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Low and high temperatures for the control of cowpea beetle, callosobruchus maculatus (F.) (coleoptera: Bruchidae) in chickpeas
Journal of Stored Products Research 47 (2011) 244e248
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Low and high temperatures for the control of cowpea beetle, callosobruchus maculatus (F.) (coleoptera: Bruchidae) in chickpeas M. Loganathan b, D.S. Jayas a, *, P.G. Fields c, N.D.G. White c a
Department of Biosystems Engineering, University of Manitoba, Winnipeg, Manitoba, Canada Indian Institute of Crop Processing Technology, Thanjavur, Tamil Nadu, India c Cereal Research Centre, Agriculture & Agri-Food Canada, Winnipeg, Manitoba, Canada b
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 21 March 2011
Chickpea (Cicer arietinum L.; Leguminasae) is an important pulse crop grown, around the world. The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (Coleoptera: Bruchidae), which is the most important field-carry-over storage pest of pulses. The management of this insect in storage using chemicals leads to insecticide residues in grains and insecticide resistance development in insects. Thermal disinfestation is one of the means of physical insect control. Eggs, larvae, pupae and adults were held at 42 or 0 C for varying durations. Pupae and adults were equally heat tolerant. The lethal time to reduce survival by 50% (LT50) at 42 C for eggs, larvae, pupae and adults were 18, 57, 78 and 71 h, respectively. Pupa was the most cold-tolerant stage. The LT50 at 0 C for eggs, larvae, pupae and adults were 3, 8, 10 and 4 d, respectively. The LT50 for pupae were 4907, 4262, 336, 36 and 13 min at the grain temperature of 42, 45, 50, 55 and 60 C, respectively. The LT50 of pupae at 0,5,10 and 15 C were 274, 122, 7 and 2 h, respectively. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
Keywords: Cicer arietinum Callosobruchus maculatus High and low temperatures
1. Introduction Chickpea (Cicer arietinum L.) is an important legume crop grown around the world. Chickpea is used as whole grain, split dhal and also as powder for preparation of various snack foods. The world production of chickpea is 8.8 Mt (million tonnes), of which India produces 6.3 Mt (FAO statistics, 2007). The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), which is the most important fieldcarry-over storage pest of pulses; cowpea, chickpea, green gram, black gram and red gram, throughout the tropics (NRI, 1996). This insect also causes secondary infestation during pulse storage, and may cause total loss within three months (Singh and Jackai, 1985). The bruchids can cause heavy losses in terms of both quantity and quality (Metcalf and Metcalf, 1993). Conventional chemicals, grain protectants and fumigants, are extensively used around the world to control insect pests in stored commodities. Being an internal feeder, it is very difficult to control the larval stage of C. maculatus with insecticides. The management of this insect in storage using chemical insecticides leads to insecticide residues in grains and insecticide resistant populations. Therefore, there is a need for the ecologically benign methods to control cowpea weevil on chickpea. * Corresponding author. Tel.: þ1 204 474 9404; fax: þ1 204 474 7568. E-mail address: [email protected] (D.S. Jayas).
Temperature management is one of the most promising biorational insect management tools for farm stored grain and grain processing industries (Fields, 1992; Dosland et al., 2006; Phillips and Throne, 2010). There are a few studies that have examined the management of bruchids by extreme temperatures. Adult mortality of C. maculatus increased with increased duration of solarisation (exposure period to sun) in Nigeria (Lale, 1998). Johnson et al. (2010) studied the potential of radio frequency (RF) energy to control insect pests in dried pulse products; the heat tolerance of the cowpea weevil was evaluated and compared to the tolerance of previously studied insects. They also compared the dielectric properties of both the insect and the grain. The cowpea weevils heat at a faster rate than the grain by the RF heating. The heating of the grain was more uniform by the addition of 60 C forced hot air with RF treatment and movement along a conveyor belt. Wang et al. (2010) examined the quality of the RF-treated product, and reported that there was no significant difference in the quality between RF-treated and untreated chickpeas. The dry heating of chickpea for 10 min at 120 C is used as one of the methods for reducing the anti-nutritional factors and reduced 46% of a-galactosides and 27% of tripsin inhibitor activity (Frias et al., 2000). The application of hot air is an easy, simple and environmentally friendly method in grain processing industries. Mullen and Arbogast (1979) investigated the time-mortality relationships for eggs of five species of store-product insects, and
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M. Loganathan et al. / Journal of Stored Products Research 47 (2011) 244e248
245
Table 2 Lethal time (days) to kill 50 or 95% of the population of various life stages of the C. maculatus exposed to 0 C. Stage LT50 (95% CL) (d) LT95 (95% CL) (d) Slope SE Intercept SE X2 (df) Egg Larva Pupa Adult
Fig. 1. The equilibration time required for grain to reach the set temperature at 42e60 C.
