Jacobs Mobolade Adesina

Field assessment of insecticidal efficacy of some plant aqueous extracts in reducing cowpea pod-sucking bug Acanthomia tomentosicollis Stâl (Hemiptera: Coreidae) infestation and damage

Array of pest complex and yield reduction due to insect pests is one of the major constraints for low productivity of cowpea. The insecticidal efficacy of Spondias mombia, Momordica charantia, Mitrocarpus villosus and Chenopodium ambrosioides crude aqueous extracts was assayed for suitability in controlling the pod-sucking bug Clavigralla tomentosicollis Stâl (Hemiptera: Coreidae) on cowpea. The field experiment was laid out in a randomised complete block design with two treatments replicated three times at the Teaching and Research Farm of Rufus Giwa Polytechnic, Owo, Ondo State, in 2012. One kilogram of plant leaves was pounded using mortar and pestle and soaked in 3 L of cold water overnight. The extracts were applied at 10% (v/w) and sprayed every week for four weeks and a synthetic insecticide (Lambda cyhalothrin) was used as reference to compare the effectiveness of the plant extracts. Results of the experiment show that the plant extracts caused considerable reduction in the insect population; similarly, yield attributes corresponded positively with the effectiveness of the treatment and were at par with the synthetic insecticide. However, among the plots treated with aqueous plant extracts, the plot treated with S. mombia performed better than other plant extracts in terms of number of uninfested pods (55.34), plots treated with C. ambrosioides, having least number of damaged (infested) pods (6.0), and plots sprayed with S. mombia, having highest number of harvested pods (62.67), uninfested pods (55.34) and seed weight (0.18 kg). This study is probably the first reported case of the potential of the evaluated plant extracts for the control of insect pests of field crops. Therefore, the present study suggests the use of all the tested plant extracts, as they have been found to be very promising biopesticides in the control of cowpea pod-sucking insect pests. Thus, the extracts could be a good alternative to the synthetic insecticides on organically managed farms as well as on farms of limited-resource farmers in the tropics and subtropics.

Phytochemical composition and insecticidal potentials of some plant aqueous extracts in suppressing Podagrica spp. (Coleoptera: Chrysomelidae) Infestation on Okra (Abelmoschus esculentus L. Moench)

Foliar application of 25% w/v crude aqueous extracts Calotrophus procera (Aiton) W.T. Aiton, Canarium schweinfurthii (Engl.) and Bryscocarpus coccineus (Schum. & Thonn.) were evaluated for their insecticidal activity in reducing Podagrica infestation on okra. Results showed that plants extracts significantly suppress Podagrica spp. infestation and protect okra plant from severe leaves defoliation, with C. schweinfurthii (21.67 and 20.14) and B. coccineus (23.07 and 24.55) showing promising insecticidal activity. The yield attributes from okra sprayed with Lambda cyhalothrin did not differ significantly compared to those sprayed with botanical insecticide despite having highest yield attributes. Qualitative phytochemical screening revealed the presence of Triterpenoids, Steroids, Flavonoids, Phlobatanins, Saponins, Tannins, Cardiac glycoside and Anthraquinones. Alkaloids and Anthraquinones were not detected in C. procera and C. schweinfurthii while Triterpenoids and Phlobatanins were absent C. schweinfurthii . The presence of these phytochemicals indicates that the plants possess insecticidal properties responsible for significant reduction in Podagrica spp. infestation, severity of leaves damaged and improved okra yields. Performance of the treatments is rated in the following order: Lambda cyhalothrin > B. coccineus > C. schweinfurthii > C. procera , with B. coccineus and C. schweinfurthii having similar treatment means in all the parameters evaluated. In light of the foregoing, crude extracts of B. coccineus and C. schweinfurthii could be utilized as suitable alternative to synthetic insecticide in sustainable okra production

