TIME-LAGS IN INSECT RESPONSE TO PLANT PRODUCTIVITY - SIGNIFICANCE FOR PLANT INSECT INTERACTIONS IN DESERTS

1. The interactions between the univoltine mirid bug Capsodes infuscatus and its food plant, the geophyte Asphodelus ramosus, were studied in the Negev desert for a 5 year period. The bug feeds mainly on Asphodelus inflorescence meristems, flowers and fruits, and in some years may destroy more than 95% of the plant population expected fruit production. 2. Asphodelus expected fruit production fluctuated widely during the study period, but was not related to precipitation. Capsodes density was related to the plant expected fruit production, but with a 1 year time lag. In years of high inflorescence production, a high per-capita reproduction of the bug resulted in a dense bug population in the following year. This dense population then decimated the plant fruit production, became food limited and had a low per-capita reproduction. 3. This kind of time lag is expected to be common among desert insect herbivores that specialize in using ephemeral resources. The rare years of high plant production are in general preceded and followed by years of low plant production. Hence, in years which contribute most to plant reserves (seed, underground storage organs), insect herbivores are relatively rare as a result of food limitation in preceding low production years. But the insect populations which build up during years of high plant production decimate their food resources and become food limited in subsequent years with low plant production. 4. Thus, herbivorous insects seem to have a limited ability to affect plant population dynamics in desert ecosystems. In contrast, the potential appears to be much greater for herbivorous insects to be regulated by their food plants.