EFFECT OF OPTICAL BRIGHTENERS ON THE EFFICACY OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) NUCLEAR POLYHEDROSIS-VIRUS IN FOREST PLOTS WITH HIGH OR LOW-LEVELS OF NATURAL VIRUS

Doses of a standard formulation of Gypchek (gypsy moth NPV) containing the sunscreen Orzan and a sticker were evaluated against gypsy moth, Lymantria dispar (L.), along with experimental aqueous formulations of Gypchek in which Orzan was replaced by stilbene disulfonic acid optical brighteners, Phorwite AR (1991) or Blankophor BBH (1992), that had acted as potentiating agents for the virus in laboratory tests. The treatments were applied to gypsy-moth-infested small (0.02 ha) forest plots where preliminary studies had demonstrated high (1991) or low (1992) levels of natural gypsy moth NPV. In 1991, treatments included two lower concentrations of Gypchek with the formulation containing Orzan as well as the formulation containing Phorwite AR. In 1992, treatments were the lower dose of Gypchek with two levels of Blankophor BBH, one dose of cell-culture-produced gypsy moth NPV with one level of Blankophor BBH, Blankophor BBH alone, and untreated control plots. The 1991 treatments containing Phorwite AR had significantly higher levels of gypsy moth larval mortality and significantly reduced LT50s compared with equivalent treatments containing Orzan. The Phorwite AR increased the mortality of gypsy moths (caused by the natural virus) to that of the high dose of applied virus without Phorwite AR. In 1992, all treatments containing Blankophor BBH with the low dose of virus had levels of gypsy moth larval mortality equal to or higher than the standard formulation with the higher dose of virus, significantly higher levels of gypsy moth larval mortality than the standard formulation with the lower dose of virus, and significantly reduced LT50s compared with either of the treatments containing Orzan. Natural gypsy moth NPV levels remained low in the control plots, and Blankophor BBH applied alone significantly increased the mortality of gypsy moths.