Stored Grain Pests and Current Advances for their Management

During the offseason, when fresh food is not available, humans have to consume stored grain food. Unfortunately, these stored grains are later infested with many pests. Foods stored in bags and bins are very much susceptible to infestation with several pests which can cause extensive post-harvest losses, spoilage, and less demand in markets, causing a huge economic crisis. Hence, successful management of stored grain pests becomes necessary to prevent these from insect pests. Current approaches for their management are one of the promising goals, as it includes preventive practices, monitoring, sanitation, and identification of main pathogens. Different management strategies of all the common stored grain pests viz. grain weevils, grain borers, grain moths, flour moths, mealworms, grain and flour beetles, booklice, mites, and parasites are enlisted here.

Assessing Storage Insect Pest infestations and Faecal dropping of Rodent in Stored Grains from two districts of Southwestern Ethiopia

This study was designed to assess the occurrence of major insects and rodent pest infestations in stored grain from two districts of Southwestern Ethiopia. Omo Nada and Bako Tibe districts were purposively selected because they are potential maize and sorghum growing regions with high postharvest losses. A total of 160 farmers’ stores from both the districts were randomly selected. The grain samples used in the present study were stored for five different time periods, ranging from 1 to 5 months and from the same farmers’ stores, to identify storage insect pest, determine grain weight loss and insect damage. The results showed that the dominant insect species in maize and sorghum grains were weevils (Sitophilus spp.) followed by the Angoumois gelechiid (Sitotroga cerealella Olivier) and flour beetles (Tribolium spp.). High number of insects were recorded from both plastered and un-plastered gombisa and polypropylene bags. Additionally, the amount of every insect pest in each storage container recorded per 100 g grain increased because the duration of grain storage increased. There have been 0.33-1.29g and 0.44-1g of rodent droppings per 100g sample of maize and sorghum grains, respectively. This showed that faecal dropping per 100 g grain increased along with increase in storage period. Grain damage showed significant (P<0.05) differences over the storage periods across the studied districts. A similar trend was observed for weight loss in each of the grains all districts. These results indicated that farmers are incurring a substantial grain loss to insects and rodent pests. Hence, there is an urgent need to devise appropriate tactics for protecting the losses in farm-stored maize and sorghum in Ethiopia.

Assessing Storage Insect Pests and Faecal dropping of Rodent in Stored Grains in two districts of Southwestern Ethiopia

This study was designed to assess major insects and occurrence of rodent infestation in stored grain in two districts of south western Ethiopia. Omo Neda and Bako Tibe districts were purposively selected supported their potential growing of maize and sorghum grain, and high postharvest losses in these selected areas. A total of 160 farmers’ stores from both districts were randomly selected. The grain samples used in the present study were stored for 5 different time periods, ranging from 1 to 5 months and from the same farmers’ stores, to identify storage insect pest and to determine grain weight loss and insect damage. The results showed that the dominant insect species in maize and sorghum grains were weevils (Sitophilus spp.) followed by the Angoumois gelechiid (Sitotroga cerealella Olivier) and flour beetles (Tribolium spp.). High numbers of insects were recorded from both plastered and un-plastered gombisa and polypropylene bags. Additionally, the amount of every insect pest in each storage container recorded per 100 g grain increased because the duration of grain storage increased. There have been 0.33–1.29 and 0.44-1g droppings per 100-g sample of maize and sorghum grain, respectively. Grain damage showed significant differences over the storage periods across the study districts. A similar trend was observed for weight loss for each of the grains in all districts. These results indicated that farmers are incurring a substantial grain loss to insects and rodent pests. Hence, there is an urgent need to devise appropriate tactics for protecting the losses in farm-stored maize and sorghum in Ethiopia.

Assessing Storage Insect Pests and Faecal dropping of Rodent in Stored Grains in two districts of Southwestern Ethiopia

