Siwei Liu1, Thomas W. Phillips1, Franklin H. Arthur 2 and Doug Vangundy3 (1)Oklahoma State University,

Stillwater, OK (2) USDA ARS, Manhattan, KS (3)Wellmark International 12200 Oenton Dr. Dallas, TX

Effects of Combining Methoprene and Aeration Against Stored Grain Insects

Introduction

Over the past decade IPM has been implemented for stored grain. And the

uses of reduced-risk insecticides and non-chemical controls have increased.

Insect growth regulators such as JH analogues have very low toxicity for

humans, but affect or disrupt the normal growth and development of

insects by interfering with development. The first objective of our study

was to compare and contrast methoprene, Diacon II, used as a top-

dressing alone, as a complete grain mass treatment alone, or complete

treatment combined with grain aeration to prevent insect infestation of

wheat stored in field. The second objective was to determine the stability of

Diacon II residues on stored wheat and to verify its activity against insects

by laboratory bioassays.

Acknowledgments

USDA-CSREES PMAP and RAMP programs for partially funding this work.

Mr. Edmond Bonjour provided support.

Summer aeration was able to cool grain in this study 10-15 °C below that of

non-aerated grain (Fig. 4). A cost-benefit analysis of the use of aeration fans in

this study showed our fans ran for an average 893.8 hours in 10 months. It cost

$ 0.0026 per kg grain, or about $0.07 per bu. Aeration is expensive and it is very

difficult to get the grain below 20 °C during summer in Oklahoma. Aeration

may be more cost-effective during the fall and winter time. Most insect pest

species are very sensitive to temperature below 20 °C and the moisture contents

below 12-13 %. In Oklahoma it is possible and worthwhile to store grain at

temperatures close to 5 °C in the winter season following fall aeration.

Materials and Methods 

  Insects:

Field study: Sixteen 500-bu bins (Fig. 1) filled with new hard red winter

wheat were used at the Oklahoma State University Stored Product

Research and Education Facility. The treatments were aeration only as a

control, treatment of the top 50 cm methoprene (top-dressing), complete

grain mass treatment of methoprene and a combination of aeration and

methoprene. Methoprene was applied at the label rate of 1 ppm in all

cases. After all bins were treated, 100 adults each of RFB, LGB, and RGB

were added weekly into each bin for four weeks. The OPI system for

temperature monitoring and aeration-control was used to turn the fans on

or off to cool grain in designated bins using ambient cool air (night time).

Fans were programmed to turn on when air temperature dropped below

grain temperature.  Probe trap (Fig. 2) and

Grain trier (Fig. 3) samples were taken monthly.

Plodia interpunctellaIndianmeal moth, IMM

Tribolium castaneumRed flour beetle, RFB

Rhyzopertha dominicaLesser grain borer, LGB

Cryptolestes ferrugineusRusty grain beetle, RGB

Sitophilus oryzaeRice weevil, RW

Laboratory bioassay: Bioassay samples of grain from experimental bins

were taken immediately after treatment and 5 and 10 months following

treatment. Twenty-five 0-1 day old eggs of IMM were placed in 120 ml jars

with 40 g wheat (of which 20 g were crushed) and held a in growth

chamber. Fifty RFB, LGB, or RW adults were placed in 240 ml jars by

species with 100 g wheat (5 g crushed for RFB), and placed in a growth

chamber (Fig. 4.). IMM egg-hatch was checked after 1 week and count

normal adult development was made after 6 – 8 weeks. Parent beetles were

removed after 1 week and F1 progeny were counted after 6 weeks. Grading

and methoprene residue analysis were carried out at both the beginning

and the end of this study.

Tab. 1. Mean adults (SE) captured during 7 days in probe trap in wheat bins

treated with methoprene and aeration at six times during storage (N=4 )

Species andTreatment

Mean ± (SE)

19-Aug 16-Sep 14-Oct 11-Nov 9-Dec 28-Apr

T. castaneumAerationTop

Methoprene

Methoprene + Aeration

1017.50 A(227.57) b

660.25 AB(242.47) a

772.50 AB(383.41) a

250.25 B(33.20) a

1974.75 A(491.75) a

974.25 AB(473.69) a

340.25 B(243.02)ab

301.00 B(73.32) a

41.75 AB(16.87) c

153.00 A(79.31) b24.25 B(7.49) bc 7.25 B(0.95) b

22.00 AB(11.74) c

46.00 A(28.12) b5.00 B(1.00) c5.50 B

(1.32) b

79.00 A(50.49) c

33.75 A(30.45) b1.75 A(1.44) c0.00 A(0.00) b

2.50 A(1.04) c

1.50 AB(0.78) b0.25 B(0.25) c0.00 B(0.00) b

Tab. 2. Mean (SE) adult density ( per Kg) from grain trier samples taken in wheat

bins treated with methoprene and aeration at six times during storage (N=4)

