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Selectiveness of Cnaphalocrocis medinalis to Host Plants
Rice Science, 2012, 19(1): 4954 Copyright © 2012, China National Rice Research Institute Published by Elsevier BV. All rights reserved
Selectiveness of Cnaphalocrocis medinalis to Host Plants LIU Fang, CHENG Jian-jun, JIANG Tao, SU Wen, XU Shuai (College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China) Abstract: A field experiment was conducted to study the selectiveness of Cnaphalocrocis medinalis Güenée (commonly known as the rice leaffolder or rice leafroller) towards five rice varieties (Yangfujing 8, Yangdao 6, Shanyou 136, Huaidao 9 and Ningjing 1) and three weed species (Echinochloa crusgalli, Leptochloa chinensis and Leersia hexandra). The results showed that the rice varieties carried significantly higher numbers of C. medinalis moths and eggs than the weed species. Among the rice varieties, Yangfujing 8 was associated with a higher moth number. However, there was little difference in the number of C. medinalis eggs among the rice varieties. Additionally, a laboratory experiment was performed to investigate the olfactory response of female C. medinalis towards volatile compounds from different rice varieties, as well as its oviposition preference towards these rice varieties. The volatiles of Yangfujing 8, Yangdao 6 and Shanyou 136 attracted C. medinalis similarly to those of TN1. In contrast, the volatiles of Huaidao 9 and Ningjing 1 clearly deterred C. medinalis. Nevertheless, C. medinalis did not exhibit clear oviposition preference towards any of the five tested rice varieties. Key words: Cnaphalocrocis medinalis; host selection; host plant; rice variety; weed species
The rice leaffolder, Cnaphalocrocis medinalis Güenée (Lepidoptera: Pyralidae) is a migratory pest that damages rice throughout southeast and northeast Asia (Ding and Su, 2002). In the past, this insect only posed problems occasionally and at local scales. But since 1970, it has become a frequent occurrence pest (Zhu et al, 2000). In recent years, a series of major outbreaks of C. medinalis has been persisted in paddy fields of Jiangsu Province, China, causing a severe threat to rice production (Yang et al, 2004). The larvae of C. medinalis feed on young rice leaves during the tillering stage or on flag leaves during the booting to heading stage. Although the injured plants have a considerable repair capacity during the tillering stage, this may still result in great yield losses during the late growth stage of rice (Fabellar et al, 1994). In years when there is an outbreak of C. medinalis, severely infested fields reach 30%80% yield reduction (Kushwaha, 1988). C. medinalis has a broad host range, including graminaceous crops of rice, corn, sugarcane, wheat and sorghum, as well as some graminaceous weed species (Joshi et al, 1987; Khan et al, 1996), among which rice is the most preferred host (Yadava et al, 1972; Khan et al, 1988). The volatiles from rice plants significantly affected the behavior of C. medinalis. Leaffolder moths laid significantly fewer eggs on TN1 plants treated with distillate extracts from two wild resistant rice species, Oryza officinalis and O. punctata, than on TN1 plants treated with distillate extracts from resistant cultivated rice (Velusamy et al, 1990). Received: 18 February 2011; Accepted: 5 May 2011 Corresponding author: LIU Fang ([email protected])
Ramachandran et al (1990) determined the olfactory response of C. medinalis towards 91 volatile compounds of plant origin using electroantennograms (EAGs) and discovered that both female and male moths displayed a strong EAG response towards green leaf odor. Male moths showed a higher response than females towards saturated and unsaturated aliphatic aldehydes, whereas female adults exhibited a significantly stronger olfactory response towards five components: terpinen-4-ol, carveol, dihydrocarveol, (-)-myrtenal and peritlaldehyde. It has been reported that the commercial rice varieties in Jiangsu Province, China exhibited considerable variation in resistance to C. medinalis and the resistance is closely related to the contents of reducing sugars, silicon and wax in rice plants (Xu et al, 2007; Wang et al, 2008). Nevertheless, it remains unknown whether the resistance mechanisms of the current commercially used resistant varieties are associated with volatile chemicals found in rice. This study examined the selectiveness of C. medinalis towards different host plants, thus providing a reference for explaining the resistance mechanisms of resistant varieties, as well as offering a basis for behavioral control of this pest.
MATERIALS AND METHODS Host plants The host plants in the field experiment included three graminaceous weed species: Leersia hexandra Swartz, Leptochloa chinensis (L.) Nees and Echinochioa crusgalli (L.) Beauv. var., and five rice varieties: Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and
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Shanyou 136. In the laboratory experiment, six rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6, Shanyou 136 and TN1, were used to test the selectiveness of C. medinalis towards the volatiles of different varieties. In the oviposition preference experiment, rice varieties were the same as those in the field experiment. Seeds of Yangfujing 8 and Shanyou 136 were provided by the Agricultural Institute of Lixiahe Area, Jiangsu Province, China. TN1 seeds were provided by the China National Rice Research Institute. Seeds of Yangdao 6, Huaidao 9 and Ningjing 1 were purchased from the Yangzhou Tianyuan Seeds Co., Ltd, China. The three weed species, L. hexandra, L. chinensis and E. crusgalli, were collected from paddy fields of Yizheng City, Jiangsu Province, China. Insects C. medinalis moths were captured with sweep nets in the experimental rice fields of Yangzhou University, China in July 2010. Individual pairs of moths were placed into a bottle (diameter 6.5 cm, height 10.0 cm) filled with paper strips for oviposition, along with a cotton swab soaked with 5% honey. The bottles were then covered with a piece of black cloth. The cotton swab was immediately replaced if it was contaminated with mildew or wing scales. Before larvae hatched, paper strips containing eggs were cut with scissors, and pieces of the paper strips harboring approximately 100 eggs were placed into a cage (diameter 44.5 cm, height 90.0 cm) containing rice plants (about 4555 d old). Fresh rice plants were provided daily to feed C. medinalis larvae. The emerged adults were used for behavioral response and oviposition preference experiments. Experimental protocols Number of moths and eggs on different field host plants The experiment was conducted in Yizheng City (32°17 N, 119°10 E), Jiangsu Province, China in 2010. The tested host plants included five rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and Shanyou 136, and three graminaceous weed species, L. hexandra, L. chinensis and E. crusgalli. Each tested plant was grown in a plot of 7 m × 9 m. A belt of 0.5 m was used to divide two neighboring plots. Each host plant had four replications. One plot was considered as a replication. The 32 plots for the 8 tested plants were randomly arranged. The tested host plants were transplanted on 25 June and subsequently subjected to regular fertilizer and water management regimes. On 15 August, 25% Buprofezin WP (Liyang Zhongnan
