The Senegalia macrostachya seeds used for mass rearing and various tests were purchased from local farmers in the town of Toma, latitude 12˚45'45'' longitude 2˚54'01'', located in the Boucle du Mouhoun region of the Nayala province (located 315 km from Ouagadougou). These seeds were not pre-treated after harvesting. They were then sorted manually to eliminate those that were malformed or showed signs of insect emergence holes. The apparently healthy seeds obtained after this sorting process were stored in a laboratory freezer at −18˚C throughout the duration of the experiment to eliminate any potential prior infestations.

The animal material used consisted of a strain of Caryedon furcatus isolated from S. macrostachya seeds obtained from pods harvested directly from spontaneous vegetation in Laye, 35 km from Ouagadougou on the Ouaga-Ouahigouya road. This strain was maintained at the Laboratoire d’Entomologie Fondamentale et Appliquée (LEFA) at the Université Joseph KI-ZERBO using a mass rearing system under the following conditions: 35.42˚C ± 4.31˚C and 40.97% ± 2.26% relative humidity. The procedure involved placing six 50 g batches of healthy seeds in contact with 15 pairs of C. furcatus insects in six Plexiglas rearing boxes (length = 14 cm; width = 10.5 cm; height = 3.5 cm). The boxes were then covered with mosquito netting and incubated until adult emergence. To maintain the strain in the laboratory, this same process is repeated as soon as the adults emerge.

One hundred (100) pairs of C. furcatus up to 48 hours old were brought into contact with 500 g of healthy S. macrostachya seeds introduced into a Plexiglas box (length = 30 cm; width = 19 cm; height = 14.5 cm). The box was then incubated at 35.42˚C ± 4.31˚C and 40.97% ± 2.26% relative humidity for monitoring until adult emergence. The contact time between insects and seeds was 24 hours. At the end of this period, the insects were removed from the Plexiglas box. After the insects were removed, 20 seeds, with a maximum of one egg each, were collected daily from the Plexiglas box and placed in a Petri dish to form a batch of seeds, which were then stored in a freezer at −18˚C. This operation stopped when the adults emerged. The 20 seeds in each batch constituted 20 replicates. As soon as emergence began, all seed batches stored in the freezer were removed for dissection after soaking in water for 24 to 48 hours. Seed dissection was carried out using a dissecting kit, with the aim of collecting the larva attached to each seed to describe it and measure its length and width. A binocular magnifier (Leica EZ4HD) equipped with a measurement function was used for this purpose. The distinction between the different larval stages was based on the morphological changes observed in the most representative individuals of each stage. Ten individuals from each post-embryonic developmental stage were selected for these measurements.

To determine the duration of the different larval stages, the various dates from oviposition to the date when the seeds were placed in the freezer were recorded. Additionally, to monitor the overall development of the insects, the dates from oviposition to insect emergence (from the first to the last) were noted. Sex determination was performed using a Leica EZ4HD magnifying glass, which provided better visualization of sternite V. This sternite is distinctly emarginated in males but not in females.

As soon as they emerged, insects under 24 hours old were isolated and placed in pairs in Petri dishes containing 20 g of S. macrostachya seeds. A total of forty pairs was formed to constitute 40 replications. After twenty-four hours, the insects were transferred to new dishes. This process was repeated daily until the females died. The average temperature and relative humidity during this test were 35.42˚C ± 4.31˚C and 40.97% ± 2.26%, respectively. Monitoring the eggs from hatching to adult emergence allowed us to determine some biodemographic parameters that constitute key indicators for assessing the proliferation potential of this pest population, which will enable its impact to be anticipated and control or management strategies to be adapted. These parameters include:

Development time (DD): It represents the time elapsed between egg laying and adult emergence. This parameter provides insight into the speed of infestations and the resulting damage to stocks. This makes it possible to anticipate periods of high risk and implement more effective pest management strategies. It is estimated using the equation:

$DD={\displaystyle \sum nixi}/{\displaystyle \sum xi}$

$xi$: number of insects emerging per day; $ni$: corresponding number of days.

Intrinsic rate of natural increase (Rm): This is the population growth rate attributable to natural population movement. It is a key parameter that will enable us to understand this insect’s ability to proliferate under our conditions. It was obtained using the formula of [12] :

$R_m=\ln \left(NS\right)/T+1/2L$

L = female lifespan; N = average number of eggs laid per female; S = larval survival rate; T = development time; ln = natural logarithm

Finite growth rate (λ):

$\lambda ={\text{e}}^{R_m}$

The net reproduction rate (R₀): it is the average number of female offspring produced by each female during her lifetime. It is estimated by the formula:

$R_0={\displaystyle \sum lxmx}$

l_x is the probability of survival from the egg stage to the beginning of class x, m_x is the average number of female offspring per female of age x, x is the age class.

