THE INSECT TAXA ON CASHEW (ANACARDIUM OCCIDENTALE L.) PLANTS DURING THE FLOWERING AND FRUITING PERIODS IN THE NORTHERN REGION, GHANA

ABSTRACT
There have been debates whether insects that visit cashew during the flowering and fruiting periods are the same. The main problem arises as whether the insects that visit the plant during the flowering are the same that visit during the fruiting period. Field survey was conducted in ten farms in the Northern Region from December 2014 to April 2015 to identify and assess insects taxa on cashew in farms close to natural forest and farms away from natural forest, during cashew flowering and fruiting periods. Total insect species enumerated in farms close to the forest during the flowering period was 6161, with a mean number of 1232.2 (SD = 250.7) and diversity of 3.34. In farms greater than 5km away from the forest, the total number of insect species enumerated was 2745, with a mean of 549 (SD = 103.2) and diversity of 3.56. During the fruiting period, total insect species collected in farms close to the forest was 4665, with a mean number of 933 (SD = 143.5) and diversity of 3.13. In farms away from the forest, total insect species enumerated was 2056, mean 411.2 (SD = 52.1) and diversity 3.14. Insect diversity was greater during the flowering period in farms close to the forest than the fruiting period. Also, no significant difference was found between the diversity of insects on cashew plant in farms close and away from the forest during both the flowering and the fruiting periods. Most of the species that occurred during the flowering period were not the same as those that occurred during the fruiting period though some shared the same family. The result also shows that insect composition was not influenced by closeness to forest.


CHAPTER ONE
INTRODUCTION
Background of the Study
The development of plants has changed the global environment into an extremely useful resource for the herbivore community. In the natural ecosystems, plants and insects are constantly interacting with each other in a complex way. These two organisms are closely connected such that, insects provide several beneficial services including defence, dispersal and pollination to plants while plants provide shelter, oviposition sites and food, which are the three main factors necessary for insect reproduction (Mello & Silva-Filho, 2002).

On the other hand, depending on the amount of insect attack, herbivorous insects might be enormously detrimental to plants leading to death. Plant-insect interaction is a dynamic system, subjected to a repeated disparity and change (Mello & Silva-Filho, 2002). Numerous plants devote their resources in protecting their flowers against insects because some insects are usually unproductive pollinators (Bleil, Blüthgen, & Junker 2011).

Impending enemies of pollinators might chemically inhibit pollen germination, may reduce pollen viability or may be floral nectar thieves because most ants cause pollen damage.

In some cases, the more a plant invests in growth, the more it invests in resources such as nesting structures and extra floral nectar for insects. Insect selection might help mechanisms that add to the plant’s allotment to growth at the outflow of its allocation to reproduction. Insect–pollinator conflicts or direct insect–plant conflicts have seldom been documented in mutualistic insect–plant systems (Gómez, Bosch, Perfectti, Fernández & Abdelaziz, 2007). However, many plants have evolved chemical or physical devices against insects on their flowers which are pollinator’s or fruit eaters(Gómez et al., 2007).

Plants development set up a number of defences against herbivores including herbivores insect. A principal defence is the production of toxins to poison the attackers. Other strategies comprise the growth of thorns and tough inedible tissue to put off herbivores, and the enrolment of parasitoids and predators that attack herbivores (Meunier, Dalecky, Berticat, Gaum& McKey, 1999). Chemical defences are all over and more or less undoubtedly vital for plant survival, but other defences are also important, varied, and not always obvious. Plants build up tough polymers such as cellulose, lignin, tannins and silicates, which reduce palatability. Furthermore, by minimizing the nutritive value of their tissues plants may power an herbivore (particularly an insect) to consume more (Bhattacharya, Viswakarma, Bhat, Kirti & Chopra. 2002).

Although this strategy may not appear beneficial, it really forces the herbivore to consume larger amounts of plant toxins. Thorns, barbs, stings and sticky resins exuded from resin ducts, lactifers, or trichomes physically interfere with herbivory and trap or kill herbivores. Lectins and proteinase inhibitors produced in response to grazing hinder digestion (Fürstenberg-Hägg, Zagrobelny, & Bak, 2013). The benefit of a defence would emerge to be apparent. Energy and photosynthetic assimilates of the plant leave a resource for survival and reproduction of the plant relatively than that of the secondary consumers.

