Life table simulations of a univoltine codling moth, Cydia pomonella, population 2. Impact of immigration on the effectiveness of codling moth granulovirus sprays

ABSTRACT

The potential for immigrant adult codling moths, Cydia pomonella (L.), to reduce the efficacy of the granulovirus (CpGV) against a univoltine population was investigated using published life tables for codling moth on apple trees in Nelson, New Zealand. Simulated life tables over eight generations incorporated mortality >90% from CpGV sprays and combined this with immigration rates ranging from 0 to 1 adult per tree. Without immigration, there were 5 damaged fruits per million by the eighth generation from an initial population of 1.22 adults per tree but only 9 per 100 million had fresh damage or larvae that could trigger phytosanitary rejection. Higher-yielding modern orchards reduced this fresh damage to 5 per 100 million harvested fruit. New Zealand exports apples to markets with zero tolerance of codling moth (Codling Moth Sensitive Markets [CMSM] programme), and immigration of 1 female per 100 trees was projected to pose a risk of failure to meet quarantine requirements with one freshly damaged fruit per 112,000, or per 202,000 in a modern high-density orchard. This confirms the wisdom of using an integrated suite of control methods in CMSM, of which CpGV is only one. Similarly, immigration of one female per 1000 trees or 3 ha had much lower risk but could also threaten exporting if reliance was placed solely on CpGV, with one fresh damage or larva per 2 million harvested fruit. A commitment to the removal of neglected host trees of codling moth in the environs of orchards is recommended.

KEYWORDS:

• Granulovirus
• immigration
• modelling
• Cydia pomonella
• tortricidae
• life table

Acknowledgements

I am most grateful to my colleagues Jim Walker and John Charles for their valuable and constructive comments on an earlier draft of this paper. I thank Christopher R. Wearing for statistical advice.

Disclosure statement

No potential conflict of interest was reported by the author(s).