found that the C. maculatus eggs to be among the most coldtolerant, with LD50 values of 2.7, 1.3 and 0.3 h at 10, 15 and 20 C, respectively. The efficacy of cold storage disinfestation of black-eyed peas, Vigna unguiculata (L.) infested with C. maculatus was also examined by Johnson and Valero (2003). Based on laboratory experiments, they also reported that the egg stage was significantly more cold-tolerant and the adult stage was least coldtolerant at 18 C. In commercial cold storage facilities, there was complete egg mortality after 14 days of cold storage (18 C) and highest survival of eggs located at the centre of the bin. This was due to the slowest cooling rate at the centre of the bin. The insect species, stage of development, eggs on surface, size of grain and temperature-exposure time combinations determine the survival of insects at extreme temperatures (Fields, 1992). It is useful to know the relationship between life stage and temperature to design control measures. In general, the conditions needed to control the target insect should not affect the quality of the grain, but the margin of safety before damage occurs can be narrow, necessitating close control of the heating process and subsequent cooling (Banks and Fields, 1995). The present study was designed to identify the most tolerant stage of the insect for low and high temperatures and different temperature-exposure time combinations needed to kill the various stages of C. maculatus in chickpea. 2. Materials and methods 2.1. Insect culture The bruchid beetle, C. maculatus was cultured on chickpea in plastic containers held at 30 1 C and 60 10% RH in the dark. The freshly emerged adults were allowed to lay eggs on chickpeas for 24 h. The grains with single eggs were separated and used for experiments with egg, larvae and pupae. As the insect development occurs inside the grain, five grains were dissected in 3 d interval to confirm the stage of development (Bhalla et al., 2008). 2.2. Maintenance of temperatures The required temperatures were maintained in an oven (Thermolyne, Asheville, NC, USA) and observed using thermocouples
3.1 8.1 9.8 4.2
(2.9e3.3) (7.9e8.3) (9.6e10.1) (4.1e4.4)
4.1 9.0 11.3 5.0
(3.9e4.4) (8.8e9.5) (2.0e11.8) (4.8e5.2)
10.7 26.7 20.8 18.1
1.4 5.3 0.74 0.3 24.2 2.9 2.0 20.7 2.1 2.2 11.3 1.4
5.0 3.3 12.7 9.6
(34) (34) (34) (34)
(0.255 mm diameter wire) and dataloggers (Onset, Bourne, MA, USA) at various locations inside the oven. Dataloggers were within 0.5 C of a calibration thermometer (Ertco, Cole-Palmer Instrument Co., Montreal, Canada). The grains were kept at 30 1 C and 60 10% RH for 24 h before being used for the experiments. The time taken to reach the required grain temperature was also observed when conducting the experiments. The temperature within the grain was measured every 30 s by a thermocouple wire inserted into a hole drilled in the grain. The hole around the thermocouple was sealed with putty to ensure the thermocouple was measuring the temperature inside the kernel. These grains were kept in vials at different places inside the oven to measure the range of temperatures. The time taken for reaching required grain temperatures of 42, 45, 50, 55 and 60 C were observed using different sets of grains with six thermocouples. To maintain 0 C, the vials with chickpeas with the different insect stages were placed in crushed ice in an insulated box and kept in a cold room at 2 C. The vials were placed in a cold room at 5 C. To rapidly cool the grains to 10 C and 15 C, test tubes with chickpeas with different stages, were placed in a bath with ethylene glycol (Isotemp 3016, Fisher Scientific, Inc, Pittsburgh, U.S.A). The temperature within the grain was monitored as described for higher temperatures. 2.3. Survival of different developmental stages at low and high temperatures The following developmental stages were used; 24e48 h old eggs, 14-d old larvae, pupae (grains with windows) (Bhalla et al., 2008) and 2-d old adults. There were 20 grains per vial (25 mL), one immature individual/grain and four replicates. At 42 C, the adults and immature stages were exposed for 0, 6, 12, 24, 36, 48, 60, 72, 84, 96 and 108 h. For each duration, four vials were removed and placed at 30 1 C and 60 10% RH. Similarly, at 0 C, the adults and immature stages were exposed for 1, 3, 5, 7, 8, 9, 10, 11, 12, 13 days. The exposure period started when the grain reached the target temperature. 2.4. Survival of pupae and eggs at different temperatures Pupae were found to be the most heat and cold-tolerant stage and were used for subsequent tests. There were 20 grains per vial (25 mL), one pupa/grain and three replicates. The pupae were exposed for 36, 48, 60, 72, 84, 96, 108, 120 h at 42 C; for 12, 24, 36, 48, 60, 72, 84, 96 h at 45 C; for 150, 200, 250, 300, 325, 350, 375, 400 min at 50 C; for 24, 27, 30, 33, 36, 39, 42, 45 min at 55 C and for 9, 10, 11, 12, 13, 14, 15, 16 min at 60 C.
Table 1 Lethal time (min) to kill 50 or 95% of the population of various life stages of the C. maculatus exposed to 42 C. Stage
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
Egg Larva Pupa Adult
17.7 57.4 79.7 71.1
23.9 88.2 93.7 91.8
9.3 7.7 18.2 11.6
(16.7e18.7) (55.0e59.8) (78.2e81.2) (59.7e83.4)
(22.4e25.9) (79.8e89.8) (91.4e96.7) (79.4e189.6)
1.0 0.5 1.5 0.8
Intercept SE
X2 (df)
12.3 13.6 34.6 21.4
5.6 25.3 12.3 66.3
1.2 1.0 2.9 1.5
(38) (38) (38) (38)
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M. Loganathan et al. / Journal of Stored Products Research 47 (2011) 244e248
Table 3 Lethal time (min) to kill 50 or 95% of the pupae of C. maculatus exposed to different constant high temperatures.
Temperature ( C)
LT50 (95% CL) (min)
LT95 (95% CL) (min)
Slope SE
Intercept SE
X2 (df)
42 45 50 55 60
4906.5 4261.8 335.5 35.6 12.8
5764.1 5137.0 355.2 38.2 13.8
18.3 15.8 51.8 41.6 39.5
67.6 6.9 57.3 5.7 130.9 15.1 64.6 6.8 43.8 4.4
15.3 8.1 5.9 56.4 0.2
(4778e5038) (41334390) (332e339) (34.8e36.4) (12.7e13.0)
(5561e6054) (4939e5415) (350362) (37.3e39.8) (13.6e14.1)
1.7 1.6 6.0 4.4 4.0
(22) (22) (22) (22) (22)
Table 4 Lethal time (h) to kill 50 or 95% of the pupae of C. maculatus exposed to different constant low temperatures.
Temperature ( C)
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
0 5 10 15
274 122 7.0 1.8
289 152 7.4 2.5
53.3 13.4 52.6 10.3
(268e279) (117e126) (6.9e7.1) (1.7e1.9)
(283e300) (145e161) (7.3e7.6) (2.3e2.6)
Similarly, the pupae were exposed for 8, 9, 10, 11, 12, 13, 14 and 15 days at 0 C; for 24, 48, 72, 96, 144, 168 and 192 h at 5 C; for 30, 270, 300, 330, 360, 390, 420 and 450 min at 10 C and for 30, 60, 90, 120,150, 180, 210 and 240 min at 15 C. The eggs were also compared for cold tolerance at various low temperatures. The eggs were exposed for 12, 24, 48, 72, 96, 144 and 168 h at 0 C; for 12, 24, 48, 72, 96, 144 and 168 h at 5 C; for 30, 270, 300, 330, 360, 390, 420 and 450 min at 10 C and for 30, 60, 90, 120,150, 180, 210 and 240 min at 15 C. 2.5. Mortality of insects
6.3 1.3 6.1 0.9
Intercept SE
X2 (df)
129.9 27.9 44.4 2.7
46.0 8.1 7.8 12.7
15.4 2.7 5.1 0.3
(22) (22) (22) (22)
regression, y ¼ 36.31e0.55x, (where y ¼ time in min and x ¼ temperature in C; r2 ¼ 0.91), shows that for every 1 C rise in oven temperature from 42 to 60 C, the time required for grain in the vials to reach equilibration with the oven decreased by 33 s (Fig. 1). The time required for the grains to reach the set temperature decreased with a decrease in temperature; at 0 C it took approximate 6 h, while it only took 30 min at 15 C. The linear regression, y ¼ 333 þ 23.4x, (where y ¼ time in min and x ¼ temperature in C; r2 ¼ 0.897), showed that for every 1 C drop in temperature from 0 to 15 C, the time required for grain in the vials to reach equilibration decreased by 23 min.
