Pheromone trapping true armyworm in rice: How much does trap location matter temporally and spatially?

In California rice, true armyworm (Mythimna unipuncta) larvae can rapidly show up in fields and defoliate fields. Small larvae are difficult to find, so current monitoring efforts have emphasized an early warning system using pheromone-baited traps. Each year, two distinct peaks in moth flights are evident. While the link between adult moth captures and larval infestations is imperfect, high captures of moths is an indication that a a flight of moths has occurred and that significant egg laying in fields may have occurred. These pheromone traps have value in rice IPM, but there are still unknowns about just how much moth captures vary across landscape and how much trap captures are influenced by trap placement. We used a grid of pheromone-baited bucket traps spread across many rice fields in a two-year study to evaluate the temporal and spatial relationships between trap captures. In the grid, bucket traps were spaced 0.80 apart. Traps were checked weekly and moths counted. We used correlation and SADIE analyses to test if subsequent captures were linked for individual traps, if the magnitude of the two peaks are correlated for individual traps, and if trap captures are spatially aggregated at the spatial scale tested. We found that while there were some limited temporal correlations, there was also a substantial amount of spatial variability. In addition, captures were aggregated in only a minimal manner. These results will help refine trapping programs for true armyworm in rice, along with moth pests in other cropping systems.