1. Introduction
Nearly 690 million people suffer from hunger worldwide with an increase of 60 million over the past five years [1] [2] . In 2021, 924 million people suffered from a lack of food security, including 322 million in Africa [3] ). This difficult situation leads us to reflect on the possible contribution of NTFPs to food self-sufficiency. For example, tamarind fruits (Tamarindus indica L.) are non-timber forest products (NTFPs) from the Caesalpinioideae subfamily, which could be a source of food and income for people in Africa. Indeed, almost all parts of the tree are used [4] ; the ripe fruit of the sweet type is usually eaten fresh, while the sour (acidic) fruits are processed into juice, jam, syrup and sweets.
However, in Burkina Faso, tamarind as many legumes [5] [6] [7] is damaged during storage. Caryedon serratus Olivier is one of the main pests of T. indica, causing huge losses to stocks [8] . The rate of seed germination could be greatly reduced as a result of insect activity [9] , which could hinder the plant’s natural regeneration. Control methods have been put in place to protect stocks. The methods applied in Burkina Faso by some growers, such as the use of pick bags and steaming of T. indica fruits [10] , are not applied to large stocks. In addition to knowledge of the problem of T. indica seed storage in the farming environment, we also need to know something about the life cycle of this insect. [11] [12] assert that knowledge of fecundity, development time, longevity, average weight of first-generation individuals and adult sex ratio of an insect pest is more than necessary to develop effective control methods for commodity protection. Our study on the biodemographic parameters of C. serratus is part of the same dynamic in order to provide alternatives for better preservation of T. indica pods.
2. Material
2.1. Study Conditions
The study was carried out in Laboratoire d’Entomologie Fondamentale et Appliquée (LEFA) of Université Joseph KI-ZERBO (Ouagadougou, Burkina Faso). The mean temperature was 27.51˚C ± 2.34˚C and relative humidity ranged to 46.76% ± 15.27%. The duration of the experiment was 80 days.
2.2. Animal Material
The animal material used was C. serratus individuals from Manga’s zone. This strain of C. serratus was isolated from naturally infested T. indica pods in this zone. These strains were maintained through successive rearing on tamarind from the same area in the Laboratoire d’Entomologie Fondamentale et Appliquée (LEFA) of Université Joseph KI-ZERBO Université (Ouagadougou, Burkina Faso).
2.3. Plant Material
The plant material used for this study consisted of T. indica pods. These tamarind pods were purchased with the women in the Manga’s zone. Once transported in the laboratory, T. indica pods were first sorted to exclude those with holes or rotting. They were then placed in a freezer at −18˚C in the Laboratoire d’Entomologie Fondamentale et Appliquée (LEFA) of Université Joseph KI-ZERBO Université (Ouagadougou, Burkina Faso) in order to eliminate any previous infestation.
3. Methodology
3.1. Embryonic Development
100 healthy T. indica pods were placed in contact with ten pairs of C. serratus for 24 hours for oviposition. The adults were then removed and 25 pods, each carrying a maximum of two eggs, were distributed in 450 ml dishes, in five batches of 5 pods each, in 5 replicate. The batches of pods thus formed were placed in incubation until the embryo appears inside the chorion. The boxes were daily removed and the pods they contained were individually observed under a Leica binocular loupe to count the number of eggs containing an embryo. The pods carrying these eggs were then removed from the boxes. The incubation time during this study was 13 days. The embryonated egg shows a reddish spot representing the embryo’s head capsule.
3.2. Reproductive Potential of C. serratus
As soon as the new generation of insects appeared, a pair of C. serratus aged less than 24 h was placed in contact with 4 healthy pods for 24 h in a 450 ml dish. Every day, the pair was removed and transferred to another box containing 4 new healthy pods until the female died. All boxes were then incubated in the laboratory at a temperature of 27.51˚C ± 2.34˚C and relative humidity of 46.76% ± 15.27%. A total of 20 replicates were carried out in order to increase the precision and validity of the significance test. After the withdrawal of each pair, the eggs laid daily by the female were counted; the number of hatched and unhatched eggs was also counted daily until the end of hatching. The hatched egg was whitish in color, while the unhatched egg remained translucent [13] . From the onset of emergence until the end, the males and females emerging each day were counted and removed from each box.