Vials with the various life stages were placed at 30 1 C and 60 10% RH after the heat or cold exposure. After 12 h, adults were sifted out of the grains and the number of live and dead counted. Eggs, larvae and pupae were held until emergence of adults. Mortality of all immature stages was based on those that failed to emerge to adults. Adult emergence from the untreated controls was used as an estimate of the number of insects treated and to calculate treatment mortality.
3.2. Survival of different development stages
2.6. Data analyses
3.3. Survival of pupae and eggs at different temperatures
The time-mortality data of each C. maculatus stage at high and low temperatures were subjected to probit analysis (Finney, 1971) to estimate the time required to kill 50 or 90% of the insects (LeOra software, Petaluma, CA, USA).
The lethal time for pupae was investigated at various temperatures. The LT50 values were 4907, 4262, 336, 36 and 13 min at the grain temperatures of 42, 45, 50, 55 and 60 C, respectively (Table 3). As the pupal stage was found to be most cold-tolerant at 0 C, the lethal time required to kill the pupa was investigated at various low temperatures. The LT50 values were 274, 122, 7.0 and 1.8 h at the grain temperatures of 0, 5, 10, and 15 C, respectively (Table 4). Previous data (Johnson and Valero, 2003) showed that the egg was the most cold-tolerant stage, so we also tested the egg at various low temperatures. The LT50 values were 44, 19, 6.4 and 1 h at the grain temperatures of 0, 5, 10, and 15 C, respectively (Table 5), and were consistently lower than the pupae.
3. Results 3.1. Time to attain target temperature The time required for the grains to reach the set high temperature decreased with an increase in temperature; at 42 C it took approximate 15 min, while it only took 4 min at 60 C. The linear
Pupa and adult stages were the most heat tolerant stages with LT50 of 79.7 and 71.1 h, respectively at 42 C, followed by larva and egg stages being the least tolerant (Table 1). Pupal stage was the most cold-tolerant with LT50 of 9.8 h at 0 C, the cold tolerance of different stages from lowest to highest at 0 C was; egg < adult < larva < pupa (Table 2).
Table 5 Lethal time (h) to kill 50 or 95% of the eggs of C. maculatus exposed to different constant low temperatures.
Temperature ( C)
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
0 5 10 15
44 19 6.4 1.0
69 32 6.7 1.3
6.4 5.8 58.0 10.6
(40e47) (17e21) (6.3e6.5) (0.9e1.1)
(63e78) (28e39) (6.6e6.9) (1.2e1.5)
0.6 0.7 7.0 1.7
Intercept SE
X2 (df)
10.4 7.4 46.7 0.2
10.1 4.2 7.2 2.2
1.0 0.9 5.6 0.2
(22) (22) (22) (22)
M. Loganathan et al. / Journal of Stored Products Research 47 (2011) 244e248
247
Table 6 Tolerant stages of C. maculatus to low and high temperatures. Temperature
Ranking of tolerance
Stages not tested
Mode of treatment
Reference
High High High Low Low (18)
Pupa ¼ Adult > Larva > Egg Fourth instar larvae > Egg > adult Pupa > Larva > Egg > Adult Pupa > Larva > Adult > Egg Egg > Pupa ¼ Larva
e Pupa e e Adults
Hot air Solar heating Heat block system Cold air Commercial Freezer
Present study Murdock and Shade (1991) Johnson et al. (2010) Present study Johnson and Valero (2003)
4. Discussion 4.1. Most tolerant stage of C. maculatus The current study showed that pupal and adult stages were the most heat tolerant. This is in agreement with Johnson et al. (2010) who found that the pupal stage was the most heat tolerant, but different than Murdock and Shade (1991), who found that the larval stage was the most tolerant. Unlike our study, both these studies found that adults were the least tolerant stage (Table 6). Possible reasons for these differences are: all these three studies use different sources of heat, different rates of heating, different strains of C. maculatus and the insects were reared and tested on different pulses. Further research is needed to determine which of these factors is responsible for the differences in stage specific tolerance of heat. The chickpea seed will provide some thermal buffering for the larvae and pupae that are inside the seed. However, this can not be a significant factor in our studies, because the time required to reach 42 C was only 14 min, whereas it took over 18e80 h to get 50% mortality. The cowpea weevil is relatively cold-tolerant insect (Reichmuth et al., 2007). For most of other species of storedproduct insects, eggs are often the most susceptible stage to low temperatures (Fields, 1992). But we found that the pupa is the most cold-tolerant stage. In contradictory to this, the results of laboratory experiments conducted with life stages of C. maculatus in blackeyed peas by Johnson and Valero (2003), reported that the egg stage was significantly more tolerant than all other immature stages. Controlling insect eggs in packaged commodities by means of lethal low temperatures was studied by Mullen and Arbogast (1979) and reported that exposure of packaged commodities for 28 h at 10 C was required to achieve LD95 for the eggs of C. maculatus. The present study also showed that exposing eggs along with grains to 10 C for 8 h will achieve 100% mortality. Earlier research conducted in commercial cold storage facilities found that that all life stages of C. maculatus were killed at 18 C within 14 days (Johnson and Valero, 2003), however these long durations were required for the large seed bulk to achieve the low temperature in the centre of the seed mass. As with the heat studies discussed above, there are a number of differences between the studies that could account for the differences in results. 4.2. Implications for control To get complete control of C. maculatus of pupae we recommend the following temperature-exposure times: 42 C for 4 d, 45 C for 3 d, 50 C for 6 h, 55 C for 45 min and 60 C for 15 min, 0 C for 13 d, 5 C for 7 d, 10 C for 8 h, 15 C for 3 h. As the pupae were the most tolerant stage in our studies, these conditions should control all stages. Lale and Vidal (2003) reported that no progeny development from adult bruchid beetles exposed to 40 C. So, even if there is some survival from the heat treatment, the population growth will be lower. The quality of the chickpea after the heat treatment should be verified. Wang et al. (2010) examined the quality of the RF-treated
