Feeding preferences of Phyllotreta herbivores to winter rape and chosen weeds

Abstract

In model experiments with leaf disks from Brassica napus L. subsp. napus and thlaspi arvense L. and Sinapis arvensis L. in spring periods (May-June) of 2006-2007 feeding preferences of Phyllotreta herbivores to the above-mentioned crop and two common weeds were investigated. In seedlings of identical ontogenetic stages insignificantly higher feeding injuries were recorded in B. napus. Between the two monitored weeds insignificantly higher herbivory was found in S. arvensis compared to t. arvense. In a comparison of older crop and younger weeds and vice versa, flea beetles significantly preferred the four-leaf seedling stage to the cotyledon seedling stage irrespective of the monitored plant species. Though generally in feeding preference of flea beetles a general drift B. napus > S. arvensis > t. arvensis was recorded, the sequence of leaves also played its role under conditions of this experiment.Keywords: feeding preference; crop; weeds; Brassicaceae; herbivory; Phyllotreta spp.; model experiments Recently, the role of injurious pests in agroecosystems has been re-evaluated, both of entomofauna and weeds, aimed to maintain the high level of biodiversity in agroecosystems.It is known that a subcritical amount of weeds increases the level of biodiversity and favourably influences the occurrence of pest antagonists.In this context the importance of weeds for pests themselves is evaluated less frequently, or the importance of another crop by way of "trap of pests" (Trdan et al. 2005) or biostrips (Lethmayer et al. 1997) in order to eliminate or compensate negative impacts of pests on the crop.Just from this point of view this paper is based on the question if some weeds could be preferred by herbivores. Considering the opinion that oilseed crops and cruciferous vegetables are of high economic importance and that cruciferous plants are ideal for biological studies as their chemistry is well understood and they support pest species from a wide range of insects (Finch & Collier 2000) the species of the genus Phyllotreta and family Brassicaceae were used in this study for model experiments.Feeding preferences of Phyllotreta spp. between (Brassica napus L. subsp. napus) -crop and (thlaspi arvense L.) and (Sinapis arvensis L.) -common weeds were investigated. MATERIAL AND METHODSModel experiments were conducted in the Crop Research Institute at Prague-Ruzyně in spring periods of 2006-2007.