JCBPS; Section B; August 2020 –October 2020, Vol. 10, No. 4; 659-672, E- ISSN: 2249 –1929 [DOI: 10.24214/jcbps.B.10.4.65972.]

Journal of Chemical, Biological and Physical Sciences

An International Peer Review E-3 Journal of Sciences Available online atwww.jcbsc.org Section B: Biological Sciences

CODEN (USA): JCBPAT Research Article

Foraging and pollination activities of Xylocopa inconstans (: ) on Crotalaria retusa (Fabaceae) in Dang (Ngaoundéré, )

EGONO NDEME Carole Christèle*, KINGHA TEKOMBO Bernice Mireille, TCHUENGUEM FOHOUO Fernand-Nestor

*Laboratoire de Zoologie Appliquée, Département des Sciences Biologiques, Faculté des Sciences, Université de Ngaoundéré, B. P. 454, Ngaoundéré, Cameroun

Received: 10 September 2020; Revised: 16 September 2020; Accepted: 28 September 2020

Abstract: To evaluate the impact of Xylocopa inconstans on pod and seed yields of Crotalaria retusa, foraging and pollination activities of this b e e were studied at Dang. From August to September 2016 and 2017. A total of 540 flowers were labeled and divided in four treatments: two treatments differentiated according to the presence or absence of protection of flowers regarding X. inconstans and other visits; the third with flowers protected and uncovered when flowers where opened, visited once by X. inconstans visits then rebagged and the fourth with flowers uncovered and rebagged without the visit of or any other organism. The seasonal rhythm of activity, its foraging behavior on flowers and its pollination efficiency were evaluated. Results show that, six insect species visit C. retusa flowers. Xylocopa inconstans was the most frequent visitor on flowers with 78.37% of 525 visits. This bee intensely and exclusively harvested nectar. The greatest mean number of individuals foraging simultaneously per 1000 flowers was 58. Through its pollination efficiency on C. retusa, X. inconstans has significantly increased the number of seeds/pod by 5.73% and the percentage of normal seeds by 4.39%. Hence, conservation of X. inconstans nests close to C. retusa individuals is recommended to improve this Fabaceae seed production as well as the maintenance of the carpenter bee populations in the region. Keywords: Xylocopa inconstans, Crotalaria retusa, pollination, yields, Dang.

659 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

INTRODUCTION

The productivity of many plants around the world is largely dependent on the activity of anthophilous insects [1]. Thus, a third of the world's food is directly or indirectly dependent on the activity of pollinating insects [2]. Knowledge of the interactions between floral insects and plants is necessary for better crop management. In fact, pollinating insects are of great ecological importance, since they stabilize plant biodiversity by contributing to the production of seeds and fruits, and economically by improving the quantity and quality of agricultural yields [3]. Therefore, the conservation of pollinators is essential for food security and the maintenance of biodiversity in general [4]. Crotalaria retusa is a Fabaceae native to the tropics of Africa and Asia [5]. The plant produces nectar and pollen which are attractive to insects [6]. It is used as a green manure since it has the capacity to fix atmospheric nitrogen thanks to bacteria living in the nodules of its roots [5]. Leaf decocté is used in to fight fever; the roots are used in combination with other plant species to fight colic [5]. The seeds are used in as a purgative and in Nigeria as an anthelmintic [7]. In Cameroon, little is known about the relationship between C. retusa and anthophilous insects. In order to improve agricultural production in Cameroon in a sustainable way, it is wise to intensify research on entomophilic pollination. The few results published at the end of in-depth studies carried out on the pollination of C. retusa by flower-growing insects including X. inconstans are those provided by the investigations carried out in Andhra [6]. Rajesh et al. [6] reported that the main pollinators of C. retusa are Hymenoptera including wood xylocope. None of this research addresses the pollinating efficacy of X. inconstans on Fabaceae. The present work is a contribution to the control of the relations between C. retusa and the wood xylocope, for their optimal management in Cameroon. More specificly, these are: a) To determine the place of X. inconstans in the floral entomofauna of C. retusa ; b) To study the activity of X. inconstans on the flowers of this Fabaceae ; c) Assess the impact of flowering insects including X. inconstans on pollination and fruit and seed yields of C. retusa ; d) To determine the pollinating efficiency of X. inconstans on Fabaceae.