product and reported that there were no significant differences in the quality between RF-treated and untreated chickpeas. Murdock and Shade (1991) found that the temperatures and exposure times necessary to disinfest the cowpeas had no significant effect on the cooking time and germination of cowpea seeds. It was also reported that the dry heating (not exceeding 120 C and 10 min) of chickpea is used as one of the methods for reducing the anti-nutritional factors and reduced 46% of a-galactosides and 27% of tripsin inhibitor activity (Frias et al., 2000). Thermal disinfestation may also help in reducing these anti-nutritional factors. Generally, low temperature does not adversely affect seeds, so detailed studies on the effects of low temperatures are not needed. Even though different approaches have been used for heat and cold disinfestation in modern system of grain storage, the choice of which process is appropriate will depend on local costs of energy, construction and operating costs. 4.3. Future research The present study suggested the temperature-exposure time combinations required for the control of C. maculatus in chickpea, which are sometimes different than previous studies (Murdock and Shade,1991; Johnson and Valero, 2003; Johnson et al., 2010). Further research is needed to determine the possible reasons for the differences between the studies. This work was conducted at constant temperatures. In commercial facilities with large seed bulks, it is difficult to uniformly heat and cool the pulses. Further studies with dynamic temperature-time regimes should be conducted to determine the efficacy of these recommendations in commercial seed bulks. Mathematical models could be developed to predict mortality in under these conditions (Boina et al., 2008; Jian et al., 2010). Further study is needed to determine whether these lethal temperatures are detrimental to the quality of chickpea. Acknowledgements We thank V. Chelladurai and T. Senthilkumar for their support during the study, and Tannis Mayert for her technical assistance. We thank Government of Manitoba and Indian Ministry of Food Processing Industries for funding this study. References Banks, H.J., Fields, P.G., 1995. Physical methods for insect control in stored grain ecosystems. In: Jayas, D.S., White, N.D.G., Muir, W.E. (Eds.), Stored Grain Ecosystems. Marcel Dekker, Inc, New York, pp. 353e410. Bhalla, S., Gupta, K., Lal, B., Kapur, M.L., Khetarpal, R.K., 2008. Efficacy of various non-chemical methods against pulse beetle, Callosobruchus maculatus (Fab.). In: Endure International Conference on Diversifying Crop Protection, 12e15 October 2008, La Grande-Motte, France. pp. 1e4. Boina, D.B., Subramanyam, B., Alavi, S., 2008. Dynamic model for predicting survival of mature larvae of Tribolium confusum during facility heat treatments. Journal of Economic Entomology 101, 989e997. Dosland, O., Subramanyam, Bh., Sheppard, K., Mahroof, R., 2006. Temperature modification for insect control. In: Heaps, J. (Ed.), Insect Management for Food Storage and Processing. American Association for Cereal Chemistry, St. Paul, MN, pp. 89e103.
248
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FAOSTAT, 2007. Food and Agricultural Commodities Production. http://faostat.fao. org/site/339/default.aspx. Fields, P.G., 1992. The control of stored-product insects and mites with extreme temperatures. Journal of Stored Products Research 28, 89e118. Finney, D.J., 1971. Probit Analysis. Cambridge University Press, London. Frias, J., Vidal-Valverde, C., Sotomayor, C., Diaz-Pollan, C., 2000. Influence of processing on available carbohydrate content and anti-nutritional factors of chickpeas. European Food Research and Technology 210, 340e345. Jian, F., Jayas, D.S., Fields, P.G., Abdelghany, A.Y., 2010. Comparison of five developed models to predict survival rates of young larvae of Stegobium paniceum (L.) (Coleoptera: Anobiidae) under heat treated temperatures. In: Carvalho, O.M., Fields, P.G., Adler, C.S., Arthur, F.H., Athanassiou, C.G., Campbell, J.F., FleuratLessard, F., Flinn, P.W., Hodges, R.J., Isikber, A.A., Navarro, S., Noyes, R.T., Riudavets, J., Sinha, K.K., Thorpe, G.R., Timlick, B.H., Trematerra, P., White, N.D.G. (Eds), Proceedings of the10th International Working Conference on Stored Product Protection, 27 Junee2 July, 2010, Estoril, Portugal, Julius-Kühn-Archiv, Berlin, Germany, pp. 678e687. Johnson, J.A., Valero, K.A., 2003. Use of commercial freezers to control cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae) in organic Garbanzo beans. Journal of Economic Entomology 96, 1952e1957. Johnson, J.A., Wang, S., Tang, J., 2010. Radio frequency treatments for insect disinfestation of dried legumes. In: Carvalho, O.M., Fields, P.G., Adler, C.S., Arthur, F.H., Athanassiou, C.G., Campbell, J.F., Fleurat-Lessard, F., Flinn, P.W., Hodges, R.J., Isikber, A.A., Navarro, S., Noyes, R.T., Riudavets, J., Sinha, K.K., Thorpe, G.R., Timlick, B.H., Trematerra, P., White, N.D.G. (Eds), Proceedings of the10th International Working Conference on Stored Product Protection, 27 Junee2 July, 2010, Estoril, Protugal, Julius-Kühn-Archiv, Berlin, Germany, pp. 688e694.
Lale, N.E.S., 1998. Preliminary studies on the effect of solar heat on oviposition, development and adult mortality of the cowpea bruchids Callosobruchus maculatus (F.) in the Nigerian savanna. Journal of Arid Environments 40, 157e162. Lale, N.E.S., Vidal, S., 2003. Effect of constant temperature and humidity on oviposition and development of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on bambara groundnut, Vigna subterranean (L.) Verdcourt. Journal of Stored Products Research 39, 459e470. Metcalf, R.L., Metcalf, R.A., 1993. Destructive and Useful Insects: Their Habits and Control. R.R. Dinnelley & Sons Company, Chicago, Illinois. Mullen, M.A., Arbogast, R.T., 1979. Time temperature relationships for various stored product insect eggs and chilling times for selected commodities. Journal of Economic Entomology 72, 476e478. Murdock, L.L., Shade, R.E., 1991. Eradication of cowpea weevil (Coleoptera: Bruchidae) in cowpeas by solar heating. American Entomologist 37, 228e231. NRI (National Resource Institute), 1996. Insect Pests of Nigerian Crops: Identification, Biology and Control. Chatham, NRI, U.K. Phillips, T.W., Throne, J.E., 2010. Biorational approaches to manage stored product insects. Annual Review of Entomology 55, 375e397. Reichmuth, C., Schoeller, M., Ulrichs, C., 2007. Stored Product Pests in Grain; Morphology-Biology-Damage-Control. Agroconcept, Verlagsgesellschaft, Berlin. Singh, S.R., Jackai, L.E.N., 1985. Insect pests of cowpea in Africa: their life cycle, economic importance and potential for control. In: Singh, S.R., Rachiek, O. (Eds.), Cowpea Research, Production and Utilisation. Wiley Interscience Publications/John Wiley and Sons Ltd, Chichester, pp. 217e231. Wang, S., Tiwari, G., Jiao, S., Johnson, J.A., Tang, J., 2010. Developing post harvest disinfestation treatments for legumes using radio frequency energy. Biosystems Engineering 105, 341e349.
