INSECT DIVERSITY OF COCOA (THEOBROMA CACAO L.) BEANS STOCKS FROM HAUT-SASSANDRA REGION AND THEIR IMPACTS (DALOA, CÔTE D’IVOIRE).

Cocoa storage is a potential opportunity for insect infestation. The objective of this study was to identify insects and assess their damage to stored cocoa beans from the Haut-Sassandra region. To do this, 3 samples of 3 Kg of cocoa beans were collected per locality. These samples were stored for 30 days in


ISSN: 2320-5407
Int. J. Adv. Res. 7 (10), 393-401 394 average of 1,700,000 tonnes (Kébé et al., 2006;ICCO, 2018). Despite this remarkable performance, the sustainability of cocoa farming in Côte d'Ivoire is compromised by several biotic constraints, including diseases, pest, rodent and parasitic plant attacks (Kébé et al., 2006;Kouamé et al., 2016). Concerning diseases, Phytophthora and Loranthus attacks lead to significant production losses. Virus disease such as swollen shoot destroys the cocoa tree after 3 to 5 years (Chingandu et al., 2017). Stored cocoa beans are often subject to losses of a variable and complex nature, most of which are attributed to insects, micro-organisms and rodents (Kekeunou et al., 2006;Tah et al., 2016). Indeed, cocoa can be infested initially in the field, during post-harvest treatments and storage by several insect species and other pests. If these infestations are not initially treated with effective fumigation before shipment (Doumbia and Kouassi, 2009), these species will survive during transport to traders, processors and manufacturers. Thus, it is therefore necessary to know the entomofauna of cocoa bean stocks in the Haut-Sassandra region. This knowledge will allow effective pest control. This study is part of the improvement of cocoa storage conditions. The objective of this work is to update the list of insects associated with cocoa bean stocks and to assess their damage to the beans during storage.

Study site
The cocoa beans samples from the 2017-2018 seasons were collected from farmers in 6 localities (Bazra, Bédiala, Boguedia, Gadouan, Zaïbo and Zoukougbeu) in the Haut-Sassandra region, Center West of Côte d' Ivoire (Fig 1). These localities were chosen for their high production. The samples were sent to Jean Lorougnon Guédé University in Daloa for study. The city of Daloa is located at 6°53 North latitude and 6°27 West longitude from Côte d'Ivoire. During the study period, the temperature of the storage room varied between 28.4 and 30.5°C and the relative humidity between 67.53 and 82.42%.

Inventory and insect dynamics of cocoa bean stocks
Inventory of stock insects were carried out on the lots of field cocoa beans which had not undergone any chemical treatment. These bean were collected from 6 localities in the Haut-Sassandra region. In each locality, a 2 kg lot was taken from the stocks of cocoa of 5 producers. The beans were removed at different locations from the cocoa bags (two ends and in the center) according to regulation N o 401/2006 (CE) (Commission of the European Communities, 2006). These 5 elementary samples were grouped together to form an overall sample of 10 kg (Regulation No. 401/2006). From this overall homogenized sample, 3 samples of 3 kg of cocoa beans were made per locality. These batches were stored for one month to allow the hatching of any insect eggs. After one month of storage, each sample was sieved every 15 days in a muslin observation cage for 120 days. Live or dead adults insects harvested in each lot were observed under binocular magnifying glass and counted. The living are returned to the lots from which they 395 were removed. Counting is done directly by species after sorting. The number of adults per species has been noted. Species identification was done using identification key (Weidner and Rack, 1984;Delobel and Tran, 1993).

Evaluation of damage during storage time
The estimate of damage to cocoa beans is done by evaluating the proportion of beans carrying pest attack holes in a sample. It is made according to the counting and weighing method (MCP). Thus, three samples of 1 kg of cocoa beans not bearing holes were made. The number of beans corresponding to 1 kg has been account. Each month, after the sieving session, each sample was divided into two fractions: the first consisting of perforated beans and the second consisting of beans without holes. The damage of each fraction was estimated as a percentage after counting. The evaluation was done monthly, for four months. The estimate of damages was done by the following formula (Boxall,1998) : With: A : total number of cocoa beans; B : number of cocoa beans with holes

Estimate the relative weight loss of cocoa beans
Relative loss is the degree of transformation of a bean following a pest's infestation by comparing it to an intact bean. It is evaluated every month for four months. The Counting and Weighing (MCP) method is used to determine the relative weight loss of cocoa beans. It ignores the determination of the beans moisture content; then it compares the standard internal value of the intact cocoa beans with that of the damaged cocoa beans. The sample removed from the stock after sieving is divided into two batches: on the one hand the intact cocoa beans and on the other hand the infested cocoa beans. The beans of each batch are weighed and counted. The relative weight loss is then evaluated according to the formula of Adams and Schulten (1978): A : total number of cocoa beans; B : number of damaged beans C : number of intact beans; D : weight of the damaged beans E : weight of intact beans; P : relative weight loss After each survey, the counted cocoa bean samples are returned to the bags of the corresponding batches.

