Topical Application of Synthetic Hormones Terminated Reproductive Diapause of a Univoltine Weed Biological Control Agent

Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Variability in weed biological control : effects of foliar nitrogen on larval development and dispersal of the alligatorweed flea beetle, Agasicles hygrophila

Host quality can have dramatic effects on performance of biological control agents but its importance is understudied. We used a combination of field measurements and laboratory experiments to determine the range of foliar nitrogen (FN) that larvae of the alligatorweed flea beetle (Agasicles hygrophila) are exposed to in the field and its importance to larval development and dispersal. Seasonal variability in FN was assessed at field sites spanning southern to northern Louisiana every 2–3 weeks during the growing season for four years. In a series of laboratory experiments, alligatorweed FN was manipulated to examine its influence on larval development and survival (under different temperature regimes), adult biomass, and dispersal of the biological control agent, A. hygrophila. Foliar nitrogen and rearing temperature had strong independent effects on larval development rate. We demonstrated that increasing nitrogen in leaf tissues shortens larval A. hygrophila developmental time and increases survival to adulthood, regardless of exposure temperature during development. It also suggests that foliar nitrogen may have important effects on biological control of alligatorweed, particularly as a result of seasonal variation in temperature and plant nutrition at field sites and could contribute to observed variation in A. hygrophila efficacy in the field.

Phytopathogenic fungi with potential as biocontrol agents for weeds of importance in crops of Antioquia, Colombia

Background Use of phytopathogenic fungi for the biocontrol of weeds represents a promising path in the search for new management alternatives that allow reducing negative effects on the environment and the generation of biotypes having resistance to herbicides. The first step in developing weed biological control programs is to determine the plants and their natural enemies with the highest affinity and potential to achieve effective biocontrol. The objective of the present study was to evaluate the phytopathogenic potential of fungal isolates on four economically important weeds including: Rumex crispus L., Digitaria horizontalis Willd, Persicaria nepalensis (Meisn.) Miyabe, and Thunbergia alata Bojer ex Sims, as a possible biocontrol agent. Results Morphological and molecular identification of nine phytopathogenic isolates of weeds was achieved, according to the sequencing of the ITS, β-Tub2, and TEF1-α regions. Pathogenicity of the following species on original hosts was confirmed: Colletotrichum cigarro, Epicoccum draconis, and Didymella rumicicola on R. crispus; Bipolaris sp., on D. horizontalis; Bipolaris zeicola, Phialemoniopsis curvata, and Stemphylium beticola on P. nepalensis and, Alternaria thunbergiae and Nigrospora sphaerica on T. alata. These could be, fairly, considered the first worldwide reports of such interactions, except for A. thunbergiae and Bipolaris sp. The most virulent interactions according to the AUDPC value corresponded to (R. crispus × D. rumicicola), (D. horizontalis × Bipolaris sp.), (P. nepalensis × S. beticola) and (T. alata × A. thunbergiae), with an incidence of 100%. Conclusion These strains were proposed for future research as potential biocontrol agents, which represented a great resource for the possible generation of new bio-herbicides.

Using Chemical Ecology to Enhance Weed Biological Control

In agricultural systems, chemical ecology and the use of semiochemicals have become critical components of integrated pest management. The categories of semiochemicals that have been used include sex pheromones, aggregation pheromones, and plant volatile compounds used as attractants as well as repellents. In contrast, semiochemicals are rarely utilized for management of insects used in weed biological control. Here, we advocate for the benefit of chemical ecology principles in the implementation of weed biocontrol by describing successful utilization of semiochemicals for release, monitoring and manipulation of weed biocontrol agent populations. The potential for more widespread adoption and successful implementation of semiochemicals justifies multidisciplinary collaborations and increased research on how semiochemicals and chemical ecology can enhance weed biocontrol programs.