Use of NeemPro®, a neem product to control maize weevil Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae) on three maize varieties in Cameroon

Background

In sub-tropical and tropical regions, Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) is the main pest of stored maize grain [1]. In Cameroon, maize is the main food crop and S. zeamais alone has already caused 80 % of grain damage during the period of storage [2]. Demissie et al. [3] reported that once the grains are damaged, this will reduce the market value, the percentage of germination, the weight and the nutritional value. That is why in Africa, effective and cheap methods are needed to reduce the damage caused by S. zeamais and so, to reduce food insecurity [3]. Infestation control of stored grains pests is primarily achieved by the use of synthetic chemical insecticides. However, due to environmental concerns and human health hazards of chemical insecticides, plant materials with insecticidal properties remain one of the most important locally available, biodegradable and inexpensive methods for the control of pests of stored products [4, 5].

Azadirachtin, the active insecticidal ingredient of Azadirachta indica A. Juss, (Meliaceae) [6], is found to be an environment-friendly pesticide and has many desirable properties. It is also selective with short persistence, toxic to target pests, has minimal toxicity to non-target and beneficial organisms and caused less damage to the ecosystem [6-9]. For these reasons, it has generated enormous worldwide interest due to its potential as a new insect pest control agent [10].

One way of promoting neem is to develop proprietary products. The knowledge of the high potency of azadirachtin against a wide variety of crop pests has now resulted in the development of many commercial neem formulations (CNFs) such as Nimbecidine, Econeem Plus, Soluneem, Limonool, Neemgold, Fortune Aza, NeemAzal TM-F, Margocide-OK, Neemark, Neem Oil Emulsion, Neem Plus, Neemrich, Neemosan, Neemta 2100, Nimlin, Margosan-O, Bioneem, Suneem [11, 12]. These formulations provide two great advantages. Firstly, the fragile natural resource, azadirachtin, is highly unstable in the seeds and the potency of the seeds is lost exponentially upon storage. Secondly, CNFs provide an avenue to conserve this resource by reducing the rate of loss of azadirachtin in many folds [12]. Hence it is important to generate further information on the biochemical effect of azadirachtin and its commercial insecticides. The objective of this study was to evaluate the efficacy of NeemPro® against the maize weevil on three maize varieties in the laboratory. This formulation protected stored bambara groundnut against the infestation of Callosobruchus maculatus F. (Coleoptera: Chrysomelidae: Bruchinae) in the Adamawa region of Cameroon [13]. However, this is the first report of the same product in the protection of stored grains of three maize varieties, the most cultivated ones in Cameroon, against the infestation of S. zeamais.

Methods

Maize varieties

Grains of three maize varieties presented in Table 1 were collected from the Institute of Agricultural Research for Development (IARD), Nkolbisson-Yaounde (Cameroon). The moisture content of the grains was 11.30, 11.50 and 13.20 for CLH103, CMS8501 and SHABA, respectively. [ Table Omitted - see PDF ]

Table 1

Genetic nature, grain surface texture and grain colour of the maize varieties used for the experiment

Variety

Genetic nature

Grain surface texture

Grain colour

CLH103

Hybrid

Semi-dent

Yellow

CMS8501

Composite

Corned

White

SHABA

Composite

Dent

White

Insects rearing

Maize weevils were reared on whole clean, undamaged and disinfested maize grains SHABA, the composite mostly grown by Adamawa farmers under ambient laboratory conditions. Adult weevils were obtained from a colony kept since 2005 in the Laboratory of Entomology at the University of Ngaoundere. Maize grains were sterilised in cold chamber at ?14 °C for 21 days to kill any incipient infestation. The sterilised grains were conditioned during 14 days prior to rearing or bioassay processes. Twenty adults were released into ten glass jars (900 ml capacity) containing 500 g of conditioned grains each. The adults were removed after 2 weeks and the grains were kept under ambient laboratory conditions [temperature (T) = 21.9-24.4 °C and relative humidity (RH) = 75.3-78 %] for the development of progenies. Adults aged 7-14 days and mixed sexes were used for all bioassays.

Commercial insecticides

A commercial neem product, NeemPro® concentrated powder containing 0.1 % NeemAzal (0.03 g/kg Azadirachtin A) and mineral clay (diatomaceous earth) was provided by Trifolio-M GmbH Company, Lahnau, Germany. Malagrain DP 5 (5 % Malathion) was purchased from an agric-products shop at Ngaoundere, Cameroon.