Thirty newly-emerged males and thirty newly-emerged females were weighed using a OHAUS brand sensitive scale; their size was also measured using software associated with a LEICA magnifying glass. The number of cocoons formed and the number of larvae unable to weave a cocoon were counted.
A pod can be considered healthy when it is neither damaged nor contains another form of life (eggs, larvae or insects).
At the end of monitoring, the following parameters are evaluated:
· Development time: This is the time between the egg-laying and its emergence as an adult. It is estimated using the following equation:
xi: number of insects emerging per day; ni: corresponding number of days.
· Intrinsic rate of natural increase (r): It is the rate of population growth attributable to the natural movement of the population. It was obtained through the equation of [14] .
L = female lifespan; N = average number of eggs laid per female; S = larval survival rate; T = development time; ln = natural logarithm.
· Generation time (GT): It reflects the average time between two consecutive generations in the genealogy of a population. It is estimated by the formula of [15] .
GT = T (development time) + average age of a female when all her eggs are laid.
· Population doubling time (D.T.): It is the time required for the population to double in size, it was determined by using [16] formula.
3.3. Statistical Analysis
The data collected was entered into the Excel 2016 spreadsheet, which was used to make various graphics. Statistical processing of the data was carried out using R software, 4.1.0 version. Statistical tests were performed according to the scheme proposed by [17] .
We first performed a normality test followed by a homogeneity test for all measured variables. Thus, we performed Student’s t-test to compare adult lifespan, number of emerged individuals, height and weight of emerged individuals as a function of sex. The significance level was 5%.
4. Results
4.1. Average Longevity of C. serratus Adults
The average lifespan of C. serratus, all sexes combined, was 14 days. However, the average lifespan differed significantly according to sex (t1;38 = 2.33, P = 0.025). Females lived longer, with an average lifespan of around 16 days, compared with males, who averaged around 13 days (Figure 1).
4.2. Average Number of Eggs Laid, Hatching Rate
The eggs laid measure around 1 mm in length and 0.57 mm in width (Table 1). These eggs were deposited on pods averaging 6.66 g and 16.59 cm thick.
The average number of eggs laid by C. serratus’s female during her lifetime was around 34 (Table 2). With a hatching rate of 89.28 ± 9.76, the average number of infertile eggs is 3.85.
4.3. Daily Fecundity of C. serratus’s Female
C. serratus’s female laid an average of two eggs on the first day. The number of eggs laid increases until it reaches a maximum peak on the 4th day, then gradually decreases until day 14, after which no more eggs were laid (Figure 2).
4.4. Development Time and Parameters of Caryedon serratus
It is estimated that 66.63% of eggs laid gave rise to adults, i.e. 22 individuals per female. This means that 17.12% of larvae from C. serratus eggs failed to reach the adult stage and thus died at the larval stage (Table 3). We can see that the
![]()
Figure 1. Average longevity of C. serratus males and females.
![]()
Table 1. Physical Characteristics of eggs and seeds.
![]()
Table 2. Hatching rate, number of hatched et sterile eggs.
embryo is established as early as the 3rd day, and the incubation time extends over 9 days. The total development of C. serratus in our study took around 64 days (Table 3).
4.5. Development Time, Average Percentages of Cocooned Larvae, Larvae Dead Inside the Seed and Larvae Unable to Weave a Cocoon
When larvae reached the 4th stage, they used the seed to weave a cocoon to complete their development cycle. While 83% of larvae from hatched eggs were able to weave cocoons, the remainders were unable to continue their development, i.e. around 8% died inside the seed and 9% outside (Table 4).
![]()
Figure 2. Evolution of the average number of eggs laid per day by a female C. serratus over her lifespan.
![]()
Table 3. Emergence and mortality rates.
![]()
Table 4. Average percentages of larvae that weaved a cocoon, larvae that died inside the seed and larvae that were unable to weave a cocoon.
4.6. Monotoring of Larvae after Cocoon Formation
88.69% of the larvae that were able to weave a cocoon were able to complete their development by emerging to give birth to adults (Figure 3). However, 11.31% were unable to reach the last phase of their development and thus died inside the cocoons. Cocoons formed by C. serratus larvae average 6.78 mm in length and 4.19 mm in width.
