DISTANCE AND RATE OF SPREAD OF ANTICARSIA-GEMMATALIS (LEPIDOPTERA, NOCTUIDAE) NUCLEAR POLYHEDROSIS-VIRUS RELEASED INTO SOYBEAN

The nuclear polyhedrosis virus of Anticarsia gemmatalis (Hubner) was released into soybean fields at two sites in Louisiana. The spread of the virus outside release plots was monitored by sampling A. gemmatalis larvae, predatory arthropods and parasitoids of A. gemmatalis, and soil. According to A. gemmatalis sampling, the virus spread at a rate of 0.8 and 1.2 m/d at the Crowley and Baton Rouge sites, respectively, within almost-equal-to 6 wk after it was released. The virus spread distances of up to 44 and 58 m at Crowley and Baton Rouge, respectively, during that season. The rate of spread detected in A. gemmatalis was significantly (P < 0.01) correlated with the rate detected by sampling and bioassay of predatory arthropods and parasitoids, primarily the former. There also was circumstantial evidence implicating birds and farm machinery in viral transport; 80% (n = 15) of bird droppings sampled at the Baton Rouge site during viral spread contained viable A. gemmatalis nuclear polyhedrosis virus. The rate of spread did not differ by direction from release plots. The prevalence of viral disease decreased at increasing distances from release plots for 3 yr after release at the Crowley site and during the 1st yr at Baton Rouge. The amount of virus in soil after the first season at the Crowley site decreased from 3,598 polyhedral inclusion bodies per gram in the release plots to 131 and <1 polyhedral inclusion bodies per gram at distances of 46 and 114 m, respectively, but this decrease was not significant.