Stemborers are a major constraint to the production of rice in the Kou Valley, Burkina Faso. Biological control is a good alternative to the use of agrochemicals that are harmful to human and animal health, and the environment. A survey of natural enemies of stemborers was conducted during the 2014 rice-cropping season across three transplanting periods (P1, P2 and P3). Plant and insect samples were collected by mowing and trapping at weekly intervals until harvest, starting 21 days after transplanting, and examined microscopically. Immature stages of the parasitized stemborers were reared to maturity for a positive identification of the parasitoids. Three genera of stemborers were identified:Chilo(Lepidoptera: Pyralidae),Maliarpha(Lepidoptera: Pyralidae) andSesamia(Lepidoptera: Noctuidae). TheChilogenus was the most important with an average percentage of 41.4% of the pre-imaginal population in P2 followed byMarliarpha(1.1%) andSesamia(0%). A total of 15 hymenopteran parasitoid species that included nine genera and seven families were identified. All the parasitoids were associated withChiloand only two of the species parasitizedMaliarpha. The most frequent parasitoids encountered wereBracon testacerofatus,Goniozus indicus,Dolichogenidea oryzaeandBraconspp. A total of 28 predator species were recorded from 22 genera, 6 orders and 15 families.Leucaugesp.,Agriocnemissp.,Lycosa pseudoannulataandLycosasp. were the most important predators with frequencies reaching 15% of the arthropods caught in some fields. These results will be employed to develop a sustainable system to manage rice stemborers.
The shea caterpillar Cirina butyrospermi is an important insect, highly valued as a human food item in Burkina Faso. However, its appearance is seasonal due to its univoltine cycle. This study therefore investigated the possibilities of breaking the nymphal diapause by changing the environmental factors and through the hormonal treatment of prepupae and pupae using bovine insulin and 20-hydroxyecdysone. Changes in humidity and temperature did not result in emergence, suggesting a mandatory nature of the diapause in C. butyrospermi. Injection of 20-hydroxyecdysone between 20 and 40 ng on 20 C. butyrospermi pupae resulted in 15.24 and 47.5% emergence, respectively. The incubation time varied between 40 and 38 days, respectively. No emergence was observed with the injection of bovine insulin. Dipping of C. butyrospermi larvae and pupae in solutions of 20-hydroxyecdysone resulted in similar rates of emergence between the two stages, with slight variations between individual doses: (1) for larvae, emergence was recorded at 10, 8, 5 and 15 mg/l with 98.5, 62.14, 25.73 and 24.16%, respectively; the incubation times varied from 39 days at 5 mg/l to 26 days at 20 mg/l; and (2) for pupae, emergence occurred between 5 and 20 mg/l, with the highest emergence rate recorded at 10, 8 and 15 mg/l with 94.58, 65.83 and 29.58%, respectively; the incubation times varied from 53 days for the lowest dose (5 mg/l) to 37 days (20 mg/l); the best emergence rate of 94.58% coincided with an incubation time of 43 days at 10 mg/l. No emergence was observed beyond 20 mg/l in both stages. Hormonal treatment with 20-hydroxyecdysone did not affect the fecundity of C. butyrospermi, with the fecundity of artificially emerging adults overlapping with that of naturally emerging adults. The emergence rate for both was similar. These results contribute to a better understanding of the physiology of this insect, constituting a breakthrough in its sustainable use as human food.
1 The effect of transgenic cotton Bollgard II on the abundance of nontarget arthropods was assessed under field conditions in three areas in Burkina Faso for four successive years (2010)(2011)(2012)(2013). 2 The experiment was carried out on two 0.5-ha plots of which one was seeded with the Bollgard II and one with the non-Bacillus thuringiensis Berliner (Bt) isogenic cultivar. 3 Over four collection methods [plastic bagging (28 collections), water trap (28 collections), beat cloth (six collections) and pitfall traps (six collections)] and 4 years, no statistically significant differences were detected between Bollgard II and the conventional control for 45 out of 48 comparisons. 4 Differences detected were rather random and not consistently detected across collection methods, sites and/or years. Thus, these differences were not indicative of a consistent response associated with the trait and are not considered biologically meaningful in terms of an adverse environmental impact (nontarget arthropod abundance) of Bollgard II compared to conventional cotton receiving six insecticide sprays.
The African rice midge, Orseolia oryzivora H. & G., is an important insect pest in Burkina Faso. Our study was conducted from 2017 to 2019 in three irrigated rice schemes including Banzon, Karfiguéla and Vallée du Kou in Western Burkina Faso. The objective of this study was to investigate the ecology of the insect pest. In each rice scheme, four plots of 500 m 2 each, spread 50 m apart were randomly selected in farmers' fields and used for the study. In each plot, a light trap was implemented along one of the diagonals of the plot. Each light trap consisted of a yellow plastic round bowl containing soapy water almost at half the bowl and a torch. The bowl had a capacity of 4.5 l, a diameter of 28 cm and a height of 10.5 cm. The torch had 3 batteries of 1.5 V each, 30 cm long and 1 cm diameter. The torches were lit every night at 6 pm and off at 6 am. Four hundred tillers were collected per month from the cultivated rice and from each of the alternative hosts of the rice midge in order to evaluate the monthly gall count, pre-imaginal populations and parasitism associated with O. oryzivora and its cousin, O. bonzii that is hosted by Paspalum scrobiculatum. The number of O. oryzivora's adults caught in the light traps was higher during the wet season than the dry season. The level of larval parasitism ranged from 6.16% (Banzon) to 14.29% (Vallée du Kou). The highest level of pupal parasitism (13.73%) was recorded in Vallée du Kou. The damage of O. oryzivora was observed on the wild rice species, O. longistaminata in all three sites. The highest levels of parasitism associated with O. bonzii were recorded in Karfiguéla (20.08% and 25.21% for larval parasitism and pupal parasitism, respectively
Lepidopterous stem borers cause extensive damage in irrigated rice in Burkina Faso and regularly compromise the harvest of the dry season rice in the rice-growing area of la Vallée du Kou in western Burkina Faso. Yield of losses of 40% were observe during the dry season. The study conducted during the wet season in 2015 examined the effects of areas and of transplanting dates on the evolution of population of stem borer's damage and of parasitism. Rice irrigation area of la Vallée du Kou was divided into three areas within which 12 farmers were selected on the basis of three dates of transplanting rice; they were total 36 for the days three transplanting dates. According to agronomic evaluation, the transplantation dates are influence by the number of tillers and by the number of panicles. The maximum average number of tillers was observed in the second area within the first date of transplantation. Otherwise the second area and the second date recorded the highest number of panicles. Entomological observations were carried on every 7 days from the 21 th day to 91 th day after rice transplanting in each of the 36 fields. Late transplanting (August) are the most exposed to Orseolia oryzivora attacks. The genus Chilo spp, Maliarpha and Diopsis spp were the most important pests in rice plants on the perimeter of la Vallée du Kou. Periods of greatest damage were observed in tillering. They were responsible for the deadhearts damage, for white panicles and for the highest rates. These damages were recorded during the first date of rice transplanting. Parasitism associated with the genus Chilo was observed in the first transplanting date. The hectare average yields were most important in the second transplanting date of within the third area. These results on the pre-imaginal populations are important data. These data can be taken into account to improve the development of a strategy to fight against the major insect pests of rice plants. All these elements are linked to the climatic variations.
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