Toxicity tests and F1 progeny production

The application rates of NeemPro® were 0.75, 1.5, 3 and 6 g/kg after preliminary studies. These rates were obtained by adding 0.0375, 0.075, 0.15 and 0.3 g of the insecticide powder to 50 g of maize grains of each variety in a glass jar and shaken well by hands during 4 min to get uniform coating. Twenty (7-14 days old) adult weevils of mixed sexes were introduced into each jar. Each treatment was repeated four times. Treated and untreated controls were included. In the treated control, 0.025 g of Malagrain was introduced in 50 g grains of each maize variety (0.5 g/kg, recommended dose). For untreated control, neither NeemPro® nor Malagrain was used. All treatments were maintained in the laboratory at T of 21.7-25.6 °C and RH of 76.1-79 %, registered by a thermo-hygrometer EL-USB-2 (RH/TEMP DATA LOGGER) (Chine). The T and RH data were registered each 2 h from the beginning of the weevils rearing to the end of the experiments. Mortality was recorded 1, 3, 7 and 14 days after the infestation [14]. The mortality was corrected for control mortality using Abbott's formula [15].

On the 14 days post-infestation, where treatments were kept undisturbed for oviposition since the first day of the infestation, all insects were removed and the different jars containing grains were kept under the same experimental conditions (T = 22.6-25.6 °C and RH = 72.5-80 %). The counting of F1 adults was done once a week for 5 weeks to avoid overlapping between the first and the second generations commencing 5 weeks post-infestation. The percent reduction in adult emergence or reproduction inhibition rate (IR %) was computed according to Chebet et al. [16] as shown in the following equation:

[Math Processing Error]Reproduction inhibition rate(%)=(CN?TN)CN×100

where CN is the number of newly emerged adult insects in the untreated control and TN is the number of newly emerged adult insects in the treated grains.

Population increase and grain damage

Four rates (0.75, 1.5, 3 and 6 g/kg of NeemPro® powder and 0.5 g/kg of Malagrain) for 200 g of each maize variety grain were admixed as described above. A lot of 30 adult insects of mixed sexes (7-14 days old) were introduced into each jar of each maize variety grain including treated and untreated controls. Each treatment with the same dosage for each variety was repeated four times. After 4 months, the numbers of alive and dead insects were removed and counted for each jar. Damage assessment was performed by measuring the weight of the sieved powder and that of the grains without powder (final weight). The amount of grain powder (frass plus faeces) was expressed as the total powder minus the weight of insecticide powder used. The percentage of grain weight loss was calculated by using the count-and-weigh method [17].

[Math Processing Error]Grain weight loss(%)=[(Wu×Nd)?(Wd×Nu)Wu(Nd+Nu)]×100

where Wu is the weight of undamaged grains, Nd the number of damaged grains, Wd the weight of damaged grains and Nu the number of undamaged grains. All treatments were maintained in the laboratory conditions (T = 24.1-25.6 °C and RH = 70.7-74.5 %).

Seed germination

To assess the viability of seeds, seed germination test was similarly conducted according to the procedure described earlier by Demissie et al. [3] where 30 undamaged grains of each maize variety seed in each jar were randomly selected. The number of germinated seeds was recorded after 10 days.

Data analysis

The Statistical Analysis System [18] was used to analyse the data. Data on percentage of mortality, production of F1 progeny, seed damage and seed germination were firstly arcsine-transformed [square root (x/100)]. The number of F1 progeny produced was also log-transformed (x + 1). It is the transformed data that were subjected to the ANOVA procedure. The Tukey studentized test at P = 0.05 was used for mean separation. Finally, Probit analysis [19] was applied to determine lethal dosages causing 50 % (LC50) and 95 % (LC95) of S. zeamais mortality at 3, 7 and 14 days after treatment.