Rice Science, Vol. 19, No. 1, 2012
Chemical Industry Co., Ltd, China.) was applied at 187.5 g/hm2 to control rice planthoppers. Additionally, 12.5% Jinggangmycin AS (Zhengjiang Tonglu Huifeng Biochemistry Co., Ltd, China) was applied at 187.5 g/hm2 to control rice sheath blight. Between 26 July and 9 September, moths in a half plot were counted by driving moths from the tested plants with bamboo poles (diameter 1.5 cm, length 150.0 cm). This was performed once every 4 d when the moth belonged to the fifth generation in China (the third generation in Jiangsu Province), and once every 2 d when the moth belonged to the sixth generation in China (the fourth generation in Jiangsu Province). On 30 July, 12, 22 and 28 August, the numbers of C. medinalis eggs on the tested plants were determined with the 5-point sampling method in a plot. Each point was represented by host plants from two hills. That is to say, the numbers of C. medinalis eggs on 10 hills were counted per plot. The numbers of C. medinalis moths and eggs derived from the field investigation were converted to the corresponding number per 100 hills. Behavioral responses of C. medinalis moths towards volatiles of different rice varieties A Y-shaped olfactory detector was used to examine the selectiveness of C. medinalis towards volatiles from the field experimental rice varieties, as well as from the variety TN1, which can obviously attracted C. medinalis (Velusamy et al, 1990). The Y-shaped olfactory detector was composed of tubes with 20-cm in length and 4-cm in internal diameter. The angle of its two arms was 75°. The glass tubing connectors were all in standard 24# ground joints. The two side arms were connected with two silicone tubes to two odor containers that both consisted of a glass tube with 5-cm in diameter and 30-cm in length. Approximately 50 g of 4555 d old rice plants were placed into the two odor containers. Air was passed through an activated carbon filter (diameter 1.8 cm, length 10.0 cm), followed by a bottle containing distilled water, thereby cleaning the air and increasing the humidity before entering the odor containers. The exhaust port was connected to the major arm of the Y-shaped tube, where female moths were released. The rate of air flow was adjusted to 400 mL/min. During bioassay, each female moth was introduced into the release port of the olfactory detector via a small tube. Each moth was observed for 5 min, starting from the moment when it left the small tube. Positive selection was defined as a moth entered over 10 cm into a side arm and stayed there for over 1 min within the 5 min duration. Otherwise, the moth was
Data were analyzed by SPSS 13.0. The data of numbers of C. medinalis moths and eggs per 100 hills derived from the field investigation were transformed to logarithms of (number +1) prior to being analyzed. The field experimental data and laboratory data (oviposition preference towards different rice varieties) were subjected to analysis of variance and subsequently examined by Tukey’s honest significant difference test to detect the differences between the treatments. The data from the behavioral experiment (behavioral response towards volatiles of different rice varieties) were analyzed by chi-square (2) test.
RESULTS
Number of C. medinalis moths on different host plants in the fields
The numbers of C. medinalis moths on different host plants in the fields are shown in Table 1. Between 26 July and 12 August, the number of C. medinalis L. hexandra 0.00 ± 0.00 c 0.00 ± 0.00 c 0.00 ± 0.00 b 0.00 ± 0.00 b 0.00 ± 0.00 b 0.00 ± 0.00 c 0.00 ± 0.00 c 0.06 ± 0.04 c 0.22 ± 0.10 b 1.09 ± 0.32 c 0.80 ± 0.21 c 0.38 ± 0.09 b 1.57 ± 0.40 bc 1.99 ± 0.74 bc 2.34 ± 0.56 c 3.37 ± 1.00 c 3.62 ± 0.66 c 1.89 ± 0.27 ab 2.15 ± 0.80 c 1.22 ± 0.19 ab 5.10 ± 0.68 a
Oviposition preference of C. medinalis towards different rice varieties The rice plants were arranged in a circular fashion (Liu et al, 1998). Specifically, plants of the five rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and Shanyou 136, were transplanted into plastic buckets with a diameter of 26 cm and a height of 25 cm. Each bucket harbored 4 hills for one rice variety. The seedlings were allowed to grow to the tillering stage (at 4555 days old) before testing. Then, five buckets containing the five rice varieties were placed into a shroud (Length × Width × Height, 1.5 m × 1.5 m × 1.5 m) constructed of mesh. The five buckets were arranged in a 1.5-m diameter circle. On 25 August, 30 pairs of C. medinalis adults were introduced into the shroud, along with cotton swabs soaked with 5% honey. The eggs and newly hatched larvae on the different rice varieties were counted on 2 September. Egg numbers were defined as the combined counts of observed eggs and larvae. For each rice variety, five replicates were carried out. E. crusgalli 0.00 ± 0.00 c 0.00 ± 0.00 c 0.00 ± 0.00 b 0.00 ± 0.00 b 0.03 ± 0.03 b 0.03 ± 0.03 bc 0.03 ± 0.03 c 0.29 ± 0.08 c 0.32 ± 0.04 b 3.69 ± 0.47 b 3.11 ± 0.29 b 3.01 ± 0.86 ab 3.62 ± 0.42 ab 1.92 ± 0.20 bc 2.50 ± 0.64 bc 5.35 ± 0.38 bc 3.94 ± 1.14 bc 0.64 ± 0.22 cd 3.33 ± 0.50 bc 0.71 ± 0.31 b 0.71 ± 0.24 c
Data analysis F=5.40; df=7,24; P=0.0008 F=14.69; df=7,24; P<0.0001 F=6.41; df=7,24; P=0.0003 F=5.53; df=7,24; P=0.0007 F=5.49; df=7,24; P=0.0007 F=12.40; df=7,24; P<0.0001 F=21.17; df=7,24; P<0.0001 F=9.97; df=7,24; P<0.0001 F=10.91; df=7,24; P<0.0001 F=49.75; df=7,24; P<0.0001 F=27.21; df=7,24; P0.0001 F=9.77; df=7,24; P0.0001 F=12.41; df=7,24; P0.0001 F=9.22; df=7,24; P0.0001 F=16.71; df=7,24; P0.0001 F=22.14; df=7,24; P0.0001 F=17.06; df=7,24; P0.0001 F=16.68; df=7,24; P0.0001 F=4.70; df=7,24; P=0.0020 F=4.60; df=7,24; P=0.0022 F=10.62; df=7,24; P0.0001
Statistics
considered to have shown no preference. At least 32 female moths were tested for each treatment. After testing 10 insects, the two side arms were switched to eliminate a potential impact of side-arm-position on the behaviors of the tested moths. Every time when the treatments were changed, the whole apparatus was thoroughly cleaned with 95% ethanol. The assays were conducted between 5:00 pm and 9:00 pm at (28±2) °C.
