The biology and ecology of Ochrimnus mimulus (Stal, 1874): an assessment of its coevolution with Baccharis in Brazos County, Texas

Abstract

The biology, ecology and behavior of Ochrimnus mimulus are described as they relate to its host plant, Baccharis spp. The ecological association between 0. mimulus and Baccharis was examined to determine temporal life cycle correspondence and insect host specificity. 0. mimulus is host specific for Baccharis and extremely host specific for asteraceous plants, both in the field and in dichotomous choice oviposition experiments. 0. mimulus population size and constitution fluctuate on an annual cycle that tightly corresponds to reproductive events in the plant's life cycle. The average population size of adult 0. mimulus per Baccharis bush in Brazos County, Texas is 165 in September, 101 in October and 64 in November. 0. mimulus adults are numerous on Baccharis in September, adults and nymphs are found from October through December, and from January until August the insect leaves the plant, often gathering in hibernaculae. The seed feeding habit of the insect, its oviposition behavior and egg shape appear specifically adapted for Baccharis dwelling. The egg and first through fifth instars of 0. mimulus are described along with their stadia and phenology. Photoperiod and food availability both influence oviposition in 0. mimulus females, and when these factors are combined there is an interactive effect. Food availability also influences the stadia of 0. mimulus nymphs. Field observations of anti-predator behavior in 0. mimulus demonstrate that its coloration is utilized in an aposematic display. Both nymphs and adults aggregate when disturbed, and they exude a distinctive odor. The insect was distasteful to Anolis carolinensis and these lizards displayed learned avoidance of 0. mimulus after an initial feeding attempt. It is clear that the insect uses volatile chemical deterrents, possibly ones derived from Baccharis. A coevolutionary relationship between 0. mimulus and Baccharis is a plausible explanation for many of the observed results.