Behavioural responses in three ichneumonid pollen beetle parasitoids to volatiles emitted from different phenological stages of oilseed rape

Abstract

Pollen beetles ( Meligethes spp.; Coleoptera: Nitiduliae) are a major pest of oilseed rape, Brassica napus L. (Brassicaceae) in northern Europe. Phradis interstitialis Thomson, P. morionellus Holmgr., and Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) are among the most frequent pollen beetle parasitoids. These three species differ in temporal occurrence, as well as in preferred host stage. The behavioural responses of female parasitoids to odours from oilseed rape at bud and flowering stage were evaluated in two-choice experiments. The role of visual stimuli was examined by combining green and yellow colours with odour stimuli. All three species were attracted to odours from the bud stage of oilseed rape. Tersilochus heterocerus was attracted to odours of flowering rape, but the two Phradis species avoided the flower odours. However, when the odours of flowering rape were combined with yellow, and odours of the bud stage were combined with green, P. interstitialis was equally attracted to both stimuli, and T. heterocerus showed an increased preference for flower odours, while no effect of colours could be found in P. morionellus . The observed differences in responses between the parasitoids may reflect differences in their biology and may be involved in the niche segregation of these often coexisting species. The volatile blends released from the two phenological stages were identified and compared. Clearly, odours can be reliable cues for differentiating between oilseed rape in the bud and flowering stage. Of 20 identified compounds, 18 were released at a significantly higher rate from flowering plants. The terpenes sabinene, myrcene, limonene, and ( E , E )-α -farnesene were the dominant volatiles in the bud and flower headspace. A group of aromatic compounds including benzaldehyde, methyl benzoate, and phenyl acetaldehyde were mainly released from flowering rape.

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

“…Olfactometer studies found that the three main species of pollen beetle parasitoid were all attracted to volatiles from OSR in the bud stage; however, there was an interesting finding of niche separation between the three competing species as they each displayed preferences for volatiles from insect infestations at different stages of OSR development that corresponded to their preferred host growth stage (Jonsson et al 2005;Berger et al 2015). After landing on the host-plant, T. heterocerus female parasitoids have also been shown to be attracted to volatiles from their pollen beetle host larvae (Straka et al 2013;Berger et al 2015).…”

“…Ideally, this should be a 'dead-end' trap crop (Shelton and Badenes-Perez 2006) such as Raphanus sativus (L.) Domin (Veromann et al 2014). Biological control of the pollen beetles in the trap crop could be enhanced by attracting natural enemies using attractant lures based on host-plant volatiles (Jonsson et al 2005;Jöns-son and Anderson 2007) or volatiles from their host larvae (Straka et al 2013;Berger et al 2015), but this concept is still in the early research phase. As the push component, volatiles from lavender essential oil (Lavandula angustifolia) were found to be effective in deterring pollen beetles in laboratory bioassays (Mauchline et al 2005(Mauchline et al , 2008 and in both semi-field and field trials (Mauchline et al 2013).…”

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

“…Phradis interstitialis Thomson, Phradis morionellus Holmgr. and Tersilochus heterocerus Thomson are among the most frequent pollen beetle parasitoids (Jönsson et al, 2005). Among these three parasitoids, the parasitoid P. morionellus attacks larvae inside oilseed rape buds and flowers and also feeds on the flowers (Jönsson and Anderson, 2007 and references therein).…”

“…The attraction to the most effective unbaited yellow traps was enhanced 1.7-3.3 times with the addition of a lure comprising a mixture of allyl, 3-butenyl, 4-pentenyl and 2-phenylethyl isothiocyanate. Jönsson et al (2005) analysed behavioural responses in three ichneumonid pollen beetle (M. aeneus) parasitoids (P. interstitialis, P. morionellus and T . heterocerus) to volatiles emitted from different phenological stages of oilseed rape.…”

Niche separation of pollen beetle parasitoids

“…While earlier literature suggested that this happens by random walking, host finding can be better understood by the search for physical and chemical cues of host presence, under the assumption that a parasitoid using such cues would have a reproductive advantage over parasitoids that search randomly (Vinson, 1976;Casas, 2000). For pollen beetle parasitoids, there is evidence for the use of OSR odors and visual stimuli: Jönsson et al (2005) found that P. morionellus avoided odors of flowering OSR and was attracted to bud odors similarly to P. interstitialis, while T. heterocerus was attracted to flower stimuli. This suggests that P. morionellus and T. heterocerus differ more than was supposed by earlier workers, and that the host and plant stage preferences of these three related species deserve closer attention.…”