MATERIAL AND METHODS

Study site and biological material: The investigations were carried out on the campus of the University of Ngaoundéré, from August to October 2016 and 2017, flowering periods of C. retusa. The study station is a circular area of 1500 m in radius centered on the bee house (latitude: 42.264 N; longitude: 13° 53.945 E; altitude : 1106 m) of the Applied Apidology Unit of the Faculty of Sciences of the University of Ngaoundéré. Ngaoundéré's climate is Sudano-Guinean, mild and cool, characterized by two seasons: a rainy season (April to October) and a dry season (November to March). The plant material consisted of the plants of C. retusa growing within the campus and belonging to a population covering an area of 500 m2. C. retusa plants studied were selected from 150 flowering plants. The material consisted mainly of insects, including several individuals of X. inconstans naturally present in the environment of the study site. 660 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Determination of the mode of reproduction of Crotalaria retusa: On August 10, 2016 as on August 15, 2017, 240 flower buds (or eight per plant) were tagged on 30 plants of C. retusa and two treatments consisting of:  Treatment 1 (2016) or 3 (2017) : 120 flower buds labelled and left in open pollination ;  Treatment 2 (2016) or 4 (2017): 120 flower buds labelled and protected from insects using gauze cloth bags (1 mm mesh) [8]. For each observation season and at the end of flowering, the number of pods formed was counted in each of the treatments. For each treatment, the fruiting index (Ifr) was calculated using the following formula:

Ifr = (Fb / Fa),

Where Fb is the number of pods formed and Fa the number of viable flowers initially borne [8]. The difference between the fructification indices of the two treatments made it possible to assess the rates of allogamy (TC) and autogamy (TA) according to the formulas below [9]:

TC = {[(Ifr X - Ifr Y) / Ifr X] * 100}, where Ifr X and Ifr Y are the average fruiting indices in the treatment of flowers left free pollinating (X) and in the treatment of flowers protected from insects (Y) respectively ;

TA = 100 - TC.

Determination of the place of Xylocopa inconstans in the floricultural entomofauna of Crotalaria retusa : From August 24 to 26, 2016 and from August 31 to September 3, 2017, observations were made every day, on the flowers of treatments 1 and 3 respectively, according to five daily time slots : 9 - 10 a.m., 11 - 12 p.m., 1 : 00 p.m. - 2 : 00 p.m., 3 : 00 p.m. - 4 : 00 p.m. and 5 : 00 p.m. - 6 : 00 p.m. For each of these time slots, the different insects encountered on open flowers were counted. Since the insects were not marked, the cumulative results were expressed by the number of visits [10]. The data on the frequency of visits of the various floricultural insects identified made it possible to determine the place of X. inconstans in the anthophilic entomofauna of C. retusa. The frequency of insect visits to flowers of C. retusa (Fi) was calculated using the following formula:

Fi = {[(Vi) / Vt] * 100},

Where Vi is the number of visits of insect i on the flowers of the free flower treatment and Vt the number of visits of all insects on these same flowers [10]. The insects except A. mellifera active on the flowers of C. retusa were captured (1 to 5 individuals per species) using an entomological net, stored in vials containing 70% ethanol, at the Except for Lepidoptera which were preserved in curls, according to the recommendations of Borror & White [11], then pinned, dried and identified. Study of the activity of Xylocopa inconstans on the flowers of Crotalaria retusa: The floral products (nectar or pollen) taken by X. inconstans were noted during the same dates and time slots as for the duration of the visits. A bee which plunges its trunk into a flower is a nectar collector; if using its legs and mandibles it scrapes the anthers, it is a pollen collector [10].

