| Some plants have defence mechanisms that help avoid damage caused by insect feeding or oviposition. It has been documented that intercropping with tomato (Lycopersicon esculentum) can suppress populations of the key insect pests in cauliflower fields. This study selected tomato as a repellent plant and cauliflower (Brassica oleracea) as a host plant. The study was conducted in a provincial standard demonstration site located in Minqing County of central Fujian (26°10’41"N, 118°48’10"E). The experiment was designed with a ratio of 0%,10%,30% and 50% of tomato intercropped in cauliflower-based fields, using a randomized-block design. It aimed to find the optimal ratio of intercropped tomato with cauliflower to promote biocontrol in the fields. In the laboratory, the effect of tomato volatiles on the oviposition of Plutella xylostella were also examined. The behavioral responses of P. xylostella to tomato volatile compounds were measured by the Y-shaped olfactometer. Finally, the electroantennogram (EAG) and Y-shaped olfactometer were used to examine the behavioral responses of P. xylostella to selected compounds to screen the active substances. The main results were as follows:(1) The results of intercropping showed that the number of Lipaphis erysimi Kaltenbach were significantly suppressed in the intercropping fields and the inhibitory efficacy increased with the intercropping ratio (0%< 10%< 30%< 50%). During the peak period of L. erysimi, the 30% and 50% intercropping treatment could both similarly significantly reduce the number of L. erysimi. These two treatments also similarly reduced the populations of Phyllotreta striolata. Intercropping with tomato had no effects on the population of Pieris rapae. For natural enemies, the number of Cotesia plutellae in the cauliflower field and the ratios of C. plutellae to Plutella xylostella increased in intercropped fields compared to monoculture. There were no significant differences among the three intercropped fields. Intercropping with tomato had no effect on spiders.(2) The oviposition of P. xylostella was monitored and showed that there was no significant difference among treatments (F=1.212, df1=5, df2=54, P=0.316), suggesting that tomato volatiles had no oviposition inhibition effect on P. xylostella. Tomato volatiles had significant repellent effects on female moths (t=-6.635, df= 5, P=0.001) and male moths (t=-2.298, df=5, P=0.033) in the Y-shaped olfactormeter.(3) The EAG responses of P. xylostella to selected compounds at different concentrations were measured. For the same volatile, the EAG responses were enhanced with increasing concentrations. Male moths were observed to have stronger EAG responses to 1 μL/mL β-caryophyllene,1μL/mL 6-methy-5-hepten-2-one,10 μL/mL 6-methy-5-hepten-2-one,100 μL/mL (Z)-3-hexen-l-ol,100 μL/mL (R)-(+)-limonene,100 μL/mL 6-methy-5-hepten-2-one than female moths. Female moths had stronger EAG responses to 1 μL/mL a-pinene than male moths. The EAG responses of other substances had no significant differences between genders. At the same concentration, P. xylostella responded more intensely to hexanal, (Z)-3-hexen-l-ol,6-methy-5-hepten-2-one, methyl salicylate than to other substances. In general, moths showed strong EAG responses to most volatiles of middle or high concentrations and almost no response to volatiles of low concentrations. For the blends, male moths were observed to have stronger EAG responses to blends 1,2,3 and 5 than female moths. Blends 1,3,5, and 6 produced strong EAG responses in P. xylostella with relative EAG values greater than 150%.(4) The behavioral responses of P. xylostella to 10 volatile compounds and 6 blends of these compounds were tested in the Y-shaped olfactometer. The results showed that difference of both substance and concentration could cause different behavioural responses of P. xylostella. Among the different volatile compounds, 6-methy-5-hepten-2-one had a repellent effect on female moths and (Z)-3-hexen-1-ol had a repellent effect on male moths at the concentration of 1 μL/mL. 6-methy-5-hepten-2-on, hexanal, (Z)-3-hexen-l-ol, a-phellandrene and methyl salicylate acted as repellents to female moths and a-pinene, (Z)-3-hexen-1-ol, hexanal, 6-methy-5-hepten-2-one acted as repellents to male moths at the concentration of 10 μL/mL. At a concentration of 100 μL/mL, hexadecane attracted P. xylostella, and a-phellandrene, α-pinene, (R)-(+)-limonene,6-methy-5-hepten-2-on and (Z)-3-hexen-1-ol repelled the moth, while hexanal and β-caryophyllene only repelled male moths. In general, moths showed strong responses to most volatiles of high concentrations and almost no response to volatiles of low concentrations. Among the tested blends, blends 4,5, and 6 had repellent effects on P. xylostella, while blends 2 and 3 had repellent effects only on male moths. Among all repellent substances, the repellent ratios of blends 3 and 6 to male moths were significantly higher than hexanal and blend 2, and the repellent ratios to female moths had no significant differences. |
PDF Full Text Request