain insect pests had a strong correlation with time of year with highest recorded numbers from January to May. Correlation analysis showed insect-generated grain dust from boring and feeding activity to be the best indicator of P. truncatus presence in stores (r = 0.70), while a moderate correlation (r = 0.48) was found between P. truncatus numbers and storage insect parasitic wasps, and grain damage levels significantly correlated with the presence of Tribolium castaneum (r=0.60). Models were developed for predicting P. truncatus infestation and grain damage using parameter selection algorithms and decision-tree machine learning algorithms with 10-fold cross-validation. The P. truncatus population size prediction model performance was weak (r = 0.43) due to the complicated sampling and detection of the pest and eight-week long period between sampling events. The grain damage prediction model had a stronger correlation coefficient (r = 0.93) and is a good estimator for in situ stored grain insect damage. The models were developed for use under southern Africa climatic conditions and can be improved with more input data for greater precision models to build decisionsupport tools for maize-based production systems.