The biology, habits and nature of damage caused by chrysomelids in beans

Studies on the biology and damage caused by bean pests Diabrotica balteata and Cerotoma facialis have been conducted at CIAT since 1977. The biology of the 2 species is similar in many aspects. Life cycle is as follows: eggs, 6-7 days; 1st larval instar, 3-4 days; 2nd instar, 2-3 days; and 3rd instar, 4-5 days. Prepupae last 2-5 days and pupae, 5-9 days. Adult life-span lasts from 16-44 days, during which females lay between 150-474 eggs. Both species preferrably oviposit in soil cracks near the roots of the host plant. Although adults of both species feed on the foliage of bean plants, their larvae can also cause damage to germinating plants. Adults can also act as vectors of several viral diseases. In trials related to the damage caused by larvae of Diabrotica and Cerotoma, it was concluded that the 2nd and 3rd instar larvae can cause severe damage to germinating plants, but only up to 14 days after planting. Cerotoma is more specific to beans than Diabrotica Survival of D. balteata larvae is less in beans. Eight field expt. were conducted to study the influence of adult feeding on bean yields. Both Diabrotica and Cerotoma can cause significant reductions in production only when high levels of infestations (4 adults/plant) occur during the 1st 2 wk.of the crop, and to a lesser extent when infestation coincides with the flowering stage (29-36 days). Implications of critical periods on the rational management of these pests are discussed. Graphics and tables on the results are included (CIAT)