Date No. of C. medinalis adults per 100 hills (mean ± SE) (Month-Day) Yangfujing 8 Yangdao 6 Shanyou 136 Ningjing 1 Huaidao 9 L. chinensis 07-26 0.35 ± 0.15 abc 0.51 ± 0.12 ab 0.64 ± 0.31 a 0.06 ± 0.04 bc 0.00 ± 0.00 c 0.00 ± 0.00 c 07-30 1.22 ± 0.45 ab 1.25 ± 0.17 ab 1.89 ± 0.17 a 0.67 ± 0.16 bc 0.83 ± 0.21 b 0.00 ± 0.00 c 08-04 0.35 ± 0.03 ab 0.42 ± 0.17 ab 0.22 ± 0.06 ab 0.61 ± 0.13 a 0.51 ± 0.19 a 0.00 ± 0.00 b 08-06 0.42 ± 0.03 ab 0.13 ± 0.09 b 0.29 ± 0.11 ab 0.67 ± 0.11 a 0.38 ± 0.26 ab 0.00 ± 0.00 b 08-08 0.64 ± 0.13 a 0.26 ± 0.16 ab 0.19 ± 0.06 ab 0.35 ± 0.10 ab 0.29 ± 0.13 ab 0.00 ± 0.00 b 08-10 0.74 ± 0.16 a 0.45 ± 0.11 ab 0.51 ± 0.07 a 0.77 ± 0.05 a 0.58 ± 0.19 a 0.00 ± 0.00 c 08-12 0.80 ± 0.19 ab 0.71 ± 0.12 ab 0.58 ± 0.13 b 1.22 ± 0.06 a 0.58 ± 0.11 b 0.00 ± 0.00 c 08-14 2.72 ± 0.48 a 1.22 ± 0.27 abc 0.87 ± 0.58 bc 1.96 ± 0.36 ab 1.67 ± 0.37 ab 0.19 ± 0.08 c 08-16 5.10 ± 0.72 a 2.98 ± 0.47 a 4.13 ± 2.39 a 4.33 ± 0.87 a 4.42 ± 0.54 a 0.42 ± 0.11 b 08-18 10.13 ± 0.29 a 9.68 ± 0.92 a 12.85 ± 2.25 a 10.58 ± 1.09 a 7.82 ± 0.55 a 1.54 ± 0.25 c 08-20 9.29 ± 0.93 a 9.87 ± 1.13 a 9.17 ± 2.95 a 8.78 ± 1.31 a 6.06 ± 0.85 ab 0.22 ± 0.06 c 08-22 7.34 ± 1.39 a 6.06 ± 0.99 a 5.77 ± 3.66 a 8.21 ± 1.46 a 5.16 ± 0.91 a 0.35 ± 0.11 b 08-24 9.29 ± 0.69 a 6.83 ± 1.86 a 6.41 ± 3.19 ab 8.46 ± 0.57 a 5.96 ± 0.67 a 0.06 ± 0.04 c 08-26 10.74 ± 1.11 a 7.34 ± 0.45 a 7.53 ± 3.54 ab 6.63 ± 0.77 ab 3.78 ± 0.74 abc 0.48 ± 0.25 c 08-28 9.23 ± 0.92 a 7.05 ± 0.99 a 6.28 ± 2.43 abc 8.91 ± 0.99 a 6.09 ± 0.41 ab 0.22 ± 0.10 d 08 30 14.26 ± 1.13 a 9.29 ± 1.73 ab 11.83 ± 2.88 ab 10.71 ± 0.71 ab 7.56 ± 0.77 ab 0.83 ± 0.17 d 09-01 11.12 ± 1.49 a 8.14 ± 0.96 ab 7.85 ± 2.08 abc 6.03 ± 0.64 abc 4.39 ± 0.48 bc 0.32 ± 0.11 d 09-03 3.01 ± 0.40 a 1.51 ± 0.24 bc 2.31 ± 0.48 ab 2.02 ± 0.11 ab 1.70 ± 0.11 ab 0.10 ± 0.10 d 09-05 11.09 ± 1.54 a 5.93 ± 1.84 abc 7.82 ± 1.76 ab 4.71 ± 0.49 abc 6.47 ± 1.24 abc 3.40 ± 1.24 bc 09-07 2.92 ± 0.50 a 1.70 ± 0.25 ab 2.08 ± 0.72 ab 1.28 ± 0.32 ab 1.89 ± 0.35 ab 0.48 ± 0.13 b 09-09 1.83 ± 0.14 bc 1.47 ± 0.29 bc 2.92 ± 0.51 ab 1.63 ± 0.36 bc 2.02 ± 0.60 bc 0.80 ± 0.18 c Different letters in a row indicate significant differences between treatments (P < 0.05).
Table 1. Number of C. medinalis adults on the different host plants.
LIU Fang, et al. Selectiveness of Rice Leaffolder to Host Plants 51
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indicating that C. medinalis does not prefer the volatile chemicals released by these two rice varieties. However, C. medinalis did not exhibit an apparent preference towards the volatiles of Yangfujing 8, Shanyou 136 and Yangdao 6 compared to that of TN1 (Fig. 2).
moths in the fields was low. The moths were mainly concentrated on rice plants, while the three weed species were associated with very few moths. From 14 August, the moth level in the fields began to increase. Between 14 August and 5 September, there were significant differences of the C. medinalis moth on the different tested host plants. In general, the levels were higher on rice than on weeds. Among the rice varieties, Yangfujing 8 was associated with a higher moth number (seeing the data derived on 14 August, 1 and 3 September). Additionally, on 9 September, it was observed that the moths on L. hexandra were significantly higher than those on the other plants apart from the rice variety Shanyou 136.
Oviposition preference of C. medinalis towards different rice varieties C. medinalis adults were found to exhibit no significant difference (F = 0.50; df = 4, 20, P = 0.7335) in fecundity on Shanyou 136, Yangdao 6, Yangfujing 8, Ningjing 1 and Huaidao 9, indicating that the leaffolder moth has no apparent oviposition preference towards any of the five experimental rice varieties (Fig. 3).
