Evolution of herbicide resistance in weeds: initial frequency of target site-based resistance to acetolactate synthase-inhibiting herbicides in Lolium rigidum

© 2002 Nature Publishing GroupThe frequency of individuals resistant to two acetolactate synthase (ALS)-inhibiting herbicides in three previously untreated populations of Lolium rigidum was determined. The frequency of individuals resistant to the sulfonylurea herbicide sulfometuron-methyl varied from 2.2 x 10⁻⁵ to 1.2 x 10⁻⁴ and the frequency of individuals resistant to the imidazolinone herbicide imazapyr varied from 1 x 10⁻⁵ to 5.8 x 10⁻⁵ depending on the population. Application of sulfometuron-methyl selected individuals with a herbicide-insensitive ALS, which was also cross-resistant to imazapyr. The high initial frequency of individuals resistant to ALS-inhibiting herbicides in L. rigidumpopulations never previously exposed to these herbicides helps explain the rapid evolution of herbicide resistance in this species once ALS-inhibiting herbicides were used

A new multistage dynamic model for biological control exemplified by the host–parasitoid system Spodoptera exigua–Chelonus oculator

Over the last few decades, important advances have been made in our understanding of host-parasitoid relations and their applications to biological pest control. Not only has the number of agent species increased, but new manipulation techniques for natural enemies have also been empirically introduced, particularly in greenhouse crops. This makes biocontrol more complex, requiring a new mathematical modelling approach appropriate for the optimization of the release of agents. We developed a temperature- and stage-dependent dynamic mathematical model of the host-parasitoid system with an improved functional response. The model is appropriate not only for simulation analysis of the efficiency of biocontrol agents, but also for the application of optimal control methodology for the optimal timing of agent releases, and for the consideration of economic implications. Based on both laboratory and greenhouse trials, the model was validated and fitted to the data of Chelonus oculator (F.) (Hym.: Braconidae), a biological control agent against the beet armyworm, Spodoptera exigua Hübner (Lep.: Noctuidae). We emphasize that this model can be easily adapted to other interacting species involved in biological or integrated pest control with either parasitoid or predator agents