ABSTRACT
Farmers are faced with a lot of problem in monitoring insect pests of stored cowpea. The standard probe trap is used to monitor C. maculatus infestations in stored cowpea but it is not efficient in trapping the insect due to variation in atmospheric conditions leading to inappropriate management decisions regarding the action threshold. Its perforation size (3 mm) is specific to C. maculatus which cannot be used for other larger bruchids like C. subinotatus, infecting cowpea. A research was carried out in the Entomology Laboratory of Nigerian Stored Products Research Institute, Kano, Nigeria, between March and October 2016, to examine the possibility of incorporating light into a locally fabricated probe trap, with the aim of developing an improved trap for detecting bean weevil. Six different colour lighted probe traps were evaluated, together with a control and a standard trap in order to determine the performance of respective trap in the detection of cowpea weevils. Each treatment was repeated three times, in three different insect densities: low (3 insects per kilogram of cowpea grain), medium (7 insects per kg) and high (15 insects per kg). Two weights of grains (10 kg and 100 kg) were used to determine the effect of grain volume on the performance of the fabricated probe trap. Trap catches was recorded every 24 hours for five days. Data collected was subjected to ANOVA and means were separated using SNK at 5 % confidence level. The result indicated that ambient light source was more effective in improving the performance of the modified probe trap for early detection of C. maculatus infesting stored cowpea, thresholds for management decisions were also determined and the fabricated trap was economically profitable; hence, objectives of the study were achieved. Commercialization of the improved probe trap is therefore recommended.
TABLE OF CONTENTS
Title page – – – – – – – – – i
Declaration – – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgement – – – – – – – – v
Abstract – – – – – – – – – vi
Table of Contents – – – – – – – – vii
List of Tables – – – – – – – – – viii
List of Figures – – – – – – – xiv
List of Plates – – – – – – – – – xv
List of Appendices – – – – – – – – xvi
CHAPTER ONE
1.0 Introduction – – – – – – – – 1
1.1 Justification – – – – – – – – 3
1.2 Objectives of the Study – – – – – – 4
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CHAPTER TWO
2.0 Literature Review – – – – – – – 5 2.1 Black Eyed Pea – Vigna unguiculata (L.) – – – – 5 2.2 Monitoring as an Integrated Pest Management Tool – – – 7
2.3 Cowpea Bruchid – – – – – – – 10
2.3.1 Insect Morphology – – – – – – – 10
2.3.2 Life history – – – – – – – 11
2.3.3 Host range and distribution – – – — – – 13
2.4 History of Insect Sampling and Trapping System – – – 14
2.5 Standard Probe Trap – – – – – – – 16
2.6 Factors Affecting Insect Trap Catch – – – – – 17
2.6.1 Type of insect – – – – – – – – 17
2.6.2 Temperature – – – – – – – – 18
2.6.3 Relative humidity (RH) – – – – – – 18
2.6.4 Presence of crevices – – – – – – – 18
2.6.5 Pesticide – – – – – – – – 18
2.6.6 Light intensity and colour – – – – – – 19
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2.6.7 Food and odour – – – – – – – 19
2.6.8 Time – – – – – – – – – 20
2.6.9 Trapping duration – – – – – – – 20
2.7.0 Trap position – – – – – – – – 20
2.7.1 Insect density – – – – – – – – 20
2.7 Insect Response to Traps – – – – – – 21
2.8 Insect Colour Vision – – – – – – – 22
2.9 Trapping and Interpreting Captures of Stored Grain Insects – – 23
2.10 Economic Threshold Levels for Stored Product Insects – – 26
CHAPTER THREE
3.0 Materials and Methods – – – – – – 28
3.1 Research Location – – – – – – – 28
3.2 Trap Development – – – – – – – 28
3.2.1 Materials for fabrication of probe trap – – – – 28
3.2.2 Fabrication and coupling procedure – – – – – 28
3.2.3 Trap description – – – – – – – 30
3.3 Research Materials – – – – – – – 31
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3.4 Evaluation of Light Sources – – – – – – 31
3.5 Procurement and Disinfestations of Cowpea Grains – – – 33
3.6 Determination of Moisture Content of Cowpea Grains used – – 33 3.7 Insect Culture – – – – – – – – 34 3.8 Trial of the Modified Trap Using 10 and 100 kg Cowpea Sample – 34 3.8.1 Barrier control – – – – – – – – 35 3.8.2 Experimental layout – – – – – – – 36 3.8.3 Use of traps – – – – – – – – 38 3.8.4 Inspection of traps – – – – – – – 39 3.9 Data Analysis – – – – – – – – 40 3.10 Cost benefit analysis – – – – – – – 40
CHAPTER FOUR
4.0 Results – – – – – – – – – 42 4.1 Fabricated Trap and its Components – – – – – 42
4.2 Results of Illuminance Intensity of Individual Light Colours – 45
4.3 Daily Trap Catches – – – – – – – 46
4.4 Day One Trap Catches at Different Population Density – – 47
4.5 Total Trap Catches – – – – – – – 48
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4.6 Evaluation of Trap Catches at Different Population Densities – – 49
4.7 Correlation of Trap Catches between Population Density and Light
Intensity – – – – – – – – – – 51
4.8 Correlation of Trap Catches between Trapping Duration, Population
Density and Volume of Grain – – – – – – – 51
4.9 Pest Population Detected by the Modified Trap – – – 52
4.10 Cost and Benefits of Modified Probe Trap – – – – 53
CHAPTER FIVE
5.0 Discussions – – – – – – – 55
5.1 Fabricated Trap and its Components – – – – 55
5.2 Results of Illuminance Intensity of Respective Lights Colours – 56
5.3 Daily Trap Catches – – – – – – 56
5.4 Day One Trap Catches at Different Population Densities – – 56
5.5 Total Trap Catches – – – – – – 56
5.6 Evaluation of Trap Catches at Different Population Densities – 57
5.7 Correlation of Trap Catches between Population Density and
Light Intensity – – – – – – – – – 58
5.8 Correlation of Trap Catches between Trapping Duration, Population
Density, and Volume of Grain – – – – – – – 58
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5.9 Pest Population Detected by the Modified Trap – – – 59
5.10 Cost and Benefits of Modified Probe Trap – – – – 60
CHAPTER SIX
6.0 Summary, Conclusions and Recommendations – – – 61
6.1 Summary – – – – – – – – 61