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Low and high temperatures for the control of cowpea beetle, callosobruchus maculatus (F.) (coleoptera: Bruchidae) in chickpeas M. Loganathan b, D.S. Jayas a, *, P.G. Fields c, N.D.G. White c a
Department of Biosystems Engineering, University of Manitoba, Winnipeg, Manitoba, Canada Indian Institute of Crop Processing Technology, Thanjavur, Tamil Nadu, India c Cereal Research Centre, Agriculture & Agri-Food Canada, Winnipeg, Manitoba, Canada b
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 21 March 2011
Chickpea (Cicer arietinum L.; Leguminasae) is an important pulse crop grown, around the world. The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (Coleoptera: Bruchidae), which is the most important field-carry-over storage pest of pulses. The management of this insect in storage using chemicals leads to insecticide residues in grains and insecticide resistance development in insects. Thermal disinfestation is one of the means of physical insect control. Eggs, larvae, pupae and adults were held at 42 or 0 C for varying durations. Pupae and adults were equally heat tolerant. The lethal time to reduce survival by 50% (LT50) at 42 C for eggs, larvae, pupae and adults were 18, 57, 78 and 71 h, respectively. Pupa was the most cold-tolerant stage. The LT50 at 0 C for eggs, larvae, pupae and adults were 3, 8, 10 and 4 d, respectively. The LT50 for pupae were 4907, 4262, 336, 36 and 13 min at the grain temperature of 42, 45, 50, 55 and 60 C, respectively. The LT50 of pupae at 0,5,10 and 15 C were 274, 122, 7 and 2 h, respectively. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
Keywords: Cicer arietinum Callosobruchus maculatus High and low temperatures
1. Introduction Chickpea (Cicer arietinum L.) is an important legume crop grown around the world. Chickpea is used as whole grain, split dhal and also as powder for preparation of various snack foods. The world production of chickpea is 8.8 Mt (million tonnes), of which India produces 6.3 Mt (FAO statistics, 2007). The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), which is the most important fieldcarry-over storage pest of pulses; cowpea, chickpea, green gram, black gram and red gram, throughout the tropics (NRI, 1996). This insect also causes secondary infestation during pulse storage, and may cause total loss within three months (Singh and Jackai, 1985). The bruchids can cause heavy losses in terms of both quantity and quality (Metcalf and Metcalf, 1993). Conventional chemicals, grain protectants and fumigants, are extensively used around the world to control insect pests in stored commodities. Being an internal feeder, it is very difficult to control the larval stage of C. maculatus with insecticides. The management of this insect in storage using chemical insecticides leads to insecticide residues in grains and insecticide resistant populations. Therefore, there is a need for the ecologically benign methods to control cowpea weevil on chickpea. * Corresponding author. Tel.: þ1 204 474 9404; fax: þ1 204 474 7568. E-mail address: [email protected] (D.S. Jayas).
Temperature management is one of the most promising biorational insect management tools for farm stored grain and grain processing industries (Fields, 1992; Dosland et al., 2006; Phillips and Throne, 2010). There are a few studies that have examined the management of bruchids by extreme temperatures. Adult mortality of C. maculatus increased with increased duration of solarisation (exposure period to sun) in Nigeria (Lale, 1998). Johnson et al. (2010) studied the potential of radio frequency (RF) energy to control insect pests in dried pulse products; the heat tolerance of the cowpea weevil was evaluated and compared to the tolerance of previously studied insects. They also compared the dielectric properties of both the insect and the grain. The cowpea weevils heat at a faster rate than the grain by the RF heating. The heating of the grain was more uniform by the addition of 60 C forced hot air with RF treatment and movement along a conveyor belt. Wang et al. (2010) examined the quality of the RF-treated product, and reported that there was no significant difference in the quality between RF-treated and untreated chickpeas. The dry heating of chickpea for 10 min at 120 C is used as one of the methods for reducing the anti-nutritional factors and reduced 46% of a-galactosides and 27% of tripsin inhibitor activity (Frias et al., 2000). The application of hot air is an easy, simple and environmentally friendly method in grain processing industries. Mullen and Arbogast (1979) investigated the time-mortality relationships for eggs of five species of store-product insects, and
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Table 2 Lethal time (days) to kill 50 or 95% of the population of various life stages of the C. maculatus exposed to 0 C. Stage LT50 (95% CL) (d) LT95 (95% CL) (d) Slope SE Intercept SE X2 (df) Egg Larva Pupa Adult
Fig. 1. The equilibration time required for grain to reach the set temperature at 42e60 C.
