Activity and persistence of the nuclear polyhedrosis virus of the celery looper (Lepidoptera : Noctuidae) with a feeding stimulant and a stilbene-derived enhancer

A nutrient-based feeding stimulant and a diaminostilbene disulfonic acid-de rived enhancer (fluorescent brightener, Blankophor BBH(R); Burlington Chemi cal, Burlington, NC) were evaluated as adjuvants for the nuclear polyhedros is virus of the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), agains t the beet armyworm, Spodoptera exigua (Hubner), on collard, Brassica olera cea L. (Acephala group), cv. 'Vates'. Tests included holding larvae on spra yed potted plants in the laboratory and bioassays of foliage collected from sprayed plants in the field. The feeding stimulant increased virus-caused mortality in all tests. The enhancer increased virus-caused mortality in th e bioassays of field-collected foliage but not in the test of potted plants . Treatments with both materials maintained the greatest levels of activity over time in the field. At the concentration tested on potted plants (up t o 0.5% of the spray), the enhancer may have acted as a feeding deterrent. T herefore, on the whole plants, where the larvae were free to move around, e ffects on feeding behavior may have reduced the effectiveness of the enhanc er. In the bioassay of field-collected foliage, larvae were confined on sma ll pieces of foliage and, thus, did not have the option of moving away from the enhancer. Because the enhancer and the feeding stimulant have both bee n previously reported to also protect viruses from degradation by ultraviol et light, exposure to sunlight in the field could also have contributed to differences in larval mortality.