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

1. The interactions between the univoltine mirid bug Capsodes infuscat us and its food plant, the geophyte Asphodelus ramosus, were studied i n the Negev desert for a 5 year period. The bug feeds mainly on Asphod elus inflorescence meristems, flowers and fruits, and in some years ma y destroy more than 95% of the plant population expected fruit product ion. 2. Asphodelus expected fruit production fluctuated widely during the study period, but was not related to precipitation. Capsodes densi ty was related to the plant expected fruit production, but with a 1 ye ar time lag. In years of high inflorescence production, a high per-cap ita reproduction of the bug resulted in a dense bug population in the following year. This dense population then decimated the plant fruit p roduction, 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 year s of high plant production are in general preceded and followed by yea rs of low plant production. Hence, in years which contribute most to p lant reserves (seed, underground storage organs), insect herbivores ar e relatively rare as a result of food limitation in preceding low prod uction years. But the insect populations which build up during years o f high plant production decimate their food resources and become food limited in subsequent years with low plant production. 4. Thus, herbiv orous insects seem to have a limited ability to affect plant populatio n dynamics in desert ecosystems. In contrast, the potential appears to be much greater for herbivorous insects to be regulated by their food plants.