Number of C. medinalis eggs on different host plants in the fields There were significant differences in the number of C. medinalis eggs among different tested plants (For 30 July, F = 7.75, df = 7, 24, P = 0.0001; for 12 August, F = 15.01, df = 7, 24, P < 0.0001; for 22 August, F = 8.39, df = 7, 24, P < 0.0001, and for 28 August, F = 8.50, df = 7, 24, P < 0.0001). In general, the numbers of C. medinalis eggs on rice were higher than those on weeds. However, no significant difference was found for the number of eggs among the different rice varieties. Among the different weed species, there was only one case of a statistical difference, in which the egg counted on L. hexandra on 28 August (20.0 ± 0.0 per 100 hills) was significantly higher than that on L. chinensis (5.0 ± 5.0 per 100 hills) (Fig. 1).
DISCUSSION In the field experiment, the rice varieties were found to harbor a significantly higher burden of C. medinalis than the weeds for both moths and eggs, indicating that rice is a preferred host of C. medinalis. This is consistent with a previous laboratory study conducted by Khan et al (1996). Xu et al (2007) compared semi-natural population life tables of C. medinalis on five regular cultivated rice, Yangjing 9538, Huaidao 9, Yangfujing 8, Yangdao 6 and Shanyou 63. They discovered that C. medinalis exhibited the lowest index of population trend on Huaidao 9, indicating a strong resistance capacity of this variety against C. medinalis. In contrast, Yangfujing 8 showed the highest index of population trend, and was therefore concluded to be sensitive to C. medinalis. In this study, the field data indicated that
Behavioral responses of C. medinalis towards volatile compounds from different rice varieties Compared with TN1, significantly fewer female moths chose the volatiles of Ningjing 1 and Huaidao 9, 300 300
Yangfujing 8
No. of eggs/ 100hills
No. of eggs per 100 hills
Yangdao 6 250 250
a
Shanyou 136 Ningjing 1
200 200
150 150
Huaidao 9 Leptochloa chinensis
a
ab
ab
Echinochloa crusgalli Leersia hexandra
100 100
ab
a a
a a
a a
ab
a
a bc
50 50 00
ab ab
a
ab b b b
2010-7-30 2010-07-30
c
a a
bc
ab
c
bc
b
c 2010-8-12 2010-08-12
2010-8-22 2010-08-22
2010-8-28 2010-08-28
Date Date(year-month-day) (Year-Month-Day)
Fig. 1. Fecundity of C. medinalis on the different host plants (rice varieties). The data are displayed as the mean ± SE. Different letters indicate significant differences between treatments (P < 0.05).
a
LIU Fang, et al. Selectiveness of Rice Leaffolder to Host Plants
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Treatments
2 value
Yangfujing 8 vs TN1
21
2.53ns
11
Ningjing 1 vs TN1
5.28*
6
24
7.03**
5
21
2.53ns
4 4
9
Huaidao 9 vs TN1
23
8
Yangdao 6 vs TN1
11
Shanyou 136 vs TN1
13
19
0.78ns
TN1 vs TN1
15
17
0.03ns
30
20
10
0
No.of female adults to the odor
3
10
20
3
30 0
10
No.of no response female adults
No. Nofo.eggs per/ hill hill ofeggs
Fig. 2. Behavioral responses of female adults of C. medinalis towards volatiles from different rice varieties. ** and * indicate significant differences at 0.01 and 0.05 levels, respectively; ‘ns’ indicates no significant difference.
77 66 55 44 33 22 11 00
aa
aa
aa a
a
a
a
Shanyou 136
Yangdao 6
Yangfujing 8
Ningjing 1
Huaidao 9
Shanyou 136 Yangdao 6 Yangfujing 8 Ningjing 1 Huaidao 9 Rice varieties
Rice variety Fig. 3. Oviposition preference of C. medinalis towards different rice varieties. The data are displayed as the mean ± SE. The same letter above the bars indicates no significant differences between treatments (P < 0.05).
the number of C. medinalis moths on Yangfujing 8 was relatively higher than that on Huaidao 9, although no apparent difference of fecundity was detected for moths between the two rice varieties. In the laboratory experiment, C. medinalis was clearly observed to avoid the volatiles of Huaidao 9 and Ningjing 1. However, the moth was found to harbor no apparent oviposition preference towards the five tested rice varieties. Taken together, C. medinalis adults displayed a considerable host selectiveness, but not oviposition preference towards different rice varieties. Plant volatiles play an important role in the host selection and oviposition of herbivorous insects because these products regulate multiple insect behaviors, such as attracting herbivores towards host plants, stimulating insect feeding and guiding insects to choose oviposition sites (Du, 2001). Kairomones produced by plants, containing pest-attracting components may be used as an attractant for pest control (Zhao et al,
2004). Currently, control of C. medinalis is achieved mainly through chemical methods, but using behavioral modulation to control the pest is worth exploring. In this study, it was discovered that C. medinalis clearly avoided the volatiles produced by Huaidao 9 and Ningjing 1, indicating that there were differences in volatile composition among the rice varieties. In the future, it may be beneficial to study the volatile composition of different rice varieties and then to screen components exhibiting C. medinalisattracting activities for the purpose of developing trapping technologies against this pest.
ACKNOWLEDGEMENTS The authors thank Professor FU Qiang of China National Rice Research Institure and XU Jian of Agricultural Institute of Lixiahe Area, Jiangsu Province, China for providing rice seeds. This study was supported by the Special Fund for Agro-scientific Research in the Public Interest of China (Grant No. 200903051).
