Study on host plants for reproduction of Chilo suppressalis

    Study on host plants for reproduction of Chilo suppressalis Wei-Hua Jiang, Hai-Dong Li, Xiong-Feng Cheng, Jian-Ren Ye, YongBin Feng, Zhao-Jun Han PII: DOI: Reference:

S1226-8615(15)00085-0 doi: 10.1016/j.aspen.2015.07.009 ASPEN 677

To appear in:

Journal of Asia-Pacific Entomology

Received date: Revised date: Accepted date:

31 March 2014 6 July 2015 14 July 2015

Please cite this article as: Jiang, Wei-Hua, Li, Hai-Dong, Cheng, Xiong-Feng, Ye, JianRen, Feng, Yong-Bin, Han, Zhao-Jun, Study on host plants for reproduction of Chilo suppressalis, Journal of Asia-Pacific Entomology (2015), doi: 10.1016/j.aspen.2015.07.009

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ACCEPTED MANUSCRIPT Study on host plants for reproduction of Chilo suppressalis 1 ☆

Wei-Hua Jianga, Hai-Dong Lia, Xiong-Feng Chenga, Jian-Ren Yeb, Yong-Bin Fengb, Zhao-Jun

Key Laboratory of Integrated Management of Crop Diseases and Pests (Ministry of Education), College of Plant

Protection, Nanjing Agricultural University, Nanjing 210095, China Plant Protecting Station of Wenling City, Wenling 317500, China

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b

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Hana,*

ABSTRACT

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The rice stem borer, Chilo suppressalis, is generally considered to be a polyphagous pest. The current study challenges this view by investigating its oviposition preference, larval survival and

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development on different host plants under both laboratory and field conditions. Rice and water-oat populations of the borer inhabiting on corresponding plants respectively have partial

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reproductive isolation based on previous studies. In a laboratory multiple-choice test, C.

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suppressalis adults from rice population laid most of eggs on water-oat (46.5% of total eggs) and rice (43.8%), with very few laid on wheat (3.6%), sugarcane (4.0%) and maize (2.0%). Field

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surveys supported the laboratory study and found no egg on the plants other than rice and water-oat. Neonate inoculation experiments performed in field and laboratory showed that larval survival rate was much higher on rice (49.1%-51.2%) and wheat (36.5%-44.1%) than that on

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water-oat (10.7%-10.8%), maize (1.2%-7.2%), sugarcane (0-1.5%) and weeds (2.4%). These results were discussed with the data reported from water-oat population and it was concluded that C. suppressalis is not a typical polyphagous pest. Rice population mainly reproduces on rice and use water-oat only as minor host, and water-oat population breeds better on water-oat than on rice as reported. Neither populations could thrive on the other recorded host plants, which are used for the supplementary nutrition sources of larvae. These findings provide useful information for the development of control strategies to prevent C. suppressalis laying eggs on rice seedlings in early spring, hence effectively reducing population density of this pest in rice fields. Keywords： ☆

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,

distribution, and reproduction in any medium, provided the original author and source are credited. * Corresponding author. Tel.:+86 25 84395245. E-mail address: [email protected]

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Chilo suppressalis Oviposition

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Survival rate

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Host plant

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Introduction

A sound knowledge of host range and feeding habits of pests is very important in

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developing efficient integrated pest management (IPM) strategies. The rice stem borer,

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Chilo suppressalis (Walker), has long been regarded as a polyphagous insect and over

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40 species have been reported as host plants, including rice, water-oat, wild water-oat, maize, sugarcane, rape, broad bean, wheat, and winter cover greens (Shen 1965; Li

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and Li, 1996). But, this traditional view has recently been questioned. First, C. suppressalis has host-associated biotypes (rice- and water-oat- populations) that show

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differences in host preference behaviors, larval feeding and development, and female fecundity (Koike et al., 1981; Konno, 1998). In addition, partial reproductive isolation has been reported between populations living on different hosts (e.g. rice vs. water-oat) (Konno and Tanaka, 1996; Samudra et al, 2002; Ding et al, 2013). Second, Hou et al. (2010) studied the recorded hosts and reported that wheat and maize are not effective reproductive hosts for water-oat-population of C. suppressalis. Water-oat is generally planted as a minor vegetable crop and its cultivated area is much less than rice. Here we report the results from studies on the reproduction hosts of C. suppressalis rice-associated population. 2