Oviposition Deterrent and Egg Hatchability Suppression of Secamone Afzelii ( Schult ) K. Schum Leaf Extract on Callosobruchus Maculatus ( Fabricius ) ( Coleoptera : Chrysomelidae )

The efficacy of oil extracted from the leaves of Secamone afzelii was evaluated in the laboratory against Callosobruchus maculatus infesting stored cowpea. Leaf extracts from S. afzelii were obtained through the soxhlet extraction method using methanol and hexane as the solvent. Each of the extracts was tested by exposing five pairs of adult beetles to various levels of 0.5, 1.0, 1.5 and 2.0 ml corresponding to 2.5, 5.0, 7.5 and 10.0% v/w concentrations admixed with 20g cowpea in three replications respectively, in a Completely Randomized Design (CRD). Control treatment was set along. The results showed that oviposition and percentage egg hatched were significantly (P <0.05) suppressed on seeds treated with higher treatment level of extracts. Leaf extract with hexane at 2 ml (10.0% v/w)/20g cowpea seeds was most effective in suppressing oviposition and egg hatched. Therefore, S. afzelii exhibit promising degree of oviposition deterrent and ovicidal properties and, thus, have a great potential for use as a plant-based biopesticide as an alternative to synthetic insecticides for controlling C. maculatus infestation on stored cowpea grains.

Entomo Toxicity of Xylopia Aethiopica and Aframomummelegueta in Suppressing Oviposition and Adult Emergence of Callasobruchus Maculatus ( Fabricus ) ( Coleoptera : Chrysomelidae ) Infesting Stored Cowpea Seeds

The cowpea beetle, Callosobruchus maculatus (Fabricus) (Coleoptera: Chrysomelidae), is a major pest of stored cowpea militating against food security in developing nations. The comparative study of Xylopia aethiopica and Aframomum melegueta powder in respect to their phytochemical and insecticidal properties against C. maculatus was carried out using a Complete Randomized Design (CRD) with five treatments (0, 1.0, 1.5, 2.0 and 2.5g/20g cowpea seeds corresponding to 0.0, 0.05, 0.075, 0.1 and 0.13% v/w) replicated thrice under ambient laboratory condition (28±2°C temperature and 75±5% relative humidity). The phytochemical screening showed the presence of flavonoids, saponins, tannins, cardiac glycoside in both plants, while alkaloids was present in A. melegueta and absent in X. aethiopica. The mortality of C. maculatus increased gradually with exposure time and dosage of the plant powders. X. aethiopica caused 75.15% adult mortality and A. meleguta exerted 85% mortality at 120 hrs post infestation. Maximum oviposition deterrent activity was observed with X. aethiopica (54.26%) compared to A. melegueta (51.32%). Conclusively, both plants showed highly useful bioactivity against C. maculatus in suppressing oviposition and adult emergence and, therefore, can be used in formulating ecofriendly herbal insecticides.

Effects of initial infestation levels on damage to resistant and susceptible cowpea by Callosobruchus maculatus (Fabr.)

Cowpea cultivars Ife Brown and IT84S-2246-4 were screened for resistance and susceptibility to Callosobruchus maculatus (Fabr.) infestation using different insect densities. The number of eggs laid on the seeds; number of seed bearing eggs and seed without eggs; mean number of eggs per seed; number of F1 progeny; number of seed with and without holes; mean number of seed with hole; and developmental time increased as insect population increased. Significantly, more eggs were laid on the seed of Ife Brown (Susceptible cowpea variety) than on IT84S-2246-4. However, low adult emergence and high development period were observed on IT84S-2246-4, indicating clear cultivar difference at all insect population. The assessment of the first filial generation (F1 progeny) of the two varieties showed further that oviposition reduced in the insect that emerged from IT84S-2246-4 (resistant variety) when reared on Ife Brown cowpea seeds. Irrespective of cowpea varieties used in the experiment, egg laid and adult emergence by C. maculatus significantly increased with an increase in insect density.