ABSTRACT
The study investigated the lethal and sublethal effects of imidacloprid on stingless bee. Imidacloprid is a nicotinic acetylcholine receptor agonist that impair memory formation in bees and which also affect sucrose consumption of stingless bee. This test was carried out in order to determine the effects of acute oral toxicity of imidacloprid and also if it affect the sucrose consumption of stingless bee. In order to carry out this study, adult worker stingless bees were collected from their hive at the Biological Garden, Obafemi Awolowo University Campus, Ile-Ife, Osun State, Nigeria. The bees were exposed to the different concentrations of imidacloprid (i.e. 0.25, 0.50, 1.00, 2.00 and 4.00 mg/L) and acclimatized at a temperature of 220C in the laboratory. The highest mortality was recorded at the highest concentration of 4.00 mg/L with mean percentage of 83.3 % mortality and the lowest mortality was recorded at control with a mean percentage of 3.3 % mortality. Mortality increased overtime but there was no significant difference between the duration of exposure of the bees. The amount of sucrose consumed at 24 hours was highest at 0.25 mg/L with mean value of 0.0779 g and lowest at 4.0 mg/L with mean value of 0.0400 g. Also at 48 hours, the sucrose consumption 1.00 mg/L with mean value of 0.0835 g and was lowest at 0.5 mg/L with mean value of 0.0042 g. Thus the result obtained shows that there was no significant difference in the amount of sucrose consumed by the stingless bees at different concentration of the test substance at 24 and 48 hours. Further study should therefore be conducted on the lethal and sublethal effects of imidacloprid on stingless bee.
TABLE OF CONTENTS
Title…………………………………………………………………………………………………………………..page
Certification………………………………………………………………………………………………………..ii
Dedication………………………………………………………………………………………………………….iii
Acknowledgement………………………………………………………………………………………………iv
Table of contents…………………………………………………………………………………………………v
List of plates…………………………………………………………………………………………………….viii
List of figures……………………………………………………………………………………………………..ix
List of tables………………………………………………………………………………………………………..x
List of appendices………………………………………………………………………………………………..xi
Abstract……………………………………………………………………………………………………………..xii.
CHAPTER ONE: INTRODUCTION
Biology of stingless bees.……………………………………………………………….1
Economic importance of stingless bees pollination in commercially growncrops……………………………………………………………………………..2
CHAPTER TWO: LITERATURE REVIEWS
2.1 Biology of Stingless Bees……………………………………………………………….5
2.2 Stingless Bees and the environment…………….……………..…………………………8
2.3 Pesticide use and its effects on Stingless Bees…………………………………………..8
2.3.1 Pesticides Usage in Nigeria…………………………………………………………………….9
2.4 Neonicotinoids……………………………………………………………………………10
2.5 Imidacloprid……………………………………………………………………………..12
2.5.1 Effects of imidacloprid on sucrose consumption……………………………..………..16
CHAPTER THREE: MATERIALS AND METHODS
3.1 Collection of Stingless Bee Workers…………………………………………………….18
3.2 Toxicity Test……………………………………………………………………………..18
3.2.1 Range Finding Test……………………………………………………………………18
3.2.2 Acute Oral Toxicity Test………………………………………………………………22
3.3 Statistical Analysis………………………………………………………………………22
CHAPTER FOUR: RESULTS
4.1 Mortality…….…………………………………………………………………………..24
4.2 Sublethal Effect………………………………………………………………………….24
4.2.1 Sucrose Consumption…………………………………………………………………24
CHAPETR FIVE: DISCUSION, CONCLUSION AND Â Â Â Â Â RECOMMENDATION
5.1 Toxicity Effect of Imidacloprid on Stingless Bee (Meliponula bocandei)…………….29
5.2 Sublethal Effect of Imidacloprid on Stingless Bee……………………………………..30
5.2.1 Sucrose Consumption…………………………………………………………………30
5.3 Conclusion……………………………………………………………………………….31
5.4 Recommendation………………………………………………………………………..31
REFERENCES…………………………………………………………………………….32
APPENDICES……………………………………………………………………………..46
CHAPTER ONE
INTRODUCTION
 1.1 Biology of Stingless Bees
Stingless bees are widely distributed and adapted to the tropical and neotropical ecosystems of the world but the genus Meliponula is unique to Africa (Eardley, 2004; Henske and Krausa et al., 2015). There are several hundreds of species existing worldwide, which vary considerably in colour, body and colony size (Roubik, 1992; Michener, 2000). It is estimated that 400 to 500 different species of stingless bees are known, but new species are identified every year. The number of bees a colony can contain ranges from some few hundred to more than a hundred thousand bees; however, this differs from species to species (FAO, 2009).
