2022 Volume 9 Issue 1

Diversity of Insects on Four Cashew Nut Varieties Inflorescences “Anacardium occidentale L.” in Niofoin “Côte d’Ivoire”


Yalamoussa Tuo, Drissa Coulibaly, Mouhamadou Koné, Soumaila Traoré, Klana Koné, Kouakou Hervé Koua
Abstract

Cashew nut represents the third most exported agricultural product of Côte d’Ivoire. However, the yield production of cashew is still low likely due to many factors including under-pollination. This study aims to identify the insects visiting cashew tree inflorescences at Niofoin in northern Côte d’Ivoire. Observations were made in a cashew orchard measuring two hectares. Insects visiting the inflorescences were captured and identified. A total of four cashew nut varieties (Yellow Benin, Henry, Costa Rica, and James) were observed. The daily activity of honey bee Apis mellifera, considered here as the number of flower visits made by a bee in one minute to an inflorescence, was evaluated on the inflorescences from 5 a.m. to 6 p.m. The findings showed 16 families belonging to 7 orders. Among the insect families, Apidae emerged as the most abundant family (32.15%). Apis mellifera (Apidae) was the main visitor of cashew tree inflorescences. His activity was stronger on "Yellow Benin" and "Henry" varieties compared to "James" and "Costa Rica" varieties. For all varieties of cashew trees, honey bee activity varied throughout the day with two peaks, one between 7 a.m. and 8 a.m. and the other between 5 p.m. and 6 p.m. It was inversely proportional to temperature (p < 0.05; r = - 0.59) and evolved in the same direction with relative humidity (p < 0.05; r = 0.49). This study, although preliminary, remains quite relevant because it will help to boost cashew production in northern Côte d’Ivoire through the pollinators’ involvement.


How to cite this article
Vancouver
Tuo Y, Coulibaly D, Koné M, Traoré S, Koné K, Koua K H. Diversity of Insects on Four Cashew Nut Varieties Inflorescences “Anacardium occidentale L.” in Niofoin “Côte d’Ivoire”. Entomol Appl Sci Lett. 2022;9(1):31-8. https://doi.org/10.51847/IkQ2Hu7Kcp
APA
Tuo, Y., Coulibaly, D., Koné, M., Traoré, S., Koné, K., & Koua, K. H. (2022). Diversity of Insects on Four Cashew Nut Varieties Inflorescences “Anacardium occidentale L.” in Niofoin “Côte d’Ivoire”. Entomology and Applied Science Letters, 9(1),31-38. https://doi.org/10.51847/IkQ2Hu7Kcp

Diversity of Insects on Four Cashew Nut Varieties Inflorescences “Anacardium occidentale L.” in Niofoin “Côte d’Ivoire”

 

Yalamoussa Tuo1, Drissa Coulibaly1*, Mouhamadou Koné1, Soumaila Traoré1, Klana Koné2, Kouakou Hervé Koua2

 

1Department of Animal Biology, U.F.R. Biological Sciences, University Peleforo GON COULIBALY of Korhogo, Côte d’Ivoire, BP 1328 Korhogo, Côte d’Ivoire.

2Department of Zoology, Animal Biology and Ecology, U.F.R. Biosciences, University Felix Houphouët-Boigny of Abidjan, Côte d’Ivoire, 22 BP 1611 Abidjan 22, Côte d’Ivoire.