This study was designed to assess major insects and occurrence of rodent infestation in stored grain in two districts of south western Ethiopia. Omo Neda and Bako Tibe districts were purposively selected supported their potential growing of maize and sorghum grain, and high postharvest losses in these selected areas. A total of 160 farmers’ stores from both districts were randomly selected. The grain samples used in the present study were stored for 5 different time periods, ranging from 1 to 5 months and from the same farmers’ stores, to identify storage insect pest and to determine grain weight loss and insect damage. The results showed that the dominant insect species in maize and sorghum grains were weevils (Sitophilus spp.) followed by the Angoumois gelechiid (Sitotroga cerealella Olivier) and flour beetles (Tribolium spp.). High numbers of insects were recorded from both plastered and un-plastered gombisa and polypropylene bags. Additionally, the amount of every insect pest in each storage container recorded per 100 g grain increased because the duration of grain storage increased. There have been 0.33–1.29 and 0.44-1g droppings per 100-g sample of maize and sorghum grain, respectively. Grain damage showed significant differences over the storage periods across the study districts. A similar trend was observed for weight loss for each of the grains in all districts. These results indicated that farmers are incurring a substantial grain loss to insects and rodent pests. Hence, there is an urgent need to devise appropriate tactics for protecting the losses in farm-stored maize and sorghum in Ethiopia.

Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait

Theory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters.

Tribolium beetles as a model system in evolution and ecology

Flour beetles of the genusTriboliumhave been utilised as informative study systems for over a century and contributed to major advances across many fields. This review serves to highlight the significant historical contribution thatTriboliumstudy systems have made to the fields of ecology and evolution, and to promote their use as contemporary research models. We review the broad range of studies employingTriboliumto make significant advances in ecology and evolution. We show that research usingTriboliumbeetles has contributed a substantial amount to evolutionary and ecological understanding, especially in the fields of population dynamics, reproduction and sexual selection, population and quantitative genetics, and behaviour, physiology and life history. We propose a number of future research opportunities usingTribolium, with particular focus on how their amenability to forward and reverse genetic manipulation may provide a valuable complement to other insect models.

Immune stimulation alters chemical profiles of Tribolium castaneum

Rapid recognition of disease cues is essential for preventing pathogenic infections and for disease management in group-living animals. Healthy individuals across taxa can detect illness in other conspecifics and adjust their responses to limit further infections of themselves and the group. However, little is known about potential changes in chemical phenotypes due to disease, which may mediate these responses. We here asked whether individual immune experience resulting from wounding or the injection of heat-killed bacteria of Bacillus thuringiensis (i.e., immune priming) leads to changes in the chemical profiles of adult red flour beetles (Tribolium castaneum). This group-living insect species is a well-studied example for both immune priming as a form of innate immune memory and niche construction via 'external immunity', i.e., the secretion of quinone-containing antimicrobials into the flour. Upon interaction with wounded conspecifics, naive beetles were previously found to not only up-regulate immunity, but moreover reduce gene expression of the evolutionary capacitor HSP90, an effect that has the potential to enhance adaptability. We here used gas chromatography-flame-ionisation detection (GC-FID) to study the composition of stink gland secretions and cuticular hydrocarbons (CHCs) of immune-primed and wounded beetles compared to controls. The overall profiles as well as target compounds of the stink gland secretions showed transient, slight changes after these treatments, particularly in wounded females. Priming and wounding led to pronounced changes in CHC profiles with increases in the proportion of methyl-branched alkanes. Furthermore, we found sex-specific differences, that were particularly pronounced in the CHCs, although the changes due to immune stimulation were overall similar in both sexes. We suggest that CHCs are potential candidates for the transfer of information related to individual immunological experience into the group.

Rating knockdown of flour beetles after exposure to two insecticides as an indicator of mortality

Knockdown and mortality of adults of the red flour beetle, Tribolium castaneum (Herbst) and the confused flour beetle, Tribolium confusum Jacquelin du Val, were assessed after exposure to two contact insecticides, chlorfenapyr and cyfluthrin, on a concrete surface. Individuals were rated on a scale for knockdown of exposed adults according to their mobility from 1, representing immobilized adults to 5, representing normally moving (similar to the controls). Only cyfluthrin gave immediate knockdown. Adults were rated at 1, 3 and 7 days post-exposure. After the final assessment, adults were discarded and the same procedure was repeated for 5 consecutive weeks with new adults exposed on the same treated surfaces. Despite initial knockdown, many individuals did not eventually die after exposure to cyfluthrin. In contrast, adults exposed to chlorfenapyr were not initially knocked down after exposure but most died after 7 days. These trends were similar during the entire 5-week residual testing period. The storage of the treated dishes in illuminated or non-illuminated conditions did not affect the insecticidal effect of either insecticide. The results of the present study can be further implemented towards the design of a “lethality index” that can serve as a quick indicator of knockdown and mortality rates caused after exposure to insecticides.