Western Corn Rootworm (WCR), Diabrotica Virgifera Virgifera Le Conte – Several Years of Research in Western Part of Romania

Abstract

Diabrotica virgifera virgifera Le Conte (Coleoptera: Chrysomelidae), known as western corn rootworm (WCR), is an important pest for maize crops from Romania, after corn borer larvae. Fourteen years ago, this pest has entered in our country. Since its introduction Diabrotica v. has been spreading in western part of Romania and many investigations were started by us to understand very well the morphology, eco-biology and control of the species. 
 First occureance and activity period. The immature developmental stages of WCR (larvae, pupae, eggs) have been observed for the first time in Romania, in soil sample during 2000-2002. Adults’ activity developed from during June to September.The males have appeared earlier than females with approximate 4-6 days. The females have begun to lay eggs in middle of July. In soil, the larvae were observed from May to August and pupae were observed from June until August, too.
 Colour variability. In monitoring activities, the most of specialists use the color criterion for establishing males and females. However, this is not so precise method, because the great variability of color what is frequently in many populations. Therefore, we tried to eliminate any doubt regarding sex ratio. 
 Influence of weather and geographical areas. Based on our data during 2003-2005, we can emphasize a very serious influence of air temperature and rainfall on WCR flight dynamics in adults. Regarding the altitude, we observed a decreasing number of WCR adults at once the altitude increase. 
 Control strategies. In preventive control avoiding monoculture play a main role, because the larvae survived only maize roots. Some researches realized in western part pointed efficacy of seed treatments (using imidacloprid, clothianidin, thiametoxam) against larval populations. Very important is using a chemical product (thiametoxam) against adults (like an additionally product). From an-polluting method may mention follows: pheromone traps, color traps, autochthonous natural enemies. The spider species Argiope bruennichi (Araneae:Araneidae) and Theridion impressum (Araneae:Theriidae) are able to diminish significantly population of adults, especially in appearance of maize silk.