Location: Pest Management Research Unit
Title: Progressive suppression of key Brassica napus L. volatiles after pollination by pollen-feeding Meligethes aeneus F. Authors
|Piesik, Darius -|
|Wenda-Piesik, Anna -|
|Sendel, Sebastian -|
|Tabaka, Piotr -|
|Buszewski, Boguslaw -|
Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 5, 2013
Publication Date: N/A
Interpretive Summary: Some plants have insect pollinators at one life stage (e.g., adult) that often also feed on the plant at a different life stage (e.g., larva). Thus, such plants face the challenge of attracting an adult insect with visual and chemical cues to pollinate the plant, but then not attract the same insect after pollination to avoid receiving eggs that will hatch and feed on the plant. We examined volatile compound emission from flowers of rape oilseed plants, which can attract a beetle (major European pest of rape oilseed) that pollinates flowers but adults and larvae feed on pollen and nectar to cause yield losses; dose responses of beetle adults to single key volatile compounds involved with floral attractiveness were also assayed. Pollinated plants had progressive suppression of three major floral volatiles (lilac aldehydes A & B, verberone) involved with beetle attraction, so that by 3 days following pollination the levels of these floral volatiles were reduced by 50-90% compared to control plants. More minor volatile compounds were suppressed to a smaller degree, and one volatile compound was transiently induced in pollinated plants. Adult beetles had dose responses that showed attraction to each of three volatiles (lilac aldehydes A & B, and verberone) singly at doses at or greater than levels released by rape oilseed flowers, but were repelled at doses much greater than that released by single plants. Thus, the volatile suppression after pollination of rape oilseed flowers by this beetle allows a rape oilseed plant to benefit from floral pollination, but may reduce the likelihood of attracting the beetle pest for future feeding that leads to yield loss.
Technical Abstract: Insect pollination and pollen-feeding can reduce plant volatile emissions and future insect floral attraction, with oviposition having different effects. Meligethes aeneus F. (Coleoptera: Nitidulidae), is a pollen-feeding pest beetle of oilseed rape, Brassica napus L. (Brassicaceae). We measured plant VOC emission over 72 hr from two types of 24 hr M. aeneus exposure to B. napus: pollen-feeding vs. flower bud injury and oviposition. The most abundant constitutive volatile organic compounds (VOCs), lilac aldehydes A (LA A) & B (LA B) and veratrole (VER), had 30-40% reductions from M. aeneus pollen-feeding exposure at 24 hr and 50-90% reductions by 72 hr, with greater reductions after bud injury and oviposition. Linalool (LIN), a common herbivore-induced plant volatile (HIPV), emission did not change at 24 hr, but was induced 6- to 7-fold 48 hr after both exposure treatments. By 72 hr, LIN had even greater (10-fold) induction after bud injury and oviposition, but no induction from pollen-feeding. Three common HIPVs (ß-caryophyllene, = ßCAR (E)-ß-farnesene = EßFAR, and (Z)-ß-ocimene = ZßOCI) were progressively induced up to 2.5-fold 72 hr after floral bud injury and oviposition. We assayed M. aeneus adult behavioral responses to LA A and B, and VER. Both M. aeneus sexes were attracted to higher concentrations than single plant constitutive emission for these VOCs, but avoided much higher doses. Progressive LA A and B, and VER, emission reductions might help plants (e.g., B. napus) to avoid future interactions with pollen-feeding pest herbivores (e.g., M. aeneus). After bud injury and oviposition, HIPV induction could help plants deter future oviposition and/or attract natural enemies to deposited eggs.