l-menthol isolated from the essential oil of Mentha arvensis and seven of its acyl derivatives were tested for contact and vapour toxicity, and ovicidal and repellent activity against the storage pests Callosobruchus maculatus F., Rhyzopertha dominica F., Sitophilus oryzae L. and Tribolium castaneum Herbst. Menthyl propionate and l-menthol were highly toxic in contact assays and vapour toxicity assays respectively. l-menthol was also found to be strongly repellent (82–100% at 0.353 μg/cm2 dose) against all the insects, while menthyl acetate was highly ovicidal against T. castaneum.

A study was conducted to elucidate the effects of protein fractions isolated from maize (Zea mays L.) seeds on the development and survival of the Mexican bean weevil, Zabrotes subfasciatus (Boh.) (Coleoptera: Bruchidae). Maize seeds were fractionated into albumins, globulins, prolamins, glutelins and a residue and the bruchids reared on artificial seeds composed of susceptible background bean flour enriched with the different protein fractions. Survival (as indicated by LD50) and development (as indicated by WD50) of 20-day-old larvae of the bruchid were negatively affected by most of the fractions. The albumins and globulins were the most detrimental to Z. subfasciatus, significantly affecting both its survival and development.

Tannin extracts of two sorghum, Sorghum bicolor (L.) Moench. cultivars, BKS5 and BTX 623 were assessed for their bioactivity against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and the angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), in whole wheat flour pellets, and against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in whole wheat flour at three treatment levels. The number of adult progeny was reduced and number of days to emergence increased by tannins extracted from both sorghum cultivars at all treatment levels. However, the effects were not significant in all cases. In a short-term (25 days) feeding test using S.oryzae adults, the presence of sorghum tannins from cv. BKS 5 in the pellets significantly reduced feeding by the insects.

This study was conducted to identify the individual biochemical factors involved in the resistance observed in a few Mexican bean accessions against the bean weevil, Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae). Soluble proteins from different bean genotypes were separated by fractionated acetone precipitation. Insects were reared on artifical seeds composed of a susceptible background bean flour enriched with the different protein fractions. At low doses (2% w/w), the 0–20% and 20–40% acetone fractions of the resistant bean accessions G 12954 and G 12880 inhibited larval growth of the bean weevil, but not of a related species, the Mexican bean weevil, Zabrotes subfasciatus (Boheman). The 0–20% fraction caused the highest mortality of first instar larvae. The 60–80% acetone fraction contains general resistance factors, like α-amylase and protease inhibitors, which when enriched in artifical seeds led to a strong depression of insect growth for resistant and susceptible bean accessions alike. These factors should also be taken into account in breeding for multigenic, durable resistance, in order to exploit the synergism between general and specific resistance factors.

Tropical environments provide optimum conditions for insect growth and multiplication in the ideal medium of food stored by humans. Some insects begin infestation in the field and continue attack in storage. Other species diapause and remain in cracks and crevices in granaries or feed on grain residues while awaiting the new harvest. Since most of the tropical produce is for subsistence, the losses resulting from severe insect attack contribute to malnutrition and famine. In central stores and warehouses commodity management is poor and large amounts are lost to insects. In countries where heavy insecticide and fumigant pressure is maintained to preserve food stocks, insects rapidly build up resistance. The solutions for the future are to reduce dependence on pesticides and utilize in an integrated way the cultural, biological and physical techniques developed in recent years for safer storage and the successful preservation of strategic reserves for food security.

Investigations on storage insects infesting stored groundnuts was carried out in farms, markets, stores and out-door storage sites in order to find out the source of infestation. Farm samples were found to be free from infestation. Freshly harvested groundnuts that were just stacked into pyramids were also free from infestation. However, groundnuts stacked into pyramids at central storage areas of Kano and Gusau were highly infested following a year of storage. Groundnuts from stores and markets were moderately infested. The most abundant and widely distributed insect pests were Tribolium castaneum (Herbst) and Oryzaephilus mercator (Fauvel). Ephestia cautella (Wlk.) constituted less than 1% of insect pests found on the groundnuts, but Plodia interpunctella (Herbst) was absent in out-door pyramid storage.

Groundnuts kept in in-door storage had high moisture content, while nuts from farm and open air pyramid storage had low moisture content. Lipid, peroxide and free fatty acid (F.F.A) values from groundnuts were directly related to the levels of infestation.