Jatropha curcas L. (Euphorbiaceae), is native to Mexico or neighboring regions of Central America ([1]). The species was spread by humans all over the world a long time ago and is now domesticated in many tropical and sub-tropical regions of the world. In Burkina Faso, as in many other African countries, the shrub was introduced since colonization and, in the last two decades, it has been cultivated in all regions of the country.
Jatropha curcas is well known throughout the world for its different uses ([1]; [2]; [3]). Various parts of the plants are used in cosmetics and herbal medicine, as well as fuel wood. The plant is also used to prevent erosion and as living fence to protect crops. Indeed, the curtine, a toxin contained in the leaves, keeps animals away because of its bad smell and taste. However, the main purpose of the worldwide adoption of J. curcas in recent decades was the production of biofuel, its seeds containing oil that is suitable for biodiesel production ([4]; [5]). Waste products can also be used as fertilizers and to produce biogas. It was also claimed that J. curcas cultivation enhanced socioeconomic development while reclaiming marginal and degraded lands in semi-arid regions ([1]; [6]). However, seed yields have been much lower than expected, which, together with other factors such as the low price for seeds and the limited valorization of by-products, resulted in a dramatic decline of J. curcas plantations worldwide ([7]; [8]; [9]; [10]; [11]). Low yields largely resulted from the fact that plantations of J. curcas were implemented on a global scale without the necessary crop improvement, proper field validation and standardization of agronomic practices and high quality certified planting materials ([12]). The occurrence of serious damage caused by pests and diseases, often largely unknown to the farmers, was often cited among the factors affecting yields and hampering the adoption of J. curcas ([13]; [12]; [14]; [11]), but there are very few studies relating pests and diseases to yield loss ([15]).
Many insects, fungi, bacteria and viruses attack roots, stems, leaves, flowers and fruits of J. curcas in sub-Saharan Africa ([16]; [17]; [18]; [14]; [19]; [20]). Among these, beetles of the genus Aphthona (Col.: Chrysomelidae) are among the most prevalent. These are small insect pests whose adults feed on the leaf surface, causing many small holes.
These insects are particularly damaging to young plants, which can die from continuous defoliation [21]. Even when the plant is not killed, its growth and fruiting are severely hampered ([16]; [22]; [19]; [23]). While several species occur on J. curcas in Africa ([24]), in Burkina Faso, the species Aphthona whitfieldi Bryant is the most widespread and causes important damage on plants ([23]; [21]). It is also suspected to cause significant yield losses ([22]). Aphthona whitfieldi Bryant is a beetle of the Chrysomelidae family. According to [24], the large family Chrysomelidae is divided into 19 subfamilies including that of the subfamily Alticinae and brings together around 37,000 herbivorous species distributed throughout the world. The subfamily Alticinae includes more than 90 genera including the genus Aphthona. Almost every species is oligophagous and therefore feeds exclusively on plants belonging to the same family or even the same genus. Elliptical or oval in shape, these small Coleoptera measuring less than 2.5 mm are rather difficult to observe. Indeed, when disturbed, they propel themselves using their powerful hind legs much like a flea, hence their English name of "Flea beetles" [25]. The adult has a white color immediately after emergence then turns to the red color a week later which will be its final coloration (Picture 1).
Generally, flea beetles are pests that can disrupt the development of young plants and cause economic damage through their activity of peripheral or internal gnawing of the leaf blades of different crops [26].
Mating takes place on the shoots of plants, and adult females subsequently lay their eggs on the soil surface or in the soil, on or near the base of the stem. Females of A. whitfieldi typically lay a total of 100–300 eggs in their lifetime, in a series of small groups of 20–30, every 3–5 days ([27]; [28]). Normally, the stage of embryonic development takes an average of 18 days at 22 ° C ([28]). Newly hatched larvae begin to feed on very small roots first before attacking larger roots as they develop ([29]). Aphthona whitfieldi overwinters as diapausing larvae for 3–4 months in soil and on or near roots when temperature drops below 3 ° C. Larval development begins in spring when the temperature reaches 26 ° C and pupation occurs in early summer ([28]; [29]). The adults emerge from the ground throughout the summer and begin to feed on the leaves and flowers. Adults can survive for up to 4 months ([30]). Adult flea beetles damage plants by feeding on the surface of leaves and stems, resulting in numerous small holes in the surface of the leaf as if small balls [31] have hit it. With intense feeding, damage can kill the plant, especially young plants ([32]). Aphthona whitfieldi uses many sensory signals (smell, taste and vision) to locate its host plants ([33]). This insect was identified by ([34)]) as the main insect pest of J. curcas in Sub-Saharan Africa. It is widespread in Mali, Burkina Faso, Guinea, Ghana, Nigeria, Sudan and South Sudan. Aphthona whitfieldi is an oligophagous insect since in Burkina Faso, it is associated only with plant species of the genus Jatropha [(35)]). However, so far, there is no data in the scientific literature that can relate the damage caused by A. whitfieldi to yield losses. This study was conducted in Southern Burkina Faso with the aim of assessing the real impact of A. whitfieldi on yield and to relate visual damage levels to yield loss, to contribute to a more effective control of this insect pest in the region.