High temperature combined with carbon dioxide enriched or reduced oxygen atmospheres for control of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

J. stored Prod. Res. Vol. 28, No. 4, pp. 235238, Printed in Great Britain. All rights reserved

1992 Copyright

0

0022-474X/92 $5.00 + 0.00 1992 Pergamon Press Ltd

HIGH TEMPERATURE COMBINED WITH CARBON DIOXIDE ENRICHED OR REDUCED OXYGEN ATMOSPHERES FOR CONTROL OF TRIBOLIUM CASTANEUM (HERBST) (COLEOPTERA: TENEBRIONIDAE) EDWIN L. SODERSTROM,’ DAVID G. BRANDL’

and BRUCE MACKEY*

‘Horticultural Crops Research Laboratory, USDA-ARS, 2021 South Peach Avenue, Fresno, CA 93727, U.S.A. and %lSDA-ARS, Western Regional Research Center, Albany, CA 94710, U.S.A. (Received for publication 29 June 1992)

Abstract-Heat combined with controlled atmospheres increased mortality of Tribolium castaneum (Herbst) larvae when temperatures of 238°C were combined with carbon dioxide enriched or oxygen deficient atmospheres. Preconditioning of larvae to treatment temperature for 24 or 48 hr prior to controlled atmosphere treatments at 38°C significantly reduced larval mortality relative to a 1 hr preconditioning. Heat combined with controlled atmospheres can significantly reduce treatment time. However, if heat is applied prior to the application of controlled atmospheres, the time of treatment must be extended.

INTRODUCTION

Insect disinfestation treatments for harvested agricultural commodities ideally provide fast treatment times and precise control of treatment conditions to obtain the prescribed level of insect mortality. Jay (1986) reported that application of a 99% carbon dioxide (CO,) atmosphere at high temperatures (32, 38 and 43°C) reduced the exposure time for 99% mortality of Tribolium castaneum (Herbst) from 24 hr at 32°C to 6 hr at 38 and 43°C. Reducing the required exposure time would be advantageous when commodities are being received in large volumes at the processors, and for reducing the number and size of treatment facilities. Chen er al. (1991) showed that brief temperature preconditioning of insects to increased temperature protected them from injury from further exposure to high temperature. The objective of this research was to evaluate high temperatures combined with CO2 enriched or oxygen (0,) deficient atmospheres for improving postharvest insect control of T. castaneum, and to determine if preconditioning of T. castaneum to a high temperature would alter the degree of insect mortality. MATERIALS

AND

METHODS

Tribolium castaneum (Herbst) was obtained from USDA-AR& Savannah, GA and reared at 27 f O.YC, 60 k 5% r.h. with a photoperiod of 16: 8 (L: D) on a diet of 14 parts rice bran, 5 parts whole wheat flour, and 1 part brewers’ yeast. For testing, 4-5 wk old larvae were placed 50 per 25 ml plastic vial containing 2 g diet. Last instar larvae are generally reported to be the most CO, tolerant stage (Jay, 1984) and were therefore used for this research. Atmospheres, enriched with carbon dioxide (CO,) or deficient in oxygen (O,), were obtained by blending CO? or nitrogen (N2) with air and humidified using methods and test equipment described by Soderstrom et al. (1990). Carbon dioxide enriched atmospheres were 60, 90, 95, or 98% CO, in air and O2 deficient atmospheres were 0.5, 1, 2, or 5% O2 with the balance mainly consisting of N, . All atmospheres were humidied to 60% r.h. using a glycerol-water solution. The atmosphere flow rate was continuous at 30 cm’/min through each individual vial equipped with a rubber stopper having inlet and outlet tubes. Exposure time to the atmospheres was 6 hr. Control insects were exposed to flowing air for 6 hr at 27°C 60% r.h. Post-treatment holding conditions were 27°C and 60% r.h. 235

EDWIN L. SODERSTROMet al.

236

Two tests were conducted. In the first test, the interaction of high temperatures of 38,40, or 42°C with CO2 enriched or O2 deficient atmospheres was tested. Six vials (50 larvae per vial) were treated with each temperature x atmosphere combination shown in Table 1. All treatments, conducted in walk-in environmental chambers, were replicated 3-5 times. The insects were preconditioned to the treatment temperature for 1 hr followed by the 6 hr exposure to the treatment atmosphere. The second test evaluated the effect of high temperature (38°C) preconditioning for 1,24, or 48 hr on subsequent treatments with CO2 enriched or O2 deficient atmospheres at 38°C. Two vials (100 larvae total) were treated at each preconditioning time followed by the atmosphere-temperature combination. The 6 hr treatments were replicated 4-5 times. Mortality was determined by counting and removing emerged adults at weekly intervals for 4 wk. In some cases the emerged adults were dead when collected, however they were treated as survivors if eclosion was complete. Data were corrected using Abbott’s formula (1925), transformed into logits to stabilize the variance, and analyzed with the General Linear Models Procedure (SAS Institute, 1987). The test of the interaction between temperature and atmosphere was carried out in a split plot design with temperature as the whole plot treatment and atmosphere as a subplot treatment. Standard errors and corresponding degrees of freedom were adjusted for the bilevel error structure using the methods of Milliken and Johnson (1984). The test of the interaction between the duration of temperature preconditioning and atmospheres was a randomized complete block design. In both cases separate analyses were performed on the COz. enriched and 0, deficient treatments. Predicted mortalities and 95% confidence limits (in logit units) were determined from the model and back transformed to provide predicted percentage of mortalities.