661 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

The durations of visits per flower were recorded on the same dates as for the frequency of visits, during four daily time slots: 10 - 11 a.m., 12 p.m. - 1 p.m., 2 p.m. - 3 p.m. and 4 p.m. - 5 p.m. The reset stopwatch was started as soon as a bee landed on a flower and stopped as soon as it left. The duration of the visit thus carried out corresponds to the value delivered by the chronometer [10]. The abundances of foragers (greatest number of individuals simultaneously active on a flower and on 1000 open flowers) [12] and the speed of foraging (number of flowers visited per minute) [12] were recorded on the same dates and slices. Schedules as for the durations of visits. As soon as a forager landed on a flower, the previously zeroed stopwatch was started and the number of flowers visited counted as it passed from one flower to another. The timer was stopped as soon as the insect was lost to follow-up or left the C. retusa flower. Foraging speed (Vb) was calculated using the following formula:

Vb = (Fi / di) * 60,

Where di is the duration given by the stopwatch (in seconds) and Fi the number of flowers corresponding to di [13]. The influence of wildlife (interruption of visits by competitors or predators) was systematically recorded when timing the duration of visits per flower. The influence of flora (passage of foragers from the flower of C. retusa to another plant species and vice versa) was assessed by direct observations in the field. During each day of observation, the temperature and hygrometry of the study station were recorded, every 30 minutes, from 6 a.m. to 6 p.m., using a portable thermo hygrometer installed in the shade [12]. The physical effects of cloudiness, sun, wind and rain were also noted [10]. Assessment of the impact of flowering insects including Xylocopa inconstans on the production of Crotalaria retusa : In addition to the implementation of treatments 1 to 4, 600 flower buds were labelled on 50 plants (at the rate of 12 flower buds per plant) to constitute four treatments :  Treatment 5 (2016) or 7 (2017) : 200 flower buds protected, then discovered, visited exclusively by X. inconstans before being protected again. As soon as each flower bud in treatments 5 or 7 had bloomed, the gauze cloth was gently removed and the flower left free pollination observed for one to 10 minutes, to note its possible visit by X. inconstans. After this manipulation, the flower was again protected and was no longer handled [14]. Flowers that were not visited were included in treatments 6 or 8 [15] ;  Treatment 6 (2016) or 8 (2017) : 100 flower buds protected, then discovered and protected again, without visiting an insect or any other organism. As soon as each flower bud in treatments 6 or 8 bloomed, the gauze was gently removed and the blooming flower observed for one to 10 minutes, avoiding its visit by an insect or other organism. After this manipulation, the flower was again protected and was no longer handled [15]. When the fruits ripened in treatments 5, 6, 7 and 8, they were harvested and their number counted. The assessment of the impact of anthophilous insects including X. inconstans on fruit production of C. retusa was based on the impact of flowering insects on pollination, the impact of pollination on C. retusa fruiting and comparison of fruit production (fruiting rate, percentage of number of seeds per pod and percentage of normal or well-developed seeds) of treatments 1, 2, 3, 4, 6 and 8. For each year of investigation, the fruiting rate due to floricultural insects including X. inconstans (Fri) is calculated using the following formula:

662 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Fri = {[(FX - FZ) / (FX + FY - FZ)] * 100} [16],

Where FX, FY and FZ are the fruiting rates in treatments X (flowers left free pollination), Y (flowers protected from insects) and Z (flowers protected, discovered and then protected again, without visiting insects or any other organism) respectively. For a treatment, the fruiting rate (F) is: F = (number of fruits formed / number of viable flowers initially borne) * 100 [14]. Percent seed number per pod and percentage normal seed attributable to flower insects were calculated using the same method as for fruiting rate. Estimation of the pollinating efficiency of Xylocopa inconstans on Crotalaria retusa ; The contribution of X. inconstans in the fruiting rate, the percentage of the number of seeds per pod and the percentage of normal seeds were calculated using data from treatments 5, 6, 7 and 8. For each observation period, the fruiting rate due to X. inconstans was calculated using the following formula:

FrA = {[(FA - FZ) / FA] * 100} [16],

Where FA is the rate of fructification in treatment A (flowers protected, then discovered, visited exclusively by X. inconstans and again protected). The contributions of X. inconstans in the percentage of the number of seeds per pod and the percentage of normal seeds were calculated in the same way as for the rate of fruiting. Data processing : Data were processed using descriptive statistics (calculation of means, standard deviations and percentages), student's t test (comparison of two means), ANOVA (comparison of more than two means), Pearson's correlation coefficient (r) (study of linear relationships between two variables) and chi-square (χ2) (comparison of percentages), using Microsoft Excel 2010 and R 2.13.0 software.