Results

Adult weevil mortality

The results of the phytotoxicity tests showed that NeemPro® caused significant mortality to S. zeamais in the three maize varieties (Table 2). Mortality increased with powder content and time post-exposure. At the highest dosage of 6 g/kg, 100, 95 and 89 % adult weevil mortality was achieved in CLH103, CMS8501 and SHABA, respectively, within 14 days of exposure. For the same time-point and in the same order, the lowest dosage of 0.75 g/kg caused 43, 18 and 10 % weevil mortality. The LC50 and LC95 values are presented in Figs. 1 and 2, respectively. After 14 days of exposure, CLH103 recorded better LC50 and LC95 values of 0.04 and 0.13 g/kg, respectively. Within 1 day of exposure, adult weevils exposed to Malagrain were dead and that was on the three maize varieties. [ Table Omitted - see PDF ]

Table 2

Corrected mortality of Sitophilus zeamais exposed to NeemPro® after 1, 3, 7 and 14 days on three maize varieties under laboratory conditions

Maize variety/content (g/kg)

% Mortality (mean ± SE)-exposure period (days)

1

3

7

14

CLH103

0

0 ± 0

0 ± 0c

0 ± 0b

0 ± 0c

0.75

0 ± 0

5 ± 2bc

32.5 ± 13.92ab

42.5 ± 9.24b

1.5

0 ± 0

30 ± 13.69abc

52.5 ± 22.59ab

92.5 ± 4.33a

3

0 ± 0

30 ± 3.54ab

71.25 ± 15.73a

92.5 ± 4.33a

6

2.5 ± 1.44

43.75 ± 11.43a

76.25 ± 12.81a

100 ± 0a

F value

3 ns

4.83*

4.36*

75.94***

CMS8501

0

0 ± 0

0 ± 0b

0 ± 0d

0 ± 0c

0.75

0 ± 0

3.75 ± 2.39b

19.73 ± 4.11c

17.73 ± 6.48bc

1.5

0 ± 0

7.5 ± 3.23ab

56.78 ± 8.04b

57.95 ± 20.73ab

3

0 ± 0

17.5 ± 5.95ab

77.80 ± 12.37ab

87.65 ± 6.15a

6

1.25 ± 1.25

38.75 ± 11.43a

93.1 ± 4.28a

94.55 ± 2.42a

F value

1 ns

6.63**

32.99***

16.28***

SHABA

0

0 ± 0

0 ± 0c

0 ± 0b

0 ± 0c

0.75

0 ± 0

3.75 ± 2.39bc

10 ± 4.56b

10.45 ± 3.56bc

1.5

0 ± 0

8.75 ± 1.25ab

24.25 ± 13.75ab

26.20 ± 5.18b

3

0 ± 0

12.5 ± 3.23ab

55 ± 9.35a

67.58 ± 11.92a

6

0 ± 0

25 ± 7.36a

63.75 ± 12.64a

89.13 ± 6.32a

F value

-

6.47**

8.4***

33.18***

Means in the same column for the same maize variety, followed by the same letter do not differ significantly at P = 0.05 (Tukey's test); Number of replicates: 4; * P < 0.05; ** P < 0.01; *** P < 0.001; F value: a ratio of two variances-the "between group" variance and the "within-group" variance

[ Table Omitted - see PDF ]

Table 3

Progeny production of Sitophilus zeamais on grains of three maize varieties treated with NeemPro® under ambient laboratory conditions

Maize variety/content (g/kg)

Mean number of F1 adult progeny

% reduction in adult emergence relative to control

CLH103

Malagrain

0 ± 0b

100 ± 0a

0

85.75 ± 17.31a

0 ± 0c

0.75

14.25 ± 3.82b

84.25 ± 3.52b

1.5

4.5 ± 1.66b

93.95 ± 2.57ab

3

2.25 ± 0.75b

96.75 ± 1.51a

6

1.25 ± 1.25b

98.48 ± 1.52a

F-value

20.56***

375.89***

CMS8501

Malagrain

0 ± 0d

100 ± 0a

0

125.25 ± 4.59a

0 ± 0c

0.75

38.25 ± 10.84b

68.58 ± 9.65b

1.5

17.75 ± 4.44bc

85.58 ± 4.03ab

3

6.25 ± 2.75 cd

94.83 ± 2.35ab

6

2.75 ± 1.8d

97.7 ± 1.5a

F-value

75.92***

69.62***

SHABA

Malagrain

0 ± 0c

100 ± 0a

0

79.25 ± 4.94a

0 ± 0c

0.75

44.75 ± 8.17ab

42.33 ± 11.99b

1.5

32 ± 7.87bc

58.28 ± 1.28ab

3

20.75 ± 8.25bc

72.5 ± 11.21ab

6

9.75 ± 4.23c

87.03 ± 5.67a

F value

15.04***

13.07***

Means in the same column for the same maize variety, followed by the same letter do not differ significantly at P = 0.05 (Tukey's test); Number of replicates: 4; *** P < 0.001; F value: a ratio of two variances-the "between group" variance and the "within-group" variance