found that the C. maculatus eggs to be among the most coldtolerant, with LD50 values of 2.7, 1.3 and 0.3 h at 10, 15 and 20 C, respectively. The efficacy of cold storage disinfestation of black-eyed peas, Vigna unguiculata (L.) infested with C. maculatus was also examined by Johnson and Valero (2003). Based on laboratory experiments, they also reported that the egg stage was significantly more cold-tolerant and the adult stage was least coldtolerant at 18 C. In commercial cold storage facilities, there was complete egg mortality after 14 days of cold storage (18 C) and highest survival of eggs located at the centre of the bin. This was due to the slowest cooling rate at the centre of the bin. The insect species, stage of development, eggs on surface, size of grain and temperature-exposure time combinations determine the survival of insects at extreme temperatures (Fields, 1992). It is useful to know the relationship between life stage and temperature to design control measures. In general, the conditions needed to control the target insect should not affect the quality of the grain, but the margin of safety before damage occurs can be narrow, necessitating close control of the heating process and subsequent cooling (Banks and Fields, 1995). The present study was designed to identify the most tolerant stage of the insect for low and high temperatures and different temperature-exposure time combinations needed to kill the various stages of C. maculatus in chickpea. 2. Materials and methods 2.1. Insect culture The bruchid beetle, C. maculatus was cultured on chickpea in plastic containers held at 30 1 C and 60 10% RH in the dark. The freshly emerged adults were allowed to lay eggs on chickpeas for 24 h. The grains with single eggs were separated and used for experiments with egg, larvae and pupae. As the insect development occurs inside the grain, five grains were dissected in 3 d interval to confirm the stage of development (Bhalla et al., 2008). 2.2. Maintenance of temperatures The required temperatures were maintained in an oven (Thermolyne, Asheville, NC, USA) and observed using thermocouples
3.1 8.1 9.8 4.2
(2.9e3.3) (7.9e8.3) (9.6e10.1) (4.1e4.4)
4.1 9.0 11.3 5.0
(3.9e4.4) (8.8e9.5) (2.0e11.8) (4.8e5.2)
10.7 26.7 20.8 18.1
1.4 5.3 0.74 0.3 24.2 2.9 2.0 20.7 2.1 2.2 11.3 1.4
5.0 3.3 12.7 9.6
(34) (34) (34) (34)
(0.255 mm diameter wire) and dataloggers (Onset, Bourne, MA, USA) at various locations inside the oven. Dataloggers were within 0.5 C of a calibration thermometer (Ertco, Cole-Palmer Instrument Co., Montreal, Canada). The grains were kept at 30 1 C and 60 10% RH for 24 h before being used for the experiments. The time taken to reach the required grain temperature was also observed when conducting the experiments. The temperature within the grain was measured every 30 s by a thermocouple wire inserted into a hole drilled in the grain. The hole around the thermocouple was sealed with putty to ensure the thermocouple was measuring the temperature inside the kernel. These grains were kept in vials at different places inside the oven to measure the range of temperatures. The time taken for reaching required grain temperatures of 42, 45, 50, 55 and 60 C were observed using different sets of grains with six thermocouples. To maintain 0 C, the vials with chickpeas with the different insect stages were placed in crushed ice in an insulated box and kept in a cold room at 2 C. The vials were placed in a cold room at 5 C. To rapidly cool the grains to 10 C and 15 C, test tubes with chickpeas with different stages, were placed in a bath with ethylene glycol (Isotemp 3016, Fisher Scientific, Inc, Pittsburgh, U.S.A). The temperature within the grain was monitored as described for higher temperatures. 2.3. Survival of different developmental stages at low and high temperatures The following developmental stages were used; 24e48 h old eggs, 14-d old larvae, pupae (grains with windows) (Bhalla et al., 2008) and 2-d old adults. There were 20 grains per vial (25 mL), one immature individual/grain and four replicates. At 42 C, the adults and immature stages were exposed for 0, 6, 12, 24, 36, 48, 60, 72, 84, 96 and 108 h. For each duration, four vials were removed and placed at 30 1 C and 60 10% RH. Similarly, at 0 C, the adults and immature stages were exposed for 1, 3, 5, 7, 8, 9, 10, 11, 12, 13 days. The exposure period started when the grain reached the target temperature. 2.4. Survival of pupae and eggs at different temperatures Pupae were found to be the most heat and cold-tolerant stage and were used for subsequent tests. There were 20 grains per vial (25 mL), one pupa/grain and three replicates. The pupae were exposed for 36, 48, 60, 72, 84, 96, 108, 120 h at 42 C; for 12, 24, 36, 48, 60, 72, 84, 96 h at 45 C; for 150, 200, 250, 300, 325, 350, 375, 400 min at 50 C; for 24, 27, 30, 33, 36, 39, 42, 45 min at 55 C and for 9, 10, 11, 12, 13, 14, 15, 16 min at 60 C.
Table 1 Lethal time (min) to kill 50 or 95% of the population of various life stages of the C. maculatus exposed to 42 C. Stage
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
Egg Larva Pupa Adult
17.7 57.4 79.7 71.1
23.9 88.2 93.7 91.8
9.3 7.7 18.2 11.6
(16.7e18.7) (55.0e59.8) (78.2e81.2) (59.7e83.4)
(22.4e25.9) (79.8e89.8) (91.4e96.7) (79.4e189.6)
1.0 0.5 1.5 0.8
Intercept SE
X2 (df)
12.3 13.6 34.6 21.4
5.6 25.3 12.3 66.3
1.2 1.0 2.9 1.5
(38) (38) (38) (38)
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M. Loganathan et al. / Journal of Stored Products Research 47 (2011) 244e248
Table 3 Lethal time (min) to kill 50 or 95% of the pupae of C. maculatus exposed to different constant high temperatures.
Temperature ( C)
LT50 (95% CL) (min)
LT95 (95% CL) (min)
Slope SE
Intercept SE
X2 (df)
42 45 50 55 60
4906.5 4261.8 335.5 35.6 12.8
5764.1 5137.0 355.2 38.2 13.8
18.3 15.8 51.8 41.6 39.5
67.6 6.9 57.3 5.7 130.9 15.1 64.6 6.8 43.8 4.4
15.3 8.1 5.9 56.4 0.2
(4778e5038) (41334390) (332e339) (34.8e36.4) (12.7e13.0)
(5561e6054) (4939e5415) (350362) (37.3e39.8) (13.6e14.1)
1.7 1.6 6.0 4.4 4.0
(22) (22) (22) (22) (22)
Table 4 Lethal time (h) to kill 50 or 95% of the pupae of C. maculatus exposed to different constant low temperatures.
Temperature ( C)
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
0 5 10 15
274 122 7.0 1.8
289 152 7.4 2.5
53.3 13.4 52.6 10.3
(268e279) (117e126) (6.9e7.1) (1.7e1.9)
(283e300) (145e161) (7.3e7.6) (2.3e2.6)
Similarly, the pupae were exposed for 8, 9, 10, 11, 12, 13, 14 and 15 days at 0 C; for 24, 48, 72, 96, 144, 168 and 192 h at 5 C; for 30, 270, 300, 330, 360, 390, 420 and 450 min at 10 C and for 30, 60, 90, 120,150, 180, 210 and 240 min at 15 C. The eggs were also compared for cold tolerance at various low temperatures. The eggs were exposed for 12, 24, 48, 72, 96, 144 and 168 h at 0 C; for 12, 24, 48, 72, 96, 144 and 168 h at 5 C; for 30, 270, 300, 330, 360, 390, 420 and 450 min at 10 C and for 30, 60, 90, 120,150, 180, 210 and 240 min at 15 C. 2.5. Mortality of insects
6.3 1.3 6.1 0.9
Intercept SE
X2 (df)
129.9 27.9 44.4 2.7
46.0 8.1 7.8 12.7
15.4 2.7 5.1 0.3
(22) (22) (22) (22)
regression, y ¼ 36.31e0.55x, (where y ¼ time in min and x ¼ temperature in C; r2 ¼ 0.91), shows that for every 1 C rise in oven temperature from 42 to 60 C, the time required for grain in the vials to reach equilibration with the oven decreased by 33 s (Fig. 1). The time required for the grains to reach the set temperature decreased with a decrease in temperature; at 0 C it took approximate 6 h, while it only took 30 min at 15 C. The linear regression, y ¼ 333 þ 23.4x, (where y ¼ time in min and x ¼ temperature in C; r2 ¼ 0.897), showed that for every 1 C drop in temperature from 0 to 15 C, the time required for grain in the vials to reach equilibration decreased by 23 min.