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Rice Science, Vol. 19, No. 1, 2012 mechanisms of resistance of different rice varieties to the rice leaffolder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae). Acta Ecol Sin, 51(12): 1265–1270. (in Chinese with English abstract) Xu L, Wang F, Wu J C, Wang Q X. 2007. Life table parameters of a semi-natural population of Cnaphalocrocis medinalis (Güenée) on different rice varieties and changes in sugar content in rice plants after insect infestation. Acta Ecol Sin, 27(11): 4547–4554. (in Chinese with English abstract) Yadava C P, Santaram G, Israel P, Kalode M B. 1972. Life-history of rice leaf-roller, Cnaphalocrocis medinalis Güenée (Lepidoptera: Pyralidae) and its reaction to some varieties and grasses. Ind J Agric Sci, 42: 520–523. Yang R M, Zhu Y Q, Diao C Y, Zhang F. 2004. Causes of the outbreak of Cnaphalocrocis medinalis in Jiangsu Province in 2003 and its control strategies. China Plant Prot, 24(2): 11–14. (in Chinese with English abstract) Zhao D X, Gao J L, Chen Z M. 2004. Research progress of behavioral orientation of phytophagous insects to their host plants. Chin J Trop Agric, 24(2): 62–68. (in Chinese with English abstract) Zhu Z R, Shang H W, Cheng J A, Chen X. 2000. Effects of methamidophos to Cnaphalocrocis medinalis (Güenée) and its natural enemies on rice. Plant Prot, 26(4): 7–9. (in Chinese with English abstract)
Selectiveness of Cnaphalocrocis medinalis to Host Plants LIU Fang, CHENG Jian-jun, JIANG Tao, SU Wen, XU Shuai (College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China) Abstract: A field experiment was conducted to study the selectiveness of Cnaphalocrocis medinalis Güenée (commonly known as the rice leaffolder or rice leafroller) towards five rice varieties (Yangfujing 8, Yangdao 6, Shanyou 136, Huaidao 9 and Ningjing 1) and three weed species (Echinochloa crusgalli, Leptochloa chinensis and Leersia hexandra). The results showed that the rice varieties carried significantly higher numbers of C. medinalis moths and eggs than the weed species. Among the rice varieties, Yangfujing 8 was associated with a higher moth number. However, there was little difference in the number of C. medinalis eggs among the rice varieties. Additionally, a laboratory experiment was performed to investigate the olfactory response of female C. medinalis towards volatile compounds from different rice varieties, as well as its oviposition preference towards these rice varieties. The volatiles of Yangfujing 8, Yangdao 6 and Shanyou 136 attracted C. medinalis similarly to those of TN1. In contrast, the volatiles of Huaidao 9 and Ningjing 1 clearly deterred C. medinalis. Nevertheless, C. medinalis did not exhibit clear oviposition preference towards any of the five tested rice varieties. Key words: Cnaphalocrocis medinalis; host selection; host plant; rice variety; weed species
The rice leaffolder, Cnaphalocrocis medinalis Güenée (Lepidoptera: Pyralidae) is a migratory pest that damages rice throughout southeast and northeast Asia (Ding and Su, 2002). In the past, this insect only posed problems occasionally and at local scales. But since 1970, it has become a frequent occurrence pest (Zhu et al, 2000). In recent years, a series of major outbreaks of C. medinalis has been persisted in paddy fields of Jiangsu Province, China, causing a severe threat to rice production (Yang et al, 2004). The larvae of C. medinalis feed on young rice leaves during the tillering stage or on flag leaves during the booting to heading stage. Although the injured plants have a considerable repair capacity during the tillering stage, this may still result in great yield losses during the late growth stage of rice (Fabellar et al, 1994). In years when there is an outbreak of C. medinalis, severely infested fields reach 30%80% yield reduction (Kushwaha, 1988). C. medinalis has a broad host range, including graminaceous crops of rice, corn, sugarcane, wheat and sorghum, as well as some graminaceous weed species (Joshi et al, 1987; Khan et al, 1996), among which rice is the most preferred host (Yadava et al, 1972; Khan et al, 1988). The volatiles from rice plants significantly affected the behavior of C. medinalis. Leaffolder moths laid significantly fewer eggs on TN1 plants treated with distillate extracts from two wild resistant rice species, Oryza officinalis and O. punctata, than on TN1 plants treated with distillate extracts from resistant cultivated rice (Velusamy et al, 1990). Received: 18 February 2011; Accepted: 5 May 2011 Corresponding author: LIU Fang ([email protected])
Ramachandran et al (1990) determined the olfactory response of C. medinalis towards 91 volatile compounds of plant origin using electroantennograms (EAGs) and discovered that both female and male moths displayed a strong EAG response towards green leaf odor. Male moths showed a higher response than females towards saturated and unsaturated aliphatic aldehydes, whereas female adults exhibited a significantly stronger olfactory response towards five components: terpinen-4-ol, carveol, dihydrocarveol, (-)-myrtenal and peritlaldehyde. It has been reported that the commercial rice varieties in Jiangsu Province, China exhibited considerable variation in resistance to C. medinalis and the resistance is closely related to the contents of reducing sugars, silicon and wax in rice plants (Xu et al, 2007; Wang et al, 2008). Nevertheless, it remains unknown whether the resistance mechanisms of the current commercially used resistant varieties are associated with volatile chemicals found in rice. This study examined the selectiveness of C. medinalis towards different host plants, thus providing a reference for explaining the resistance mechanisms of resistant varieties, as well as offering a basis for behavioral control of this pest.
MATERIALS AND METHODS Host plants The host plants in the field experiment included three graminaceous weed species: Leersia hexandra Swartz, Leptochloa chinensis (L.) Nees and Echinochioa crusgalli (L.) Beauv. var., and five rice varieties: Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and
50
Shanyou 136. In the laboratory experiment, six rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6, Shanyou 136 and TN1, were used to test the selectiveness of C. medinalis towards the volatiles of different varieties. In the oviposition preference experiment, rice varieties were the same as those in the field experiment. Seeds of Yangfujing 8 and Shanyou 136 were provided by the Agricultural Institute of Lixiahe Area, Jiangsu Province, China. TN1 seeds were provided by the China National Rice Research Institute. Seeds of Yangdao 6, Huaidao 9 and Ningjing 1 were purchased from the Yangzhou Tianyuan Seeds Co., Ltd, China. The three weed species, L. hexandra, L. chinensis and E. crusgalli, were collected from paddy fields of Yizheng City, Jiangsu Province, China. Insects C. medinalis moths were captured with sweep nets in the experimental rice fields of Yangzhou University, China in July 2010. Individual pairs of moths were placed into a bottle (diameter 6.5 cm, height 10.0 cm) filled with paper strips for oviposition, along with a cotton swab soaked with 5% honey. The bottles were then covered with a piece of black cloth. The cotton swab was immediately replaced if it was contaminated with mildew or wing