Are bioinsecticides able to effectively substitute chemicals in the control of insect pests of okra (Abelmoschus esculentus L. Moench) in Cote d'Ivoire?

Objective: Okra (Abelmoschus esculentus, Malavaceae) production faces pest and disease attacks that leads to use of chemical pesticides. This study was performed to compare effectiveness of the bioinsecticide Levo 2.4 SL (Oxymatrin 2% and Prosular 0.4%) to the chemical pesticides Abalone 18 EC (Abamectin 18g/l) and Viper 46 EC (Acetamiprid 16g/l and Indoxacarb 30g/l) against okra insect pests in Cote d'Ivoire. Methodology and Results: So a field experiment was carried out at Bonoua (05°16'17N; 03°35'40 W) in the South East of Cote d’Ivoire, in a Randomized Complete Block Design (RCBD) with four replications and four treatments; Levo 2.4 SL, Abalone 18 EC, Viper 46 EC and the Control. Insect communities, damages and yield profit rate were assessed and analyzed with Statistica 7.1 at 5%. The inventory of insect allowed the identification of 28 species distributed into 19 families and 10 orders. The main pest insects observed were Hemiptera; Aphis gossypii (41.59%), Bemisia tabaci (39.11%), Jacobiasca sp (1.26%) and Dysdercus wolkerii (1.44%), Coleoptera; Podagrica decolorata (9.03%) and caterpillars of Lepidoptera; Syllepte derogate (1.36%). Then control plots presented no healthy plants (0%), while the bioinsecticide (Levo 2.4 SL), and the chemical insecticides; Abalone 18 EC and Viper 46 EC presented respectively 60%, 77.5% and 90% of healthy plants (index 0). Overall, the effectiveness of the bioinsecticide to control insect pests appeared similar to those of the chemical pesticides. However, Levo 2.4 SL seems to be less effective against Aphis gossypii and Dysdercus wolkerii populations. Highest fruit yield of okra was recorded in treated plot with Viper 46 EC (12.55±0.98 t/ha), followed by Abalone 18 EC (12.2±0.8 t/ha) and Levo 2.4 SL (11.15±1.09 t/ha). Whereas, the lowest yield obtained from control plots was 6.84±0.15 t/ha. The yield profit rates were 62.82; 78.18 and 83.28% respectively for Levo 2.4 SL, Abalone 18 EC and Viper 46 EC when compared to the control. The control of insect pests by the bioinsecticide and the chemical insecticides increased significantly the okra yield. Conclusion and application of Results: Therefore, the bioinsecticide can be eco-friendly alternative to control insect pest of okra in Cote d’Ivoire. Then, the bioinsecticide Levo 2.4 SL can be proposed to limit damages caused by chemicals on the environment and human health.Keywords: Bioinsecticide, Levo 2.4 SL, Abelmoschus esculentus, insect pests, Cote d’Ivoire

Impact of Soil Fertility Management Practices on Insect Pests and Diseases of Maize in Southwest Cote d’Ivoire

Objectives: Integrated soil fertility management (ISFM) is essential for sustainable management of tropical soils. However, soil fertility management is able to affect plant susceptibility to pests and diseases. The study investigated impact of soil fertilization practices on maize pests and diseases during two identical and simultaneous trials setup in South-West Cote d'Ivoire.Methodology and Results: Experiments were laid out using complete randomized block designs with three replicates and four treatments: (1) control; (2) chemical fertilization; (3) fertilization with cattle manure; (4) association “maize + legume” combined with chemical fertilization. Overall, 22 insect species collected and two diseases (maize streak disease and curvularia leaf spots) observed at both sites. Only cattle manure clearly increased pest and disease damages. The use of cattle manure significantly increased leaf infestation rate and maize streak disease frequency at both sites. Similar impact of NPK and cattle manure was obtained on maize yields either in monocropping or in mix cropping.Conclusions and application of findings: This study clearly confirmed that ISFM is able to affect plant susceptibility to pests and diseases. Cattle manure attracted a diversity of insects of diverse functional groups such as air-borne pests. These latter affected some plant parts; in this case, maize leaves which infestation rate significantly increased. This attraction for multitude insects may increase vector-borne diseases such as maize streak which frequency significantly increased at both sites. Consequently, despite the potential of cattle manure to increase maize yield, their use as organic fertilizer requires to take some precautions. So, the promotion of cattle manure as organic fertilizer in substitution of chemical fertilizer in tropical regions where it is available is encouraged. However, it should be converted into compost or pre-treated for optimal use in agriculture. Finally, mix cropping could be suggested for optimization of economic profit.Keywords: Maize, leaf infestation, maize streak disease, soil fertility management, cattle manur

