Corn Rootworm

Coleoptera: Chrysomelidae (Diabrotica spp.)


There are two species of corn rootworm that are important insect pests of corn: western (WCR) and northern (NCR) corn rootworms. WCR adults are about 6 mm long and are yellow in colour with cream spots on their wing cover. Females are slightly larger than males and the female’s stripes are more pronounced than the male’s stripes. Sometimes the black stripes on males overlap and make the wings appear solid black. Adult NCRs are the same size as WCR and are solid yellowish-green in colour. There are no distinctive markings to differentiate males’ and females’ NCR. Larvae of both WCR and NCR are white and slender, and fully grown larvae are about 13 mm long having brown heads and a dark patch on the tail end. Both adults and the larval stage cause severe damage to corn plants.

Life Cycle

Eggs of both WCR and NCR are deposited in the top 30 cm of soil near the corn plants in late summer. The eggs overwinter in the soil and the larvae emerge from late spring to early summer of the upcoming year. The larvae feed on corn roots for four to six weeks and then pupate in the soil. The pupa matures within five to ten days and the adult emerges. Corn rootworm males appear one week before the first emergence of female beetles because males need time to complete sexual development. After the emergence of females, they start to mate. The female deposits the egg clutch and continues feeding to mature more eggs to lay them. This process of female feeding, egg maturation, and egg-laying is repeated until all eggs have been laid. Females of WCR and NCR lay approximately 1000 and 300 eggs, respectively. Both WCR and NCR have one generation per year


Both corn rootworm larvae and adults cause severe damage to corn plants. Newly emerged larvae feed on root hairs and outer root tissue. The second and third instar larvae feed on the root tips of nodes and tunnel into the roots. Larvae feeding reduces the water and nutrient uptake of corn and stops the growing point at the tips of the roots. Damaged roots weaken to the extent that the plants grow in a gooseneck-like shape. These plants often pollinate poorly and are difficult to harvest, contributing to yield losses. Adult beetles can also cause damage by feeding on the corn leaves and making the leaves partially or totally stripped. Then they move to silk and pollen as they develop and result in yield reduction.



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