Population doubling time (DT): It is the time required for the population to double in size. It was determined by using the formula of [13]

$DT=\ln 2/Rm$

The freshly laid egg is translucent and sticks to the seed wall, with an oblong shape. The egg measures approximately 1.00 ± 0.08 mm in length and 0.65 ± 0.03 mm in width ( Table 1 ). Hatching occurs on average 72 hours (3.33 ± 0.58 days) after laying. At this stage, a reddish (or black) spot can be seen inside the egg, representing the head capsule of the first-stage larva.

The length and width of the larvae increase significantly from L1 to L4 ( Table 1 and Table 2 ). However, the length of the pupa is less than that of the L4 larva, contrary to their width ( Table 1 ). The development time also increases gradually from L1 to L4, as well as from L4 to the pupa and from the pupa to the adult ( Table 3 ).

The first instar larva (L1) is whitish, globular, and characteristic of the chrysomelid type ( Figure 1 ), measuring approximately 0.99 ± 0.09 mm in length and 0.56 ± 0.1 mm in width ( Table 1 ). Forty-eight hours after hatching, the larva begins to actively burrow into the seed. During this process, the larva ejects tegument and cotyledon debris into the chorion, which turns a whitish-yellow colour. After an average of 96 hours, it has completely penetrated the seed. The average time from the egg stage to the L1 stage is nine (9) days ( Table 3 ).

Once inside the seed, the 1st instar larva does not significantly change shape. It undergoes two molts and gradual growth, progressing through the second (L2) and third (L3) instars ( Figure 1 ). The second instar larva measures an average of 2.38 ± 0.21 mm in length ( Table 1 ). It is strongly curved and yellowish-white in colour. The average time for a larva to transition from the 1st to the second instar is 3.25 days ( Table 3 ). The third instar larva ( Figure 1 ) is also curved, yellowish in colour, and begins to show segmentation on its body. Its average length and width are 3.68 ± 0.25 mm and 1.53 ± 0.19 mm, respectively ( Table 1 ). The L2 larva takes an average of four (4) days to develop into the L3 stage ( Table 1 ).

The fourth larval stage (L4) ( Figure 1 ) weaves a translucent membranous cocoon on the outside of the seed. This cocoon is yellowish-white in colour and morphologically distinct from the L1, L2, and L3 stages. It is covered with a reddish pubescence, clearly visible under a magnifying glass. Body segmentation is also clearly visible, and the legs and antennae appear as translucent outlines. The average L4 larva measures 5.7 ± 0.58 mm in length and 2.62 ± 0.30 mm in width ( Table 1 ). The average time for L3 larvae to transition into L4 is 5.1 ± 0.88 days ( Table 3 ).

Pupae, the final immature stage, are initially whitish-yellow ( Figure 2(a) ) and resemble the adult, with an average length of 4.92 ± 0.29 mm and a width of 2.63 ± 0.15 mm ( Table 1 ). As the pupa develops, it gradually turns reddish-brown, eventually maturing into an adult ( Figure 2(b) ). Initially, the pupa has a single dark black spot at the eye level, which soon develops into several black spots. These spots darken over time, and the eyes become large and prominent, while the mandibles also turn dark black.

The pupa resembles the adult with an elongated, oval body and strongly dilated, denticulate posterior femora along the ventral edge ( Figure 2(b) ). The antennae are long and translucent in the pre-pupal stage. They are composed of segments. On average, the transition from L4 to pupa takes 6.08 days, while the transition from pupa to adult takes approximately 10.2 days. The mature adult stage begins with light-brown imagos covered in russet pubescence. Under our experimental conditions, the overall development duration was an average of 34.09 ± 4.3 days.

The average lifespan of Caryedon furcatus is 7.52 ± 2.06 days. However, this lifespan varies significantly by gender (P = 0.0001). Thus, the lifespan of females is relatively longer (around 8.6 days) than that of males (around 6.45 days).

On average, female C. furcatus lay 25.40 ± 10.85 eggs during their lifetime. The average laying period is 7 days. The number of eggs laid, which was zero on the first day, increases to a median of 7.85 eggs on the second day. However, the median number of eggs laid on the 2nd and 3rd days is not statistically different. This number then gradually decreases to a median of 2 eggs on the 5th day and then does not vary significantly until the 6th day, after which no eggs were laid ( Figure 3 ). The estimated average egg hatching rate is 86.42 ± 25.67%. Ninety-two point zero three percent (92.03%) of larvae from hatched eggs complete their development until emergence, representing an emergence rate of 79.53% ( Table 4 ).

Table 5 shows a natural growth rate of 0.072 per day. Thus, C. furcatus population multiplies 1.074 times per day (λ) with a doubling time (DT) of 9.63 days. A female is capable of producing 11 female offspring (R0) in one generation.

The first adult emergences were observed on day 27 (minimum) and ended on day 41 (maximum) after oviposition. There was low emergence on day 41, with less than 1% of individuals emerging. There was no emergence from day 30 to 36. Emergences mainly occurred between the 37th and 40th day. The maximum number of individuals emerged (7 individuals) on the 39th day ( Figure 4 ). After the 41st day, no more individuals emerged.