Application of synthetic herbivore‐induced plant volatiles causes increased parasitism of herbivores in the field

Abstract

We previously reported that Cotesia vestalis (Hymenoptera, Braconidae), a parasitoid of diamondback moth (DBM) (Plutella xylostella; Lepidoptera, Plutellidae) larvae, was attracted to volatiles from crucifer plants infested by moth larvae kept in a desktop acrylic box, and that a blend of four DBM‐induced plant volatiles was responsible for this attraction. In this study, using a specially designed dispenser to release the four compounds, we demonstrated that the wasp was attracted to intact komatsuna plants (Brassica rapa var. perviridis). The experiments were performed in a climate‐controlled room, which was approximately 1000 times larger than the acrylic box used previously. Similarly, using the dispenser in the field, C. vestalis females were attracted to intact komatsuna plants with the dispenser from a distance of three metres. We also examined the effect of the volatile blend on the incidence of parasitism of DBM larvae in the field. Three small containers containing DBM‐infested komatsuna plants with dispensers, and three control containers containing only infested plants (control) were arranged in two lines running perpendicular to a komatsuna field in which both DBM larvae and C. vestalis populations were maintained, at distances of 12, 30 and 70 m. The results showed that the incidence of DBM parasitism was significantly higher in containers containing dispensers than in the control containers, suggesting that the blend could potentially be applied to DBM control in agroecosystems.

Uninfested plants and honey enhance the attractiveness of a volatile blend to a parasitoid Cotesia vestalis

“…The DBM and C. vestalis were reared as described by Uefune et al. (). Newly emerged adults of DBM and C. vestalis were maintained separately in acrylic cages (35 cm × 25 cm × 30 cm) and were provided with a 50% (v/v) honey solution as food in a climate‐controlled room (25 ± 3°C, 60 ± 10% relative humidity, 16L:8D) for 3–4 days to ensure mating.…”

“…The lid of the bottle contained a hole (diameter: 12 mm) through which a piece of polypropylene thread (diameter: 12 mm, length: 70 mm) was placed to facilitate the mixture's evaporation (Kugimiya, Uefune, Sano, & Takabayashi, ). The concentration used in this study was 0.01% based on our previous experiments under field conditions (Uefune et al., ). The amount of the TEC solution in one attractant bottle was 25 ml.…”

“…The two lines were 3 m apart. The distance between the boxes was determined based on our previous field experiment (Uefune et al., ). The release point (1 m high: positioned between the two lines) was 5 m downwind of the odour sources.…”

“…We identified attractive compounds emitted from DBM‐infested cabbage plants, which are a mixture of sabinene, n ‐heptanal, α‐pinene and ( Z )‐3‐hexenyl acetate (hereafter called the attractant) (Shiojiri et al., ). In addition, C. vestalis learned the attractant (Uefune et al., ).…”

Field Life-Tables and Key Mortality Factors of Plutella xylostella Infesting Sole and Onion Intercropped Cabbage

“…Bertolaccini et al, (2011) demonstrated that Diadegmainsulare and Oomyzussokolowskii were found to be the most successful parasitoids against P. xylostella. Cotesia vestalis was found attracted to blend of sabinene, n-heptanal, α-pinene, and (Z)-3 hexenyl acetate at ratios 1.8:1.3:2.0:3.0 (Uefune et al, 2012). In South Africa, it is the most efficient species often accounting for more than 80 % of total parasitism levels of P. xylostella (Nofemela, 2013;Bopape et al, 2014).…”