Vials with the various life stages were placed at 30 1 C and 60 10% RH after the heat or cold exposure. After 12 h, adults were sifted out of the grains and the number of live and dead counted. Eggs, larvae and pupae were held until emergence of adults. Mortality of all immature stages was based on those that failed to emerge to adults. Adult emergence from the untreated controls was used as an estimate of the number of insects treated and to calculate treatment mortality.
3.2. Survival of different development stages
2.6. Data analyses
3.3. Survival of pupae and eggs at different temperatures
The time-mortality data of each C. maculatus stage at high and low temperatures were subjected to probit analysis (Finney, 1971) to estimate the time required to kill 50 or 90% of the insects (LeOra software, Petaluma, CA, USA).
The lethal time for pupae was investigated at various temperatures. The LT50 values were 4907, 4262, 336, 36 and 13 min at the grain temperatures of 42, 45, 50, 55 and 60 C, respectively (Table 3). As the pupal stage was found to be most cold-tolerant at 0 C, the lethal time required to kill the pupa was investigated at various low temperatures. The LT50 values were 274, 122, 7.0 and 1.8 h at the grain temperatures of 0, 5, 10, and 15 C, respectively (Table 4). Previous data (Johnson and Valero, 2003) showed that the egg was the most cold-tolerant stage, so we also tested the egg at various low temperatures. The LT50 values were 44, 19, 6.4 and 1 h at the grain temperatures of 0, 5, 10, and 15 C, respectively (Table 5), and were consistently lower than the pupae.
3. Results 3.1. Time to attain target temperature The time required for the grains to reach the set high temperature decreased with an increase in temperature; at 42 C it took approximate 15 min, while it only took 4 min at 60 C. The linear
Pupa and adult stages were the most heat tolerant stages with LT50 of 79.7 and 71.1 h, respectively at 42 C, followed by larva and egg stages being the least tolerant (Table 1). Pupal stage was the most cold-tolerant with LT50 of 9.8 h at 0 C, the cold tolerance of different stages from lowest to highest at 0 C was; egg < adult < larva < pupa (Table 2).
Table 5 Lethal time (h) to kill 50 or 95% of the eggs of C. maculatus exposed to different constant low temperatures.
Temperature ( C)
LT50 (95% CL) (h)
LT95 (95% CL) (h)
Slope SE
0 5 10 15
44 19 6.4 1.0
69 32 6.7 1.3
6.4 5.8 58.0 10.6
(40e47) (17e21) (6.3e6.5) (0.9e1.1)
(63e78) (28e39) (6.6e6.9) (1.2e1.5)
0.6 0.7 7.0 1.7
Intercept SE
X2 (df)
10.4 7.4 46.7 0.2
10.1 4.2 7.2 2.2
1.0 0.9 5.6 0.2
(22) (22) (22) (22)
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Table 6 Tolerant stages of C. maculatus to low and high temperatures. Temperature
Ranking of tolerance
Stages not tested
Mode of treatment
Reference
High High High Low Low (18)
Pupa ¼ Adult > Larva > Egg Fourth instar larvae > Egg > adult Pupa > Larva > Egg > Adult Pupa > Larva > Adult > Egg Egg > Pupa ¼ Larva
e Pupa e e Adults
Hot air Solar heating Heat block system Cold air Commercial Freezer
Present study Murdock and Shade (1991) Johnson et al. (2010) Present study Johnson and Valero (2003)
4. Discussion 4.1. Most tolerant stage of C. maculatus The current study showed that pupal and adult stages were the most heat tolerant. This is in agreement with Johnson et al. (2010) who found that the pupal stage was the most heat tolerant, but different than Murdock and Shade (1991), who found that the larval stage was the most tolerant. Unlike our study, both these studies found that adults were the least tolerant stage (Table 6). Possible reasons for these differences are: all these three studies use different sources of heat, different rates of heating, different strains of C. maculatus and the insects were reared and tested on different pulses. Further research is needed to determine which of these factors is responsible for the differences in stage specific tolerance of heat. The chickpea seed will provide some thermal buffering for the larvae and pupae that are inside the seed. However, this can not be a significant factor in our studies, because the time required to reach 42 C was only 14 min, whereas it took over 18e80 h to get 50% mortality. The cowpea weevil is relatively cold-tolerant insect (Reichmuth et al., 2007). For most of other species of storedproduct insects, eggs are often the most susceptible stage to low temperatures (Fields, 1992). But we found that the pupa is the most cold-tolerant stage. In contradictory to this, the results of laboratory experiments conducted with life stages of C. maculatus in blackeyed peas by Johnson and Valero (2003), reported that the egg stage was significantly more tolerant than all other immature stages. Controlling insect eggs in packaged commodities by means of lethal low temperatures was studied by Mullen and Arbogast (1979) and reported that exposure of packaged commodities for 28 h at 10 C was required to achieve LD95 for the eggs of C. maculatus. The present study also showed that exposing eggs along with grains to 10 C for 8 h will achieve 100% mortality. Earlier research conducted in commercial cold storage facilities found that that all life stages of C. maculatus were killed at 18 C within 14 days (Johnson and Valero, 2003), however these long durations were required for the large seed bulk to achieve the low temperature in the centre of the seed mass. As with the heat studies discussed above, there are a number of differences between the studies that could account for the differences in results. 4.2. Implications for control To get complete control of C. maculatus of pupae we recommend the following temperature-exposure times: 42 C for 4 d, 45 C for 3 d, 50 C for 6 h, 55 C for 45 min and 60 C for 15 min, 0 C for 13 d, 5 C for 7 d, 10 C for 8 h, 15 C for 3 h. As the pupae were the most tolerant stage in our studies, these conditions should control all stages. Lale and Vidal (2003) reported that no progeny development from adult bruchid beetles exposed to 40 C. So, even if there is some survival from the heat treatment, the population growth will be lower. The quality of the chickpea after the heat treatment should be verified. Wang et al. (2010) examined the quality of the RF-treated
