The addition of molasses to the Cryptophlebia leucotreta granulovirus formulation improves its efficacy against Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae), a pest of citrus in South Africa

Abstract

Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), commonly referred to as false codling moth, is an important pest of citrus in southern Africa. Given its quarantine status in markets to which a large portion of the fresh produce is exported, its management in citrus orchards is essential. This management typically follows a systems approach in which baculovirus-based biopesticides, such as Cryptogran™ (Betabaculovirus cryleucotreta), are considered an important component of pre-harvest control strategies. It has previously been demonstrated that adding molasses with Cryptogran™ improves field performance, further reducing the number of T. leucotreta infested fruit. However, the reason for this improvement was never determined. This study aimed to understand the role that molasses may have on the behaviour of T. leucotreta first instars under laboratory conditions, leading to this improved field efficacy, and to confirm conclusively if the addition of molasses to the virus formulation improved efficacy across a further six field trials. In the laboratory, larvae exposed to molasses-treated oranges at either a concentration of 0.25% or 0.50% moved around the surface of the oranges less and also penetrated the oranges less compared to larvae exposed to non-molasses-treated oranges. This suggested that molasses, as a phagostimulant, encouraged larval feeding quicker and longer. This will promote the uptake of the biopesticide infective units and is likely the reason for the recorded improved field efficacy of Cryptogran™ when combined with molasses across all six field trials compared to its application alone. These two sets of experiments confirm conclusively that the addition of molasses to the virus formulation improves its efficacy and should be standard practice in the industry.