RESULTS

Mode of reproduction of Crotalaria retusa: In 2016, the allogamy rate (TC) was 25% and the autogamy rate (TA) 75%; in 2017 TC was 16.67% and TA 83.33%. For the two combined study seasons, TC is 20.84% and TA is 79.16%. Therefore, C. retusa has a mixed allogamous-autogamous mode of reproduction, with predominance of autogamy. Place of Xylocopa inconstans in the anthophilous entomofauna of Crotalaria retusa : In 2016 and 2017, respectively, 268 and 783 visits of six and five insect species were recorded on C. retusa flowers. Table 1 presents the list of these insects, with their percentages of visits. It emerges from this table that :

(a) Xylocopa inconstans ranks first with 70.89% of visits in 2016 and 85.56% in 2017. (b) The difference between these two percentages is very highly significant (χ2 = 28.91; P < 0.001).

663 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Table 1 : Insects recorded on the flowers of Crotalaria retusa in 2016 and 2017 in Dang, number and percentage of visits by different insects.

Insects 2016 2017 Total 2016/2017

Order Famil y Genre, Species n1 P1 (%) n2 P2 (%) nT PT (%) Hymenoptera Apidae Xylocopa inconstans (ne) 190 70,89 670 85,57 430 78,23 Xylocopa olivacea (ne) 52 19,40 - - 52 9,7 Megachilidae Chalicodoma cincta (ne, po) 1 0,37 98 12,52 49 6,44 Chalicodoma rufipes (ne, po) 17 6,34 10 1,28 14 3,81 Megachile bituberculata (ne, po) 7 2,61 1 0,13 4 1,37 Lepidoptera Danaus chrysippus (ne) 1 0,37 4 0,51 3 0,44 TOTAL Visites 268 100 783 100 526 100 Species 6 5 6

n1 : number of visits to 80 flowers over 3 days in 2016 ; n2 : number of visits to 100 flowers over 4 days in 2017 ; p1 and p2 : percentages of visits ; p1 = (n1 / 268) * 100 ; p2 = (n2 / 783) * 100 ; nT = total number of visits ; pT = total percentage of visits ; ne : harvest of nectar ; po : pollen collection. Comparison of the percentages of visits to Xylocopa inconstans (2016 / 2017): χ2 = 28.91; (ddl = 1; P < 0.001).

664 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Activity of Xylocopa inconstans on the flowers of Crotalaria retusa

Floral products collected: During each flowering period, foragers of X. inconstans visited the flowers of C. retusa and collected the nectar there exclusively and intensely (Figure 1).

Figure 1 : Xylocopa inconstans collecting nectar from a flower of Crotalaria retusa

Rate of visits to Xylocopa inconstans according to the daily observation time slots: Figure 3 shows the variations in the average ambient temperature, the average ambient hygrometry and the number of visits of X. inconstans on the flowers of C. retusa according to the daily time slots of the investigation. It can be seen from this figure that the activity of X. inconstans on the flowers of C. retusa took place from 9 a.m. to 6 p.m., with a peak between 1 p.m. and 2 p.m.

Figure 3 : Variations in temperature, hygrometry and the number of visits of Xylocopa inconstans on the flowers of Crotalaria retusa according to the observation time bands in 2016 and 2017 in Dang.

Rate of Xylocopa inconstans visits according to the rate of blooming of Crotalaria retusa flowers: Figure 2 shows the variations in the number of blooming C. retusa flowers and the number of visits by X. inconstans according to the dates of observation. It can be seen from this figure that overall, the number of visits of X. inconstans is proportional to the number of flowers blooming on C. retusa. The correlation between these two parameters is not significant in 2016 (r = 0.93; ddl = 1 ; P > 0.05) whereas it is positive and significant in 2017 (r = 0.95 ; ddl = 1 ; P < 0.05).