product and reported that there were no significant differences in the quality between RF-treated and untreated chickpeas. Murdock and Shade (1991) found that the temperatures and exposure times necessary to disinfest the cowpeas had no significant effect on the cooking time and germination of cowpea seeds. It was also reported that the dry heating (not exceeding 120 C and 10 min) of chickpea is used as one of the methods for reducing the anti-nutritional factors and reduced 46% of a-galactosides and 27% of tripsin inhibitor activity (Frias et al., 2000). Thermal disinfestation may also help in reducing these anti-nutritional factors. Generally, low temperature does not adversely affect seeds, so detailed studies on the effects of low temperatures are not needed. Even though different approaches have been used for heat and cold disinfestation in modern system of grain storage, the choice of which process is appropriate will depend on local costs of energy, construction and operating costs. 4.3. Future research The present study suggested the temperature-exposure time combinations required for the control of C. maculatus in chickpea, which are sometimes different than previous studies (Murdock and Shade,1991; Johnson and Valero, 2003; Johnson et al., 2010). Further research is needed to determine the possible reasons for the differences between the studies. This work was conducted at constant temperatures. In commercial facilities with large seed bulks, it is difficult to uniformly heat and cool the pulses. Further studies with dynamic temperature-time regimes should be conducted to determine the efficacy of these recommendations in commercial seed bulks. Mathematical models could be developed to predict mortality in under these conditions (Boina et al., 2008; Jian et al., 2010). Further study is needed to determine whether these lethal temperatures are detrimental to the quality of chickpea. Acknowledgements We thank V. Chelladurai and T. Senthilkumar for their support during the study, and Tannis Mayert for her technical assistance. We thank Government of Manitoba and Indian Ministry of Food Processing Industries for funding this study. References Banks, H.J., Fields, P.G., 1995. Physical methods for insect control in stored grain ecosystems. In: Jayas, D.S., White, N.D.G., Muir, W.E. (Eds.), Stored Grain Ecosystems. Marcel Dekker, Inc, New York, pp. 353e410. Bhalla, S., Gupta, K., Lal, B., Kapur, M.L., Khetarpal, R.K., 2008. Efficacy of various non-chemical methods against pulse beetle, Callosobruchus maculatus (Fab.). In: Endure International Conference on Diversifying Crop Protection, 12e15 October 2008, La Grande-Motte, France. pp. 1e4. Boina, D.B., Subramanyam, B., Alavi, S., 2008. Dynamic model for predicting survival of mature larvae of Tribolium confusum during facility heat treatments. Journal of Economic Entomology 101, 989e997. Dosland, O., Subramanyam, Bh., Sheppard, K., Mahroof, R., 2006. Temperature modification for insect control. In: Heaps, J. (Ed.), Insect Management for Food Storage and Processing. American Association for Cereal Chemistry, St. Paul, MN, pp. 89e103.
248
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FAOSTAT, 2007. Food and Agricultural Commodities Production. http://faostat.fao. org/site/339/default.aspx. Fields, P.G., 1992. The control of stored-product insects and mites with extreme temperatures. Journal of Stored Products Research 28, 89e118. Finney, D.J., 1971. Probit Analysis. Cambridge University Press, London. Frias, J., Vidal-Valverde, C., Sotomayor, C., Diaz-Pollan, C., 2000. Influence of processing on available carbohydrate content and anti-nutritional factors of chickpeas. European Food Research and Technology 210, 340e345. Jian, F., Jayas, D.S., Fields, P.G., Abdelghany, A.Y., 2010. Comparison of five developed models to predict survival rates of young larvae of Stegobium paniceum (L.) (Coleoptera: Anobiidae) under heat treated temperatures. In: Carvalho, O.M., Fields, P.G., Adler, C.S., Arthur, F.H., Athanassiou, C.G., Campbell, J.F., FleuratLessard, F., Flinn, P.W., Hodges, R.J., Isikber, A.A., Navarro, S., Noyes, R.T., Riudavets, J., Sinha, K.K., Thorpe, G.R., Timlick, B.H., Trematerra, P., White, N.D.G. (Eds), Proceedings of the10th International Working Conference on Stored Product Protection, 27 Junee2 July, 2010, Estoril, Portugal, Julius-Kühn-Archiv, Berlin, Germany, pp. 678e687. Johnson, J.A., Valero, K.A., 2003. Use of commercial freezers to control cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae) in organic Garbanzo beans. Journal of Economic Entomology 96, 1952e1957. Johnson, J.A., Wang, S., Tang, J., 2010. Radio frequency treatments for insect disinfestation of dried legumes. In: Carvalho, O.M., Fields, P.G., Adler, C.S., Arthur, F.H., Athanassiou, C.G., Campbell, J.F., Fleurat-Lessard, F., Flinn, P.W., Hodges, R.J., Isikber, A.A., Navarro, S., Noyes, R.T., Riudavets, J., Sinha, K.K., Thorpe, G.R., Timlick, B.H., Trematerra, P., White, N.D.G. (Eds), Proceedings of the10th International Working Conference on Stored Product Protection, 27 Junee2 July, 2010, Estoril, Protugal, Julius-Kühn-Archiv, Berlin, Germany, pp. 688e694.
Lale, N.E.S., 1998. Preliminary studies on the effect of solar heat on oviposition, development and adult mortality of the cowpea bruchids Callosobruchus maculatus (F.) in the Nigerian savanna. Journal of Arid Environments 40, 157e162. Lale, N.E.S., Vidal, S., 2003. Effect of constant temperature and humidity on oviposition and development of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on bambara groundnut, Vigna subterranean (L.) Verdcourt. Journal of Stored Products Research 39, 459e470. Metcalf, R.L., Metcalf, R.A., 1993. Destructive and Useful Insects: Their Habits and Control. R.R. Dinnelley & Sons Company, Chicago, Illinois. Mullen, M.A., Arbogast, R.T., 1979. Time temperature relationships for various stored product insect eggs and chilling times for selected commodities. Journal of Economic Entomology 72, 476e478. Murdock, L.L., Shade, R.E., 1991. Eradication of cowpea weevil (Coleoptera: Bruchidae) in cowpeas by solar heating. American Entomologist 37, 228e231. NRI (National Resource Institute), 1996. Insect Pests of Nigerian Crops: Identification, Biology and Control. Chatham, NRI, U.K. Phillips, T.W., Throne, J.E., 2010. Biorational approaches to manage stored product insects. Annual Review of Entomology 55, 375e397. Reichmuth, C., Schoeller, M., Ulrichs, C., 2007. Stored Product Pests in Grain; Morphology-Biology-Damage-Control. Agroconcept, Verlagsgesellschaft, Berlin. Singh, S.R., Jackai, L.E.N., 1985. Insect pests of cowpea in Africa: their life cycle, economic importance and potential for control. In: Singh, S.R., Rachiek, O. (Eds.), Cowpea Research, Production and Utilisation. Wiley Interscience Publications/John Wiley and Sons Ltd, Chichester, pp. 217e231. Wang, S., Tiwari, G., Jiao, S., Johnson, J.A., Tang, J., 2010. Developing post harvest disinfestation treatments for legumes using radio frequency energy. Biosystems Engineering 105, 341e349.