Laboratory Evaluation of Storage Bags for Infestations in Wheat Caused by Rhyzopertha dominica F. (Coleoptera: Bostrichidae) and Trogoderma granarium Everts (Coleoptera: Dermestidae) and Their Control Using Phosphine Fumigation.

Abstract

Simple SummaryWheat is commonly stored in bags in Asian countries, which include jute bags, woven plastic bags, and hermetic plastic bags. We evaluated these bags under laboratory conditions for external infestations caused by two serious pests of wheat. Considering all three bags, results showed that insects preferred to enter jute bags due to their loose fibers (termed as invasions), while no insects created holes or entered (penetrations) in woven plastic bags and hermetic plastic bags which had no such openings. In the second experiment, insects were released in jars with only two types of bags, namely woven plastic bags and hermetic plastic bags. In this case, insects created holes and penetrated into woven plastic bags but not into hermetic plastic bags. Both these experiments showed hermetic plastic bags remained safe from external infestations due to their thick and smooth plastic. The third experiment evaluated fumigation efficacy against all three bags for the pests already present in bags with grains. Results showed mortality was maximum in jute and woven plastic bags but negligible in hermetic plastic bags. The results of these experiments pinpointed deficiencies in all three bags for controlling insect infestations (external or internal) and demand alterations in these bags to successfully control such infestations.Bag storage of wheat is common in Asian countries, and common types of such bags include jute bags, woven plastic bags, and hermetic plastic bags. In order to assess infestation by two serious pests, namely Rhyzopertha dominica (Coleoptera: Bostrichidae) and Trogoderma granarium (Coleoptera: Dermestidae) in these bags, two experiments were performed. In the first experiment, three popular wheat varieties, namely Akbar, Dilkash, and Bakhar star were filled in above-mentioned miniature-size bags which were then placed in jars with three replicates per bag type and variety. Forty insects (adults for R. dominica and larvae for T. granarium) were released in the center of the jars for a period of 30 d in two different setups for both species. Data were recorded twice: after 15 d and 30 d. Results showed insects entered the jute bags only (made invasions due to its loose fibers and openings). Inside the bags, R. dominica caused more weight loss and live insects in Dilkash and Akbar varieties, while T. granarium preferred Bakhar star and Dilkash compared with their third variety. In the second experiment, only two bags, namely woven plastic bags and hermetic plastic bags filled with one variety, were tested to check damage (penetrations because no openings are present in these bags as in jute bags) to the bags. Results showed both species created holes in woven plastic bags but not in hermetic plastic bags. These results showed hermetic plastic bags remained safe from external infestation compared with the other two bags. Sometimes if insects are already present in the grains inside the bags, fumigation is needed from outside to kill the pests inside. To evaluate this, all three bags were filled with a wheat variety and were also infested with both insect species and placed in a fumigation container with nine replicates per bag type. A phosphine tablet (3.0 g) wrapped in muslin cloth was placed in a container which was then sealed, and the fumigation-induced mortality after 24 h was recorded. Results showed mortality was >95% to 100% in woven and jute bags, respectively, while mortality in hermetic plastic bags remained very low (<3%). These results revealed the least fumigant gas permeation in hermetic plastic bags compared with jute and woven plastic bags. Results of all three experiments demand immediate alteration in creation of all three bags to curtail infestation from outside (jute and woven plastic bags) as well as to generate maximum fumigation efficacy when the source of infestation is with the grains (hermetic bags).