Habitats and landscape interactions of tachinid parasitoids important in biological control of leafrollers (Lepidoptera: Tortricidae) in central Washington tree fruit
Obliquebanded and Pandemis leafrollers (OBLR and PLR) are important pests in Washington tree fruit. When orchards came to the Northwest, leafrollers adapted to fruit trees from native host plants and have become serious pests. Two tachinids account for the majority of leafroller parasitism. Because these parasitoids are generalists, and cannot overwinter on OBLR or PLR, availability of alternative hosts may be important to improving biological control and sustainable leafroller management. The goals of this study are to identify habitat types and alternate host species that these flies utilize so that these extra-orchard habitats may be targeted for conservation or enhancement.
- 1. Determine the types of habitats and the host species that are utilized by the parasitoids in the regional landscape and identify potential overwintering hosts. 2. Determine the spatial and temporal parasitoid migrations of the flies around orchards.
1. Five sites in natural or non-orchard habitats were established and monitored weekly over the growing season. These represented the principal habitat types found around orchards; xeric shrub steppe, forest, riparian, and field crops. In the established sites, sampling techniques consisted of the following: visual traps (yellow sticky cards), olfactory traps baited with HIPV compounds (benzaldehyde and cis-ol), sentinel leafroller larvae, and a passive intercept trapping system (modified Malaise trap). Other habitats were sampled opportunistically. For these samples, vegetation was sampled for tachinid-parasitized caterpillars using hand collection and net sweeps. Collected larvae were reared to determine parasitism. Hundreds of insect specimens were collected and the identifications of species are incomplete at this time. These data will show the types of habitats used by the parasitoids, the temporal aspects of habitat use, and will provide species information for alternate hosts and their host plants.
2. Three apple orchards with established leafroller populations and cooperative managers were selected. Three trapping zones were established in each orchard and olfactory and visual traps (as described above) were randomly established in a row in each zone. The zones reflected two borders butting against natural or other habitat and one zone was in the orchard interior. These data are incomplete until identification of specimens is concluded. Projected completion of the identification of specimens collected for objectives 1 and 2 is May 2010 and the final report will contain these data. Ultimately these data will show how much the flies interact with orchard borders versus interiors and possible emigration/immigration events.