ACCEPTED MANUSCRIPT The majority of previous studies on C. suppressalis have focused on host selection and adaptions (Dai et al., 2003; Lin et al., 2008), its growth and development on

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different rice varieties (Zhou, 1985), and its infestation/survival rate and fitness on

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hybrid and conventional rice varieties (Ao and Qin, 1993; Huang and Liu, 1997; Wang et al., 2012). Information on the population dynamics of C. suppressalis on hosts other than rice and the effects of different hosts on its reproduction in natural

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settings is lacking, which greatly hinders efforts to develop successful IPM strategies

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(Xue et al., 2005).

Ecological factors, such as the availability of wild reproductive host plants and

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other resources during the period of rice production, or the type of control strategies

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implemented, will greatly affect C. suppressalis populations. For example, the

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recently widespread practice of sanitized isolation culture of rice seedlings to prevent virus transmission by Laodelphax striatellus or other pests at the seedling stage has

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been attributed to reduced populations of the striped rice stem borer and the yellow rice borer in single cropping rice regions (Zhang et al., 2012). To clarify the reproductive host plants used by C. suppressalis in field, and whether the practice of sanitized isolation culture of rice seedlings actually affects population density of the rice stem borer in rice fields, we systematically investigated oviposition preference, population survival, and development of C. suppressalis on rice and other reported host plants. This study provides essential information for the development of improved IPM strategies of C. suppressalis control.

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ACCEPTED MANUSCRIPT Materials and methods

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Insects

A colony of C. suppressalis originally collected on rice plants in 2003 and subsequently reared on rice seedlings in the laboratory was used as the rice-population

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in this study. The insects were reared under the conditions of 28±1ºC, >80% relative

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humidity, and a 16L (Light): 8D (Dark) light cycle with >2000 lux illumination. Blackened eggs were used for the inoculation tests to ensure hatchability, and healthy

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Host plants tested

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pupae were used for characterization of the oviposition preference in the cage test.

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The plants tested in laboratory experiments as potential hosts of C. suppressalis were hybrid rice-KU818 (purchased in Nanjing, China), maize (purchased in Nanjing, China), water-oat, wheat and sugarcane (provided by the Plant Protection Station of Wenling city, China).

Laboratory cage tests

A multiple-choice test was conducted in wood-framed, nylon mesh cages (1.2×0.6×1 m) to characterize the oviposition preference of C. suppressalis. Pots each 4

ACCEPTED MANUSCRIPT containing a host plant were randomly placed inside each cage. Each pot （2216.88 cm）contained either one to two hills of rice (tillering stage), one to two hills of water-

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oat (tillering stage), four to six seedlings of sugarcane, four to six seedlings of maize,

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or ten plants of wheat (growing stage). All of the host plants were adjusted to 30-40 cm in height. The bottoms of the cages were covered with wet sponges to provide moisture and a suitable microclimate. Ten pairs of C. suppressalis pupae were placed

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on a layer of moistened paper in a petri dish and put into each cage. After emergence

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of the adults and oviposition, eggs were collected and counted from each host plant under test every 2 days until all the adults had died. The test was replicated three

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times in three separate cages.

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Field survey of overwintering C. suppressalis oviposition on various plants

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Survey sites were located at various villages in Wenling, Zhejiang Province (28°22′ N, 121°21′E), where heavy infestation occurs naturally. In early May 2010, when the first wave of overwintering C. suppressalis moths peaked, the number of naturally occurring egg masses on locally planed rice, wheat, maize, sugarcane, water-oat and weed naturally occurred in intact overwintering paddy fields (mainly including Beckmannia syzigachne Fern and Polypogon fugax Nees ex Steud) were surveyed using five 1-m2 sampling points in each kind of plant field. The numbers of eggs were counted under a microscope. Three fields of each host plant were surveyed (three replicates, total 15 m2). A similar survey was conducted in the same areas in early 5

ACCEPTED MANUSCRIPT May 2011.