scales. Before larvae hatched, paper strips containing eggs were cut with scissors, and pieces of the paper strips harboring approximately 100 eggs were placed into a cage (diameter 44.5 cm, height 90.0 cm) containing rice plants (about 4555 d old). Fresh rice plants were provided daily to feed C. medinalis larvae. The emerged adults were used for behavioral response and oviposition preference experiments. Experimental protocols Number of moths and eggs on different field host plants The experiment was conducted in Yizheng City (32°17 N, 119°10 E), Jiangsu Province, China in 2010. The tested host plants included five rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and Shanyou 136, and three graminaceous weed species, L. hexandra, L. chinensis and E. crusgalli. Each tested plant was grown in a plot of 7 m × 9 m. A belt of 0.5 m was used to divide two neighboring plots. Each host plant had four replications. One plot was considered as a replication. The 32 plots for the 8 tested plants were randomly arranged. The tested host plants were transplanted on 25 June and subsequently subjected to regular fertilizer and water management regimes. On 15 August, 25% Buprofezin WP (Liyang Zhongnan
Rice Science, Vol. 19, No. 1, 2012
Chemical Industry Co., Ltd, China.) was applied at 187.5 g/hm2 to control rice planthoppers. Additionally, 12.5% Jinggangmycin AS (Zhengjiang Tonglu Huifeng Biochemistry Co., Ltd, China) was applied at 187.5 g/hm2 to control rice sheath blight. Between 26 July and 9 September, moths in a half plot were counted by driving moths from the tested plants with bamboo poles (diameter 1.5 cm, length 150.0 cm). This was performed once every 4 d when the moth belonged to the fifth generation in China (the third generation in Jiangsu Province), and once every 2 d when the moth belonged to the sixth generation in China (the fourth generation in Jiangsu Province). On 30 July, 12, 22 and 28 August, the numbers of C. medinalis eggs on the tested plants were determined with the 5-point sampling method in a plot. Each point was represented by host plants from two hills. That is to say, the numbers of C. medinalis eggs on 10 hills were counted per plot. The numbers of C. medinalis moths and eggs derived from the field investigation were converted to the corresponding number per 100 hills. Behavioral responses of C. medinalis moths towards volatiles of different rice varieties A Y-shaped olfactory detector was used to examine the selectiveness of C. medinalis towards volatiles from the field experimental rice varieties, as well as from the variety TN1, which can obviously attracted C. medinalis (Velusamy et al, 1990). The Y-shaped olfactory detector was composed of tubes with 20-cm in length and 4-cm in internal diameter. The angle of its two arms was 75°. The glass tubing connectors were all in standard 24# ground joints. The two side arms were connected with two silicone tubes to two odor containers that both consisted of a glass tube with 5-cm in diameter and 30-cm in length. Approximately 50 g of 4555 d old rice plants were placed into the two odor containers. Air was passed through an activated carbon filter (diameter 1.8 cm, length 10.0 cm), followed by a bottle containing distilled water, thereby cleaning the air and increasing the humidity before entering the odor containers. The exhaust port was connected to the major arm of the Y-shaped tube, where female moths were released. The rate of air flow was adjusted to 400 mL/min. During bioassay, each female moth was introduced into the release port of the olfactory detector via a small tube. Each moth was observed for 5 min, starting from the moment when it left the small tube. Positive selection was defined as a moth entered over 10 cm into a side arm and stayed there for over 1 min within the 5 min duration. Otherwise, the moth was
Data were analyzed by SPSS 13.0. The data of numbers of C. medinalis moths and eggs per 100 hills derived from the field investigation were transformed to logarithms of (number +1) prior to being analyzed. The field experimental data and laboratory data (oviposition preference towards different rice varieties) were subjected to analysis of variance and subsequently examined by Tukey’s honest significant difference test to detect the differences between the treatments. The data from the behavioral experiment (behavioral response towards volatiles of different rice varieties) were analyzed by chi-square (2) test.
RESULTS
Number of C. medinalis moths on different host plants in the fields
The numbers of C. medinalis moths on different host plants in the fields are shown in Table 1. Between 26 July and 12 August, the number of C. medinalis L. hexandra 0.00 ± 0.00 c 0.00 ± 0.00 c 0.00 ± 0.00 b 0.00 ± 0.00 b 0.00 ± 0.00 b 0.00 ± 0.00 c 0.00 ± 0.00 c 0.06 ± 0.04 c 0.22 ± 0.10 b 1.09 ± 0.32 c 0.80 ± 0.21 c 0.38 ± 0.09 b 1.57 ± 0.40 bc 1.99 ± 0.74 bc 2.34 ± 0.56 c 3.37 ± 1.00 c 3.62 ± 0.66 c 1.89 ± 0.27 ab 2.15 ± 0.80 c 1.22 ± 0.19 ab 5.10 ± 0.68 a
Oviposition preference of C. medinalis towards different rice varieties The rice plants were arranged in a circular fashion (Liu et al, 1998). Specifically, plants of the five rice varieties, Yangfujing 8, Huaidao 9, Ningjing 1, Yangdao 6 and Shanyou 136, were transplanted into plastic buckets with a diameter of 26 cm and a height of 25 cm. Each bucket harbored 4 hills for one rice variety. The seedlings were allowed to grow to the tillering stage (at 4555 days old) before testing. Then, five buckets containing the five rice varieties were placed into a shroud (Length × Width × Height, 1.5 m × 1.5 m × 1.5 m) constructed of mesh. The five buckets were arranged in a 1.5-m diameter circle. On 25 August, 30 pairs of C. medinalis adults were introduced into the shroud, along with cotton swabs soaked with 5% honey. The eggs and newly hatched larvae on the different rice varieties were counted on 2 September. Egg numbers were defined as the combined counts of observed eggs and larvae. For each rice variety, five replicates were carried out. E. crusgalli 0.00 ± 0.00 c 0.00 ± 0.00 c 0.00 ± 0.00 b 0.00 ± 0.00 b 0.03 ± 0.03 b 0.03 ± 0.03 bc 0.03 ± 0.03 c 0.29 ± 0.08 c 0.32 ± 0.04 b 3.69 ± 0.47 b 3.11 ± 0.29 b 3.01 ± 0.86 ab 3.62 ± 0.42 ab 1.92 ± 0.20 bc 2.50 ± 0.64 bc 5.35 ± 0.38 bc 3.94 ± 1.14 bc 0.64 ± 0.22 cd 3.33 ± 0.50 bc 0.71 ± 0.31 b 0.71 ± 0.24 c
Data analysis F=5.40; df=7,24; P=0.0008 F=14.69; df=7,24; P<0.0001 F=6.41; df=7,24; P=0.0003 F=5.53; df=7,24; P=0.0007 F=5.49; df=7,24; P=0.0007 F=12.40; df=7,24; P<0.0001 F=21.17; df=7,24; P<0.0001 F=9.97; df=7,24; P<0.0001 F=10.91; df=7,24; P<0.0001 F=49.75; df=7,24; P<0.0001 F=27.21; df=7,24; P0.0001 F=9.77; df=7,24; P0.0001 F=12.41; df=7,24; P0.0001 F=9.22; df=7,24; P0.0001 F=16.71; df=7,24; P0.0001 F=22.14; df=7,24; P0.0001 F=17.06; df=7,24; P0.0001 F=16.68; df=7,24; P0.0001 F=4.70; df=7,24; P=0.0020 F=4.60; df=7,24; P=0.0022 F=10.62; df=7,24; P0.0001
Statistics
considered to have shown no preference. At least 32 female moths were tested for each treatment. After testing 10 insects, the two side arms were switched to eliminate a potential impact of side-arm-position on the behaviors of the tested moths. Every time when the treatments were changed, the whole apparatus was thoroughly cleaned with 95% ethanol. The assays were conducted between 5:00 pm and 9:00 pm at (28±2) °C.
