Bioactivities Of Orange Peel Extracts Against The Several Important Insect Pests Of Cruciferous Vegetable

The activities of peel ethanol extracts from Citrus unshiu on the major cruciferous insect pests, Spodoptera litura Fab., Spodoptera exigua Hubner, Pieris rapae L. and Myzus persicae Sulzer were preliminary investigated in laboratory. The results are summarized as follows:1. Activities of orange peel extracts against the 2nd larvae of 5. litura and S. exigua were tested by measuring antifeedant index, their body weight gains and larval mortality after the larvae fed on the extracts coated on cabbage leaves. The results indicated that the cabbage leaf consumptions and body weight gains were both reduced, and the larval mortality was increased when the larvae fed on the leaves coated with the extracts. The higher the concentration, the more obviously the effect on the pests was. The larval mortality of S. exigua was higher than that of S. litura at the same extract concentration. Both the median inhibitory concentration (IC50) and the median antifeedant concentration (AFC50) in the non-choice test for S.exigua were lower than those for S. litura. However, the AFC50 in the choice test was higher for S. exigua than for S. litura. These results in generally suggested that the bioactivities of peel ethanol extracts from C. uushiu against S. exigua is better than against S. litura.2. The peels extracts from C. unshiu had obvious oviposition deterrent, ovicidal, antifeedent, stomach toxic and growth inhibition activity on P. rapae larvae. The median concentration of oviposition deterrent at 24h were 49.77 g.L-1 and 79.23 g.L-1 in the choice and non-choice tests, respectively, with a high rate of > 95% at extract concentration of 500 g.L-1. By dipping the eggs directly into the extracts, we found that the extrats could effectively reduce the percentage of eggs hatched and the survival rate of newly-hatched larvae. Regression equations and IC50 of log concentration-dependent ovicidal probit of the orange peel extracts against the eggs were y=1.1342x+2.1783 (r=0.9685) and LC50=307.30 g.L-1. The mortality increased with increase of the extracts concentration and decreased with age of eggs at dip. However, no differences in mortality between ages of eggs had been found. In the antifeedent experiment with 2nd instar larvae, antifeedent efficiencies ofextract at 500 g.L-1 were all above 90% at 24h and 48h after feeding respectively. For the 2nd instar larvae, AFC50 of the extracts were 46.85 g.L-1 and 70.43 g.L-1 at 24h, and 21.07 g.L-1 and 72.70 g.L-1 at 48h after feeding in choice and non-choice tests. In the stomach toxicity test, over 90% 2nd larvae were killed 3d after treatment at concentration of 500 g.L-1, it was 4.64 times higher than at the control. LC50 of the extract as stomach poison were 91.31 g.L-1 and 58.70 g.L-1 at 3d and 5d after treatment, suggesting that the extracts possessed high effection against the P. rapae larvae in 2nd instar.3. The bioassays of orange peel extracts against the M. persicae in laboratory were carried out, the extracts had a powerful contact toxicity and antifeedent activity on aphis. In contact toxicity test, a time-dose-mortality model was used for analyzing the variation of mortality as affected by both time and dosage. The results showed that the higher the concentration of extracts applied on aphis, the higher mortality was, and the shorter the median lethal time was. The extracts had strong antifeedant activity to 2nd instar nymph, inhibition of feeding reached 93.62% at concentration of 500 g.L-1 after 12h. It would decreased with time and dosage. The medium antifeeding concentration (AFC50) were 124.99g.L-1, 160.81 g.L-1 and 157.62 g.L-1 at 12h, 24h and 48h after treatment, respectively. Life span of adult was shortened and fertility dropped when they were reared on the extract treated leaves. At concentration 500 g.L-1, the fertility was only 52.45% and the life span was only 70.86% of that in the control. Aphid population was inhibited when reared on the treated cabbages also, rates of inhibition offspring varied from 19.43% to 58.02% depended on concentratio...