However, the defence itself requires expenditures of these resources. Consequently, if a plant suffers comparatively with little herbivory, the rate of the defence may not be recovered in increased fitness. Furthermore, if one of numerous possible herbivores is undeterred by the plant’s defences, the advantage of the defence might not be realized. Thus, several strategies must be working that are more complicated than simple attack with toxic chemicals (Bleil, Blüthgen, & Junker, 2011).

Cashew (Anacardium occidentale L.) was introduced into Ghana by the Government in the 1960s for a forestation in the savannah (Northern region), coastal savannah (Volta, Greater Accra and Cape Coast) and forest-savannah transition zone (Brong Ahafo region). Its cultivation was also deemed necessary for tree cover in degraded areas where land recovery programmes were under way to put off more erosion (Dwomoh, 2008). Large scale farming of this crop started in 1991 and by 1997, the section under cashew cultivation nation-wide was covering 12,500 ha. Between 2000 and 2004, incentives were provided to farmers in the form of loans and improved planting materials to establish new and rehabilitate old plantations.

Consequently, there was a marked increase in acreage from 18,000 ha to 51,831 ha, with a corresponding rise in nut yield from 3,600 MT to 25,915 MT. Cashew is potentially an enormous socio-economic crop to Ghana (Opoku-Ameyaw & Appiah, 2000). The product of commercial significance is the nut, it contains 47% fat, 21% protein and 22% carbohydrate, as well as some vitamins, especially thiamine (Soares et al., 2013).

The proteins in cashew nut are whole; having all the essential amino acids, as compared to a kilogram of the nut yields about 6000 calories to 3600 from cereals, 1800 from meat and 650 from fresh citrus fruit (America & Brazil, 2008). As bulk of the fatty acids present in the nuts is unsaturated, they are easy to digest, and can therefore, be consumed safely by young and old alike (Soares et al., 2013).

A liquid obtained from the cashew, known as cashew nut shell liquid (CNSL), is used broadly in brake linings of motor vehicles, paints, varnishes and laminated products (Opoku-Ameyaw & Appiah, 2000). It is also used as a plywood adhesive and a low-cost substitute for phenol in resole resins, as a constituent to boost the tensile properties, as blaze retardants of natural rubber and as a long-life, highly bioactive, antifouling shell for marine vessels (Noix

Afrique, 2002). CNSL and other extracts from the shell are larvicidal, molluscicidal, and antifungal and antibacterial (Mitchell & Mitchell, 2004).

However, several insects are found on the cashew plant, both beneficial and non-beneficial insects at the various stages of its development (Burgio, Ferrari, Boriani, Pozzati, & Van Lenteren, 2006).There has not been much information on insect species associated with cashew in Ghana regarding either the flowers or the fruits in respect to either there are beneficial species and none beneficial. Also, at what time is an insect species referred to as beneficial or none beneficial. There is therefore the need to identify insect species that visit cashew plant during the flowering and the fruiting periods in order to close this gap. In a previous study by Aidoo (2008)who worked on cashew insect pollinators but his protocol deviated a bit from this study and it will be so bias to build on his protocol. This is because this research is more about insect taxa on cashew plants during the flowering and fruiting periods.

Furthermore, it is necessary to investigate the density, diversity, distribution of and species composition of insects that visits the cashew plant during the flowering and fruiting periods.

Statement of the Problem
The issue of insect control to boost the productivity of cashew plant leaves much to be desired. The yield of cashew has been low whether there is lack of appropriate pollinators and possible role of ants in pollen damage. Also, flower visitors assessment on flora rewards for pollination and the role of flower visitors on fruit set in Ghana is scant. The main problem arises as whether the insects that visit the plant during the flowering period are the same that visit during the fruiting period.Moreover, the knowledge of the insect behaviour on cashew and the part they are found is not enough. There is no documentary evidence to show whether all the insects that visits the cashew plant has a positive or negative impact on the plant.

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Item Type: Ghanaian Postgraduate Material  |  Attribute: 138 pages  |  Chapters: 1-5
Format: MS Word  |  Price: GH50  |  Delivery: Within 30Mins.
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