Grass growth in different parts of England in relation to invertebrate numbers and pesticide treatment

Abstract

Ryegrass swards at fourteeo widely separated sites in England were assessed for yield, botanical composition and invertebrate populations, with and without insecticide treatment during a 4-year period. Treatment with insecticide reduced the numbers of almost all invertebrate groups sampled and increased grass growth at some time at all but one site. Annual DM output was increased by 0-32% depending upon the site concerned. Evidence is presented which suggests that the yield increases were due to the suppression of aphids, plantsucking bugs, stem-boring fly larvae, and perhaps nematodes.

Top-down effects of insect herbivores during early succession: influence on biomass and plant dominance

“…Generally, our ®ndings are consistent with those of previous studies in herbaceous communities (Henderson and Clements 1977;McBrien et al 1983;Gibson et al 1987;Brown et al 1988;Gange 1989, 1992;Brown 1990;Chase 1998;Carson and Root, in press; but see Gibson et al 1990). Speci®cally, above-ground insect herbivory tends to decrease the abundance of the dominant native (cf.…”

“…Hendrix et al 1988) herbaceous species. We have documented, however, one of the few clear cases where natural levels of insect herbivory substantially lowers total standing crop biomass in a terrestrial plant community (see also Henderson and Clements 1977;Chase 1998;Carson and Root, in press). Because herbivory had a strong impact at all three widely scattered sites, our ®ndings may apply broadly to early successional systems (see below).…”

“…The most extensive investigations on the effects of insect herbivores on successional communities have been carried out in England by Brown and her colleagues Brown and Gange 1989, 1990Muller-Scharer and Brown 1995;Masters and Brown 1997). They found that above-ground insect herbivory in early successional ®elds reduced the dominance of grasses and increased species richness (see also Henderson and Clements 1977), whereas below-ground insect herbivory reduced species richness, particularly of annual and perennial forbs. Less work has occurred outside England.…”

“…Mills (1986) found that insect herbivory, independent of the in¯uence of vertebrate herbivores, was insucient to alter a post®re succession in California chaparral. Finally, few studies have directly investigated the impact of insect herbivory on standing crop biomass (e.g., Henderson and Clements 1977;Chase 1998;Carson and Root, in press). Recently, Crawley (1997) concluded that there were too few studies of insect herbivory to draw any ®rm conclusions about their role in community dynamics (see also Huntly 1991;Chase 1998).…”

The physiology of tiller death in grasses. 2. Causes of tiller death in a grass sward

“…Other (non-«xternal) causes accounted for the majority of the dead tillers, followed by grazing, and in contrast to the observation of Henderson and Clements (1977) infestation by stem-boring larvae caused very few tiller deaths. Damage by slug grazing appeared to be insignificant but grazing by rodents was more severe and resulted in the death of two plants.…”