Control of bruchid seed weevils of common bean using unique seed proteins having insecticidal properties : final report -- July 13, 1988 to July 12, 1992

Common beans are often in short supply, however, due to low yields and insect damage, especially by bruchids or weevils, the Mexican bean and common bean weevils causing an estimated $200 million in losses each year. The aim of this project was to utilize the insecticidal properties of arcelin, a protein found in seeds of wild beans, in developing resistant cultivars for biological control of these bruchid insects. Arcelin 1 type protein provided the highest resistance to Mexican bean weevil. Damage to seeds containing high levels of arcelin 1 was less than half that to normal seeds, and often approached the levels of protection provided by chemical seed treatment. When stored for up to 6 months in Honduras, seeds containing arcelin showed only 10-15% as much damage as seeds without arcelin. Although pureline cultivars containing seeds with arcelin 1 provide uniform, high levels of resistance, the possibility exists that weevils may eventually overcome this resistance. Line mixtures containing different proportions of seeds having arcelin 1, 2, 3, and 4, or no arcelin were tested. Mixtures with a large proportion of seeds containing arcelin 1 and the 4-component mixture provided levels of resistance high enough for good protection, and they may reduce the likelihood that resistance will be broken. Studies in Brazil showed results similar to those in Honduras, and it was also found that resistant, arcelin-containing lines had higher germination -- an added benefit to farmers using their own seed. Rodent-feeding studies conducted at independent labs and also under the guidance of the Centro International de Agricultura Tropical (CIAT) suggest no likely danger to humans consuming arcelin-containing seeds that are cooked properly. Arcelin is a form of lectin or phytohemagglutinin similar to the lectin found normally in beans seeds, and normal bean seeds cooked properly have caused no toxicity problems for consumers. The knowledge gained and the plant materials derived from these studies are being used in Honduras and Brazil to develop bean cultivars better suited for their particular production conditions. Resistant breeding lines developed by CIAT are being released for utilization. These studies show the importance of collaborative efforts that encompass many facets of basic and applied research; important results can accrue when fundamental knowledge is applied to an important practical problem. (Author abstract)