Apparent Increase in Biomass and Seed Productivity in Hemp (Cannabis sativa) Resulting from Branch Proliferation Caused by the European Corn Borer (Ostrinia nubilalis)

Abstract The European corn borer (Ostrinia nubilalis Hubner), or ECB, is a major pest of hemp (Cannabis sativa L.). During the course of a study of hemp germplasm and cultivar accessions, the ECB attacked the vertical stem leader of hundreds of plants. At the site of invasion the main stem was typically destroyed, and the plant became strongly branched. Although the damaged plants were an average 9% shorter, mean shoot weight was 20% heavier. Seed productivity was also greater, based on a visual scale. The practical significance of such an “overcompensation” response to insect damage, with damaged plants growing more robustly and productively than their undamaged counterparts, is controversial. Certainly, some aspects of productivity, such as fibre quality, are detrimentally affected by the ECB. The insect showed a preference for larger plants, but was indifferent to the level of tetrahydrocannabinol, the chief intoxicant of C. sativa.