0100002000030000400005000060000700008000090000

100000

Lim. M.S. Car.

Plant volatiles

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ts.

0100002000030000400005000060000700008000090000

100000

0 3 5

No. of days

Ion

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0

20000

40000

60000

80000

100000

120000

Barnyard Dallis Rice Rye Prairie Vasey

Grasses

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Chemical ecology and population dynamics of rice stink bug, Oebalus pugnax F., and natural enemies around rice plantingsChemical ecology and population dynamics of rice stink bug,

Oebalus pugnax F., and natural enemies around rice plantings

Rice stink bug (RSB), Oebalus pugnax F. (Hemiptera: Pentatomidae) is one of the most important pests of rice during grain formation in the United States (Fig. 1 and 2). The RSB punctures rice grains and sucks out its milky contents resulting in loss of both grain quality and yield (Fig. 3). A chemical ecology study was conducted to determine the volatiles induced in grass host panicles after RSB feeding occurred and if limonene, methyl salicylate or both attract RSB or natural enemies species. Effect of habitat diversity on rice stink bug population density and their movement into rice at six different rice planting sites were also studied.

1. To identify and compare panicle head space volatiles of rice stink bug hosts (healthy and fed on by RSB)

2. To determine effect of habitat diversity and bait composition on trap capture of RSB and parasitoids

Introduction

Fig 3. Damaged rice kernels due to RSB feeding

Objectives

Materials and Methods

Two-choice olfactometer bioassay and electroantennogramstudies will identify biologically active volatiles from host plants, egg masses and adult RSB that attract RSB and its parasitoids

Future Research

References

Acknowledgements

Volatiles: A comparison was made in the quantity of headspace volatiles released into air by panicles of several RSB grass hosts. Hosts were either healthy or had 20 RSB adults caged and feeding on four panicles for one, three or five days (induced volatile production). Grasses used were barnyard grass (BG), dallisgrass (DG), ryegrass, vaseygrass, prairie grass (Tall) and rice. Volatiles were collected on a Super Q trap for 8 daylight hours, eluted with 150 uldichloromethane + 10 ul ethyl caprate (a standard) and a 1 ulsample injected into gas chromatograph / mass spectrometer (GC/MS) to identify and quantify volatiles.

Trapping and Sweeping: The purpose was to evaluate baited traps for estimating density of rice stink bugs and natural enemies in and around rice fields. Yellow sticky cards (7 X 12 cm) attached to yellow pyramid traps were baited with lures releasing limonene, methyl salicylate, both or none. Six traps were placed in each of six sites adjacent to rice plantings in Arkansas. Ten sweeps were made of grass panicles adjacent to each of these traps and the adjacent rice field.

Fig 1. RSB nymphs Fig 2. RSB adult

James, D.G and T.S Price. 2004. Field-testing of methyl salicylate for recruitment and retention of beneficial insects in grapes and hops. J. Chem. Ecol. 30:1613-1628.

Tao X., Q. ZHOU, W. ZHANG, G. ZHANG and D. GU. 2002. Effects of herbivore-induced rice volatiles on the host selection behavior of brown planthopper, Nilparvata lugens. Chinese Science Bull. 47:1355-1360.

Date TrapSweep grass

Between trapsSweep

rice field

8 June 0.58 a 5.39 a --

22 June 0.97 a 5.30 a --

7 July 0.80 a 1.36 a 0.84 b

21 July 0.44 a 2.16 a 0.58 b

4 Aug. 0.30 a 1.67 a 2.42 ab

17 Aug. 0.22 a 1.14 a 3.04 a

3 Sept. 0.02 a 3.47 a 2.02 ab

Site Trap

Sweep grass between

trapsSweep

rice field

Stuttgart 1 1.0 a 7.9 a 4.0 a

Stuttgart 2 0.3 ab 2.8 ab 1.9 bc

Stuttgart 3 0.05 b 1.6 b 1.4 bc

Conway 1.0 a 4.4 ab 0.9 c

Blackwell 0.6 ab 0.9 b 2.8 ab

Geridge 0 b 0 b --

Field and laboratory assistance by Barbara Lewis and Jackie McKern.

Means followed by a different letter in each column in each group differ significantly using Tukey-Kramer HSD Test at α = 0.05

Means followed by a different letter in each column in each group differ significantly using Tukey-Kramer HSD Test at α = 0.05

Table 1. Mean number of RSB caught in traps, sweeping grass between traps and rice field adjacent to traps throughout the rice season (2005)

Table 2. Mean number of RSB caught in traps, sweepings of grass between traps and in rice field adjacent to traps from differentsites with different habitat vegetation diversity

Fig 4. GC/MS ion counts (+ SE) of volatiles induced by RSB feeding on grasses. Bars with the same letters are not significantly different at α =.05 (Tukey-Kramer HSD test )

Fig 5. GC/MS ion counts (+ SE) of volatiles induced by 0 (unfed) to 5 days of RSB feeding

Fig 6. GC/MS ion counts (+ SE) of limonene (Lim.), methyl salicylate (M.S.) and caryophyllene (Car.) induced by RSB feeding

Volatiles• Rice and vasey grass panicles produce more host-induced

plant volatiles when fed upon by RSB than do other host grasses (Fig. 4)

• Panicles fed upon 3 days had more induced volatile production than did panicles unfed and fed on for 5 days (Fig. 5)

• Fed on panicles were induced to produce significantly more limonene than methyl salicylate or caryophyllene (Fig. 6)

Trapping and Sweeping • No difference was found in RSB counts from baited and

unbaited traps (Table 1) but some dates had high counts of Meloid beetles only in the methyl salicylate baited traps

• RSB counts were more in traps and in grass sweep net samples before and after rice heading period compared to higher sweep counts in rice only during heading (Table 1)

• RSB counts were higher in traps and grass sweeps of rice fields surrounded by host grasses in Stuttgart 1 and 2 and Conway than in sites with mostly broadleaf plants and/or non-host grasses, i.e., Geridge, Stuttgart 3 and Blackwell (Table 2)

Narinderpal Singh, Donn T. Johnson, Rolfe J. Bryant and John L. Bernhardt, Department of Entomology, University of Arkansas, Fayetteville, AR 72701

Results

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