PARENT SESSION
Oral Session # 37: Invasive Species III: Grasses and Shrubs.
Presiding: C Lortie
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.

Preference of an insect biological control agent for two invasive weeds, yellow and Dalmatian toadflax.

MacKinnon, Daniel^*,1, Hufbauer, Ruth ¹, Norton, Andrew¹, Jackson, Aaron ¹, ¹ Colorado State University, Fort Collins, CO

ABSTRACT- Biological control of invasive plants is typically considered successful when biological control agents (BCAs) substantially reduce population size of these weeds. Slowing or halting the spread of invaders, although not as dramatic or noticeable, can also be considered successful control. Exotic plants tend to invade by radiation from numerous distinct patches or foci, not as a single expanding front. The abundance of these satellite foci is due to dispersal from larger populations, and these smaller patches can be of greater importance than the larger populations to the spread of invasive weeds. BCAs that reduce seed set and are good dispersers are valuable in managing invasions because they can establish on undetected (and usually smaller and less dense) weed populations that escape other types of control, decreasing the establishment future infestations. Linaria genistifolia ssp. dalmatica (Dalmatian toadflax) and Linaria vulgaris (yellow toadflax) are invasive weeds that use seed for dispersal and establishment. Brachypterolus pulicarius (Coleoptera: Kateridae) is a BCA inadvertently introduced from Eurasia to North America that reduces seed set in both toadflax species and disperses without assistance. In North America this beetle is abundant on yellow toadflax (and is thought to reduce its spread), however fewer beetles occur on Dalmatian toadflax. To explore the causes underlying this pattern, we examined whether populations of this beetle collected from both host plants differ in their host-plant preference, measured by adult occurrence and oviposition. We found that beetles from both toadflax species preferred yellow toadflax in laboratory and field experiments. Perhaps due to this preference, Brachypterolus pulicarius is found on small, isolated patches of yellow toadflax, suggesting that newly established foci of this weed have a high probability of attracting this beetle. Studies to find populations of B. pulicarius that prefer Dalmatian toadflax may help stem the spread of this weed as well.

Key words: Brachypterolus pulicarius, toadflax