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Survival rates of C. suppressalis neonates on different host plants under laboratory

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and field conditions

Rice (tillering stage), water-oat (tillering stage), sugarcane (20-30 cm in height),

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maize (about 15 days old) and wheat (growing stage) cultivated in pots in the

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laboratory were infested with approximately 30 neonates of C. suppressalis per pot. There were four replicates (pots) for each host plant. The number of surviving larvae,

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their development stage and body length were measured and recorded after cultivation

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for 10 days.

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The survival and development of artificially introduced C. suppressalis neonates were investigated in fields located in Xinhe town, Wenling city, Zhejiang Province

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(28°22′ N, 121°21′E). Cages (1×1×1 m) were set up in rice, wheat, maize, sugarcane, water-oat and fallow fields. Egg masses were placed on the leaves of every plant inside the cages on 29th April, 2010 (approximately 300 eggs per cage). There were five replicates (cages) for each type of field (plant). After 20 days, the number of C. suppressalis larvae and their development were determined. The test was repeated on 21st April, 2011.

Data analysis

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ACCEPTED MANUSCRIPT The number of eggs found in field tests was expressed as the number of eggs per 100 m2. All data were presented in Excel (Microsoft, Redmond, WA, USA) and

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analyzed using one-way ANOVA followed by Tukey’s test for mean separations using

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SPSS (SPASS Inc., Chicago, IL, USA).

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Results

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The oviposition preference of C. suppressalis on different host plants in laboratory

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Under laboratory conditions, C. suppressalis showed strong differences in

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oviposition preference among different plants. The average number of eggs laid on

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water-oat, rice, wheat, sugarcane and maize were 207, 195, 16, 18, and 9, accounting for 46.5%, 43.8%, 3.6%, 4.0%, and 2.0% of the total eggs laid, respectively (Fig. 1).

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This indicates that even under laboratory condition (limited space) C. suppressalis adults clearly prefer rice and water-oat over wheat, sugarcane and maize for oviposition. Although more eggs were deposited on water-oat than on rice in this test, the difference was not statistically significant (P>0.05). The number of eggs laid on wheat, sugarcane and maize accounted for less than 10% of the total eggs produced, and was dramatically lower than on rice and water-oat.

Comparison of oviposition of C. suppressalis on different host plants in fields

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ACCEPTED MANUSCRIPT Under field conditions, the number of eggs laid on different plants by overwintering C. suppressalis also showed a clear oviposition preference. Although

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the local population density was not high, 29 egg masses were found on rice and 11

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on water-oat during the 2-years of the survey (Table 1). However, no eggs were found on any other plants checked in the same way, including wheat, maize, sugarcane and weeds on the intact overwintering harvested paddy field. These results suggest that

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only rice and water-oat serve as effective natural oviposition hosts for C. suppressalis.

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Otherwise, C. suppressalis adults usually tends to select large and green plants (of the same rice variety) to oviposit, so that plants at the tillering and heading stage are

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apparently more attractive than those at the seedling stage (Lin et al, 2008). However,

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the number of egg masses and eggs found on tillering stage of water-oat were less

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than those found on rice seedlings in this study, suggesting that rice is preferred over water-oat as a host, although no statistical difference in the number of egg masses was

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found due to the large variation in results.

Survival rates and development status of larvae on different host plants in laboratory

The survival rates of C. suppressalis neonates artificially inoculated on different host plants in pots were significantly different (F=10.78; p=0.0003). Higher survival rates were observed on rice and wheat (51.2% and 44.1%) followed by 10.8%, 7.2% and 1.5% on water-oat, maize, and sugarcane respectively (Fig. 2). The low survival rate on water-oat was interesting as adults laid large numbers of eggs onto this plant. 8

ACCEPTED MANUSCRIPT The development of neonates on various host plants is shown in Table 2. At 10 days after inoculation the average weights and lengths of larvae on rice and wheat were

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similar at 728 and 797 mg, and 4.6 and 4.4 mm, respectively. The average weight of

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larvae on water-oat was significantly lower than those on rice and wheat (637 mg), and their average length was also shorter (4.1 mm), though not significantly so. Larvae on maize and sugarcane developed much more slowly than those on rice and

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wheat (120 and 140 mg respectively, less than 25% of the weights on rice and wheat;

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2.7 and 2.1mm respectively, about half the length of those on rice and wheat).