6.2 Conclusions – – – – – – – – 61
6.3 Recommendations – – – – – – – 62
REFERENCES – – – – – – – – 63
APPENDICES – – – – – – – – 69
CHAPTER ONE
1.0 INTRODUCTION Cowpea (Vigna unguiculata (L.) Walp) is a popular leguminous crop in Africa which is commonly known as beans, ewa (Yoruba), agwa (Igbo), or wake (Hausa) in Nigeria. The grain is rich in protein and other micronutrients necessary for healthy living. Many societies endowed with cowpea have evolved different ways of utilizing the grain for food and perhaps the reason for the coinage “naman talaka” (poor man’s meat) by Hausas of West and Central Africa (Institute for Agricultural Research Policy Brief, 2012). Rapid progress has been made in researches related to this crop, particularly since the establishment of the Grain Legume Improvement Programme at International Institute for Tropical Agriculture and the strengthening of the research program for grain legumes in a number of West African Agriculture Research Centres (Ajeigbe et al., 2008). Nigeria produces more than two million tons (Adeola et al., 2011) which represents 58 % of the total world cowpea production annually (Peace, 2015).
Cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is a cosmopolitan pest that causes considerable economic damage to dried cowpea and other related stored legumes, and is the main constraint to increased cowpea production and storage (Carlos, 2004). Carlos (2004) also stated that unprotected cowpea grains are often completely consumed by bruchids in the first 10 to 12 months of storage. C. maculatus multiplies rapidly in storage, giving rise to a new generation every month in grains at temperature of 30 oC to 35 oC and 70 % to 90 % relative humidity (RH) (Fatima et al., 2016). Grains attacked have reductions in weight, nutritional compositions, viability and
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virtually unfit for human consumption (Sarwar, 2015). Currently, emphases on the management of pests such as cowpea bruchid rely upon a combination of methods known as Integrated Pest Management (IPM) which are environmentally friendly to offer effective management (Lester, 2006). According to Amerika and Sharma (2004), inspection during storage is an important component of IPM, which prevents losses.
Insect probe trap, originally conceived by Loschiavo (1975) is a type of pitfall trap which is buried in grains and it catches insects which drop through small pitfall apertures into the trap. The device exploits the wandering behaviour of the insects which help in timely detection of insects in stored produce leading to timely control. This trap is a hollow metal plate tube with a series of perforations (holes) all along the sides. The top is a cap, and the bottom is a cone-like translucent plastic that screws in place. Inserted at various depths in grains, this type of trap can be extremely effective and a number of designs have been used (Barak et al., 1990; Neethirajan et al., 2007). Although considered of major importance, the insect probe trap is more often than not underestimated or in fact neglected, because it is time consuming and precise methods of interpreting the catch have not been adequately specified (Philips et al., 2000).
Unless improved probe traps are introduced together with a strategy for their use in commercial grain storage practice, the potential benefits of any new technique will be lost. In order to modify this important IPM tool in the form available and more acceptable among local grain handlers, investigations were conducted to search for alternative means that could facilitate the performance of the device using improvised and locally available materials (Mbogo, 2013). Some factors that can influence the efficacy of an insect trap include; Light intensity and colour (David, 1992; Weinzierl et al., 2005; Marianne and
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Rebecca, 2011; Michael and Christian, 2012; Van, 2013). Therefore, an attractant trap such as a lighted probe trap may be helpful in giving reliably early indications of the presence of bruchids that move readily in grains for necessary control measures to be initiated.
1.1 Justification
Farmers are faced with a lot of problem in monitoring insect pests of stored cowpea. The standard probe trap is used to monitor C. maculatus infestations in stored cowpea but it is not efficient in trapping the insect due to variation in atmospheric conditions, leading to inappropriate management decisions regarding the action threshold. Great numbers of insect species are attracted to light of various intensities or colours. Therefore, a lighted probe trap can be helpful in giving reliably early indications of the presence of bruchids that move readily in bulk grain. Many types of insect specimens collected with light traps are undamaged and so are good for research purpose. Use of light traps reduces the risks of pesticide residues in food, unlike insecticides. Insecticides are also effective but when used excessively, pests develop resistance. Light trapping, once standardized and targeted to the species of interest could be very effective in monitoring that species. The standard trap with 3 mm perforations is specific to C. maculatus which cannot be used for other larger bruchids like Callosobruchus subinotatus, infecting cowpea. Thus, there is a need for a probe trap that can be used to monitor all groups of insects infecting cowpea. The standard probe trap is also scarcely available to Nigerian grain handlers or where available, it’s expensive due to high rate of foreign exchange. Furthermore, since the modified probe trap can be fabricated from locally available materials, waste can be converted into wealth.
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1.2 Objectives of the Study:
To fabricate an insect probe trap for monitoring C. maculatus in stored cowpea.
To evaluate the performance of the modified probe trap on C. maculatus infesting stored cowpea.
To assess the cost benefit analysis of the fabricated probe trap.
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