The study on the biology of the insect pest was conducted in 2014 in the Léo commune, specifically in the laboratory of Fondation Fasobiocarburant. Léo is the major city of the Sissili province. It is located at 165 km, South-West of Ouagadougou; its geographical coordinates are 11˚5'N; 2˚6'W and a mean altitude of 359.36 m. Four study sites were selected. These include Biéha, Léo, Niabouri and Silly. Jatropha curcas is usually found as being part of the cropping system of the Sissili province.

The landscape ranges from tree and bush savannas to shrub savannas composed of Detarium microcarpum, Isoberlinia doka, Burkia africana, Ficus plastyphylla, Pilostigma toningii, and Daniella oliveri. The province is an agricultural and animal husbandry zone, and primarily taurine cattle are raised. Agriculture is associated with woody plants such as Mangifera indica, Anacardium occidentalis, Vitellaria paradoxa, Parkia biglobosa, Jatropha curcas and Tamarindus indica.

Pempelia spp.’s larvae were collected in the field and brought back to the laboratory and put into small plastic boxes of 50 × 40 cm. The insects were kept in conditions closed to those of the surrounding environment (30˚C temperature, 69% RH, and a photo period of 12:12 [L:D] h). The laboratory was well-ventilated thanks to large windows. Some absorbent cotton soaked with water was placed in the bottom of each breeding box in order to slightly increase the humidity that was necessary for the feeding and the development of the caterpillars. The soaking of the cotton was repeated every two days. At emergence, the feeding of the larvae was supplemented with diluted honey. Several larvae were put together in the same box in order to get couples. At each pairing, the couple was isolated in a new box. Ten couples of Pempelia spp. were bred. Every breading box was labeled with information such as the breeding date and the zone of origin. Parameters recorded in the laboratory included the number of eggs at each oviposition, the number of ovipositions per female, the places of eggs oviposition, the duration of eggs incubation, the number of developmental stages, the duration of each developmental stage and the fertility of Pempelia spp. Adults that emerged from each breeding were also fed and observed until their death. Observations were done twice daily, at 7 a.m. and 5 p.m.

1) Duration of egg incubation

The duration of incubation, DI, of eggs is the time span between the date of oviposition D₀ and the date of emergence D₁. It is determined by the following formula:

DI = D₁ − D₀

With DI = duration of incubation; D₁ = date of emergence; D₀ = date of oviposition.

2) Duration of larval instars

The duration of development, T, for a larval instar, is defined as the time spent in moving from an initial instar T_i, to the following instar T_S. It is determined by the formula below:

T = T_S − T_i

With T = duration of the instar; T_i = duration of the initial instar and T_S = duration of the immediate following instar.

This formula was used to compute the duration of each larval instar.

3) Adult life span duration

Adult life span duration, D, is the time period comprised between the date of emergence of the adult, D₀, and the date of its death, D₁. It is the difference between D₁ and D₀.

D = D₁ − D₀

4) Egg size

Eggs were laid in batches; their size was determined by measuring the size of each batch.

5) Larva and adult size

The length L of the body of larvae is comprised between the head of the insect, L₀, and its tail, L₁. It is the difference between L₁ and L₀.

L = L₁ − L₀

6) Female fecundity, fertility and sex ratio

The fecundity of a female is defined as the number of eggs laid by that female during its life’s span.

The fertility of a female is the number of adults emerged from its eggs.

The sex-ratio, r, is the ratio between the number of male adults issued from the eggs of a female over the number of females emerged from that same female.

7) Data analysis

Data collected in the laboratory were processed with the software Excel of Microsoft 2007.

The software XLSTAST version 2013 was used for statistical analysis such as:

An ANOVA used to compute:

- The mean duration of developmental stages,

- The mean length of the body at each of developmental stage.

The statistical charts were drawn using the worksheet of Microsoft Office 2007 software.

The female of Pempelia spp., after copulation, lays its eggs on the apical parts of the plant. Eggs were laid on the stems and on the apical leaves of the seedlings that were introduced inside the breeding boxes (Figure 1). The newly laid eggs have a light white coloration with a form varying from oval to round and turn yellow 3 to 4 days after egg laying.

At emergence, Pempelia spp. larvae are tiny. Newly hatched larvae molted 4 times (Figure 2). Molting is expressed by changes in the color and shape and also by exuviate discharges. The last larval instar is followed by a pre-pupal stage, a pupal stage and finally an adult. The 1^st larval instar was tiny, with a light white to yellowish coloration. Actually, the coloration changes according to the evolution of age, because the caterpillars of the 2^nd stage that were observed had a light green coloration with longitudinal stripes. The 3^rd instar has a light green coloration and dorsal longitudinal stripes. Larvae of the 4^th instar have a black head and a grey body, while those of the last instar showed a blackish brown head, with a dark reddish body which at times is longitudinal light reddish.

Table 1 illustrates the duration of the developmental stages of Pempelia spp. The average eggs’ incubation duration was 6 ± 0.52 days. The minimum incubation duration was 5 days, whereas the maximal incubation duration was 7 days.

Duration of the 1^st larval instar was 2 ± 0.49 days in laboratory conditions. The 2^nd larval instar lasted 4 ± 0.69 days during the experiment. The 5^th larval instar had the longest duration (9 ± 0.57) while the 3^rd and the 4^th larval instars had 6 and 7 days duration respectively. The pre-pupa duration was relatively short (2.50 ± 0.50 days) while the pupa and the adult (both male and female) had the same duration.

The morphometric parameters of Pempilia spp. are reported in Table 2. In this study, we used 36 eggs laid by females bred in the laboratory. The average egg size was 0.57 ± 0.00 mm. The 1^st instar larva measured in average 2.62 ± 0.04 mm. The 2^nd instar larva differed from the 1^st one by its size, 5.52 ± 0.09 mm almost twice that of the 1^st one and by its light green coloration and the presence of longitudinal lines on its abdomen. Dorsal longitudinal stripes were found on the body of the 3^rd instar which measured in average 9.48 ± 0.04 mm. The 4^th instar had a grey body and was 14.88 ± 0.01 mm long. Finally, the 5^th instar was found to be in average 21.2 ± 0.34 long. Its body was a lightly reddish and longitudinal. The pre-pupa was shorter in length (15.36 ± 2.03 mm) than the 5^th instar larva. The pupa lives in a cocoon. It measured in average 7.74 ± 0.44 mm. Pempelia spp. female adults were larger than the male adults. They had a wide abdomen with a tubular opening. The female measured in average 10.76 ± 0.47 mm while the male was found in average to be 8.46 ± 0.72 mm long.

The adults became mature some few hours after emergence. The copulation occurred at sunset and lasted for some few hours. Female adults oviposited generally one time during their life span and the number of eggs laid varied from 43 to 55 per individual. Eggs were laid in batches and the average fecundity was 55 eggs (Table 3).

We studied the fertility of 36 female adults and found an average number of 35.85 (Table 3).

The sex ratio was 1:0.44.