Is host‐plant quality responsible for the populational pulses of salt‐marsh planthoppers (Homoptera: Delphacidae) in northwestern Florida?

.1 Rare populational pulses of the sibling species of plant‐hoppers Prokelisia dolus Wilson and P.marginata (Van Duzee) occur along the Gulf Coast of Florida. Densities at least three standard deviations ahove the average number of adult planthoppers per stem host plant are exhibited during these pulses. 2 This context of rare local irruptions provides a basis for testing a component of T. C. R. White's hypothesis, which states that the trigger for insect outbreaks is an increase in the nutritional quality, in terms of available nitrogen, of host‐plant tissue. 3 In the field, over approximately five generations of these hoppers (9 months), we elevated foliar nitrogen in host plants substantially by fertilizing, six times, salt‐marsh plots of 10 m 2 with ammonium nitrate. No densities approaching a populational pulse occurred in either fertilized or unfertilized plots during the course of this study or in the year following. Fertilization did increase adult densities in the spring but this increase deteriorated over the summer months and was lost in the autumn. Host plants in fertilized plots retained high levels of nitrogen for at least the second year. 4 Several very dense pulses, of more than thirty adult hoppers per stem, occurred at other sites during the course of this study. Host‐plant nitrogen in a pulse site did not differ from that found in host plants immediately adjacent to the pulse. We conclude that increased foliar nitrogen is not the proximate cause of the populational pulse behaviour exhibited by these planthoppers. 5 We speculate that these pulses result from behavioural aggregation of adult hoppers.