Population increase, grain damage and germination

In general, the rate of increase of the population of S. zeamais was significantly reduced by NeemPro® (Table 4). From the dosages of 1.5 g/kg in CLH103 and 3 g/kg in CMS8501, the populations of the weevil were completely suppressed as in Malagrain. No alive insects were recorded after 4 months of maize storage, while with the highest content of 6 g/kg, 15 alive weevils were registered in SHABA variety. In addition, there were no significant differences between the main effects of the rate, NeemPro®, Malagrain and maize varieties in percentage grain damage, grain weight loss and germination (Table 4). However, there were slight differences of all the parameters in SHABA variety. Moreover, no undamaged grain was found in untreated tests and that was for the three maize varieties. [ Table Omitted - see PDF ]

Table 4

Population increase (mean number of progeny for 4 jars ± SE) and damage parameters of Sitophilus zeamais on grains of three maize varieties admixed with NeemPro® and stored for 4 months under laboratory conditions and percentage of seed germination

Maize variety/content (g/kg)

Number of insects alive

Grain damage (%)

Weight loss (%)

Germination (%)

CLH103

Malagrain

0 ± 0b

0 ± 0b

0 ± 0b

84.13 ± 1.24a

0

669 ± 0a

113 ± 0a

99.99 ± 0.01a

0 ± 0b

0.75

5 ± 5b

1 ± 1b

0.13 ± 0.13b

85.56 ± 2.94a

1.5

0 ± 0b

0 ± 0b

0 ± 0b

86.67 ± 1.93a

3

0 ± 0b

0 ± 0b

0 ± 0b

76.67 ± 1.93a

6

0 ± 0b

0 ± 0b

0 ± 0b

82.22 ± 2.94a

F value

86.63***

8607.81***

999.99***

218.06***

CMS8501

Malagrain

0 ± 0c

0 ± 0c

0 ± 0b

86.41 ± 1.02ab

0

748 ± 28a

106 ± 0a

99.94 ± 0.01a

0 ± 0c

0.75

40 ± 20b

5 ± 2b

1.13 ± 0.44b

85.55 ± 2.22ab

1.5

6 ± 6bc

1 ± 1bc

0.61 ± 0.61b

82.22 ± 2.94ab

3

0 ± 0c

0 ± 0c

0 ± 0b

78.89 ± 5.56ab

6

0 ± 0c

0 ± 0c

0 ± 0b

72.22 ± 294b

F value

86.63***

970.42***

17674.85***

110.92***

SHABA

Malagrain

0 ± 0d

0 ± 0b

0 ± 0b

57.73 ± 2.05c

0

762 ± 66a

98 ± 0a

99.98 ± 0.01a

0 ± 0b

0.75

476 ± 60a

81 ± 12a

58.31 ± 24.36a

26.67 ± 13.47ab

1.5

135 ± 48b

28 ± 5b

5.85 ± 1.12b

37.78 ± 2.94a

3

54 ± 21bc

12 ± 2b

1.54 ± 0b

33.33 ± 1.93a

6

15 ± 11c

7 ± 3b

0.69 ± 0.29b

30 ± 3.33a

F value

47.11***

44.29***

16.5***

6.27***

Means in the same column for the same maize variety, followed by the same letter do not differ significantly at P = 0.05 (Tukey's test); number of replicates: 4; *** P < 0.001; F value: a ratio of two variances-the "between group" variance and the "within-group" variance