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Neonates on maize and sugarcane also suffered higher mortality (Fig. 2).

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Survival rates of C. suppressalis larvae on different host plants under field condition

The survival rate and development of C. suppressalis larvae artificially inoculated

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onto different plants in fields are showed in Table 3. In 2010, the survival rates on the plants tested were ranked as wheat > rice seedlings > weeds (in fallow fields) > water-oat > maize > sugarcane, with very few survivors on maize (0.4 larvae/plant) and no survivors on sugarcane (F=4.19, P=0.0070). Over 80% of the neonates developed to the second or third instar stage on wheat, rice seedlings and weeds with some fourth-instar larvae found on rice seedlings and weeds (14.7% and 16.7%, respectively). In 2011, the ranking of larval survival on the plants was rice seedlings > wheat > water-oat > maize > weeds (in fallow field) > sugarcane (F=7.04, P=0.0004). The trend is similar to that in 2010 except that no surviving larvae were found on 9

ACCEPTED MANUSCRIPT weeds, which might be due to the high level of wilting of the weeds in 2011. The average larval survival rates on rice, wheat, water-oat, weeds, maize, and sugarcane

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were 49.1%, 36.5%, 10.7%, 2.5%, 1.2%, and 0% respectively. In addition, larval

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development was notably faster on rice and wheat compared to the other plants.

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Discussion

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Chilo suppressalis is commonly considered to be a polyphagous pest (Shen, 1965; Li and Li, 1996). However, its hosts have usually been identified by examining the

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infested plants in field or by inoculation survival experiment in laboratory. Since most

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insects can employ a range of food plants as supplements to complete their life cycle,

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especially when population densities are high and the preferred host plant is in short supply, the study of feeding habits based on the identification of hosts by recording

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occasional infestation and by no-choice inoculation rearing in laboratory may give misleading results. The current study suggests that C. suppressalis is not a typical polyphagous pest.

First, when presented with choices between various plants in laboratory cage tests, C. suppressalis deposited eggs mainly on rice and water-oat. The small number of eggs laid on plants other than rice and water-oat were probably the result of the high adult density and limited space for plant choice within the cages. C. suppressalis has been observed laying eggs on the cage walls when the moth density in rearing cages is high, and in our preliminary tests, the numbers of eggs laid on plants other than rice 10

ACCEPTED MANUSCRIPT and water-oat increased as the adult density increased, albeit consistently much less than on rice and water-oat. This is probably because when crowded, the excited moths

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shift from their preferred host plants to lay eggs on other species. More importantly,

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our field study showed that C. suppressalis rarely laid eggs on plants other than rice and water-oat. Because of the labor consuming, the sample size for the field survey was somewhat small. However, a dramatic difference was found between egg

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densities on the various plant species surveyed. Therefore, we can conclude that the

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major natural host plants for C. suppressalis egg laying are rice and water-oat only, though it could not entirely exclude the possibility that oviposition occasionally

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occurs on other plants by the survey with 30 m2 samples in two years.

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Second, our inoculation study showed that only rice and wheat could support

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significant larval survival and development of C. suppressalis. Maize and sugarcane severely delayed the larval development and led to high mortality. Water-oat was also

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an unsuitable host for larval development, which is interesting in the light of the significant number of eggs laid by overwintering adults on this plant. This is similar to the results that the trap crops for this borer, Sorghum sudanense and Vetiver zizanioides, can attract C. suppressalis to deposit eggs, but on which no offspring develop at all (Zheng et al, 2009). However, water-oat is not entirely unsuitable for C. suppressalis. Larvae can develop on water-oat, but with high mortality. We therefore conclude that although larvae of C. suppressalis can survive on many kinds of plants other than rice, rice is clearly the most suitable reproductive host for rice-population during rice growing season, while wheat may be the most suitable supplementary host 11

ACCEPTED MANUSCRIPT for overwintering larvae when rice is not available. This borer usually overwinter as 4th-6th instar larvae in diapause (with a development threshold temperature of zero

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9.3°C). The overwintering larvae may finish their larval development by feeding on

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different supplementary host plants during late autumn and early spring. Because of such a regime, C. suppressalis is very well adapted to the rice-wheat rotation system (Wang, 2006).

