Valeria Todeschini

Efficacy and residues of permethrin-incorporated nets used to protect maize grains post-harvest

BACKGROUND Pest control in post-harvest food storage represents a great challenge in the sustainable prevention of food losses, and insecticide-treated netting may represent a valid alternative to traditional practices such as the direct application of insecticides. In our work, the efficacy of a permethrin-incorporated net, in combination with polypropylene or jute sacking, was tested for the control of Sitophilus oryzae. Contamination of maize grain by permethrin from the treated netting was also evaluated. RESULTS A 98% control of S. oryzae was achieved using permethrin-treated netting. Both jute and polypropylene acted as additional barriers, increasing efficacy to 100%. The results also showed the contamination of maize kernel by permethrin released from the treated netting. The concentration of residues in maize kernels increased with increasing temperature; however, use of jute or polypropylene significantly reduced (by 87% to 97%) the concentration of residues transferred to maize kernels. CONCLUSIONS Permethrin-treated netting provided a high level of efficacy in the post-harvest protection of maize. Several factors influenced permethrin residue concentrations in grains when treated nets are used. Therefore, solutions should be found to prevent contamination of food stored in the bags that are treated with insecticides.

Use of permethrin coated nets to protect stored grain from pests infestations

Surveys carried out in some villages of Democratic Republic of the Congo showed that insect pests are a major cause of food loss for rural populations. Cereal grains are often compromised by pests in the field and during storage. Among cereals cultivated for family consumption in these areas of Africa, mainly maize and rice are both seriously infested by Coleopteran pests belonging to the genus Sitophilus. Any approach currently adopted to solve this problem, as the manual removal of visible insects, is often inadequate or insufficient. Due to the limited availability of chemical insecticides and their high price in these countries, our aim is to study a simple and cheap way to protect grain after harvest. The technology derives from anti-malaria mosquito nets, also known as insecticide treated nets or bednets, modified for the new purpose. Nets consist in fine-mesh polyester coated with permethrin (2.0%), a synthetic second generation pyrethroid that gives repellent and insecticide effect, while ensuring a high human safety. The idea is to use these nets to wrap jute bags or other containers in which grain is commonly stored in poor countries. Preliminary bioassays with adults of Sitophilus oryzae showed that knock-down values for 50 and 95% of exposed insects (KD 50 and KD 95 , respectively) were equal to 4.8 and 9.5 min. We are currently carrying out further in vivo bioassays (in Italy) and field studies (in Congo) to test the efficacy of the treated net. The coating of structures for grain preservation could be a viable sustainable strategy for limiting food losses in countries that lack resources and technologies for pest control.