Species and Treatment

Mean number per Kg ± (SE)

19-Aug 16-Sep 14-Oct 11-Nov 9-Dec 28-Apr

T. castaneumAerationTop

Methoprene

Methoprene + Aeration

11.73 A(0.89) a0.76 B

(0.44) ab 0.95 B

(0.48) a 0.58 B

(0.37) b

5.64 A(2.16) ab 2.19 AB(0.73) a 0.79 B

(0.57) a 1.86 B

(0.49) a

5.08 A(1.85) ab 2.97 AB

(1.11) a0.93 BC(0.35) a

0.36 C(0.36) b

6.36 A(4.68) ab

1.47 A(1.47) ab

0.55 A(0.55) a

0.55 A(0.35) b

3.39 A(2.20) b1.47 A

(0.79) ab0.19 A

(0.19) a 0.56 A(0.35) b

0.61 A(0.61) b0.0 A

(0.00) b0.0 A

(0.00) a 0.0 A

(0.00) b

R. dominica AerationTop

Methoprene

Methoprene + Aeration

1.25 A (0.95) a1.25 A(0.48) b0.75 A(0.48) a3.50 A

(1.85) a

1.75 A(0.63) a1.25 A(0.95) b0.25 A(0.25) a0.25 A(0.25) b

3.50 A(1.04) a

2.75 AB(1.80) b0.50 B(0.50) a0.50 B

(0.29) ab

1.25 A(0.75) a0.00 A(0.00) b0.50 A(0.29) a0.50 A

(0.50) ab

9.75 AB(8.76) a

17.75 A(9.56) a1.25 B(0.63) a

2.25 AB(1.44) ab

0.25 B(0.25) a0.00 B(0.00) b

0.75 AB(0.48) a2.00 A(0.71)ab

C.ferrugineusAerationTop

MethopreneMethoprene + Aeration

40.00 A(13.40) a

29.00 A(10.78) a

45.74 A(8.53) a

43.50 A(28.23) a

34.00 A(17.71)ab20.00 A

(6.49) a28.75 A(12.58) a

25.25 A(7.03) a

26.25 A(9.58) ab

14.50 AB(11.24) a

2.75 B(1.04) b

5.25 AB(2.56) b

24.25 A(13.37)ab

7.00 AB(1.73) a1.50 B(0.87) b3.25 B(2.14) b

5.25 A(1.93) b7.25 A(2.50) a0.00 B(0.00) b0.75 B

(0.75) b

43.50 A(12.28) a11.50 B(10.19) a0.00 B(0.00) b

1.00 B

(0.41) b

R. dominica AerationTop

Methoprene

Methoprene + Aeration

2.71 A(0.72) ab0.58 B(0.19) b

1.35 AB(0.37) a

1.70 AB(0.76) a

2.83 AB(0.86) ab4.04 A(1.43) a0.95 B

(0.71) ab0.92 B

(0.46) ab

4.36 A(1.15) a

2.25 AB(1.54) ab0.74 B

(0.43) ab1.10 AB

(0.47) a

2.42 A(0.94) ab

2.01 AB(1.13) ab0.18 B(0.18) b

0.37 AB(0.21) ab

3.76 A(0.31) a1.29 B

(0.56)ab 0.55 BC

(0.35)ab0.00 C(0.00) b

1.60 A(1.60) b0.37 A(0.21) b0.00 A(0.00) b0.00 A(0.00) b

C. ferrugineus AerationTop

Methoprene

Methoprene + Aeration

6.40 A(2.85) b1.74 AB

(0.86) ab0.96 AB(0.19) a

0.96 B(0.57) ab

17.66 A(2.22) ab

1.47 B(1.00) ab

0.40 B(0.40) b

1.48 B(0.79) a

12.04 A(3.47) ab

0.55 B(0.35) ab

0.00 B(0.00) b

0.18 B(0.18) ab

22.40 A(12.95)ab2.92 AB

(1.82) ab0.00 B

(0.00) b1.47 B

(0.67) a

31.00 A(3.78) a

3.13 B(1.25) a0.00 C

(0.00) b0.19 C

(0.19) ab

1.04 A(2.27) b

0.00 B(0.00) b

0.00 B(0.00) b

0.00 B(0.00) b

Means in the same column with the same capital letters are not significantly different, and mean in

the same row with the same small letters are not significantly different. LSD procedure at P<0.05.