RESULTS

AND DISCUSSION

Increased concentrations of CO, or reduced concentrations of O2 progressively caused greater mortalities to T. custaneum larvae (Table 1). Increasing temperature with these atmospheres also resulted in progressively greater mortalities. The analyses of variance of adjusted mortalities, expressed as logits, are presented in Table 2. In both analyses, temperature and atmosphere main effects were significant (P < 0.05). Temperature x atmosphere interaction was also significant and showed a linear temperature effect within atmosphere; however the P value for the quadratic temperature effect of O2 deficient atmospheres was low (P = 0.065), but not significant. Plots of LSMEANS of logits (Fig. 1) show CO* enriched atmospheres as linear with respect to temperature while some 0, deficient atmospheres have curvature as suggested by the near significance of the interaction quadratic effect. The significant interaction term of the ANOVA is an indication of synergism or interference between main effects. The positive and increasing slopes (with higher CO, concentrations or lower O2 concentrations) in these plots show a synergistic effect with these atmospheres and temperatures. Table 2.Analysis of variance of logit (of adjusted mortality) of T. co~mnerun larvae treated at high temperature combined with CO, enriched or 0, deficient atmosuheres Table 1. Predicted percent mortality (95% confidence limits) of T. c(~sfaneum larvae treated for 6 hr at high temperatures combined with CO* enriched or Oz deficient atmospheres Temperature (“C) Concentration (%)

38

40

42

CO, enriched atmospheres 60

90 95 98

0.5

1.0 2.0

5.0

10.3(4.9-20.3) 42.1 (24.7-61.8) 54.9 (35.3-73.0) 87.3 (75.6-93.9)

15.2(6.4-32.0) 70.8 (49.8-85.5) 89.7 (78.1-95.5) 99.1(97.M9.7)

18.3(8&35.4) 82.5 (65.8-92.0) 99.5 (98.8-99.8) 99.8 (99.699.9)

76.4(62.&86.1) 40.4 (26.1-56.5) 9.2(5.0-16.3) 2.5 (1.3-4.6)

88.4(79.S93.6) 62.4 (46.476.1) 12.4(6.9-21.3) 3.9 (2.1-7.2)

99.5(99X&99.7) 96.6 (93.6-98.2) 33.8(21.0-49.4) 6.4 (3.5-l 1.6)

df

source

MS

F

P>F

21.42 5.90 253.00 16.16 30.38 2.12 -

0.0002 0.0001 0.0001 0.0001 0.0001 0.1192 -

35.34 3.19 336.43 10.26 17.81 2.70 -

0.000 I 0.0093 0.0001 0.0001 0.0001 0.0654 -

CO, enriched atmospheres Temperature Rep (temp) [error (temp)] Atmosphere Temoerature x atmosohere Lihear Quadratic Error

2 10 3 6 3 3 29

41.260 1.926 82.629 5.277 9.923 0.693 0.327

O2 dqkient atmospheres Temperature Rep (temp) [error (temp)] Atmosphere Temperature x atmosphere Linear Quadratic Error

2 9 3 6 3 3 27

29.394 0.832 87.662 2.673 4.642 0.704 0.261

Control of Tribolium castaneum

6

-61’

Pefeent 0,

Ll

I

35

1

231

42

40

35

I

I

40

42

Temperature (C)

Temperature (C)

Fig. 1. Mortality of T. castaneum larvae. exposed to CO, enriched or 0, deficient atmospheres for 6 hr. Mortalities are expressed as LSMEANS of logits (adjusted mortality).

Longer duration of larval preconditioning with a high temperature (38°C) generally decreased the effect of subsequent exposure to COz enriched and O2 deficient atmospheres (Table 3). Analyses of variance for the effects of preconditioning time combined with CO1 enriched or O2 deficient atmospheres at 38°C are in Table 4. Preconditioning time and atmosphere main effects were both significant with CO* enriched atmospheres. Preconditioning time x atmosphere interaction was not significant. The effect of preconditioning time was shown to be linear. With the O2 deficient atmospheres, atmosphere main effect was significant as was the preconditioning time x atmosphere interaction; the latter was attributable to a linear precondition time effect within the O2 deficient atmospheres. Plots of LSMEANS of logits (Fig. 2) show that increasing preconditioning time inhibited the effectiveness of the CO1 enriched atmospheres. For the O2 deficient atmospheres, preconditioning time inhibited effectiveness of the 0.5 and 1% O2 atmospheres but not the 2 and 5% O2 atmospheres. This data shows a similarity with that of Chen et al. (1991) who showed that pre-exposure of flesh flies, Sarcophuga crassipalpis Macquart, to 40°C protected them from heat injury when subsequently exposed to 45°C. The time required to heat insect infested commodities prior to controlled atmosphere application must be taken into consideration in determining exposure times for disinfesting stored commodities using high temperatures combined with controlled atmospheres. Table 4. Analysis of variance of logits (of adjusted mortality) of T. ca.rraneum larvae preconditioned to 38°C for 1, 24, or 48 hr and exoosed to CO, enriched or 0, deficient atmosoheres for 6 hr df

