E.O. Egho and S.O. Emosairue Department of Agronomy, Faculty of Agriculture, Delta State University, Abraka ABSTRACT

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1 AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , doi: /abjna , ScienceHuβ, Evaluation of native soap (local black soap) for the control of major insect pests and yield of cowpea (Vigna unguiculata (L) WALP in ASABA, Southern Nigeria E.O. Egho and S.O. Emosairue Department of Agronomy, Faculty of Agriculture, Delta State University, Abraka ABSTRACT Three concentrations of native soap namely 1, 2 and 3 percent were evaluated for the control of four major insect pests and yield of cowpea. The insect pests studied were the cowpea aphid, Aphis craccivora Koch, legume bud thrips Megalurothrips sjostedti Tryb, legume pod borer, Maruca vitrata Fab. and pod sucking bugs. The experiments were conducted in the early and late planting seasons in the Teaching and Research Farms of the Agronomy Department, Asaba Campus, Delta State University, southern Nigeria. Effect of chemicals on insect pests indicated that M. sjostedti damage was prevented at all the tested soap concentrations. Similarly, at 2% concentration, Maruca population was reduced in the early season. During the late season, all the tested soap concentrations effectively controlled A. craccivora and pod sucking bugs. At 1% concentration, M. sjostedti was effectively checked. On grain yield, the figures suggested that native soap was an insecticide for pest control in cowpea production. In particular, 2% and 1% concentrations gave cowpea yield of 57kg ha -1 and kg ha -1 respectively in the early season. It was observed however, that during the study, native soap had an inhibitory property by delaying and reducing copious flowering in cowpea. In the late season, yield were relatively low in all the soap treatments due to very low rain. The study suggests that (1) native soap is an effective bio-pesticide against cowpea insect pests (2) more grain yield could be obtained if the inhibitory factor in native soap is removed; local cowpea growers may prefer it to synthetic chemicals, since this could save cost and pose less hazards to health. Keywords: Cowpea, insect pests, native soap, early/late seasons, Asaba, Southern Nigeria. INTRODUCTION One of the arable crops extensively and intensively grown in recent times in tropical and sub-tropical regions of the world is the legume cowpea, Vigna unguiculata (L.) Walp. Man cultivates it for several purposes - its grains are rich sources of proteins (IITA, 1984; Alabi et al., 2003). It is consumed as vegetables in many African countries; it is important in fibre production (Rachie, 1985; Okigbo, 1978). Because of the prohibitory cost of meat, eggs and fish, many people in the low income class depend on it largely as cheap source of protein (Anderson, 1985). Cowpea has been described as poor man s meat (Aykyord and Doughty, 1982). In Nigeria, large scale production takes place in the drier Northern states - in the Sudan savannah. In recent times, however, the cultivation spread to southern Nigeria and the crop is being grown in the Western and Eastern states (Ejiga, 1979; FOS, 1995). The ever growing demand, partly due to man s population growth has resulted in concerted efforts to increase yield and quality grains. These have not been realised because of several production constraints while the crop is in the field and storage. It is now obvious that among the production bottlenecks, insect pests and diseases are major factors (Taylor, 1964) which seriously ravaged the crops at all growth stages (Jackai et. al., 1988) resulting in stunted growth, loss of crops and eventually, low yield at the farm level (Omongo et al., 1997), and in Africa (Olatunde et al., 1991). Insect pests of cowpea clearly identified as major and serious pests are the cowpea aphid, Aphis craccivora Koch, flower bud thrips, Megalurothrips sjostedti Tromb, the legume pod borer, Maruca vitrata Fab and a complex of pod sucking bugs among which are Clavigralla tomentosicollis, Anoplocnemis curvipes, Aspavia armigeria and Nezera viridula. A number of measures are now available to curtail the activities of insect pests in the field. The most common is the use of synthetic chemicals (Ayoade, 1975; Jackai, 1993) and increase in yield several

2 folds have been recorded (Jackai and Doaust, 1986). There is however, increasing outcry worldwide of the need to minimize the use of synthetic chemicals because of serious deleterious side effects such as environmental pollution, toxicity to mammals, users, consumers and non-target organisms and high cost of insecticides and equipment (Afun et al., 1991). Cowpea growers are therefore shifting and giving attention to other control measures such as host plant resistance (HPR) and use of non-conventional chemicals which are compatible with the environment and also devoid of the problems associated with synthetic chemicals (Arnason et al., 1989). Native soap (black soap) is made locally from the ashes of straw of millet, plantain husk and palm fruit shafts. In certain African communities, it is used to cure infections such as rashes, eczema, etc. This study evaluates the insecticidal potential in native soap for control of key insect pests of cowpea during the early and late planting seasons at Asaba. MATERIALS AND METHODS The study was conducted