Date No. of C. medinalis adults per 100 hills (mean ± SE) (Month-Day) Yangfujing 8 Yangdao 6 Shanyou 136 Ningjing 1 Huaidao 9 L. chinensis 07-26 0.35 ± 0.15 abc 0.51 ± 0.12 ab 0.64 ± 0.31 a 0.06 ± 0.04 bc 0.00 ± 0.00 c 0.00 ± 0.00 c 07-30 1.22 ± 0.45 ab 1.25 ± 0.17 ab 1.89 ± 0.17 a 0.67 ± 0.16 bc 0.83 ± 0.21 b 0.00 ± 0.00 c 08-04 0.35 ± 0.03 ab 0.42 ± 0.17 ab 0.22 ± 0.06 ab 0.61 ± 0.13 a 0.51 ± 0.19 a 0.00 ± 0.00 b 08-06 0.42 ± 0.03 ab 0.13 ± 0.09 b 0.29 ± 0.11 ab 0.67 ± 0.11 a 0.38 ± 0.26 ab 0.00 ± 0.00 b 08-08 0.64 ± 0.13 a 0.26 ± 0.16 ab 0.19 ± 0.06 ab 0.35 ± 0.10 ab 0.29 ± 0.13 ab 0.00 ± 0.00 b 08-10 0.74 ± 0.16 a 0.45 ± 0.11 ab 0.51 ± 0.07 a 0.77 ± 0.05 a 0.58 ± 0.19 a 0.00 ± 0.00 c 08-12 0.80 ± 0.19 ab 0.71 ± 0.12 ab 0.58 ± 0.13 b 1.22 ± 0.06 a 0.58 ± 0.11 b 0.00 ± 0.00 c 08-14 2.72 ± 0.48 a 1.22 ± 0.27 abc 0.87 ± 0.58 bc 1.96 ± 0.36 ab 1.67 ± 0.37 ab 0.19 ± 0.08 c 08-16 5.10 ± 0.72 a 2.98 ± 0.47 a 4.13 ± 2.39 a 4.33 ± 0.87 a 4.42 ± 0.54 a 0.42 ± 0.11 b 08-18 10.13 ± 0.29 a 9.68 ± 0.92 a 12.85 ± 2.25 a 10.58 ± 1.09 a 7.82 ± 0.55 a 1.54 ± 0.25 c 08-20 9.29 ± 0.93 a 9.87 ± 1.13 a 9.17 ± 2.95 a 8.78 ± 1.31 a 6.06 ± 0.85 ab 0.22 ± 0.06 c 08-22 7.34 ± 1.39 a 6.06 ± 0.99 a 5.77 ± 3.66 a 8.21 ± 1.46 a 5.16 ± 0.91 a 0.35 ± 0.11 b 08-24 9.29 ± 0.69 a 6.83 ± 1.86 a 6.41 ± 3.19 ab 8.46 ± 0.57 a 5.96 ± 0.67 a 0.06 ± 0.04 c 08-26 10.74 ± 1.11 a 7.34 ± 0.45 a 7.53 ± 3.54 ab 6.63 ± 0.77 ab 3.78 ± 0.74 abc 0.48 ± 0.25 c 08-28 9.23 ± 0.92 a 7.05 ± 0.99 a 6.28 ± 2.43 abc 8.91 ± 0.99 a 6.09 ± 0.41 ab 0.22 ± 0.10 d 08 30 14.26 ± 1.13 a 9.29 ± 1.73 ab 11.83 ± 2.88 ab 10.71 ± 0.71 ab 7.56 ± 0.77 ab 0.83 ± 0.17 d 09-01 11.12 ± 1.49 a 8.14 ± 0.96 ab 7.85 ± 2.08 abc 6.03 ± 0.64 abc 4.39 ± 0.48 bc 0.32 ± 0.11 d 09-03 3.01 ± 0.40 a 1.51 ± 0.24 bc 2.31 ± 0.48 ab 2.02 ± 0.11 ab 1.70 ± 0.11 ab 0.10 ± 0.10 d 09-05 11.09 ± 1.54 a 5.93 ± 1.84 abc 7.82 ± 1.76 ab 4.71 ± 0.49 abc 6.47 ± 1.24 abc 3.40 ± 1.24 bc 09-07 2.92 ± 0.50 a 1.70 ± 0.25 ab 2.08 ± 0.72 ab 1.28 ± 0.32 ab 1.89 ± 0.35 ab 0.48 ± 0.13 b 09-09 1.83 ± 0.14 bc 1.47 ± 0.29 bc 2.92 ± 0.51 ab 1.63 ± 0.36 bc 2.02 ± 0.60 bc 0.80 ± 0.18 c Different letters in a row indicate significant differences between treatments (P < 0.05).
Table 1. Number of C. medinalis adults on the different host plants.
LIU Fang, et al. Selectiveness of Rice Leaffolder to Host Plants 51
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52
indicating that C. medinalis does not prefer the volatile chemicals released by these two rice varieties. However, C. medinalis did not exhibit an apparent preference towards the volatiles of Yangfujing 8, Shanyou 136 and Yangdao 6 compared to that of TN1 (Fig. 2).
moths in the fields was low. The moths were mainly concentrated on rice plants, while the three weed species were associated with very few moths. From 14 August, the moth level in the fields began to increase. Between 14 August and 5 September, there were significant differences of the C. medinalis moth on the different tested host plants. In general, the levels were higher on rice than on weeds. Among the rice varieties, Yangfujing 8 was associated with a higher moth number (seeing the data derived on 14 August, 1 and 3 September). Additionally, on 9 September, it was observed that the moths on L. hexandra were significantly higher than those on the other plants apart from the rice variety Shanyou 136.
Oviposition preference of C. medinalis towards different rice varieties C. medinalis adults were found to exhibit no significant difference (F = 0.50; df = 4, 20, P = 0.7335) in fecundity on Shanyou 136, Yangdao 6, Yangfujing 8, Ningjing 1 and Huaidao 9, indicating that the leaffolder moth has no apparent oviposition preference towards any of the five experimental rice varieties (Fig. 3).
Number of C. medinalis eggs on different host plants in the fields There were significant differences in the number of C. medinalis eggs among different tested plants (For 30 July, F = 7.75, df = 7, 24, P = 0.0001; for 12 August, F = 15.01, df = 7, 24, P < 0.0001; for 22 August, F = 8.39, df = 7, 24, P < 0.0001, and for 28 August, F = 8.50, df = 7, 24, P < 0.0001). In general, the numbers of C. medinalis eggs on rice were higher than those on weeds. However, no significant difference was found for the number of eggs among the different rice varieties. Among the different weed species, there was only one case of a statistical difference, in which the egg counted on L. hexandra on 28 August (20.0 ± 0.0 per 100 hills) was significantly higher than that on L. chinensis (5.0 ± 5.0 per 100 hills) (Fig. 1).