Data analysis:-
Data processing was performed using the software Statistica 7.1 version. The variance analysis followed by the Newman-Keuls test at the 5% threshold allowed to compare the average number of insects of the cocoa beans of each batch, the number of cocoa bean bearing or no holes, the damage and the relative weight loss of cocoa beans. The XLSTAT 7.5 software was used to perform factorial correspondence analysis (AFC) between insect species and localities in the region to highlight the characteristic species of the region. The relative abundance of the species was determined by the formula of Zame and Gautier (1989): Ni: number of species' individuals considered; N: total number of all species' individuals combined; Ar (%): relative abundance.

Insects identified in the six localities
The identification of the collected specimens revealed on all 6 localities two orders (Coleoptera and Lepidoptera) with 10 families and 12 species. Of these 12 species, only one Ephestia cautella belonging to the order Lepidoptera and the family Pyralidae was collected.  Table 1). The variance analysis followed by the Newmans-Keuls test at 5% threshold revealed a significant difference (P-value < 0.001) between averages numbers of species collected.   (Table 3). The variance analysis followed by Newmans-Keuls test at 5% threshold showed a significant difference (P-value < 0.001) between averages numbers of species collected during storage.  Table 4). The variance analysis followed by Newmans-Keuls test at 5% threshold showed a significant difference (P-value < 0.001) between averages numbers of species collected during storage.

Zoukougbeu's locality
From the 30th to the 60th day of storage, only one species of the order Coleoptera, T. castaneum was present in stocks with an average size of 3.33 ± 0.57 individuals (60th day). S. zeamais and E. cautella appear in the stocks at 75 and 90 days respectively. T. castaneum was the most abundant species with a total of 21 individuals, representing 63.64% of the total number of insects harvested (33 individuals) ( Table 6). The variance analysis followed by Newmans-Keuls test at 5% threshold showed a significant difference (P-value < 0.05) between averages numbers of species collected during storage.

Relative abundance of species in the Haut-Sassandra region
The insects encountered throughout the sampling in the stocks of cocoa beans in the Haut-Sassandra region were 868 individuals represented by 12 species (Fig 2).  (Fig 3). The species A. advena was the most abundant in the localities of Gadouan, Bazra and Zaïbo. As for the species T. castaneum and E. cautella, they had very high numbers in the stocks of cocoa beans of the localities of Bediala and Boguedia. Concerning the species O. surinamensis it was very abundant in the locality of Bazra (Fig  3).    Table 7). The relative weight loss by the cocoa beans is very low (0.63 ± 0.04%) at the end of the first month of storage. It grows insignificantly to reach 3.73 ± 0.17% at the end of the second month of storage. Beyond this period, the loss becomes more significant with 6.84 ± 0.10% at the end of the third and 8.32 ± 0.21% at the end of the fourth month (Table 7). . This abundance may also be due to the longevity of the insect which is 2 to 10 months following the abiotic conditions and duration of the development cycle which lasts approximately one month (Delobel and Tran, 1993). Of a total of 937.33 healthy cocoa beans seen at the beginning of storage, 252 had at least one hole after 120 days of storage. This is linked to the gradual reinfestation of cocoa beans. This reinfestation could be the consequence of long-term storage. Indeed, a long-term conservation seems to favor the setting up of conditions (high humidity, mold) allowing both the development of insects already existing in the stock, as well as the appearance of new species.

Conclusion:-
This study made it possible to carry out an inventory of cocoa bean insect species in the Haut-Sassandra region. The batch monitoring of cocoa beans indicated that all lots from the fields are infested with insects. The identification of the collected specimens revealed 12 species, 10 families and 2 orders that are Coleoptera and Lepidoptera. The species encountered during all the sampling in the cocoa bean stocks were: A. advena, A. fasciculatus, C. hemipterus, C. ferrugineus, E. cautella, L. serricorne, O. surinamensis, S. zeamais, T. .castaenum, R. dominica, S. paniceum and Korynetes sp). Among these species, Korynetes sp is a species encountered for the first time in the stocks of cocoa beans. A study of the bioecology of this species on cocoa beans will determine its status as a pest or insect occasionally encountered in cocoa stocks. The most abundant species was A. advena (24.89%). Factorial analysis of the correspondences indicated that four species A. advena, T. castaneum, E. cautella, and O. surinamensis are characteristic of the region. Insect damage to cocoa beans was 26.88% at the 120th day of storage. This inventory will help to better target pests in order to develop an appropriate response.