Antistrophus minor

Antistrophus rufus

[Tooker and Hanks list Antistrophus rufus and minor emerging in numbers from both Silphium laciniatum and terebinthinaceum in the spring.]

Antistrophus species overwintered in dead Silphium stems and pupated in the early spring. We did not rear enough A. minor in cages to allow a reliable estimate of emergence time.

[Tooker and Hanks list Antistrophus rufus and minor emerging in numbers from both Silphium laciniatum and terebinthinaceum in the spring.]

Antistrophus species overwintered in dead Silphium stems and pupated in the early spring. A. rufus adults began emerging from S. laciniatum in mid-May and from S. terebinthinaceum in mid-June 2000. Although adults of both sexes have fully developed and functional wings, they did not fly readily but rather walked, with occasional hopping flights to nearby plants. On both plant species, males emerged first and were present only on dead stems of the previous year. There they guarded areas of stem where females later emerged, driving off other males by charging or butting with the head (N> 10 observations). Females mated immediately upon emerging and then moved to nearby developing Silphium stems (N> 10). As many as 20 females oviposited in one stem at the same time. Oviposition usually lasted less than 1 min (N> 10). Females oviposited in axils of S. laciniatum before bolting, but in S. terebinthinaceum they oviposited in the internodes after bolting, accounting for the greater proportion of emergence holes near stipules of S. laciniatum.

Adult A. rufus emerged in cages from S. laciniatum about 1 month earlier than from S. terebinthinaceum.

Densities of galls were significantly greater in S. laciniatum than in S. terebinthinaceum, perhaps due to its thicker stems. Galls were concentrated in the basal portions of S. laciniatumstems, but at high densities there was a greater proportion of galls in stem tops. Most galls in S. laciniatum were in proximity to stipules, which is consistent with oviposition behavior of A. rufus females. Thick clasping stipules may offer ovipositing females protection from predators and refuge for larvae from parasitoids, but offer no protection from fire (Tooker and Hanks 2004a). Galls in S. terebinthinaceum were more evenly distributed along stems, suggesting that the thinner stipules of this species provide no refuge from natural enemies

Endophytic insect communities of two prairie perennials (Asteraceae: Silphium spp.)