The nest environment is structured by activities of the colony members and also by individual behavior. This process is called stigmergy (Grassé, 1959) and plays an important role in task coordination and the regulation of building activities in many social insects (Theraulaz and Bonabeau, 1995). Foragers are a rich source of information to nest mates. They may provide detailed information on food source location to naive foragers (Nieh, 2004) and to experienced foragers (Biesmeijer and de Vries, 2001). Competition for food is most intense between more similar individuals, i.e. conspecifics from different nests (Johnson, 1974). Diets of conspecific nests are more similar than of heterospecific nests (Biesmeijer and van Nieuwstadt, 1997; Biesmeijer et al., 1999; Nagamitsu et al., 1999; Eltz et al., 2001). Stingless bees comprise a highly diverse and abundant group of eusocial bees that inhabit the tropical and subtropical parts of the world.         They form perennial colonies from which they forage year-round.
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1.2Â Economic importance of stingless bee pollination in commercially grown crops.
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Most crop plants depend on pollination for fruit and seed set. It has been estimated that about 30% of human food is derived from bee-pollinated crops (Kearns and Inouye, 1997; Klein et al., 2007). A wide variety of bee species are known to be efficient and effective pollinators of many crops (Richards, 2001; Kremen et al., 2002). Stingless bees are known to be important pollinators in tropical rainforests (Eltz et al., 2003) and good candidates for providing pollination services in agricultural ecosystems thereby increasing yield and food security (Heard, 1999; Slaa et al., 2006). They are also important pollinators of plants species in natural habitats (Kato, 1996) and similar to honey bees, most stingless bee species use pollen and nectar as food source (FAO, 2009; Kwapong et al., 2010). They have important roles as they help to disperse pollen during foraging which has led to the pollination of over 80% of world commercial crops (Slaa et al., 2006) and the hive products which are honey, propolis and wax are source of income for local communities (Kwapong et al., 2010).
In the last 20 years, pesticide use has shifted away from organophosphates and carbamates towards neonicotinoid compounds that are agonists of insect nicotinic acetylcholine receptors (nAChRs) (Ihara et al., 2006; Elbert et al., 2008). Bees come in contact with pesticides when foraging or when the hive is treated with pesticides to kill mites. Foragers can collect contaminated pollen and nectar and bring it back to the hive. In the hive, bees evaporate water from nectar to produce honey. Any pesticide in the nectar is concentrated at least 4 times in the honey. So bees can be exposed both in the field and in the hives (Bonmatin et al., 2005; Kievits, 2007). Mullin et al. (2010) found bee pollen in hives contained with imidacloprid at a median concentration of 20 ppb and a maximum concentration of 206 ppb and these levels are known to impact the health of bees. Pesticides may also contribute to Colony Collapse Disorder (CCD) thereby causing workers to disappear from their hive and leaving food, brood and even a queen (USHR, 2007; Quarles, 2008). Despite intensive research, an exact cause of CCD has not been identified. However, there is the possibility that a number of causes might be working synergistically. It has been established that over wintering bee colonies are under stress, and one of this stress is pesticide toxicity (Quarles, 2008; Spivak et al., 2011).
Among the pesticides found in bee hives by Mullin et al. (2010) were neonicotinoids which are analogue of the neurotoxin nicotine and have similar actions. Pesticides impact bee populations through direct mortality and through sublethal effects on behaviour, such as impaired memory, learning and foraging. Impaired foraging can lead to poor nutrition, and pesticides may directly impact their immune systems, making them more susceptible to disease. Sublethal effects pesticides interfere with brood development and shorten lifespans of adults (Desneux et al., 2007; Henry et al., 2012; Pettis et al., 2012; Wu et al., 2012). The use of pesticides have been licenced in many countries, and these pesticides include pyrethroids, neonicotinoids, organophosphate, aminophosphate etc (Bonmatin et al., 2014).
Neonicotinoids are group of pesticides that are systemic on plants, they are also neurotoxic chemicals which are used to kill pests. They are applied to prevent pest outbreak and can be applied as seed coating, soil drenching, trees injection and spraying on flowering plants (Bonmatin et al., 2014). Neonicotinoids are neuro-active insecticides which target nicotinic acetylcholine (nACh) receptors in the insect nervous system, causing over-stimulation of nerve cells, paralysis and at sufficiently high doses, death (Tomizawa & Casida, 2005; Palmer et al., 2013; Moffat et al., 2015).
Acute toxicity is the most fundamental of toxicological investigations and is routinely performed as a regulatory requirement for a number of different substance and product types in order to ensure human safety. Despite the fact that imidacloprid is widely used by farmers in Nigeria, its effects on the stingless bee, M. bocandei, is still unknown hence the objectives of the study.
- To determine the oral acute toxicity of imidacloprid to the stingless bee (Â bocandei).
- Also to determine the effects of imidacloprid at different concentrations on the sucrose consumption of bocandei.
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