Abstract
The development of integrated pest management strategies becomes more and more pressing in view of potential harmful effects of synthetic pesticides on the environment and human health. A promising alternative strategy against Delia radicum is the use of trap crops. Chinese cabbage (Brassica rapa subsp. pekinensis and subsp. chinensis) is a highly sensitive Brassicaceae species previously identified as a good candidate to attract the cabbage root fly away from other crops. Here, we carried out multi-choice experiments both in the laboratory and in field conditions to measure the oviposition susceptibilities of different subspecies and cultivars of Chinese cabbages as compared to a broccoli reference. We found large differences among subspecies and cultivars of the Chinese cabbage, which received three to eleven times more eggs than the broccoli reference in field conditions. In laboratory conditions, the chinensis subspecies did not receive more eggs than the broccoli reference. We conclude that D. radicum largely prefers to lay eggs on the pekinensis subspecies of Chinese cabbage compared to the chinensis subspecies or broccoli. Some pekinensis cultivars, which received over ten times more eggs than broccoli in the field, appear especially promising candidates to further develop trap crop strategies against the cabbage root fly.
Highlights
Phytophagous insects vary considerably both in their host range and selectivity within that host range and must face numerous choices in the different stages leading to host acceptance [1,2,3]
Our results showed a significantly higher oviposition on pekinensis, which could suggest a preference of D. radicum females for plants with low GSL content
Even the best hosts in the device might not have stimulated enough some gravid females with low oviposition pressure, in particular because the plants were small. This point is crucial and will have to be elucidated for the development of an efficient trap crop since such a plant must be capable of eliciting egg deposition in most females approaching the crop, including those that have only a moderate oviposition pressure. Both our laboratory and field results confirm that in a choice situation, many more D. radicum eggs will be laid on Chinese cabbage subsp. pekinensis than on broccoli
Summary
Phytophagous insects vary considerably both in their host range and selectivity within that host range and must face numerous choices in the different stages leading to host acceptance [1,2,3]. It has long been known that D. radicum prefers some cultivated hosts to others [28,29] with an especially strong preference for Chinese cabbage (Brassica rapa L.) [30] This plant has been proposed as a good trap crop candidate [31] and has more recently been used in two field studies aimed at developing a push-pull strategy to protect broccoli crops against this pest [32,33]. These studies only tested a single Chinese cabbage cultivar among many, so the relative efficiency of diverse Chinese cabbage cultivars as D. radicum trap crops remains to be explored. Cultivars were compared in multi-choice experiments in which all cultivars were present simultaneously, both in the laboratory (where the number of D. radicum females released was controlled) and in the field under natural infestation conditions
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