ABSTRACT

Cashew nut represents the third most exported agricultural product of Côte d’Ivoire. However, the yield production of cashew is still low likely due to many factors including under-pollination. This study aims to identify the insects visiting cashew tree inflorescences at Niofoin in northern Côte d’Ivoire. Observations were made in a cashew orchard measuring two hectares. Insects visiting the inflorescences were captured and identified. A total of four cashew nut varieties (Yellow Benin, Henry, Costa Rica, and James) were observed. The daily activity of honey bee Apis mellifera, considered here as the number of flower visits made by a bee in one minute to an inflorescence, was evaluated on the inflorescences from 5 a.m. to 6 p.m. The findings showed 16 families belonging to 7 orders. Among the insect families, Apidae emerged as the most abundant family (32.15%). Apis mellifera (Apidae) was the main visitor of cashew tree inflorescences. His activity was stronger on "Yellow Benin" and "Henry" varieties compared to "James" and "Costa Rica" varieties. For all varieties of cashew trees, honey bee activity varied throughout the day with two peaks, one between 7 a.m. and 8 a.m. and the other between 5 p.m. and 6 p.m. It was inversely proportional to temperature (p < 0.05; r = - 0.59) and evolved in the same direction with relative humidity (p < 0.05; r = 0.49). This study, although preliminary, remains quite relevant because it will help to boost cashew production in northern Côte d’Ivoire through the pollinators’ involvement.

Keywords: Insects, Yellow benin, Henry, Costa rica, James, Pollinators.


INTRODUCTION

 

The cultivation of cashew nut has been introduced in the North of Côte d’Ivoire in 1960 to slow down deforestation and fight against soil erosion [1]. This enabled to increase population incomes through the associated traded products such as apple and cashew nut [2]. In 2010, the cashew nut became the third exported agricultural product from Côte d’Ivoire after cocoa and rubber [3]. This performance ranked the country the first among cashew-nut producing and exporting countries in the world [4]. However, despite the recorded gains, the current yield production of cashew (350-500 kg per hectare) is still low compared to forecasts, estimated to be 1.6 t/ha [5]. Several studies attributed partly the low productivity of cashew trees to under-pollination [6-8]. A study from India showed that 25% to 72% of pistil was not pollinated due to the lack of pollinator insects [6]. These findings support that insects are essential pollinators for cashew tree production and that their absence could therefore directly impact yield production. Past studies have suggested that wind is a pollinating agent of cashew trees [9]. Yet, up to date, very few studies highlighted the essential role of insects in cashew pollination. However, since the cashew tree is highly dependent on pollination to produce fruit, not all insects that visit its flowers participate equally in the pollen transfer. Thus, various studies, particularly in Brazil and India, have sought to determine which insects are the most efficient in pollinating the cashew tree flower. In Brazil, where the cashew tree originated, direct observations of insects visiting flowers and counting pollen grains have shown that honey bee (Apis mellifera), although not native, is the most efficient pollinator of cashew tree in northeastern Brazil [7]. In India, the observations have shown that the insects which visit cashew trees' flowers are ants and bees, mainly. Moreover, in Ivory Coast, the first country producer of cashew, very little data exists on the pollinating fauna of this speculation. This study aims to fill these knowledge gaps on cashew pollination. The global objective was to know the entomofauna of cashew tree inflorescences. Specifically, this study aims (i) to assess the diversity of insects visiting the cashew inflorescences (ii) to assess the impact of cashew varieties on bee diversity, and (iii) to assess the activity of Apis mellifera on the cashew tree inflorescences. The study was carried out on four cashew trees varieties (Yellow Benin, Henry, Costa Rica, and James) in Korhogo, northern Côte d’Ivoire.

MATERIALS AND METHODS

Study area

This study was carried out in the department of Korhogo during the dry season. The dry season was chosen as it corresponds to the flowering period of cashew trees. The study site (Niofoin) is located between 8o26 - 10o27 LN; 5o17 - 6o19 LW in the North of Côte d’Ivoire. The department is situated 600 km away from Abidjan, the capital of Côte d’Ivoire. It belongs to the Sudano-Sahelian climate whose rhythm of seasons is regulated by Intertropical Front displacement [10]. The climate is characterized by a rainy season from May to October (max. precipitation in September) and a dry season from November to April, characterized by the harmattan from December to February. The average annual rainfall varies between 1100 mm and 1600 mm and the average annual temperature varies between 25° C and 35° C [11].

