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