| Plutella xylostella,diamondback moth (DBM) is one of the most major pests of cruciferous plants. We studied the effects of different concentrations of tomato extracts on diamondback moth larvae feeding acticity, and to study the relationship between the sensilla and DBM larvae feeding by paraffin section observation and scanning electron microscope(SEM). We figured out the distribution and types of sensilla of DBM larvae, which provide the basis for the electrophysiological study of DBM larvae, and the theoretical basis for the guidance of the comprehensive management of DBM larvae.The results were as follows:1 Effect of different parts of the tomato extract on DBM larvae feeding activityTomato stems, leaf extract all have significant antifeedant effect on DBM larvae feeding activity, the antifeedant rate increased with the increase of the concentration of the extracts, there were significant differences on antifeedant rate, time and function. On the 1st day, the antifeedant effect of tomato stem extracts on DBM larvae was higher than that of leaf at the concentration of 100mg/mL, the antifeedant rate reached 70.70%, while 50mg/mL antifeedant rate reached 51.17%, but on the 2nd day, antifeedant effect was the opposite, the leaf extract is greater than stems, the antifeedant rate reached 53.32% with leaf extract at 100mg/mL.2 Sensilla types and distribution of DBM larvaeThere were 7 types of sensilla of DBM larvae:sensilla basiconica, sensilla styloconica, sensilla chaetica, sensilla placodea, sensilla trichodea, sensilla digit and sensilla furcatea. In shape, sensilla trichodea can be divided into ST I and ST?; sensilla chaetica can be divided into SC I and SC?; sensilla furcatea can be divided into SF I andSF II, SF ?. Head is mainly distributed sensilla basiconica, sensilla styloconica, sensilla chaetica, sensilla digit, sensilla trichodea and sensilla furcatea, the same sensor distribution in different parts of the body were also different. Sensilla types of foot is single, mainly include sensilla chaetica, sensilla trichodea, and sensilla basiconica near the crochet. There were 2 types of sensors in the thorax and abdomen:sensilla placodea and sensilla trichodea.3 Effect of sensilla of DBM larvae on feeding amountUsing 5M HCl to remove the sensilla of head, thorax and abdomen, body of DBM larvae, we observed the changes of feeding behavior. The results showed that the feeding capacity of DBM larvae decreased after the treatment. When remove the sensilla of DBM larvae head, on the 1st day and the 2nd day after treatment feeding area were respectively:27.24±1.89mm~2,21.65±7.75mm~2, and feeding area of control group were:78.21±9.82mm~2?73.36±3.86mm~2; When remove the sensilla of DBM larvae thorax and abdomen, on the 1st day and the 2nd day of feeding area were respectively:30.03±8.71mm~2?27.84± 5.72mm~2, and feeding area of control group were:93.22±4.27mm~2?72.19±3.86mm~2. When remove the sensilla of DBM larvae body, on the 1st day and the 2nd day of feeding area were respectively:17.76± 4.61mm~2?N6.87±6.75mm~2, and feeding area of control group were:72.09±5.09mm~2?115.94±18.10mm~2. And after the removed, the feeding area of DBM larvae was not decreased with the increase of the concentration of the extract of the tomato.4 Effect of sensilla of DBM larvae on feeding selectivityAfter using 5M HCl to remove the sensilla of head, thorax and abdomen, body of DBM larvae,we found that the feeding selectivity was altered. After removal of sensilla of DBM larvae body, the ratio between the feeding area on the host leaf smeared with 25mg/mL of the tomato stem extracts and that on control changed to 2.31:1 on the 1st day, while it was 0.52:1 when lavae intact fed on the host leaf with the same concentration of the extracts.lt showed the treated larvae consumed much more leaf smeared with the extract which demonstrated antifeed activities previously. When only removal sensilla of head was ablated the ratio was 1.34:1. When removal of sensilla of both thorax and abdomen, and treated with 50mg/mL of the extracts, the ratio turned into 0.85:1, and decreased the antifeeding activity of the tomato extract. The effect of sensilla on feeding activity of the larva varied and it indicated the importance of sensilla on different part of the body. All sensilla play the role on feeding activity. The most important sensilla are on the head. Some sensilla on thorax and abdomen play roles as well. |
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