Mechanisms of seedling mortality by subterranean insect herbivores

The nature of the mortality of germinating seeds of Vicia sativa, the common vetch, was investigated in a pot trial under controlled conditions. Chafer and tipulid larvae were restricted by nylon mesh partitions to enable radicle and/or hypocotyl herbivory to occur. The effects of the two insects were very similar. In control situations, an average of 88% of the viable seed sown recruited successfully. Hypocotyl and radicle herbivory had similar effects on seedling mortality, with recruitment of viable seed sown being reduced to 52%. When both modes of attack occurred together, successful recruitment was only 34%. Feeding on both plant parts resulted in an average post-emergence mortality of 14% of the seed sown, but the effect on pre-emergence mortality was of greater importance, amounting to 41%. The mechanisms by which soil-dwelling herbivores may cause seedling mortality in the field are discussed.