Bioactivity Of Citrus Peel Extracts From Citrus Unshiu Against Diamondback Moth, Plutella Xylostella L.

Laboratory studies were conducted to determine the efficacy of orange (Citrus unshiu Marcov.) peel extracts against adults and larvae of Plutella xylostella with three different solvents (ethanol, acetone and petroleum ether). The main results are as follows:(1)The extracting rate in ethanol was the largest (6.14% ), followed by petroleum ether and acetone, the difference in the rate, however, was not significant between the solvents. The method of extract need to be improved.(2)All three extracts presented strong oviposition deterent effect against the DMB adults. The order of oviposition deterrent effect was ethanol > acetone > petroleum ether. It is apparent that extracts was more effective in the choice test than in the non-choice test. The higher their concentrations were, the stronger ovipositions deterrent effect as. The total number of eggs laid by the DBM moths decreased on brassica plants with increase of high concentrations in non-choice test.(3)The extracts of acetone and petroleum ether had no effect to the hatching rate and egg development duration, but they were toxic to the newly hatched larvae of Plutella xylostella. The ethanol extract displayed high potentials of ovicidal action, hatching rate of eggs decreased significantly when the concentration increased from 31.25g/L to 500g/L. The ethanol extract of higher concentration significantly prolonged the eggs' development durations, and reduced the survival rate of the newly hatched larvae were survived.(4)The extracts of three solvents had stronger antifeedant activity towards 3rd-instar larvae of Plutella xylostella. In choice test, the medium antifeedant concentration (AFC50) against 3rd-instar larvae was 51.12g/L for ethanol extract, 96.63g/L for acetone extract and 121.45g/L for petroleum ether; under non-choice conditions, the AFC50 were 300.45g/L, 811.30g/L and 928.91g/L for ethanol, acetone and petroleum ether, respectively. The ethanol extract had a strong contacttoxicity, causing 45% mortality of Plutella xylostella at concentration of 500g/L, while both acetone extract and petroleum ether extract showed no contact toxicity activity. Although the larvae were fed on treatment leaf-disks at concentration of 500g/L for 4 days, no extract exhibited any evidence of stomach toxicity towards 3rd-instar larvae of Plutella xylostella, however, the pupae weight was significantly lower than that in the control. All extracts showed growth-inhibition effect against Plutella xylostella with a time dependent inhibition. The lower the larvae age were, the higher inhibited effect displayed.(5) When the adults were fed on the ethanol extract at concentration of 500g/L, the mortality rate of female and male were 33.3% and 53.3%, respectively, and no female laid eggs. No adult died at concentration of 31.25g/L, but the number of eggs laid were only a quarter of that in the control.