Population variability of a native and an introduced herbivore of carrots (Apiaceae)

Long-term, twice weekly, trap catches of the native carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae), and the introduced carrot rust fly, Psila rosae (Fabricius) (Diptera: Psilidae), were used to test the hypothesis that native populations fluctuate less from year-to-year than those of introduced species, because the native species has had more time to adapt to temporal variability in its habitat than an introduced species. Variability in annual abundance was estimated for 33 years, and for 11-year or 16–17-year subsets of the 33-year time series. Temporal population variability was quantified as PV, a proportion between 0 and 1. The native carrot weevil had a PV of 0.39, less than that of the introduced carrot rust fly with a PV of 0.67, supporting the hypothesis. Generation 1 for both species showed a decline in PV over three decades consistent with the hypothesis that adaptation to variability in the habitat leads to lower PV. Over 33 years, the carrot weevil developed a second generation with a PV of 0.70, higher than that of the first generation, which is consistent with the hypothesis that adaptation is required to stabilise population dynamics in a new habitat, in this case a new temporally defined habitat.

Effect of intercropping carrot (Daucus carota L.) with two aromatic plants, coriander (Coriandrum sativum L.) and summer savory (Satureja hortensis L.), on the population density of select carrot pests

Intercropping, or the use of different aspects of the interaction between organisms in ecosystems, can be classified as an ecological method that limits harmful human interference in the environment, especially the consumption of chemicals. The impact of intercropping carrot with corianderCoriandrum sativumL. and summer savory Satureja hortensisL. on the occurrence of select carrot pests was estimated in the years 2010-2011. Intercropping had a significant effect on the decrease of the number of roots damaged by carrot rust flyPsila rosae.During harvest, the least number of damaged roots was observed in combination with summer savoryS. hortensisL. The number of carrot psyllidTrioza viridulaZett. and aphids on carrot leaves and roots damaged by nematodes was significantly lower on plots where carrot was intercropped. Intercropping both herbs had a positive influence on the number of beneficial insects. In all of the years of the study, the highest number of Coccinellidae and Syrphidae were observed on plots where carrot was intercropped with coriander.