DISCUSSION In the field experiment, the rice varieties were found to harbor a significantly higher burden of C. medinalis than the weeds for both moths and eggs, indicating that rice is a preferred host of C. medinalis. This is consistent with a previous laboratory study conducted by Khan et al (1996). Xu et al (2007) compared semi-natural population life tables of C. medinalis on five regular cultivated rice, Yangjing 9538, Huaidao 9, Yangfujing 8, Yangdao 6 and Shanyou 63. They discovered that C. medinalis exhibited the lowest index of population trend on Huaidao 9, indicating a strong resistance capacity of this variety against C. medinalis. In contrast, Yangfujing 8 showed the highest index of population trend, and was therefore concluded to be sensitive to C. medinalis. In this study, the field data indicated that
Behavioral responses of C. medinalis towards volatile compounds from different rice varieties Compared with TN1, significantly fewer female moths chose the volatiles of Ningjing 1 and Huaidao 9, 300 300
Yangfujing 8
No. of eggs/ 100hills
No. of eggs per 100 hills
Yangdao 6 250 250
a
Shanyou 136 Ningjing 1
200 200
150 150
Huaidao 9 Leptochloa chinensis
a
ab
ab
Echinochloa crusgalli Leersia hexandra
100 100
ab
a a
a a
a a
ab
a
a bc
50 50 00
ab ab
a
ab b b b
2010-7-30 2010-07-30
c
a a
bc
ab
c
bc
b
c 2010-8-12 2010-08-12
2010-8-22 2010-08-22
2010-8-28 2010-08-28
Date Date(year-month-day) (Year-Month-Day)
Fig. 1. Fecundity of C. medinalis on the different host plants (rice varieties). The data are displayed as the mean ± SE. Different letters indicate significant differences between treatments (P < 0.05).
a
LIU Fang, et al. Selectiveness of Rice Leaffolder to Host Plants
53
Treatments
2 value
Yangfujing 8 vs TN1
21
2.53ns
11
Ningjing 1 vs TN1
5.28*
6
24
7.03**
5
21
2.53ns
4 4
9
Huaidao 9 vs TN1
23
8
Yangdao 6 vs TN1
11
Shanyou 136 vs TN1
13
19
0.78ns
TN1 vs TN1
15
17
0.03ns
30
20
10
0
No.of female adults to the odor
3
10
20
3
30 0
10
No.of no response female adults
No. Nofo.eggs per/ hill hill ofeggs
Fig. 2. Behavioral responses of female adults of C. medinalis towards volatiles from different rice varieties. ** and * indicate significant differences at 0.01 and 0.05 levels, respectively; ‘ns’ indicates no significant difference.
77 66 55 44 33 22 11 00
aa
aa
aa a
a
a
a
Shanyou 136
Yangdao 6
Yangfujing 8
Ningjing 1
Huaidao 9
Shanyou 136 Yangdao 6 Yangfujing 8 Ningjing 1 Huaidao 9 Rice varieties
Rice variety Fig. 3. Oviposition preference of C. medinalis towards different rice varieties. The data are displayed as the mean ± SE. The same letter above the bars indicates no significant differences between treatments (P < 0.05).
the number of C. medinalis moths on Yangfujing 8 was relatively higher than that on Huaidao 9, although no apparent difference of fecundity was detected for moths between the two rice varieties. In the laboratory experiment, C. medinalis was clearly observed to avoid the volatiles of Huaidao 9 and Ningjing 1. However, the moth was found to harbor no apparent oviposition preference towards the five tested rice varieties. Taken together, C. medinalis adults displayed a considerable host selectiveness, but not oviposition preference towards different rice varieties. Plant volatiles play an important role in the host selection and oviposition of herbivorous insects because these products regulate multiple insect behaviors, such as attracting herbivores towards host plants, stimulating insect feeding and guiding insects to choose oviposition sites (Du, 2001). Kairomones produced by plants, containing pest-attracting components may be used as an attractant for pest control (Zhao et al,
2004). Currently, control of C. medinalis is achieved mainly through chemical methods, but using behavioral modulation to control the pest is worth exploring. In this study, it was discovered that C. medinalis clearly avoided the volatiles produced by Huaidao 9 and Ningjing 1, indicating that there were differences in volatile composition among the rice varieties. In the future, it may be beneficial to study the volatile composition of different rice varieties and then to screen components exhibiting C. medinalisattracting activities for the purpose of developing trapping technologies against this pest.
ACKNOWLEDGEMENTS The authors thank Professor FU Qiang of China National Rice Research Institure and XU Jian of Agricultural Institute of Lixiahe Area, Jiangsu Province, China for providing rice seeds. This study was supported by the Special Fund for Agro-scientific Research in the Public Interest of China (Grant No. 200903051).
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Rice Science, Vol. 19, No. 1, 2012 mechanisms of resistance of different rice varieties to the rice leaffolder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae). Acta Ecol Sin, 51(12): 1265–1270. (in Chinese with English abstract) Xu L, Wang F, Wu J C, Wang Q X. 2007. Life table parameters of a semi-natural population of Cnaphalocrocis medinalis (Güenée) on different rice varieties and changes in sugar content in rice plants after insect infestation. Acta Ecol Sin, 27(11): 4547–4554. (in Chinese with English abstract) Yadava C P, Santaram G, Israel P, Kalode M B. 1972. Life-history of rice leaf-roller, Cnaphalocrocis medinalis Güenée (Lepidoptera: Pyralidae) and its reaction to some varieties and grasses. Ind J Agric Sci, 42: 520–523. Yang R M, Zhu Y Q, Diao C Y, Zhang F. 2004. Causes of the outbreak of Cnaphalocrocis medinalis in Jiangsu Province in 2003 and its control strategies. China Plant Prot, 24(2): 11–14. (in Chinese with English abstract) Zhao D X, Gao J L, Chen Z M. 2004. Research progress of behavioral orientation of phytophagous insects to their host plants. Chin J Trop Agric, 24(2): 62–68. (in Chinese with English abstract) Zhu Z R, Shang H W, Cheng J A, Chen X. 2000. Effects of methamidophos to Cnaphalocrocis medinalis (Güenée) and its natural enemies on rice. Plant Prot, 26(4): 7–9. (in Chinese with English abstract)