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Adult oviposition preference and the growth, survival, and reproduction of

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offspring on a plant are important criteria in assessing that plant as a suitable reproductive host for an insect (Thompson 1988; Cowley et al., 1992). The

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reproductive host plants should be suitable for adult oviposition, successful

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completion of larvae development and maintaining of sufficient population growth

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under natural environment conditions. Obviously, not all reported host plants are necessarily preferred reproduction hosts of C. suppressalis in nature. The results of

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our oviposition preference and neonate inoculation tests with the rice-population of C. suppressalis suggest that maize and sugarcane might not be natural hosts of C. suppressalis, since neither adults nor larvae could thrive on them. Winter wheat, green cover crops and weeds are probably also unsuitable since we did not record C. suppressalis actually choosing to lay eggs on them. In addition, winter wheat growing season only overlaps with overwintering C. suppressalis when their population density is generally low, and the moths are unlikely to choose wheat for oviposition. Therefore, wheat is probably not a natural reproductive host although wheat could serve as a good host for C. suppressalis larval development. It is more likely that C. 12

ACCEPTED MANUSCRIPT suppressalis uses winter wheat, green cover crops and weeds as a supplemental source of nutrition or acceptable pupation site (Lin et al., 2008). Rice and water-oat meet the

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criteria for reproductive host plants. However, water-oat might be a minor host plant

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for natural rice-population of C. suppressalis, not only because it is usually planted in small cultivated areas but also because larval surviving rate on it is low. This may differ for the different host-associated populations.

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Two different populations of C. suppressalis have previously been identified.

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Yoshitake (1994) reported that a water-oat-population of the rice stem borer did not damage rice. Sun et al. (2002) and Yu et al. (2002) found that a cross-mated

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population of two C. suppressalis populations associated with two different hosts

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could produce eggs, but with a very low hatching rate. Regarding host plant

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preference, most researchers found little difference in their adult oviposition and larval feeding. However, Chen et al. (2003) found that the larval surviving of

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water-oat-population was better on water-oat than on rice. Here, our results revealed that the larvae of rice-population had a lower survival rate on water-oat than on rice. Based on oviposition preference, egg hatching rate, and larval surviving rate, Hou et al. (2010) found that rice should be the preferred host plant of a water-oat-population but that wheat, corn and the other plants tested could not be suitable. Our results here demonstrated that rice is the major reproductive host plant for rice-population, with water-oat playing a minor role. The other recorded host plants tested might serve as supplementary hosts for overwintering larvae. Thus, for C. suppressalis, only a few plants in the grass family—rice and water-oat—appear to be effective reproductive 13

ACCEPTED MANUSCRIPT host plants. Rice is the main natural host for the rice-population and water-oat should be the best breeding host for water-oat-population. Therefore, C. suppressalis is not

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typically polyphagous. The previous polyphagia classification of C. suppressalis has

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been based mainly on reports of overwintering individuals found on plants other than rice (Shi, 1959; Liu, 1960). Following Pang and Lu’s report (1966) that ―Spring flowering plants are the main source of the first generation of Chilo suppressalis‖,

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many textbooks have listed wheat, barley, oilseed rape, broad bean, etc., as the main

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host plants of the first generation of C. suppressalis. However, Pang and Lu most likely mean that C. suppressalis can use these hosts to complete their development

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over the winter, while the monophagous yellow rice borers cannot do.

