Effects of undersown clover on host‐plant selection by Thrips tabaci adults in leek

Abstract

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters -number of leaves and stem diameter -were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.

Associational Resistance and Associational Susceptibility: Having Right or Wrong Neighbors

“…Thus, competition between neighboring and focal plants may influence herbivory and the likelihood of AR or AS (Agrawal 2004, Agrawal et al 2006, Hambäck & Beckerman 2003. Competition-related changes in focal plants may include the quantity and/or quality of nutrients and antiherbivore defenses, or plant secondary metabolites used by specialists to find, accept, and initiate feeding R E (Bach 1980a;Gold et al 1990;Letourneau 1990Letourneau , 1995den Belder et al 2000), all of which may influence AR and AS. For example, focal milkweed (Asclepias syriaca) plants received up to 2.6 times the photosynthetically active radiation and 1.6 times the red to far-red ratio of light when neighboring grasses were clipped (to simulate herbivory) thereby reducing light competition (Agrawal & Van Zandt 2003).…”

The efficacy of intercropping with birdsfoot trefoil and summer savoury in reducing damage inflicted by onion thrips (Thrips tabaci, Thysanoptera, Thripidae) on four leek cultivars

“…To date, several studies have demonstrated the positive effect of different intercrops (especially from Fabaceae) on the reduction of leek damage due to onion thrips (den Belder et al 2000, Theunissen & Schelling 1996). In the current study, we determined, for the first time, the efficacy of two intercrops, birdsfoot trefoil (Lotus corniculatus) and summer savoury (Satureja hortensis), for reducing the damage caused by onion thrips on leek plants.…”

“…Although we must consider that the application of undersowing results in a loss of harvestable yield because of interspecies competition (Theunissen 1997, Theunissen & Schelling 1997, undersowing also results in a reduced need to remove weeds (Baumann et al 2000), improves the ground structure, and contributes to biodiversity. In the research that has been performed to date, the following different intercrops have been tested with leek or onion: orchard grass, lacy phacelia, buckwheat, white clover , subterranean clover (Theunissen & Schelling 1996, 1997, strawberry clover (den Belder et al 2000, Theunissen & Schelling 1998), and ryegrass (Müller-Schärer 1996. The highest reduction in onion thrips-induced damage was achieved by intercropping leek and white clover (Fabaceae).…”

The Importance and Management Option of Onion thrips, Thrips tabaci (L.) (Thysanoptera: Thripidae) in Ethiopia: A Review

“…Waiganjo et al [5] observed that intercropping snap bean with spider plant significantly reduced the population of spider mites on the former. Other intercropping systems which have significantly reduced thrips population and plant infestation include leek with clover [22]; leek with carrot, and clover with French bean [23].…”