Discussion

Results of the present study show that the active ingredient of NeemPro®, azadirachtin, caused high mortality of S. zeamais on the one hand and completely hindered or significantly reduced progeny emergence on the other hand, indicating its potential use in the management of maize weevil. Earlier, the same NeemPro® was tested for its ability to protect Bambara groundnut against the infestation of Callosobruchus maculatus, regarding adult mortality as well as F1 progeny and larval inhibition. The insecticide was admixed with Bambara groundnut seeds. The product caused 68.75 and 98.75 % adult mortality respectively within 1 and 6 days with 6 days-LC50 of 0.001 g/kg. The product completely inhibited F1 progeny production at 3 g/kg [13]. In the same vein, Nukenine et al. [20] evaluated the effectiveness of NeemAzal PC KG 0.1 (0.1 % azadirachtin A) against S. zeamais in maize grains and found that within 14 days of exposure, maximum mortality of 99 and 100 % reduction in F1 progeny were achieved at 12 g/kg. All tested concentrations completely suppressed the population increase of the weevil, had no damaged grains and recorded no weight loss.

In addition, the inhibition of S. zeamais progeny emergence and maize grain damage as a result of treatment with NeemPro® was probably due to the huge array of azadirachtin activities on the insect's hormone system. It has been proved that azadirachtin disrupts or inhibits development of insect eggs, larvae or pupae, preventing the moulting of larvae or nymphs, disrupting mating and sexual communication, deterring females from laying eggs, sterilising adults, poisoning larvae, thus preventing adult maturation by inhibiting the formation of chitin, the essential substance for the insect to form an exoskeleton [6, 10, 21, 22].

Moreover, NeemPro® protected the three maize varieties. These results corroborate earlier findings of Demissie et al. [3] who reported that Silicosec, filter cake and wood ash protected grains of three maize genotypes against S. zeamais. The rate of seed germination was not affected by NeemPro® as observed in Malagrain. Nukenine et al. [20] reported similar findings where NeemAzal did not have negative effects on maize seed germination (germination rates of 92.23 % at 3 g/kg to 97.77 % at 12 g/kg were recorded).

Besides, Neempro® was used to protect the tree maize varieties in this study. The reason of using three varieties was that a product may protect a variety more than others. Someone may conclude that a product has protected a variety from weevils' attack whereas the variety itself was resistant against the insect. This is due to the level of different physical and biochemical parameters such as grain hardness, kernel weight, protein content, pericarp thickness, moisture content showed by different varieties [23]. In the present study, the product seems to have protected CLH103 and CMS8501 varieties more than SHABA in population increase, grain damage and germination. This may be due to the moisture content of SHABA which was 13.20 against 11.30 and 11.50 for CLH103, CMS8501, respectively.

Conclusions and recommendations

The study shows that NeemPro® is very effective against S. zeamais on the grains of three maize varieties (CLH103, CMS8501 and SHABA). This insecticide, not only kills the adult weevils, but also affects their progeny production. Additionally, it protects stored grains of the three varieties for 4 months without affecting the seed germination power. However, the product seems to have protected CLH103 and CMS8501 varieties more than SHABA. Therefore, NeemPro® can be used as post-harvest grain protectant against the infestation of the noxious S. zeamais. With this in mind, further research is needed in the future to investigate the effect of this botanical insecticide on other stored products pests and to determine the biochemical parameters of the three maize varieties.

Abbreviations

CLH:

cameroon lowland hybrid

CMS:

cameroon maize selection

LCL:

lower confidence limit

UCL:

upper confidence limit

LC:

lethal concentration

Declarations

Authors' contributions

CA and ENN conceived the idea, designed the experiments and analysed the data. SPYD and GTF conducted the experiments. SPYD wrote the manuscript. All authors read and approved the final manuscript.

Acknowledgements

Authors thank Dr. Hubertus Kleeberg of Trifolio-M GmbH, Germany for providing NeemPro® powder used in this study.

Competing interests

The authors declare that they have no competing interests.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://?creativecommons.?org/?licenses/?by/?4.?0/?), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://?creativecommons.?org/?publicdomain/?zero/?1.?0/?) applies to the data made available in this article, unless otherwise stated.

References

Throne JE. Life history of immature maize weevils (Coleoptera: Curculionidae) on corn stored at constant temperatures and relative humidities in the laboratory. Environ Entomol. 1994;23:1459-71.

Nukenine EN, Monglo B, Awasom I, Tchuenguem FFN, Ngassoum MB. Farmers' perception on some aspects of maize production, and infestation levels of stored maize by Sitophilus zeamais in the Ngaoundere region of Cameroon. Cam J Biol Biochem Sci. 2002;12:18-30.