4.7. Sex Ratio, Number of Individuals of Different Sexes Emerged and Variation in Weight and Size
Analysis of Table 5 shows that there was no significant difference between the number of males and females emerged; however, there was a sex ratio of 0.96 in favor of females. However, the weight and size of the females resulting from this emergence differed significantly from those of the males.
4.8. Growth Parameters
With a generation time of around 79 days, C. serratus population doubles in size in 5.68 days, for an intrinsic rate of natural increase of 0.12 (Table 6).
![]()
Figure 3. Average percentage of larvae that have died in cocoons or given birth to adults.
![]()
Table 5. Sex ratio, number of emerged individuals and variation in mean weight and size.
The means followed by different alphabetic letters in the same lines are significantly different (P < 0.05, Student Newmann Keuls’s test).
5. Discussion
Our study shows that C. serratus is able to complete its development cycle on T. indica pods. The male’s lifespan is quite shorter than the female’s (around 16 days). The same trend was observed by [18] [19] on C. serratus. Similarly, in Caryedon furcatus, [20] observed a higher female longevity. C. serratus females laid their eggs for 14 days, with a peak on the 4th day. This oviposition period is similar to that observed by [19] [21] , who also observed a peak in oviposition on the same date. Our results showed that the female laid an average of 33 eggs during her lifetime on pods averaging 6.66 g and 16.59 cm thick. The eggs laid in our experiment measured around 1 mm in length and 0.57 mm in width, and had a hatching rate of 89.28 ± 9.76. The fecundity of the female in this study is lower than that obtained by [22] , who conducted their activity under a temperature of 29˚C and a relative humidity of 53% to 86%. Thus, the male C. serratus lived longer than the female, which laid 80 eggs on average, leading us to think, as [23] do, that egg-laying activity reduces the lifespan of females due to the energy they expend. Also, the fact that the female spends time searching for an unoccupied host would cost her a great deal of energy, leading to her death according to [24] in the case of Callosobruchus maculatus female. As adults do not feed, it is the reserves accumulated during the larval stage that they use throughout their lives ( [25] . We can therefore assume that the females used in our study would have more reserves than the males. Our observation also revealed that 66% of eggs laid gave rise to adults, i.e. 22 individuals per female. Thus, 25.60% of larvae from C. serratus eggs died at the larval stage, as they were unable to weave cocoons. Larvae that have reached the 4th stage emerged from the seeds to weave C. serratus cocoons for pupation ( [26] , although some larvae may weave cocoons inside the seed. This low rate of emergence is due to larval mortality caused by inter-larval competition, caused by the supernumerary population of larvae in the seeds. This situation led to a shortage of food resources, as we only introduced 4 pods into each box. The same observation was made by [27] on C. maculatus and by [28] on Bruchidius atrolineatus. We found a significant difference between the height and weight of C. serratus males and females. This greater size and weight in females could be physiological, enabling them to perform their egg-laying function. No difference was observed between the numbers of male and female populations. However, the sex ratio favors the female. Similar results have been observed by authors such as [29] on Rhyzopertha dominica, [30] on Spermophagus niger and [31] on C. furcatus. It appears that the embryonic duration lasted 3 days and the total development duration was 63 days for our study, which is higher than that the fundings of [22] who obtained a duration of 52 days. [21] also found an average lifespan of 55 days under conditions of 30˚C and 65% relative humidity. Furthermore, the larval lifespan (around 28 days) was roughly similar to that obtained by [22] which was around 29 days. The average time between the birth of the parents and that of their offspring in this study is 79 days. Like the total development time, this generation time in our study is quite long. This has an impact on the population duplication time, which is 5.68 days. Hence a natural growth rate equal to 0.12.
6. Conclusion
The observations made at the end of our study show that C. serratus can complete its development cycle on T. indica. The sex ratio is in favor of the female, allowing the species to remain in the stock. After hatching, the first-instar larva starts feeding on the seeds, causing damage to the pods. When the larva reaches the fourth instar, it leaves the seed to weave a cocoon. At the end of metamorphosis, the insect thus formed pierces the cocoon to emerge. Despite the losses observed at each stage of its development, C. serratus manages to cause damage to the fruit, as emerged adults lay eggs on the pods, perpetuating a new cycle. In view of the damage caused by C. serratus to tamarind stocks, if no protective measures are taken to thwart this insect, it could gradually lead to the disappearance of this tree, and therefore of these fruits.