Field observations

Data sampling was carried out on four varieties of cashew trees (Yellow Benin, Henry, Costa Rica, and James) grown over an area of 2 ha. These varieties were identified according to the model of Touré et al., based on phenotypic characters [12] (Table 1 and Figure 1). Distributed heterogeneously within the cultivated area, the four varieties of cashew trees were selected for the study due to their greater use by the local population. For each variety, the insects were observed on three trees chosen at random. During the study period, these trees were marked with different colored bands to facilitate their identification.

 

Table 1. Characteristics of the four cashew trees varieties [12]

Varieties

Tree (harbor)

Phenology

(fruit setting stage)

Apple

Nut

Color

Size

Color

Size

Henry

Multi-stemmed branched bottom

The apple is 3 to 4 times smaller in size than the nut

Net

yellow

Small

Light gray enameled with purple spots

Small

Yellow Benin

Branched bottom with multi-stemmed and basic branching

Apple and nut are relatively the same lengths

Yellow

Large

Greenish speckled with purple on the chin

Large

Costa Rica

Multi-stemmed low branch, multi-stemmed crown spreading out like a parasol

Apple and nut are relatively balanced

Yellowish

Large

Light gray with black speckles

Large

James

Low branched multi-stem with spreading habit

The apple is smaller than the nut

Red to bright red

Small

Gray, chin spotted with black

Medium to small

 

 

a)

b)

c)

d)

Figure 1. Illustration of the four cashew trees’ apple varieties (A: Yellow Benin; B: Henry; C: Costa Rica; D: James)

 

Insects’ survey

The insects were observed on the four cashew trees varieties' inflorescences, or captured using a reappearing net. Simultaneously, each variety was observed for two consecutive months (four days per week). The observations were made between 5 a.m. and 6 p.m. All data was recorded by time slot and each selected inflorescence (ten inflorescences per tree; n = 10) was observed for ten minutes. The observed insects were identified immediately, or captured and stored in alcohol (70%) then convoyed to the laboratory for identification with a binocular magnifying glass. For this study, all specimens were identified until to "family" level. Only, specimens belonging to the family of Apidae were identified up to the species. It was more representative in the number of specimens observed.

The activity of the honey bee

The activity of the honey bee was evaluated by taking into account the number of the visited flower by the bee for a given time (one minute for our study). Only one visit per inflorescence was counted for each insect. The visit was considered positive when there was a contact between the bee with the flower anthers, and negative if there was no contact. For two consecutive months (four days per week), from 5 a.m. to 6 p.m., bee activity was assessed. For each time slot, ten minutes was devoted to observing the cashew trees' variety inflorescences. The parameters such as average temperature and relative humidity were recorded during the study period.

Data analysis

A one-way analysis of variances (ANOVA) was performed to compare the relative abundances of different taxa. Pearson's correlation test was used to analyze the relationships between abiotic parameters and bee activity, a Pearson correlation test was used. All the data were processed using Statistica software version 7.1.

RESULTS AND DISCUSSION

Global diversity of insects

A total of 705 insect specimens were recorded from all the observed inflorescences. These insects belong to 16 families and have 7 orders (Coleoptera, Homoptera, Lepidoptera, Neuroptera, Hymenoptera, Heteroptera, and Diptera). Heteroptera (5 families), Hymenoptera (4 families), and Diptera (3 families) were the most diverse orders. Each of the other orders was composed of a single family (Table 2). On the other hand, the relative abundance of Hymenoptera (49.6%), Diptera (16.4%), Homoptera (15.2%), and Heteroptera (11.9%) was higher, respectively. The relative abundance of Neuroptera (0.8%) and Coleoptera (0.1%) was very low. The analysis of variances revealed a significant difference between the relative abundance of different insect orders (P = 0.000001; F = 7.121) (Table 2). Regarding the families, Apidae (32.15%) was more abundant compared to the other families. Polyphagidae (15.16%) and Syrphidae (15.01%) were moderately abundant. The other families (Formicidae, Vespidae, Melittidae, Asilidae, Sarcophagidae, Alydidae, Coreidae, Miridae, Pentatomidae, Pyrrhocoridae, Noctuidae, Chrysopidae, and Chrysomelidae) were considered to have a low abundance. A one-way analysis of variance followed by the Newman-Keuls test revealed a significant difference between the relative abundance of families (P = 0.000001; F = 10.301) (Table 2).

