Plaque assay of Heliothis zea baculovirus employing a mixed agarose overlay

The nuclear polyhedrosis virus of Heliothis zea has been titrated in Heliothis zea cells by the plaque method, using 1 percent mixed agarose containing a mixture of Seakem and Ultra pure agarose. Visible plaques, formed 8 days postinfection, ranged in diameter from 0.5 to 2 mm. Dose-response experiments indicated that a single particle initiated the formation of a plaque. The titration of Heliothis zea baculovirus by the newly described plaque method provides an accurate technique for the determination of virus concentration.