Source

MS

F

P>F

CO, enriched atmospheres

Table 3. Predicted percent mortality (95% confidence limits) of T. ca~f~eum larvae as affected by duration of preconditioning to 38°C orior to a 6 hr exoosure to CO, enriched or 0, deficient atmosoheres Preconditioning Concentration (%)

1

time (hr)

24

48

CO, enriched atmospheres 60 90

95 98

4.3 (2.&9.0\ 13.6<6.7-25.6) 22.5(11.7-38.8) 75.4(58.3-87.0)

2.6(1.1-6.2\ 17.1 i7.S-33.b) 22.8(10.8-42.0) 53.4(31.8-73.8)

2.5 11.0-5.91 6.6 i2.8-14.i) 12.7(5&26.4) 22.3(10.5-41.3)

0, defitient armospheres 0.5 1.0 2.0 5.0

81.1 (68.5-89.5) 48.1 (31.9-64.6) 6.0 (3.1-11.2) 1.1 (0.6-2.1)

56.3 (39.5-71.8) 35.7(21.!&52.3) 9.5 (5.1-17.2) 1.7 (0.9-3.3)

34.2(19.&53.6) 23.8(12.341.0) 9.5 (4.5-18.9) 6.9 (3.2-14.1)

Preconditioning time Linear Quadratic Atmosphere Rep Atmosphere x preconditioning time Error

3 4

5.228 9.790 0.667 26.342 2.108

7.01 13.12 0.89 35.31 2.83

0.0027 0.0009 0.3509 0.0001 0.0389

6 36

0.996 0.746

I .34

0.2672

2 1

I

-

0, deficient ammspheres Preconditioning time Atmosphere Rep Atmosohere x preconditioning time Linear Coydratic

2 3 3

0.191 35.890 1.349

0.43 81.09 3.05

0.6538 0.0001 0.0444

6 3 3 29

2.776 5.330 0.254 0.443

6.27 12.04 0.57 -

o.OcO3 O.OcOl 0.6367 -

EDWIN L. ~ODFMTROMet al.

238

1

24

24

48

Time (h)

Time (h)

Fig. 2. Mortality, expressed as LSMEANS of logits (of adjusted mortality), of T. casruneum larvae preconditioned to 38°C for 1,24, or 48 hr and then exposed to CO, enriched or 0, deficient atmospheres at 38°C for 6 hr.

This research shows that increasing temperature and using higher concentrations of CO2 or lower concentrations of O2 increased T. castaneum larval mortality and could be useful for reducing treatment duration. However, if commodities are preheated for several days prior to application of controlled atmospheres, insect mortality could be reduced, thus requiring a longer treatment for insect control. Acknowledgements-We

thank Overlin Zamora and Rodney Fries for technical assistance. We also thank Guy Hallman and Harold Moffitt for reviewing this manuscript.

REFERENCES Abbott W. S. (1925) A method for computing the effectiveness of an insecticide. J. Econ. Entomol. 18, 265-267. Chen Cheng-Ping, Lee R. E. Jr and Denlinger D. L. (1991) Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures. Physiol. Entomol. 16, 19-26. Jay E. (1984) Imperfections in our current knowledge of insect biology as related to their response to controlled atmospheres. In Controlled Atmosphere and Fumigation in Grain Storages (Edited by Ripp B. E. et al.), pp. 493-508. Elsevier, Amsterdam. Jay E. G. (1986) Factors affecting the use of carbon dioxide for treating raw and processed agricultural products. In GASGA Seminar on Fumigation Technology in Developing Countries, pp. 173-189. Tropical Development and Research Institute, Slough, U.K. Milliken G. A. and Johnson D. E. (1984) Analysis of Messy Data Vol. 1: Designed Experiments, pp. 296314. Lifelong Learning, Belmont, CA. SAS Institute (1987) SAS/STAT Guide for Personal Computers, version 6 edn. SAS Institute, Cary, NC. Soderstrom E. L., Brand1 D. G. and Mackey B. E. (1990) Responses of codling moth (Lepidoptera: Tortricidae) life stages to high carbon dioxide or low oxygen atmospheres. J. econ. Em. 83, 472475.