Endophagous insects and structural niches on plants: ecology and evolutionary consequences

Abstract

Summary1. The endophagous weevil Lixus elongatus was studied on two Carduus species in order to look for the impact of a structural gradient in host plant stem diameter on the life cycle and the genetic structure of this species.2. Body size of L. elongatus females was correlated positively with their fecundity and the stem diameter at the location of oviposition.3. Emerging individuals showed a significantly positive relationship of body size with the stem diameter at their pupation and emergence site. Mating behaviour was positively size‐assortative.4. Allozyme analyses indicated a gradient of genetic differentiation along body size classes and a decreasing heterozygosity with decreasing body size.5. The results led to the conclusion that a structural gradient in plants can promote body size variability in an endophagous herbivore through phenotypic constraints of the host plant and the herbivore. As size‐assortative mating translates this variability into differential gene flow between individuals of different body size, this could provide the raw material for speciation processes. Within a single host plant patch, however, further processes are necessary to split the existing genetic gradient into separate gene pools.

Interactive effects of light environment and herbivory on growth and productivity of an invasive annual vine, Persicaria perfoliata

“…3b) in the shade than in the sun, possibly indicating a less favorable habitat for weevil larvae. Other species of stem-boring insects have shown decreased larval survivorship with smaller stem size (Jeanneret and Schroeder 1992;Tscharntke 1993;Eber et al 1999;Losey et al 2002). Agrawal and Van Zandt (2003) found that when neighboring grasses were clipped to reduce light competition, focal milkweed plants had 20% shorter internode lengths and 90% thicker stems, and these plants also received significantly more damage and oviposition by a specialist stem-attacking weevil.…”

One Host Shift Leads to Another? Evidence of Host-Race Formation in a Predaceous Gall-Boring Beetle

“…That does not appear to be the case for M. convicta because as adults they spend a great deal of time foraging for pollen on non-Solidago plants (goldenrod is not flowering when they are active as adults) and we found evidence of strong assortative mating in the absence of host plants. Instead, we believe that host-associated differences in adult body size, chemical cues associated with natal host plants, or some combination generates assortative mating between the two putative host races (e.g., Eber et al 1999).…”

Body size and host range in European Heteroptera

“…Fourthly, one should use experimental approaches to test some of the hypotheses. Especially local processes like mechanical constraints on host selection lend themselves to controlled experiments (see Eber et al 1999).…”