 

 

Table 2. Diversity of insects on cashew trees inflorescences

Orders

Relative abundance (%)

Families

Relative abundance (%)

Hymenoptera (4 families)

49,6 a

Apidae

32,15 a

Formicidae

8,78 cd

Vespidae

6,8 cd

Melittidae

2,12 d

Diptera (3 families)

16,4 b

Syrphidae

15,01 bc

Asilidae

0,71 d

Sarcophagidae

0,71 d

Homoptera (1 family)

15,2 bc

Polyphagidae

15,16 b

Heteroptera (5 families)

11,9 bc

Alydidae

0,28 d

Coreidae

7,37 cd

Miridae

0,71 d

Pentatomidae

2,55 d

Pyrrhocoridae

1,13 d

Lepidoptera (1 family)

5,9 cd

Noctuidae

6,09 cd

Nevroptera (1 family)

0,8 d

Chrysopidae

0,28 d

Coleoptera  (1 family)

0,1 d

Chrysomellidae

0,14 d

 

 

Impact of cashew tree varieties on bee diversity

Variety ‘’Yellow Benin’’

The observed insects on "Yellow Benin" inflorescences belonged to twelve families divided into six orders. The orders of Hymenoptera (4 families), Diptera (3 families), and Heteroptera (2 families) included more families, respectively. The relative abundance of Hymenoptera was significantly higher than that of other orders (P = 0.000001; F = 11.174). Regarding the families, Apidae and Polyphagidae were significantly more abundant than the other families (P = 0.000001; F = 11.335).

 

Variety ‘’Henry’’

Thirteen families and six orders of insects have been identified on "Henry" inflorescences. The orders of Hymenoptera (4 families), Heteroptera (4 families), and Diptera (2 families) were more diverse, respectively. The relative abundance of Hymenoptera was significantly higher than that of other orders (P = 0.00000; F = 5.175). For the family level, Apidae and Polyphagidae were significantly more abundant than the other families (P = 0.00000; F = 12.376).

 

Variety ‘’James’’

On "James" variety inflorescences, twelve families of insects belonging to five orders were identified. The orders of Heteroptera (4 families), Hymenoptera (3 families), and Diptera (3 families) included more families, respectively. The relative abundance of Hymenoptera was significantly higher than that of other orders (P = 0.000; F = 4.145). Regarding the families, the relative abundance of Apidae and Syrphidae was significantly higher than that of other families (P = 0.0000; F = 10.319).

 

Variety ‘’Costa Rica’’

A total of ten families divided into five orders were identified. The orders of Hymenoptera (4 families) and Heteroptera (3 families) included more families, respectively. The relative abundance of Hymenoptera was significantly higher than that of other orders (P = 0.00000; F = 9.290). For the families, Apidae and Syrphidae were more abundant (P = 0.0000; F = 8.145).

 

The activity of the honey bee

The visit frequency (F) of the honey bee on the inflorescences varied significantly between the cashew trees varieties (p < 0.05). It was higher on Henry (F = 30.09%) and Yellow Benin (F = 28.32%) varieties compared to Costa Rica (22.12%) and James (19.47%) varieties. Bees were foraging Henry and Yellow Benin varieties at an average rate twice as high as that of Costa Rica and James varieties. The honey bee's activity varied throughout the day. For each variety, it was zero between 5 a.m. and 6 a.m., and quickly, it increased, reaching its maximum peak between 7 a.m. and 8 a.m. Beyond that, it gradually decreased to cancel out around 11 a.m. A resumption of activity was observed towards the end of the afternoon between 3 p.m. and 4 p.m. with an observed peak between 5 p.m. and 6 p.m. (Figure 2).