The role of formulation additives in increasing the potency of Cydia pomonella granulovirus for codling moth larvae, in laboratory and field experiments

Studies were undertaken to improve the biological efficacy of the granulovi rus (CpGV) of the codling moth, Cydia pomonella, by evaluating the performa nce of some formulation additives that might improve virus persistence and/ or virus uptake by first instar larvae. Laboratory studies, using a leaf di sc bioassay, demonstrated that 15% cane molasses incorporated within a form ulation of purified CpGV dramatically reduced the median lethal exposure ti me (LET50) to CpGV for neonate larvae at a CpGV dosage rate of 10(7) occlus ion bodies (OBs) ml(-1). Screening of a range of other compounds showed tha t sucrose, fructose and sorbitol (at 10% concentrations) and extracts of ap ple flesh and skin also gave significant reductions in the LET50 of CpGV fo rmulations containing these ingredients. Pectin, malic acid and alpha -farn esene did not significantly reduce the LET50. In a field trial, molasses in cluded at 15% (v/v) in a CpGV formulation, containing a dosage rate of 10(1 2) OBs ha(-1), gave as good control of codling moth damage as virus formula tions containing the 'sticker' 0.2% skimmed milk at higher dosage rates of 10(13) and 10(14) OBs ha(-1). Studies of CpGV persistence on foliage reveal ed no significant improvement of virus persistence on apple foliage using 1 0% or 15% molasses formulations. A second field trial demonstrated that 10% molasses, 10% sorbitol or 0.08% alpha -farnesene significantly reduced cod ling moth deep damage to fruit when these ingredients were added to formula tions of pure CpGV. Substantial sooty-mould growth (Cladosporium spp.) was observed on apple foliage treated with formulations containing molasses, in dicating that this formulation additive has secondary consequences that wou ld need to be taken into account if molasses was to be used in commercial C pGV formulations. Nonetheless, these studies clearly demonstrate that major biological improvements in CpGV performance can be achieved by the incorpo ration of formulation additives, including molasses and several other compo unds, that probably function as attractants and/or feeding stimulants for c odling moth larvae.