Monday, December 11, 2006

Tolerance to imidacloprid in the tobacco aphid, Myzus nicotianae (Hemiptera: Aphididae)

Lakshmipathi Srigiriraju, and Paul Semtner, Virginia Polytechnic and State University, Southern Piedmont AREC and Department of Entomology, 2375 Darvills Road, Blackstone, Virginia

The tobacco aphid, Myzus nicotianae (Blackman) is a key pest on tobacco, reducing the yield and quality of tobacco under severe infestations. A close relative of the tobacco aphid, the green-peach aphid, M. persicae (Sulzer) is historically known to develop resistance to all known classes of insecticides. To date, neonicotinoids, especially, imidacloprid, have proved relatively resilient to the development of resistance in managing the tobacco aphids ever since it was introduced in 1996. Admire2F, a commercial form of imidacloprid is being used on more than 90% of the tobacco acreage in Virginia, North Carolina, South Carolina and Georgia. As increased tolerance to imidacloprid has been reported in some tobacco aphid populations, this research is framed with an objective to assess possible resistance to imidacloprid in the above mentioned states. Colonies of red and green morphs of the tobacco aphids were collected, maintained under controlled conditions, tested for resistance using leaf-dip bioassay method. Mortality was determined at 72 hrs after exposure. LC50 and LC99 values were calculated by probit analysis using POLO program. The pooled data from at least two separate bioassays have shown a 30-fold difference in tolerance among the aphid populations, as compared to the standard colony, which was not exposed to imidacloprid for the past 8 years. Understanding the mechanisms underlying the resistance to these new classes of chemicals could have tremendous impact on the monitoring process for imidacloprid tolerance in tobacco aphids.

Species 1: Hemiptera Aphididae Myzus nicotianae (tobacco aphid)