Orchard host plant effects on the survival, development, reproduction, and behavior of the oriental fruit moth, Grapholita molesta (Busck)

The Oriental fruit moth, Grapholita molesta (Busck) (OFM) (Lepidoptera: Tortricidae) has become a pest of tree fruits since its introduction to the United States in the early 20th century. While it has historically been a major pest problem in peach production, outbreaks in commercial apple orchards in the eastern United States were rare until 1998. Since 1998, over 1000 loads of fruit have been rejected from processing plants in the mid-Atlantic region due to presence of live OFM larvae. The reasons for recent outbreaks are unknown, but it is possible that host-driven biological phenomena may be contributing to changes in OFM population dynamics resulting in outbreaks in apple. Studies were designed to examine the effects of host plants on OFM survival, development, reproduction, and behavior, in an effort to possibly ascertain the host-association status of eastern U.S. OFM populations, and also to gain insights into how pest modeling and management efforts may be altered to take into account various host-associated effects.; Laboratory investigations revealed that OFM adults derived from apple fruit have higher fecundity than adults that were reared on peach fruit. Additionally, adults reared from apple had higher longevity, and laid eggs over a longer period of time. Such effects could potentially affect wild populations of OFM, especially late in the season when apple fruit are a preferred feeding site. OFM ovipositional behavior is affected by host plants as well. OFM adults exhibited ovipositional preference for peach trees over apple trees in close-range choice tests in the orchard, regardless of the host-origin of larvae. Similar trends were observed with a feral OFM population at the orchard level scale, when oviposition was observed at the interface of adjacent peach and apple blocks. Data from orchard studies indicated that oviposition behavior can vary between different apple cultivars as well, adding to the complexity of the behavioral relationship. OFM larval survival in the orchard was comparable between apple and peach shoots, indicating that both hosts can potentially harbor large larval populations during the early season. OFM larvae were shown to utilize multiple shoots for feeding and development on peaches while using single shoots in apple. Survival in fruit was greatly affected by fruit maturity level, with larval survival higher in ripening peach fruit than in green, immature apple fruit. OFM larval developmental rate is also affected by the host plant. Faster larval development was observed in peach than in apple for both growing shoots and fruit. These host-driven effects clearly could impact efforts to predictively model OFM populations in commercial orchards. Host-associated effects need to be incorporated into future OFM population models and integrated control programs for both host plants.