Host Tissues and Metabolic Products as Ultraviolet Screens for the Gypsy Moth (Lepidoptera: Lymantriidae) Nucleopolyhedrosis Virus 1

Abstract

The addition of tissue extracts from first to fourth stage Lymantria dispar (L.) larvae resulted in a 2-fold increase in virus-caused mortality, after exposure to ultraviolet (UV) radiation. The addition of extracts from fifth-stage male or fifth- and sixth-stage female larvae had little effect upon virus stability. Both male and female prepupal extracts acted as UV screens. Male and female pupal extracts had some protective activity, but were not as effective as those from prepupae. The addition of adult female extract was ineffective, while the adult male extract was the most effective UV screen. The addition of fecal filtrates enhanced viral stability to radiation and the effect was concentration dependent. For example, a 1% filtrate enhanced stability by a factor of 1.23, and a 5% filtrate by a factor of 2.45. The addition of a 20% filtrate enhanced persistence by a factor of 3.66 (=70% viruscaused larval mortality). Various compounds involved in purine catabolism were examined as UV screens. At a 1% concentration, hypoxanthine, urea, and xanthine were ineffective, while allantoin and uric acid had some activity. Adenine and guanine were effective protectants of the virus. In a subsequent test, uric acid was effective at concentrations ranging from 1 to 10%. The addition of 10% uric acid to the gypsy moth nucleopolyhedrosis virus (NPV) enhanced viral stability by 3.58-fold (=ca. 81% NPV-caused mortality).