Submitted to: Journal of Entomological Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/8/2004
Publication Date: 1/1/2005
Citation: Spurgeon, D.W., Raulston, J.R. 2005. Spatial distribution patterns of the Mexican rice borer (Lepidoptera: Pyralidae) in sugar cane. Journal of Entomological Science. 40:16-24. Interpretive Summary: The Mexican rice borer is a major pest of sugarcane in the Lower Rio Grande Valley of Texas. Although the larvae, which are caterpillars, damage sugarcane by tunneling into the stalks, few studies have examined the spatial patterns of this pest and associated crop damage in harvestable sugarcane stalks. We examined the spatial patterns associated with small, medium, and large rice borer larvae, pupae, and tunnels for samples based on parts of a field (plots) or whole fields. Samples for plots were smaller than samples based on fields. Population estimates based on plots varied more than estimates based on fields, and spatial patterns for these samples also differed among fields. In contrast, spatial patterns observed for field samples were consistent among fields. This indicated that the observed spatial patterns were sensitive to sample size because the samples based on plots were too small to be accurate. Based on samples from fields, small and large larvae, and tunnels, tended to occur in clumped groups. Medium larvae were randomly distributed, and pupae were evenly distributed. Knowledge of the spatial patterns of the rice borer and its damage to sugarcane will be useful in developing accurate sampling plans, and will provide important clues about the insect's biology.
Technical Abstract: The Mexican rice borer, Eoreuma loftini (Dyar), is the primary pest of sugarcane (Saccharum spp.) in the Lower Rio Grande Valley of Texas, yet few studies have examined its economic impact. Knowledge of the spatial patterns of the rice borer and associated damage in sugarcane would be useful in designing studies to further investigate the economic importance of this pest. We examined the respective spatial patterns of larvae, pupae, tunnels, and damaged internodes using Taylor's power law, for population estimates based on plots or sites within fields, and based on fields. Estimates based on plots or sites featured smaller sample sizes and greater variability than estimates based on fields. Analyses based on plots or sites also indicated between-field heterogeneity in estimates of Taylor's b for small, medium, and large larvae, and for pupae. Such heterogeneity was not observed for total larvae, tunnels, and bored internodes. In contrast, analyses based on fields indicated that common-slopes models were appropriate for each population category. The inconsistencies between results of analyses for plots or sites compared with those for fields probably resulted from the inadequacy of population estimates derived from the smaller sized sample units. Based on samples from fields, counts exhibited mild clumping except for medium sized larvae (random distribution) and pupae (regular distribution). Potential reasons for these observed distributions are discussed. Our results indicate that counts of most population categories of the rice borer are mildly clumped, and that the observed distribution pattern is sensitive to sample size.