Use of Selected Chemical and Biological Insecticides to Control Lepidopteran Pests of Maize Fields in Central Côte d'Ivoire

Control of lepidopteran larvae, the main pests in maize fields, has become necessary since the appearance and spread of Spodoptera frugiperda. The study was carried out at the Institut National Polytechnique Houphouët-Boigny in Yamoussoukro (Central Côte d’Ivoire). The study aimed to determine the effectiveness of three chemical - Viper 46 EC (Acetamiprid 16 g/l and Indoxacarb 30 g/l), K-Optimal 35 EC (Lambdacyhalothrin 15 g/l and Acetamiprid 20 g/l) and Ampligo 150 ZC (Chlorantanlipol 100 g/l and Lambdacyhalothrin 50 g/l) - and one biological insecticide Bio-Elit (Azadirachtin, Salanin, Nimbin and Melandriol) on lepidopteran larvae in maize fields using a randomized complete block design with five treatments and three repetitions. Data on insect identification, plant infestation, damage, and yield were collected. Insects’ identification was based on morphology using identification keys. Plant damage was assessed by visually estimating the plant health status (unattacked and attacked plants). Grain dry weight was used to estimate field yield. The encountered maize field insects belonged to 10 orders: Heteroptera, Hymenoptera, Homoptera, Coleoptera, Diptera, Dictyoptera, Odonata, Orthoptera, Dermaptera, and Lepidoptera. Five lepidopteran pest larvae have been recorded. Three of them were classified as minor pests (Eldana saccharina, Ostrinia nubilalis, and Helicoverpa zea), one as important (Sesamia calamistis), and one as a major pest (Spodoptera frugiperda). On untreated plots, more than 76% of plants were moderately to heavily attacked. However, on treated plots, plants showed isolated to moderate attacks. Insecticide sprayings controlled pest populations, reduced damage, and increased yield. The yields obtained on untreated plots (2.26±0.21 t/ha) were lower than those on treated plots (3.29±0.11 to 3.60±0.09 t/ha). The yield increase rate ranged from 45.74 to 59.63%. The best control was recorded with Ampligo (59.63%) and Bio-Elit (50.83%) compared to Viper (49.41%) and K-Optimal (45.74%). Therefore, the alternating use of synthetic or biological insecticides, which are not very toxic for humans and the environment but are effective on insect pests, increases the effectiveness of the control and provides a positive response to the problem of pest resistance while protecting the environment

Damage Caused by Lepidopteran Pests on Maize Fields in Yamoussoukro, Central Côte d’Ivoire

Various larvae of Lepidoptera cause severe damage to maize crops. The dynamics of these maize larvae pests have been studied during all stages of plant development. The trial was carried out on the Institut National Polytechnique Houphouët-Boigny farm plots in Yamoussoukro (central Cote d’Ivoire). The study aims were to monitor the dynamics, determine the importance (frequency and abundance), and assess the damage of Lepidopteran pests on the maize variety EV8728 SR using a randomized complete block design with four replicates. The variety was sown on 05 September 2020. Insects were characterized with keys following on-site observation and capture of larvae on the plants. Five Lepidopteran species, grouped into three families, were counted on the plots. Spodoptera frugiperda was the most frequent (Occurrence C = 20.9%) and highly abundant (Relative Abundance Ar = 65.79%). The other Lepidoptera species were rare (C < 5%). However, Sesamia calamistis was very abundant (Ar=15.22%), while Eldana saccharina (Ar = 9.44%) and Ostrinia nubilalis (Ar = 5.25%) were abundant. Helicoverpa zea is scarcely abundant (Ar=4.3%). Furthermore, three Lepidoptera species (E. saccharina, O. nubilalis, and H. zea) were as minor pests (Damage Index I < 10%), while S. calamistis was important pest (I < 25%) and S. frugiperda was major pest (I< 75%). The populations of the insects fluctuated during crop development. The mean dried grain yield varied from 2.4±0.42 to 2.61±0.71 t/ha. Populations of S. frugiperda larvae and their damage appeared more important than those of other Lepidoptera. Knowledge of maize lepidopteran larvae is essential for effectively and efficiently controlling these pests and improving the quality and quantity of maize production