Development of a quantitative PCR method to measure intensity of Nosema carpocapsae infection in codling moth, Cydia pomonella

Codling moth, Cydia pomonella, is a notorious tree fruit pest causing severe damage to the agriculture community affecting crops such as apples, pears and walnuts. However, Nosema carpocapsae, a debilitating microsporidian disease is infecting laboratory colonies of codling moth making it difficult to study the pest. Once the spores infect laboratory colonies and field populations, it is quite problematic to control, which leads to decreased survival of caterpillars and diminished performance in adult moths. To better detect this disease in colonies, we are developing a quantitative polymerase chain reaction (Q-PCR) method to detect and amplify portion of a Nosema-specific gene and of a codling moth specific gene. We have tested six primer sets for N. carpocapsae Polar Tube Protein gene and have chosen one that appears superior. A useful codling moth primer for an Actin gene was already available in the laboratory. The ratio of when the amplified DNA of Nosema and codling moth pass an arbitrary threshold (Ct values) provides a comparative measure of abundance of the two genes. The ratio of these values represents an infection index, which we are correlating with spore counts in dilution series made from test moths. Our goal is to this measure of the intensity of the Nosema infection to test the hypothesis that the offspring of younger females would have lower Nosema infections than the offspring of older females. Comparisons of the Ct ratios in codling moth with Nosema infection rates estimated by microscopy are ongoing.