Differences in fitness traits between E and Z pheromone races of European corn borer, Ostrinia nubilias, on a range of host plants

Mason, Charles E.The European corn borer (ECB), Ostrinia nubialis (Hübner), was accidentally introduced into North America nearly a century ago. During that time it has become a major economical pest of agricultural crops, primarily feeding on corn (Zea mays L.). It is believed that two pheromone races of ECB were established during that initial introduction phase and have since become wide spread through many agricultural areas of North America. The E pheromone race being confined primarily in the eastern half of the country and the Z pheromone race ranging from the east across the mid-west to the Rocky Mountains. Each race produces its own pheromone blend of E and Z-11-tetradecenyl acetate. The E race producing predominantly E isomers and the Z race producing predominantly Z isomers. In addition to differences in pheromone blend the E and Z pheromone race have different temporal emergence patterns in the early growing season. Where the two races overlap, the E pheromone race ECB tend to emerge earlier than members of the Z pheromone race. This requires them to utilize alternative host plants early in the spring; as corn is not a suitable host plant when they typically emerge. Thus, first generation E pheromone race ECB are often found on native wild host plants or alternate early season agricultural crops. ☐ The differences in host plant utilization between the races since their introduction into the US is the focus of this research project. It is possible that ECB of the E pheromone race have evolved unique fitness and survival characteristics compared to ECB of the Z pheromone race based on their evolution on different host plants. If so, this could have major implications for future insect resistant management strategies for ECB in agricultural fields. This study attempts to quantify differences between these two strains on a range of host plant tissues including corn expressing toxins from Bacillus thringiensis. ☐ The first part of this study sought to develop a non-destructive method of sampling ECB tissue that would allow for the identification of pheromone race without sacrificing the specimen. Originally the method available for identifying the races was destructively sampling adults and identifying pheromone blends on a gas chromatogram. More recently genetic markers have been identified and this study attempted to use these markers to identify pheromone race in the larvae. Four types of insect tissue were collected for this study including: (1) larval proleg, (2) larval prothoracic leg, (3) larval frass, and (4) pupal exuvium. DNA was extracted and a modified PCR protocol was used to identify individual ECB to pheromone race. In cases where a larval leg or proleg was removed, high mortality rates were observed. Frass yielded high DNA concentrations; however, this did not translate to high rates of accurate pheromone identification. Pupal exuvium yield the most consistent rates of correct pheromone identification, however more research to perfect this protocol is suggested. ☐ The second part of this study sought to determine the differential survival between the two races using a median lethal dose (LD50) bioassay incorporating potential host plant tissue into artificial diet. By determining the LD50 of potential host plant tissues, ECB larvae could be adequately challenged to try and determine differences in growth and development with plant chemical defenses present while still leaving half the population alive. LD50 for Bt corn, hops and tomato plant tissues were estimated using lyophilized plant tissue incorporated into artificial insect diets. ECB larvae were then monitored for survival at different doses of incorporated plant tissue. Results suggested that ECB larvae of both pheromone races were comparable in their survival rates on Bt corn, hops, and tomato plant tissue. However, the amount of tissue incorporated to determine the LD50 values varied between plants. ☐ In the final part of this research, newly hatched ECB larvae of both pheromone races were reared on plant host incorporated diets at the predetermined LD50 concentration. Larvae were then measure for a range of life history traits at each stage of development including: (1) larval mid-development weights, (2) pupal weights, (3) female pheromone production, and (4) the mean number of eggs laid per female. Results suggested that there was some variation on host plant treatments within pheromone race, however there was minimal difference between E and Z pheromone race ECB. Furthermore, E race ECB seemed to have decreased fitness when compared with Z pheromone race for the mean number of eggs laid per female. Therefore, this data suggests that there were no observed advantage of one pheromone race over the other for the measurements conducted during this research.University of Delaware, Department of Entomology and Wildlife EcologyPh.D