Demissie G, Tefera T, Tadesse A. Efficacy of Silicosec, filter cake and wood ash against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) on three maize genotypes. J Stored Prod Res. 2008;44:227-31.

Cherry AJ, Bantino A, Djegui D, Lomers C. Suppression of the stem borer Sesamia calamistis (Lepidoptera: Noctuidae) in maize following seed dressing, topical application and stem injection with African isolates of Beauveria bassiana. Int J Pest Manag. 2005;50:67-73.

Isman MB. Botanical insecticides, deterrents, and repellents in modern agriculture and an increasingly regulated world. Annu Rev Entomol. 2006;51:45-66.

Schmutterer H. Properties and potential of natural pesticides from the neem tree, Azadirachta indica. Annu Rev Entomol. 1990;35:271-97.

Koul O, Isman MB, Ketkar CM. Properties and uses of Neem, Azadirachta indica. Can J Bot. 1990;68:1-11.

Ascher KRS. Non conventional insecticidal effects of pesticides available from the Neem tree, Azadirachta indica. Arch Insect Biochem Physiol. 1993;22:433-49.

Barrek S, Olivier P, Grenier-Loustalot MF. Analysis of neem oils by LC-MS and degradation kinetics of azadirachtin-A in a controlled environment: characterization of degradation products by HPLC-MS-MS. Analyt Bioanalyt Chem. 2004;378:753-63.

Mordue AJ, Blackwell A. Azadirachtin: an update. J Insect Physiol. 1993;39:903-24.

Parmar BS, Ketkar CM. Commercialization, in Neem Research and Development Randhawa NS, Parmar BS; Publication 3. New Delhi: Society of Pesticide Science; 1993. p. 270-83.

Kumar ARV, Jayadevi HC, Ashoka HJ, Chandrashekara K. Azadirachtin use efficiency in commercial neem formulations. J Curr Sci. 2003;84:1459-64.

Nukenine EN, Goudoungou JW, Mahama A, Adler C. Ability of neem seed powder and NeemPro® to protect stored bambara groundnut against the infestation of Callosobruchus maculatus F. (Coleoptera: Bruchidae) in the Adamawa region of Cameroon, in The First International Conference on Pesticidal Plants, icipe, Kenya. Book of Abstracts; 2013.

Nukenine EN, Goudoungou JW, Adler C, Reichmuth C. Efficacy of diatomaceous earth and botanical powders against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) on maize. Jul.Kühn.Archiv. 2010;425:881-7.

Abbott WS. A method of computing the effectiveness of an insecticide. J Econ Entomol. 1925;18:265-7.

Chebet F, Deng AL, Ogendo JO, Kamau AW, Bett PK. Bioactivity of selected plant powders against Prostephanus truncatus (Coleoptera: Bostrichidae) in stored maize grains. Plant Protect Sci. 2013;49:34-43.

Adams JM, Schulten GGM. Loss caused by insects, mites and micro-organims. In: Harris KL, Lindblad CJ, editors. post-Harvest Grain Loss Asseement Methods. USA: American Association of Cereal Chemists; 1978. p. 83-95.

SAS. The SAS system version 9.1 for windows. SAS Institute, Cary; 2003.

Finney DJ. Probit analysis. 3rd ed. Cambridge: Cambridge University Press; 1971. p. 68-72.

Nukenine EN, Tofel HK, Adler C. Comparative efficacy of NeemAzal and local botanicals derived from Azadirachta indica and Plectranthus glandulosus against Sitophilus zeamais on maize. J Pest Sci. 2011;84:479-86.

Karnavar GK. Influence of azadirachtin, on insect nutrition and reproduction. Proc Indian Acad Sci (Anim Sci). 1987;96:341-7.

Murugan K, Senthil KV, Jeyabalan D, Babu R, Senthil NS, Sivaramakrishnan S. Interactive effect of neem products on the control of pulse beetle, Callosobruchus maculatus (F). Neem Newsletter. 1999;15:41-4.

Siwale J, Mbata K, Mcrobert J, Lungu D. Comparative resistance of improved maize genotypes and landraces to maize weevil. Afr Crop Sci J. 2009;17:1-16.