665 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Figure 2 : Variations in the number of blooming flowers of Crotalaria retusa and the number of visits of Xylocopa inconstans to these organs according to the dates of observation in 2016 and 2017 in Dang. Abundance of foragers: In 2016, the highest average number of simultaneously active X. inconstans browsers was 1 per flower (n = 115; s = 0) and 72.12 per 1000 flowers (n = 115; s = 50.26). In 2017, the corresponding figures were 1 per flower (n = 117; s = 0) and 43.08 per 1000 flowers (n = 117; s = 15.89). The difference between the mean abundances per 1000 flowers for the two years is very highly significant (t = 45.15; ddl = 230; P < 0.001). Duration of visits per flower: The mean duration of a visit of X. inconstans per flower of C. retusa for nectar collection was 3.39 sec (n = 704; s = 2.56) in 2016 and 3.01 sec (n = 148; s = 3.39) in 2017. The difference between these two means is very highly significant (t = 17.05; ddl = 850; P < 0.001). Foraging speed: An individual of X. inconstans visited between 3 and 45 flowers per minute in 2016 then between 6 and 40 flowers per minute in 2017. The mean foraging speed was 14.16 flowers per minute (n = 248; s = 6.19) in 2016 and 23.18 flowers per minute (n = 183; s = 6.66) in 2017. The difference between these two means is very highly significant (t = 148.21; ddl = 429; P < 0.001). Influence of wildlife: In 2016 as in 2017, no interruption of the foraging activity of X. inconstans in the flowers of C. retusa by individuals of the same species or by other organisms was recorded. Influence of the surrounding flora: During the observation period, several other flowering plant species neighboring C. retusa were visited by individuals of X. inconstans for their nectar. These plants included: Cajanus cajan (Fabaceae), Cosmos sulphureus (Asteraceae), Lantana camara (Verbenaceae), and Tithonia diversifolia (Asteraceae). No change from foragers of C. retusa flowers to flowers of other plant species and vice versa was noted. Influence of some climatic factors: In addition to the variations in the number of visits, Figure 3 shows the fluctuations in average ambient temperature and humidity according to the daily observation time bands. The correlation between temperature and the number of visits by X. inconstans is not significant in 2016 (r = 0.77; ddl = 3; P > 0.05) as in 2017 (r = 0.84; ddl = 3; P > 0.05). Likewise, the correlation between this number of visits and hygrometry is not significant in 2016 (r = - 0.67; ddl = 3; P > 0.05) as in 2017 (r = - 0.71; ddl = 3; P > 0.05). During all the observation periods, four early mornings were very weakly sunny with overcast skies, three heavily rainy then slightly sunny and two foggy. During the early sunny mornings, X. inconstans' activity was intense. During and after the rains and on foggy mornings, the activity of these insects was very low or zero.

