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

Abstract

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.

A time-saving method for sealing Purdue Improved Crop Storage (PICS) bags

“…For all closing methods, the germination rates of maize grain stored in PICS bags was not different compared to the baseline value. This is in agreement with the previous studies ( Baoua et al., 2012 ; Williams et al., 2016 ; Afzal et al., 2017 ) which stated that PICS bags do not compromise the germination rate of the stored seeds. The internal temperature in PICS bags had a strong positive correlation with external temperature.…”

Efficacy of Hypoxia Against Tribolium castaneum (Coleoptera: Tenebrionidae) Throughout Ontogeny

“…This happens when the infestation level is relatively high and when the ambient temperature is warmer. These conditions promote a more rapid rate of insect metabolism, and in some cases, respiration of the grain (Williams et al 2016, Kharel et al 2018). In addition, limited oxygen supply may affect insect behavior besides survivorship.…”

Oxygen Consumption and Acoustic Activity of Adult Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) during Hermetic Storage

“…Other studies have assessed the individual insect consumption rates at normoxic conditions and found that approximately 8 mL O 2 is needed during the lifetime of C. maculatus adults (egg to adult emergence) [ 14 , 42 , 43 ]. Our findings focused on adult stages under hypoxic conditions which prompted the insects to reduce their metabolic activities.…”

“…The low oxygen levels under hermetic conditions result in the suppression of feeding, growth, development, and population expansion [ 13 , 14 , 43 , 44 ]. In addition, before the insects succumb, they respond to hypoxia by metabolic down-regulation which reduces insect movement overall.…”