Bioassays of grain samples taken soon after the grain was treated, and at 5 and 10

months of storage, showed that any grain treated with methoprene was very active

against species such as IMM (Tab. 3) and RFB (Tab. 4), for which all larval stages

are externally feeding. Methoprene was also active against LGB, normally

considered an internal feeder, but whose first instar larvae feed freely in the grain

before going inside kernels (Tab. 4). However, RW, whose larvae are entirely

internal feeders, generally escaped effects of methoprene. Chemical residue analysis

showed good coverage in our treated bins and very little degradation over 10 months

of storage. Diacon II is relatively expensive compared to other insecticides, so a low

dose is necessary. Top dressing is a good method to apply. Diacon II does not control

all pests. Therefore, it applied in combination with aeration is a good idea, which

can enhance population suppression of internal feeders in stored grain.

Fig. 4. Mean temperature °C each week from aeration and non- aeration bins

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

Date (7/21/2004-5/8/2005)

Mea

n (

SE

)

Aeration Bins

Non-Aeration Bins

Tab. 3. P. interpunctella emerge to normal adults at different storage times

Treatment

Mean % developed to normal adults ± (SE) (N = 4)

Stored 0 months Stored 5 months Stored 10 months

A

T

M

MA

98.69 (1.32) A

3.88 (2.51) B

0.00(0.00) C

0.00 (0.00) C

98.75 (1.25) A

8.00 (5.07) B

0.00 (0.00) C

0.00 (0.00) C

98.75(1.25) A

21.84 (10.55) B

0.00(0.00) C

0.00 (0.00) C

Tab. 4. The mean (SE) F1 adults per 50 parent adults produced in bioassasy of grain

removed from experimental bins at different storage times (N = 4)

Trt Stored 0 months Stored 5 months Stored 10 months

RFB LGB RW RFB LGB RW RFB LGB RW

A

T

M

MA

248.50A

(14.29)

0.00 B

(0.00)

0.00 B

(0.00)

0.00 B

(0.00)

696.75A

(36.95)

1.50 B

(1.19)

0.00 B

(0.00)

0.50 B

(0.50)

680.50 A

(30.97)

825.75 A

(20.21)

1260.0 A

(588.58)

464.50 A

(133.47)

133.25A

(22.75)

0.00 B

(0.00)

0.00 B

(0.00)

0.00 B

(0.00)

482.0 A

(15.54)

31.25 B

(25.63)

0.75 C

(0.75)

0.25 C

(0.25)

598.75 AB

(23.68)

430.50 B

(53.88)

582.25 AB

(34.31)

681.25 A

(61.18)

278.50A

(26.56)

0.00 B

(0.00)

0.25 B

(0.25)

0.25 B

(0.25)

514.75A

(44.69)

25.25 B

(8.39)

0.25 C

(0.25)

0.25 C

(0.25)

724.25 A

(55.90)

517.75AB

(81.62)

487.00 B

(50.85)

680.00AB

(100.26)

Insect numbers in grain bins varied significantly by treatment and over time as

indicated by probe trap and grain trier samples (Tab. 1 and 2). Diacon II at 1

ppm resulted in reduced numbers of insects of all three species studied, and the

methoprene treatment to the total grain mass seemed most effective, whether

with or without aeration (Tab. 1 and 2).

Analysis of grain damage, as measured by the mean number of insect-damaged

kernels per 100 g, at the end of the experiment was 9.0, 4.3, 3.3 and 2.0 for bins

with aeration control, top-dressing, total methoprene, and methoprene

combined with aeration, respectively.

Treatments. A: aeration, T: to-dress methoprene. M: methoprene total, MA: methoprene total + aeration.

Means in the same column with the same capital letters are not significantly different, and mean in

the same row with the same small letters are not significantly different. LSD procedure at P<0.05.

Treatments. A: aeration, T: to-dress methoprene. M: methoprene total, MA: methoprene total + aeration.

Results and Conclusions

Fig. 1. 500-bu bins Fig. 3. Grain trierFig. 2. Probe trap