Behavioural and chemical ecology underlying the success of turnip rape (Brassica rapa) trap crops in protecting oilseed rape (Brassica napus) from the pollen beetle (Meligethes aeneus)

Abstract

Behavioural and chemical ecology underlying the success of turnip rape (Brassica rapa) trap crops in protecting oilseed rape (Brassica napus) from the pollen beetle (Meligethes aeneus) Abstract There is increasing interest in the use of trap crops as components of integrated pest management (IPM) strategies. Understanding the mechanisms underlying host plant preferences of herbivorous pests can lead to improved effectiveness and reliability of the trap crop. We investigated the behavioural and chemical ecology underlying the success of turnip rape, Brassica rapa, trap crops in protecting oilseed rape, Brassica napus, from the pollen beetle, Meligethes aeneus, which feeds in the flowers and lays its eggs in the buds causing yield loss. Using a semi-field arena bioassay, plant growth stage was found to be a major factor in the preference of this pest for B. rapa over B. napus. Plants at early-flowering growth stages were preferred over plants in the bud stage, irrespective of species. No preference was found when both species were flowering. As B. rapa develops faster than B. napus in the field, this could explain part of the mechanism of its success as a trap crop. However, B. rapa was preferred over B. napus when both species were in the bud stage, indicating some inherent preferences for B. rapa. Responses of M. aeneus in olfactometer tests to the odours of B. napus and B. rapa at the bud and flowering growth stages, reflected those of the semi-field arena bioassay. These behavioural responses can be explained by volatile compounds associated with the flowering stage. Phenylacetaldehyde, indole and (E,E)-a-farnesene were found to be present in air entrainment samples of both plant species at the flowering growth stage, but only in those of B. rapa at the bud stage. The former two compounds were behaviourally-active in olfactometer tests. These compounds are likely to be involved in host location by M. aeneus, and, at least partially, responsible for the attractiveness of B. rapa and its success as a trap crop to protect B. napus from this pest.

Development of a Statistical Crop Model to Explain the Relationship between Seed Yield and Phenotypic Diversity within the Brassica napus Genepool

“…The increased early flowering nature of lines with long flowering duration may also have increased the unwanted presence of pollen beetle pests (Meligethes spp. ), which are attracted by the visual and olfactory properties of oilseed rape flowers [63]. Thus, within the current field trial, the unopened buds on plants of those lines that flowered earlier may have been at increased risk from feeding damage than those on plants not yet flowering, especially if pollen resources were scarce due to high intraspecific competition, and this may partly explain why it did not afford a yield advantage to be flowering earlier or over a longer period.…”

Semiochemical-based alternatives to synthetic toxicant insecticides for pollen beetle management

“…Some of the semiochemicals responsible for this attraction have been identified. Brassicogethes aeneus was found to be attracted to general floral compounds such as phenylacetaldehyde and indole in the laboratory (Cook et al 2007c) and field (Smart and Blight 2000). Their ability to detect and respond to a large number of chemically diverse plant volatiles may be an adaptation related to its polyphagous nature at this early life stage (Smart and Blight 2000).…”

“…In laboratory tests, pollen beetles have been found to be attracted to volatiles from OSR in the bud stage (Evans and AllenWilliams 1994;Cook et al 2007c;Jönsson and Anderson 2007), at the flowering stage (Evans and Allen-Williams 1994;Cook et al 2002Cook et al , 2006b, to floral volatiles from the OSR flower or part of the flower (Charpentier 1985;Byers 1992;Cook et al 2002), as well as to pollen odour (Cook et al 2002). The chemical basis for this attraction has been tested in the laboratory using electrophysiological studies and the most active compounds include 2-phenylethyl-, 3-butenyl-and 4-pentenyl-isothiocyanate, phenlyacetaldehyde and indole (Cook et al 2007c). Such attraction has also been demonstrated in the field using baited traps (Smart et al 1993(Smart et al , 1995Cook et al 2013a).…”

“…In laboratory and field tests, pollen beetles showed a preference for turnip rape (Brassica rapa L.) over OSR (B. napus) (Büchi 1990;Cook et al 2004b;Čuljak et al 2016). The mechanism of action was investigated and found to be semiochemically mediated, at least in part, due to higher release rates of phenylacetaldehyde and indole in turnip rape, particularly in the bud stage, compared to OSR (Cook et al 2007c has the potential to develop repellents and deterrents for use IPM strategies for the pollen beetle. However, effective slow-release formulations for field applications are required along with a more detailed understanding of the chemistry in order to develop this strategy.…”

Defence mechanisms of Brassicaceae: implications for plant-insect interactions and potential for integrated pest management. A review

“…With this perspective, Cook et al (2007b) investigated the behavioural and chemical ecology underlying the success of turnip rape trap crops in protecting oilseed rape from the pollen beetle (M. aeneus), which feeds in the flowers and lays its eggs in the buds. Phenylacetaldehyde and (E,E) − α-farnesene were found to be present in air entrainment samples of both plant species at the flowering growth stage, but only in those of B. rapa at the bud stage.…”