Role ofDiadegma semiclausum(Hymenoptera: Ichneumonidae) in controllingPlutella xylostella(Lepidoptera: Plutellidae): Cage exclusion experiments and direct observation

Abstract

We evaluated the role of the larval parasitoid, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), in controlling Plutella xylostella (L.) (Lepidoptera: Plutellidae) by cage exclusion experiments and direct field observation during the winter season in southern Queensland, Australia. The cage exclusion experiment involved uncaged, open cage and closed cage treatments. A higher percentage (54 Á/83%) of P. xylostella larvae on sentinel plants were lost in the uncaged treatment than the closed (4 Á/9%) or open cage treatments (11Á/29%). Of the larvae that remained in the uncaged treatment, 72 Á/94% were parasitized by D. semiclausum, much higher than that in the open cage treatment (8 Á/37% in first trial, and 38 Á/63% in second trial). Direct observations showed a significant aggregation response of the field D. semiclausum populations to high host density plants in an experimental plot and to high host density plots that were artificially set-up near to the parasitoid source fields. The degree of aggregation varied in response to habitat quality of the parasitoid source field and scales of the manipulated host patches. As a result, density-dependence in the pattern of parasitism may depend on the relative degree of aggregation of the parasitoid population at a particular scale. A high degree of aggregation seems to be necessary to generate density-dependent parasitism by D. semiclausum. Integration of the cage exclusion experiment and direct observation demonstrated the active and dominant role of this parasitoid in controlling P. xylostella in the winter season. A biologically based IPM strategy, which incorporates the use of D. semiclausum with Bt, is suggested for the management of P. xylostella in seasons or regions with a mild temperature.

Interspecific competition between Diadegma semiclausum Hellen and Diadegma mollipla (Holmgren), parasitoids of the diamondback moth, Plutella xylostella (L), feeding on a new host plant

“…We, therefore, assumed that the former species could find its niche on snowpea, whereas D. semiclausum remained predominant on cabbage. Wang et al (2004) reported that an increase in host density led to aggregation of D. semiclausum adults in the field, but density-dependant increase of parasitism rates was not observed. Later, this result was confirmed to occur in the field (Momanyi et al, 2006;Rossbach et al, 2006b;Lö hr et al, 2007).…”

Population dynamics and management of diamondback moth (Plutella xylostella) in China: the relative contributions of climate, natural enemies and cropping patterns

“…Parasitism increases with L2–L3 density. Parameters for the parasitoid were taken from Dosdall et al (2012), Wang et al (2004), and Soufbaf et al (2014).…”

Insecticidal selectivity of jayanti plant (Sesbania sesban) for integrated control of diamondback moth (Plutella xylostella)

“…Based on the LC50 on P. xylostella and D. semiclausum, the value of insecticidal selectivity (IS) can then be determined by using the formula accoording to Wang et al (2004) …”