Impact of an exotic parasitoid onPlutella xylostella(Lepidoptera: Plutellidae) population dynamics, damage and indigenous natural enemies in Kenya

Abstract

Diadegma semiclausum (Hellén) (Hymenoptera: lchneumonidae), an exotic diamondback moth parasitoid, was released in two pilot areas (Werugha in Coast Region and Tharuni in Central Province) in Kenya. Fifteen month before release, observations on the diamondback moth, Plutella xylostella (Linnaeus), and local natural enemy population dynamics and pest damage were initiated in both areas and continued for three years after release. The P. xylostella population was bimodal with higher records during dry seasons. At Werugha, the peak population of P. xylostella was 16.8 per plant (October 2001); at Tharuni it was 12.8 (February 2002). Populations at Werugha declined from three months after release and decreased from 5.4 per plant (before release) to 0.8 (year 3 after release). Concurrently, average damage (1.9 to 1.5) (on a 0-5 scale), proportion of attacked plants (72 to 31%) and proportion of plants in damage group >2 (plants with head damage) decreased (21.4 to 5.3%), while total parasitism increased from 14.4 (before) to 52.5% (year 3 after release, 90% due to D. semiclausum). At Tharuni, D. semiclausum was only recovered 3 months after release. Average populations of P. xylostella declined from 5.9 per plant (before release) to 2.4 (year 3 after release) and damage scores from 2.3 to 1.7. The proportion of plants in damage group >2 declined from 39.7 to 4.5% while overall parasitism increased from 4.2 to 40.6% (98.3% by D. semiclausum). Four species of indigenous parasitoids (Diadegma mollipla (Holmgren), Oomyzus sokolowskii (Kurdjumov), Apanteles sp. and Itoplectis sp., all primary parasitoids) were almost completely displaced by D. semiclausum. Possible reasons for the different parasitoid development between the two release areas and the displacement of the indigenous species are discussed.

Temperature-dependent phenology of Plutella xylostella (Lepidoptera: Plutellidae): Simulation and visualization of current and future distributions along the Eastern Afromontane

“…In the eastern Afromontane, cruciferous vegetables such as kale and cabbage are widely cultivated in diverse agroecologies spread along the altitudinal gradient, but DBM is a key constraint to productivity of these vegetables [33,57]. The growth and development of DBM are significantly influenced by the prevailing weather variables, especially temperature and rainfall, in the field [58]. Understanding the effects of changing climate on DBM biology and damage to crops is critical for adapting and implementing management strategies in the region.…”

Determinants of parasitoid assemblages of the diamondback moth, Plutella xylostella, in cabbage farmer fields in Senegal

“…O. sokolowskii is mainly distributed in areas of the Rift Valley and northern Ethiopia with relatively heavy insecticide use. In Kenya, DBM parasitoid fauna is dominated by Diadegma mollipla (Holmgren), Apanteles sp., C. vestalis, O. sokolowskii and Brachymeria species (L€ ohr et al, 2007;Kahuthia-Gathu et al, 2009). Releases of Diadegma semiclausum for highland brassica production in East Africa have been successful in Kenya, Uganda and parts of Tanzania (Gichini et al, 2008).…”

“…In Africa, the most common and effective larval parasitoids belong to three major genera, Apanteles, Cotesia (Braconidae) and Diadegma (Ichneumonidae) and pupal parasitoids belong to the genus Diadromus (Ichneumonidae) (Kfir, 2003). According to Lohr and Kfir (2004), diversity of the parasitoid fauna associated with P. xylostella in Africa is relatively poor.…”

Host–parasitoid population density prediction using artificial neural networks: diamondback moth and its natural enemies

“…The data were collected by the ICIPE DBM biocontrol team as described by Löhr et al (2007). Fifteen farmer‐managed cabbage farms were sampled at 2‐week intervals starting from 2 weeks after transplanting until harvest.…”