666 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Impact of floral insects including Xylocopa inconstans on pollination and production of Crotalaria retusa: While collecting nectar from a C. retusa flower, the insects were always in contact with the anthers and carried pollen. Thus, insects greatly increased the possibilities of pollination of C. retusa. Table 2 summarizes the data on the fruiting rate, the average number of seeds per pod and the percentage of normal seeds in the different treatments of C. retusa. It emerges from this table that: (a) The differences observed between the fruiting rates in treatments 1, 2, 3 and 4 are overall very highly significant (χ2 = 32.36; ddl = 3; P < 0.001). A two-by-two comparison of these percentages shows that the difference is significant between treatments 1 and 2 (χ2 = 4.02; ddl = 1; P < 0.05) and highly significant between treatments 3 and 4 (χ2 = 7, 20; ddl = 1; P < 0.01); (b) Overall, the differences between the average number of seeds per pod of treatments 1, 2, 3 and 4 are very highly significant (F = 4316.70; ddl 1 = 3; ddl 2 = 241; P < 0.001). The two-by-two comparisons of these means show that the difference is very highly significant between treatments 1 and 2 (t = 28.02; ddl = 88; P < 0.001), then between treatments 3 and 4 (t = 16. 80; ddl = 148; P < 0.001) ; (c) The differences between the percentages of normal seeds in treatments 1, 2, 3 and 4 are overall very highly significant (χ2 = 37.71; ddl = 3; P < 0.001). Two-by-two comparisons of these percentages indicate that the difference is very highly significant between treatments 1 and 2 (χ2 = 28.02; ddl = 1; P < 0.001) and not significant between treatments 3 and 4 (χ2 = 2. 06; ddl = 1; P > 0.05). The fruiting rates due to flower insects including X. inconstans were therefore 63.63% in 2016, 8.17% in 2017 and 35.90% for the two years of cumulative experimentation. The percentages of the average number of seeds per pod attributable to the influence of flower insects were 30.84% in 2016, 12.27% in 2017 and 21.56% for these two years combined. The percentage of normal seeds attributable to flower insects was 10.47% in 2016, 5.81% in 2017 and 8.14% for these two years combined. Pollinating efficiency of a floral visit of Xylocopa inconstans on the production of Crotalaria retusa : Table 2 shows the results of the comparison of the fruiting rates, the average number of seeds per pod and the percentages of normal seeds of the treatments with flowers protected from insects and then discovered and protected again without a visit from an insect or any other organism. (6 and 8) to those of treatments with protected flowers, then discovered and visited exclusively by X. inconstans (5 and 7). It emerges from this table that: (a) The differences observed between the fructification rates in treatments 5, 6, 7 and 8 are globally insignificant (χ2 = 0.88; ddl = 3; P > 0.05). The two by two comparisons of the percentages indicate that the difference is not significant between treatments 5 and 6 (χ2 = 0.00; ddl = 1; P > 0.05), then between treatments 7 and 8 (χ2 = 0. 10; ddl = 1; P > 0.05) ; (b) The differences between the average number of seeds per pod of treatments 5, 6, 7 and 8 are overall very highly significant (F = 7846.46; ddl 1 = 3; ddl 2 = 296; P < 0.001). The two-by-two comparisons of these means show that the difference is very highly significant between treatments 5 and 6 (t = 16.20; ddl = 138; P < 0.001), then between treatments 7 and 8 (t = 7.72; ddl = 158; P < 0.001) ; (c) The differences between the percentages of normal seeds in treatments 5, 6, 7 and 8 are overall very highly significant (χ2 = 40.37; ddl = 3; P < 0.001). Two-by-two comparisons of these percentages show that the difference is very highly significant between treatments 5 and 6 (χ2 = 39.63; ddl = 1 ; P < 0.001) and not significant between treatments 7 and 8 (χ2 = 3. 63 ; ddl = 1; P > 0.05). 667 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

Table 2 : Fruiting rate, average number of seeds per pod and percentage of normal seeds according to the treatments of Crotalaria retusa in 2016 and in 2017 in Dang.

Years Treatments Number of Number of pods Fruiting rate Number of seeds / Total number Number of normal % Normal flowers studied formed (%) pod of seeds seeds seeds m s 1 (FL) 80 54 67,50 13,02 4,98 768 623 81,12 2016 2 (FP) 70 36 51,43 10,86 3,44 391 363 92,84 5 (FPX) 80 70 87,50 17,07 3,09 1195 1153 96,48 6 (FPN) 80 70 87,50 15,58 3,30 1091 981 89,92 3 (FL) 100 90 90,00 16,11 4,22 1450 1294 89,24 2017 4 (FP) 80 60 75,00 14,27 3,41 856 747 87,27 7 (FPX) 100 85 85,00 17,20 2,48 1462 1348 92,20 8 (FPN) 90 75 83,33 17,67 2,33 1325 1246 94,03

FL : Flowers left in free pollination ; FP : Flowers protected from insects ; FPX : Flowers protected and having received a visit from Xylocopa inconstans ; FPN : Flowers protected, discovered and then protected again, without visits from insects or any other organism

668 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

The percentages of the average number of seeds per pod attributable to X. inconstans were therefore 8.73% in 2016, 2.73% in 2017 and 5.73% for the two years of cumulative experimentation. The percentage of normal seeds attributable to X. inconstans was 6.80% in 2016.

