Resource limitation of tephritid flies on lesser burdock, Arctium minus (Hill) Bernh. (Compositae)

Abstract

The intensity of resource exploitation by phytophagous insects is usually considered to reflect population size. For populations of two flowerhead-attacking tephritid flies, however, the resources utilised were not related to the numbers of searching adults. Tephritis bardanae Schrank attacked 11-13% of the total flowerheads each year, and Cerajocera tussilaginis (Fab) 17-65%, despite much wider and uncorrelated variation in adult numbers. Analysis of field data showed that the proportion of flowerheads used was not limited by poor flowerhead quality, but was restricted by (1) the synchronisation of adult activity with the appearance of flowerheads at the correct age for oviposition, and (2) by factors which influenced the ability of female flies to locate available heads. These restrictions were more severe in T. bardanae and explained its relatively low rate of infestation. Both tephritids tended to avoid flowerheads in open areas. The processes governing resource exploitation in each tephritid operated independently of the other, and a partial separation of the two species between flowerhead types and habitats arose simply because of their different timing of attack.

The relative importance of resources and natural enemies in determining herbivore abundance: thistles, tephritids and parasitoids

“…Anderson et al . 1989; Straw 1991; Fondriest & Price 1996) illustrate the importance of the synchronization of tephritid life cycles with the availability of host‐plant resources (in this case, open flowerheads).…”

Relationship between capitulum size and pre-dispersal seed predation by insect larvae in common Asteraceae

“…Within the family, the size of the capitulum varies in different species by about two orders of magnitude in linear dimensions. Many Asteraceae are hosts to bud-infesting, seed-eating insect larvae which can belong to a number of insect orders but are predominantly species of tephrid flies (Diptera: Tephritidae ;Straw 1991;English-Loeb and Kabran 1992;Sheppard et al 1994;Milton 1995;Scott 1996;Edwards and Brown 1997). Typically, the adult inserts one or more eggs into the capitulum while it is still in bud.…”

Differences in herbivore damage toArctium minusin open and forest habitats in its non-native range

“…Kambo and Kotanen (2014) did not report the number of larvae per capitulum, but the fraction of seeds damaged in southern populations (~40%-90%, dropping further north) was higher than found in this study (17%-49%, excluding a 5% outlier), possibly reflecting interannual variation; another study in southern Ontario (Hawthorn and Hayne 1978) reported intermediate levels of seed loss (28%-71%). Straw (1991) also found that understory plants in the UK had greater losses of seeds than plants in openings, even though these were attributable to a different family of insects (Tephritidae). He suggested that this may be due to differences in physical and chemical defences of plants in the understory and open populations, and also speculated that shaded areas may provide a better food supply and microclimate for adult insects.…”

“…In the United Kingdom pre-dispersal predation by tephritid flies was reduced in open habitats compared to shaded sites (Straw 1991). We investigated whether herbivore damage to burdock (including both seed predation and folivory) shows similar habitat-dependent patterns in its introduced range, in the presence of both introduced specialists from Europe and new enemies from North America.…”