Host rearing is a bottleneck for classical biological control of the cherry bark tortrix: A comparative analysis of artificial diets

Abstract

This paper describes a comparative analysis of the suitability of three artificial diets for the development of the cherry bark tortrix (CBT), Enarmonia formosana Scopoli (Lepidoptera: Tortricidae), to simplify the rearing process for this species and its potential classical biological control agents. The three diets tested included (1) a pinto bean-based diet modified specifically for the CBT, (2) the diet for codling moth, Cydia pomonella Linnaeus (Lepidoptera: Tortricidae), and (3) the Singh general-purpose diet. Survival from first instar to the pupal stage was very low on the pinto bean, codling moth, and Singh general-purpose diets (29, 0, and 0%, respectively). Survival was consistently greater, yet still low, for larvae that were reared through the first instar on bark and subsequently transferred to the codling moth or Singh general-purpose diets (5 and 32%, respectively). In comparison, larvae started on the pinto bean diet as second instars had a survival rate of 90%, only slightly below that of sibling larvae from the cherry bark control group (100%). Larval development time was fastest on cherry bark (36±2 days), differing significantly from that on the pinto bean diet (started as first instars: 58±2 days; started as second instars: 46±2 days), but not from the development time of larvae on the Singh general-purpose diet (44±3 days). Pupal weights were greatest for specimens from the Singh general-purpose diet (14.9±0.5 mg) and lowest for those from the pinto bean diet (started as first instar: 12.3±0.6 mg; started as second instar: 12.1±0.4 mg). Pupal weights from cherry bark were intermediate (13.5±0.6 mg). Early mortality, resulting primarily from rejection of the diet, remains to be the critical impediment in CBT rearing. It is therefore suggested that a phagostimulant from cherry bark be identified and included in an artificial diet shown to be nutritionally suitable, such as the Singh general-purpose diet or the pinto bean diet.