Selection of effective species/strains of Trichogramma (Hym., Trichogrammatidae) to control the diamondback moth Plutella xylostella L. (Lep., Plutellidae)
1993
Wuehrer, B.G. (Federal Biological Research Center for Agriculture and Forestry, Darmstadt (Germany). Inst. of Biological Plant Protection) | Hassan, S.A.
The diamondback moth Plutella xylostella has developed resistance to most insecticides in many tropical and subtropical countries. This is caused by the short lifecycle and overlapping generations of this pest. Egg parasites of the genus Trichogramma are known to be important natural enemies of this insect pest. In this work, 47 strains of Trichogramma and 2 strains of Trichogrammatoidea were tested in the laboratory for their ability to attack P. xylostella. In the test, a single parasite female was offered the choice between eggs of the target pest P. xylostella and eggs of the mass rearing host Sitotroga cerealella. The preference was determined by observing contacts of the parasite with the host eggs and assessing parasitism. All strains accepted eggs of the diamondback moth, but they varied greatly in their preference for the pest. T'oidea bactrae, T. chilonis and T. pintoi had the highest egg laying capacity. The average number of eggs layed per female was 40.5, 44.9 and 41.1 respectively. The three parasite species showed a strong preference for diamondback moth eggs. The ratio of parasitized Plutella to Sitotroga eggs was: 34.4 to 6.1, 32.8 to 12.1 and 32.0 to 9.1 respectively. The ratio of contacts with Plutella and Sitotroga eggs was: 2.6 to 0.2, 1.5 to 0.7 and 3.5 to 0.3 respectively. T. ostriniae had a slightly lower egg laying capacity than the other three species (26.9 eggs per female), but a strong preference for P. xylostella (parasitism: 19.6 to 7.3 and contacts: 2.8 to 0.2). In cage experiments the three species of T'oidea bactrae, T. chilonis and T. ostriniae were also found to have a high searching capacity for P. xylostella eggs on cabbage plants. T. pretiosum had a high egg laying capacity (53.7/female), but showed no preference in parasitism (28.2 to 25.5)
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