Niche separation of pollen beetle parasitoids

Abstract

Species with similar resource requirements are commonly assumed to competitively exclude each other, unless they differentiate their ecological niches. Hence, parasitoid wasps that use the same host species need to find some way to avoid competition. The aim of this study was to identify the role of volatile cues from oilseed rape plants and the larval host in niche separation between three coexisting parasitoid species. We examined how Phradis interstitialis, Phradis morionellus and Tersilochus heterocerus, sympatric parasitoids of Brassicogethes aeneus, differ in their abundances, distribution on buds and flowers, and oviposition behavior in the field. Furthermore, we tested their preferences for odors from uninfested and infested oilseed rape plants in the bud and flowering stage, and their preferences for odors from three developmental stages of pollen beetle larvae in a two-choice olfactometer bioassay. P. interstitialis was active in the field early in the season, preferred odors of infested buds vs. uninfested, and oviposited into buds which contained only pollen beetle eggs, while P. morionellus was active late in the season, preferred odors of infested buds as well as odors of infested flowers over uninfested, and oviposited into buds which contained only larvae. T. heterocerus was active throughout the season, and preferred odors of infested flowers over uninfested. Neither Phradis species were attracted to larval odors, whereas T. heterocerus was attracted to odors from first-instar pollen beetle larvae both in the absence of plant odors, and when presented simultaneously with uninfested plant odor. This suggests that the two Phradis species are separated on a temporal scale and that they parasitize different host stages, while the larval parasitoids P. morionellus and T. heterocerus are separated by choice of microhabitat. The former oviposits into larvae in buds, and the latter in flowers.

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

“…Additionally, several species of specialist parasitic wasp attack the larvae of pollen beetles, including Phradis interstitialis (Thomson), Phradis morionellus (Holmgren) and Tersilochus heterocerus (Thomson) which can have a significant impact on pollen beetle control (reviewed by Ulber et al (2010) and Williams and Cook (2010)). There is evidence that semiochemicals mediate prey location (Williams et al 2007b;Berger et al 2015). Exploiting the current knowledge of the semiochemistry of host location by parasitoids could enhance biocontrol of pollen beetles within an IPM system as this has been already been achieved for aphid species in arable cropping systems (Du et al 1998;Powell and Pickett 2003).…”

“…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).…”

“…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). The volatiles released at a significantly higher rate from infested rape that were shown to be detected by P. morionellus antennae in electrophysiological studies were (Z)-3-hexenylacetate, (Z)-3-hexenol, 3-butenyl isothiocyanate and (E,E)-α-farnesene (Jönsson and Anderson 2007).…”

“…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).…”

Landscape configuration affects herbivore–parasitoid communities in oilseed rape

“…We found that the incidence of P. morionellus in OSR fields was supported by forest proximity, while the opposite was found for its sibling species P. interstitialis . This may add an additional dimension to the niche separation between these two Phradis species (Berger et al 2015 ). Both are parasitoids of the rape pollen beetle.…”