A study on the searching efficiency of Trichogramma brassicae Bezd. at three thermal regimes
2010
Pezeshk, R. | Shirazi, J. | Attaran, M. R. | Shojaee, M.
The quality of augmented natural enemies secures the success of biological control programmes. Meanwhile, the host searching capability of the released biocontrol agents and parasitism/predation rates have been used as an important factor to evaluate the quality as well as the field performance of biocontrol agents. For a decade, Trichogramma brassicae has been mass produced and released with a fixed rate of 1 g/ha against different generations of Ostrinia nubilais in corn. As corn is considered a rapid growing plant and its surface increases drastically across the season, it is assumed that wasp performance would be limited by its searching capacity. Therefore, a study was taken up to measure the searching efficiency of T. brassicae at 20, 25 and 30±1 °C but all at 60±10% RH and 16:8 h L:D. Seven arenas (84, 168, 238, 1112, 2500, 3681 and 5000 cm2 in 15 replications) were prepared using glass plates. About 150 fresh Sitioroga cerealella eggs on a piece of paper (0.5×0.5 cm) was placed in one corner of an arena and a mated 0-24 h old female T. brassicae was released on the opposite orthogonal corner. Very soon, another glass plate with similar size was placed over the prepared plate keeping about 1-1.5 mm distance between them by fitting plastic gutters on 4 sides of both plates. Then, they were tightened by metal clips and kept at mentioned conditions. After 48 h, the egg masses were removed and incubated separately. Four-5 days later, they were examined and egg cards with one or more blackened eggs (parasitized) revealed the successful searched arena by the wasp. The linear regression equations obtained by arcsine transformed data showed that as the arena increased the proportion of discovered hosts decreased significantly at all temperatures. The equations at 20, 25 and 30 were Y=49.20-0.0047X (R2=0.83), Y=53.17-0.0046X (R2=0.70) and Y=49.70-0.0028X (R2=0.78). A discussion on the applied aspects of the findings is presented.
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