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This study suggests that in early spring C. suppressalis cannot make much use of

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plants other than rice to oviposit, grow completely and develop naturally in most rice growing areas. This finding provides a good basis for the effective control of the stem

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borer and could explain why the population densities of the rice stem borer and the monophagous yellow stem borer, but not the polyphagous pink stem borer, have been decreased sharply with the increasing practice of sanitized isolation culture of rice seedlings, in which rice seedlings are bred in isolated conditions. Therefore, reasonable control measures for the overwinter borers should be promoted and can effectively reduce C. suppressalis population by preventing its first generation from depositing eggs on rice seedlings.

Acknowledgement This work was supported by the Special Fund for Agro-scientific Research in the 14

ACCEPTED MANUSCRIPT Public Interest of China (201303017) and National Natural Science Foundation of China (31130045).

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Fig. 1. Oviposition preference of C. suppressalis on different host plants in laboratory.

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Bars marked with different letters are significantly different (Tukey test, P0.05)

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Fig. 2. Survival rate of the neonates of C. suppressalis on different host plants in laboratory.

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Bars marked with different letters are significantly different (Tukey test, P0.05)

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ACCEPTED MANUSCRIPT Table 1 Field survey of C. supressalis eggs on rice and water-oat in 2010 and 2011.* Numbers of egg mass per 100 m2

Numbers of egg per 100 m2

Crops

Growth stage

Rice

seedling

93.38±26.69 a

103.38±17.64 a

9171±1525 a

4586±330 a

Water-oat

tillering

33.35±6.68 a

40.02±30.00 a

1734±267 b

1901±908 b

2010

T

2011

IP

2010

AC

CE P

TE

D

MA

NU

SC R

*Mean±MS within columns followed by different letters are significantly different (t-test, P＜0.05)

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2011

ACCEPTED MANUSCRIPT

Table 2 Development of C. suppressalis on different host plants in laboratory.* Host plants

Average weight (mg)

Rice

727.63±8.24 a

Wheat

797.25±32.21 a

Water-oat

636.73±12.84 b

4.12± 0.18 a

Maize

119.52± 9.71 c

2.70± 0.15 b

Sugarcane

140.01±17.75 c

2.10±0.11 b

IP

T

Average length (mm) 4.64±0.43 a

NU

SC R

4.36± 0.28 a

AC

CE P

TE

D

MA

*Mean±SE within a column followed by different letters is significantly different (Tukey test, P0.05)

21

ACCEPTED MANUSCRIPT

Table 3 Larval survival of C. supressalis at 21 days after inoculation onto different host plants in field in

T

2010 and 2011.* Survival (%) 2011

Inoculation amounts

rice

300

34.43 ±4.15 ab

wheat

300

54.10±16.67a

18.90±8.30 b

36.50

water-oat

300

4.92 ±1.53b

16.54±9.18 b

10.73

weeds

300

4.92 ±1.53 b

0b

2.46

maize

300

1.63±1.00 b

0.79±0.79 b

1.21

sugarcane

300

0b

0b

0

63.78±20.76 a

NU

SC R

2010

IP

Type of fields

AC

CE P

TE

D

MA

*Mean±SE within a column followed by different letters is significantly different (Tukey test, P0.05)

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Average 49.10

ACCEPTED MANUSCRIPT 300

a

250

IP

T

200

150

100

50

NU

b

0

wheat

rice

b

b sugarcane

maize

MA

water-oat

SC R

Number of egg production

a

Host plants

a

CE P

AC

Survival rate

50

30

a

TE

60

40

D

70

20

b b

10

b 0

rice

wheat

water-oat

Host plants Graphical abstract

23

maize

sugarcane

ACCEPTED MANUSCRIPT Highlights •

The classification that Chilo suppressalis is commonly considered as a

C. suppressalis adults laid most eggs on water-oat and rice in a

IP

•

T

polyphagous pest has been challenged.

•

SC R

multiple-choice cage test.

Field surveys showed that no egg laid on plants other than rice and water-oat.

Larval survival rates were much higher on rice and wheat than on other

NU

•

plants tested in field or lab inoculation experiments. It suggests that the effective reproduction reproductive host of the rice

MA

•

AC

CE P

TE

D

population of C. suppressalis is rice.

24