Bionomics of Tetranychus urticae Koch on Eggplants under Various Nitrogen Regimes in Controlled Environment

Development of T. urticae was studied on the leaves of eggplant grown in hydroponics with nitrogen contents of 5 mM, 10 mM, 30 mM, and 60 mM. As the nitrogen level in hydroponics increased, it also increased in the plant whereas that of K, Ca, and Mg decreased. More nitrogen in hydroponics resulted in increased contents of water and crude protein, and decreased ash, carbohydrates, and fibers within the plant. Biomass was the heaviest as 989.5 g at 10 mM and the lightest at 60 mM. Leaf thickness and the content of chlorophyll increased as the content of nitrogen increased. Laboratory leaf disc tests obtained from plants grown at various nitrogen levels revealed that feeding and oviposition preferences of T. urticae were high at 30 mM and low at 5 mM. Ratio of damaged leaf by naturally occurring T. urticae on eggplants of 99 days post-transplant in the greenhouse was the highest as 98% at 60 mM. Degrees of damage on eggplants with and without T. urticae infestation turned up more as the differences in the levels of nitrogen in the hydroponics get bigger. No definite differences in the rate of T. urticae development was found between nitrogen treatment levels but, mortalities in immature stages dropped as the nitrogen levels went up. Adult longevity was the longest of 11.9 for female and 6.9 days for male at 60 mM. Oviposition period was also the longest as 11.7 days at 60 mM and shortened as the level of nitrogen decreased. The number of eggs oviposited was the most as 144.4 at 60 mM while it was the least as 41.0 at 5 mM. Sex ratio was 0.75 in favor of female at 10 mM. $R_o$ and T increased, no trends were detected in $r_m\;and\;{\lambda}$, while Dt decreased as the levels of nitrogen went up.

시설 재배 가지에서 질소 시비 수준에 따른 점박이응애의 생물적 특성

질소를 5, 10, 30, 60 mM 수준으로 재배한 가지잎을 먹이로 점박이응애의 발육을 조사하였다. 질소 시비수준이 증가함에 따라 식물체내 N함량은 증가하였으나 K, Ca, Mg는 감소하였으며, 수분함량과 조단백질은 증가하였지만 회분, 탄수화물, 섬유소등은 감소하였다. 질소 시비수준에 따른 수량은 10 mM처리에서 주당 989.5 g으로 가장 많았고, 60 mM처리에서 가장 적었다. 잎 두께와 엽록소함량은 질소함량이 증가할수록 증가하였다. 엽편에서 실내실험 결과 식이선호성과 산란선호성은 30 mM처리에서 높았고, 5 mM처리에서 낮았다. 온실에서 정식 99일 후 자연 발생되는 점박이응애의 피해엽률은 60 mM에서 98%로 가장 높았고 방제구와 피해구의 생육은 질소농도가 높을수록 차이가 커졌다. 점박이응애의 발육은 처리 간에 경향을 찾을 수가 없었으나 엽내 질소함량이 높을수록 각 영기별 사망률은 낮아졌다. 성충의 수명은 질소함량이 높은 60 mM처리에서 암수 각각 11.9일, 6.9일로 길었다. 산란기간도, 60 mM처리에서 11.7일로 가장 길고 질소함량이 낮아질수록 짧아졌다. 산란 수는 질소함량이 높은 60 mM처리에서 144.4개로 가장 많았고, 5 mM처리에서 41.0개로 가장 적었다. 성비는 10 mM처리에서 0.75로 암컷의 비율이 높았다. $R_o$와 T는 질소수준이 높을수록 증가하였고, $r_m$과 $\lambda$는 처리 간에 경향이 없었으며, DT는 감소하였다.