DISCUSSION

In Dang, X. inconstans is the main flowering insect of C. retusa. In Maroua, Djonwangwé et al. [17] found that X. inconstans was the second most common bee visiting the flowers of Vigna unguiculata. Further research on Fabaceae such as Phaseolus vulgaris by Kingha et al. [18] at the same study site and Phaseolus coccineus by Pando et al. [19] in Yaoundé showed that Xylocopa olivacea was the predominant insect. This could be due to the low representation of X. inconstans in Dang and Yaoundé. These results confirm data from Roubik [20] which showed that the frequency of an insect can vary from one species to another in time and space. The peak of activity of X. inconstans located between 13 h and 14 h is linked to the period of greatest availability of nectar at the level of the flower of C. retusa. The decreases in activity observed in the flowers of C. retusa after the 15 - 4 pm time slot would be linked to the reduction in the quality and / or quantity of the nectar. According to Pesson & Louveaux [1] and Kasper et al. [21], when the loot is no longer easily exploitable or when it is reduced in quantity and / or quality, the foragers reduce their activities on the flowers, so that the energy expended for the foraging is not greater than that that can be drawn from the loot. The high abundance of foragers per 1000 flowers, then the positive correlation between the number of visits of X inconstans and the number of open flowers of C. retusa show the good attractiveness of the nectar of this Fabaceae towards X. inconstant. The highly significant difference between the abundances of foragers per 1000 flowers could be explained by the number of nests of this xylocope in the experimental site. In addition, the number of blooming flowers plays an important role in the orientation of insects towards flowers [22]. The very highly significant difference between the average duration of a nectar harvesting visit in 2016 and that recorded in 2017 is linked to the availability of this product. Bees stay longer on flowers rich in nectar than on those poor in this resource [23]. During each flowering period of C. retusa, X. inconstans exclusively collected nectar. This could be explained by the need of individuals during the flowering period of C. retusa. The variations observed in foraging speeds are due in particular to the availability of this product and to the distances between the flowers exploited during the various foraging trips, as Tchuenguem [10] reported on Syzygium guineense var. macrocarpum, Callistemon rigidus and Voacanga africana in Dang. The lack of passage of foragers of C. retusa flowers to those of other neighboring plant species shows that during a foraging trip, individuals of X. inconstans were loyal to the flowers of C. retusa. Djonwangwé et al. [17] found the same result on Vigna unguiculata in the Far North of Cameroon, for the same xylocope. This phenomenon which is called floral constancy [24] is well known in honey bees. In southern Ghana, X. olivacea has also been shown to be faithful to the flowers of Luffa aegyptiaca [25]. In Cameroon, the fidelity of X. olivacea has also been reported on the flowers of : Cajanus cajan [26], Phaseolus coccineus [19], Phaseolus vulgaris [18] and Vigna unguiculata [27]. As a strongly nectariferous plant, Fabaceae C. retusa can be cultivated in the Cameroonian Adamawa to help stabilize populations of X. inconstans during the rainy season.

669 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]

Foraging … EGONO NDEME Carole Christèle et al .

When collecting nectar from the flowers of C. retusa, the X. inconstans foragers regularly came into contact with the stigma and the anthers. Increasing the number of flowers visited by a carpenter bee increases the likelihood of stigmatic contact and, therefore, the potential for pollination. In addition, when hanging on the flower, the weight of X. inconstans is sufficient to cause the stigma to come out of the keel, a phenomenon essential to trigger the release of pollen. These results confirm those obtained by Kingha et al. [18] and Tchuenguem et al. [26] with X. olivacea on the flowers of P. vulgaris and Cajanus cajan respectively. The individuals of X. inconstans can therefore intervene directly in self-pollination and all pollination.

CONCLUSION

In Dang, Crotalaria retusa is an allogamous-autogamous plant, with predominance of autogamy and which benefits strongly from entomophilic pollination. Among the insects which visit the flowers of this Fabaceae, X. inconstans is the most frequent and collects strongly and exclusively the nectar. The rate of visitation of this carpenter bee's foragers is positively correlated with the rate of blooming of C. retusa flowers. By its positive action on the pollination of the flowers visited, X. inconstans caused an increase in the average number of seeds per pod by 5.73% and in the percentage of normal seeds by 4.39%. The conservation of X. inconstans nests around C. retusa populations is advised to improve the grain production of this Fabaceae and to stabilize the wood borer populations during the rainy season REFERENCES

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Corresponding author: EGONO NDEME Carole Christèle *Laboratoire de Zoologie Appliquée, Département des Sciences Biologiques, Faculté des Sciences, Université de Ngaoundéré, B. P. 454, Ngaoundéré, Cameroun Online publication Date: 25.09.2020

672 J. Chem. Bio. Phy. Sci. Sec. B; August 2020 –October 2020, Vol. 10, No. 4; 659-672. [DOI:10.24214/jcbps.B.10.4.65972.]