There is much discussion as to why a plant becomes invasive in a new location but is not problematic in its native range. One example is yellow starthistle, which originates in Eurasia and is considered a noxious weed in the United States. We grew yellow starthistle originating from native and introduced regions in a common environment to test whether differences in growth would be observed. In growth chamber studies, seedlings originating from the invasive range were larger than seedlings from the native range after 2 wk. Seed starch content is an important component of initial seedling growth. The starch content of seeds from introduced populations was higher than that of seeds from native populations. Regression analysis showed a relationship between the amount of starch in the seeds and the weight of yellow starthistle seedlings after 2 wk growth. There was no difference in chromosome number, except in accessions originating from Sicily and Sardinia. Field studies conducted in France and Russia revealed that rosettes and mature plants grown under natural conditions were larger when grown from seeds originating from the invasive range than from seeds originating from the native range. The number of capitula per plant and stem diameters were not significant among all populations, but differences were noted. The F1 progeny of plants originating from U.S. seed, but grown and pollinated in France, showed no differences in seedling growth, mature plant characteristics, and seed starch content from the plants grown from field-collected U.S. seed. The changes in seed starch resource allocation and its relation to plant growth is useful in understanding factors that contribute to yellow starthistle's invasibility.

The effects of photoperiod on pre-imaginal development and reproductive maturation of adult females of the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), were investigated at 20?C and at photoperiods from 10L : 14D to 18L : 6D. Experiments were conducted on a laboratory strain that originated from the Russian Far East. Larvae and adults were fed on the green peach aphid Myzus persicae. Under short day conditions the pre-imaginal development was faster than under long day conditions. The acceleration of pre-imaginal development occurred when day length was shorter than 16 h and the threshold day length was ca 14 h. The rate of reproductive maturation of adult females, in contrast, was twice as high under long day conditions, with the threshold between 14L : 10D and 12L : 12D, although even under short day conditions ca 10% of the females show a tendency to mature more quickly. This difference between the thresholds of these two photoperiodic reactions indicates they are relatively independent of one another.