during the early and late planting seasons of 2005 in the Teaching and Research Farms of the Agronomy Department, Delta State University, Asaba Campus. The beds for planting were prepared with shovels and hoes and each experimental plot size was 5m x 3m with interplots space of 1.5m. Planting took place in the early season on the 29th of May 2005 and plots for the late season were planted on the 17th of September The grains planted were Ife brown, obtained from the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. Three seeds were planted per hole at planting space of 60 x 30cm (Remison, 1978e). Seeds that did not sprout were replaced four days after planting. Thinning to two per stand was done seven days after emergence. The farm was regularly weeded until plant maturity. The chemical applied on the crop for insect control was black native soap. One, two and three percent concentrations were made by dissolving 10gm, 20gm and 30gm soap respectively in 1000ml of water in a basin. The mixture of each was then left overnight. Each was filtered with muslin cloth. Chemical application commenced 25 days after planting (25 DAP). The experiment consisted of five treatments and three replicates organised into a randomised complete block design. The treatments were 1, 2 and 3% of soap concentrations, cypermethrin (a conventional insecticide as check) and control. The impact of chemicals on four major insect pests of cowpea and yield was assessed. Insect observation and data collection: A. craccivora: A. craccivora was assessed weekly by visual rating between 8 and 10 a.m. From the two middle rows of each cowpea plot, 20 stands were randomly selected and marked. Each stand was carefully inspected for infestation and the size of A. craccivora colony on each was rated on a 10 point scale (table 1) and means of the 20 stands was then calculated. Six observations were made. M. sjostedti: Damage to cowpea by M. sjostedti was determined at six days intervals when the crops were 30 DAP between 8 and 10 a.m. Twenty stands in the two middle rows of each crop were selected randomly and marked. Damage assessment was by visual rating on a scale of 1 to 9 points (table 2). Means from the 20 stands were then calculated. Four observations were made. Maruca vitrata: Maruca vitrata damage to cowpea was assessed in the evening from 3 to 5.00 p.m at 5 days intervals. Twenty flowers in the outer cowpea rows were carefully opened and examined on the spot for Maruca damage. Holes on flowers or presence of Maruca larvae were used as damage index. Means of the 20 flowers were calculated. Number of flower bud thrips in each flower was also counted when flowers were opened. Five observations were made. Pod sucking bugs (PSBs): Population of PSBS that rested on the two middle cowpea rows was estimated by counting at 45 DAP between 8.00 and 1 a.m. All PSBs beyond the nymphal state were counted. Four observations were made. Table 1. Scale for rating aphid infestation on cowpea Rating Number of aphids >500 Source: Litsinger et al. (1977) Appearance no infestation a few individual aphids a few isolated colonies several small colonies large isolated colonies large continuous colonies Yield: At 65 to 70 DAP, the matured pods in the two middle rows of each plot were hand-harvested according to treatments into black polythene bags. 939

3 The pods were sun-dried for two weeks and shelled with hands. Grains from each treatment were then weighed with weighing balance (Haus model) and the weights recorded. One hundred seeds from each treatment were randomly picked and also weighed. Table 2. Scale for rating flower bud thrips infestation on cowpea Rating Appearance 1 no browning/drying (i.e scaling) of stipules, leaf or flower buds; no bud abscission 3 initiation of browning of stipules, leaf or flower buds; no bud abscission 5 distinct browning/drying of stipules and leaf or flower buds; some bud abscission 7 serious bud abscission accompanied by browning/drying of stipules and buds; non elongation of peduncles 9 very severe bud abscission, heavy browning, drying of stipules and buds; distinct nonelongation of (most or all) peduncles. After Jackai and Singh (1988) Table 3: Scale for rating Maruca vitrata damage to cowpea Pod load (PL) Pod damage (PD) Rating Degree of podding Rating % 1 3 most (<60% peduncles bare (i.e. no pods) 31-50% peduncles bare % peduncles bare Up to 15% peduncles bare 9 Occasional bare peduncles After Jackai and Singh (1988) Yield-related components: Yield-related components studied were number of pods/ plants, pod length, number of, pod load, pod damage, pod evaluation index, aborted, wrinkled and seeds without feeding lesions. Number of pods per plant: At 65 DAP, the pods were matured. One metre ruler was placed anywhere along the two middle rows of each plot and this distance was then marked with two sticks. Cowpea pods and their stands that fell within this range (1m) were then counted. The number of pods counted was divided by the number of plants. No. of pods/plant = Number pods Number of plants Pod load and pod damage: Pod load and pod damage were assessed in the field at 60DAP when the pods were green and partially matured. From the two middle rows of each plot, the pods were visually rated (table 3). Holes and presence of frass on the pods and sticking together were used as Maruca damage index. Pod evaluation index: This was done with the formula below: PL X (9 - PD) where PL is pod load and PD pod damage (Jackai and Singh, 1988) Pod length and seed damage: Assessment of seed damage by pod sucking bugs was carried out in the laboratory. Pods at maturity were hand-harvested from the two middle rows of each plot into medium size polythene bags. The pods were sun-dried for one week. From each bag, twenty pods were randomly hand-picked. Each was measured with a flexible thread to determine its length and each carefully was opened with hand. The seeds were classified into number of seeds per pod, aborted seeds per pod, wrinkled seeds per pod and seeds with feeding lesions per pod. Data for insect observation, yield and yield related components were subjected to analysis of variance (ANOVA) and significant means separated by Fisher s Least Significant Difference Test (LSD), at 5% level of significance. RESULTS The effect of native soap and conventional insecticide application for the control of major insect pests on cowpea in the early and late seasons at Asaba is shown in Table 4. All the major insect pests except A. craccivoca occurred during the early season experiment in the study area. The treatments did not significantly (P > 0.05) reduce M. sjostedti damage to the crop when compared with the control. The control however, recorded slightly higher damage than other treatments. The flower bud thrips population was reduced significantly (P < 0.05) by the CPM when compared with the other soap treatments. Similarly, the 3% soap concentration was significantly more effective in reducing thrip population than 1 and 2% soap concentration. In the case of M. vitrata, all the treatments did not significantly ( P > 0.05) differ in reducing Maruca infestation/damage. However, CPM recorded the least Maruca damage, followed by 2% soap concentration. This was followed by 3% soap concentration and control (Table 4). All insecticide 940

4 treatment did not significantly differ in reducing PSB population when compared with the control. All the major insect pests were recorded on the crop, in the study area during the late season experiment (Table 4). With A. craccivora, all treatments except 1% soap significantly (P<0.05) reduced the insect population when compared with the control. There was however, no significant difference in effectiveness amongst soap concentrations and CPM, in reducing A. craccivora population. On M. sjostedti damage to cowpea flowers, all the treatments did not significantly (P >0.05) reduce thrips damage when compared with the control. Plots with 1% soap and CPM protection significantly (P<0.05) reduced thrips population when compared with the control. Similarly, plots protected with 1% soap concentration and CPM were significantly more effective in reducing the population when compared with 2% and 3% soap concentrations. The soap treatments did not significantly (P > 0.05) reduce Maruca damage to flowers compared with the control. However, the CPM plots were more significantly effective in reducing Maruca damage than all other treatments. Similarly, the 1% and 3% soap concentration significantly were more effective in reducing Maruca damage compared with plots protected with 2% soap concentration. All soap treated plots did not significantly (P > 0.05) reduce PSB population when compared with the control. Also, the soap treatment did not differ significantly in their effectiveness. The CPM plots significantly (P <0.05) recorded higher PSB population when compared with control and other treated plots. The seasonal effect on insect pest population under native soap application at Asaba is presented in Table 5. The population of A. craccivora was significantly higher (P < 0.05) in late season compared with early season. No difference in M. sjostedti damage to cowpea in both seasons, though early season damage was slightly higher. For the flower bud thrips, the late season population was significantly (P < 0.05) higher than early season population. Damage to cowpea flowers by M. vitrata was more in the early season and significantly (P<0.05) higher when compared with late season damage. On PSB, the late season bug population was significantly higher than the early season population. Effect of native soap on cowpea yield and yield related components during the early and late seasons experiments at Asaba is presented in Table 6. Yields were not significantly (P > 0.05) increased in plots protected with insecticide when compared with control. However, CPM protected plots had slightly higher yields than other treatments. The control recorded slightly more yields than the native soap protected plots. For the 100 seed weight, there was no significant difference among the treatments and when compared with the control. However, apart from the 3% soap protected plots, weight of seeds from the control were slightly lower than the other treatments. Similarly, pod length, number of, pod damage, aborted and wrinkled seeds per pod showed no significant difference among the treatments. For number of pods per plant, the CPM protected plots had significantly. (P < 0.05) more pods than 2% and 3% soap treatments but not significantly different from control and 1%. CPM protected plots significantly (P < 0.05) had more pod load compared with the other treatments and control. The 1%, 2% and 3% soap protected plots did not significantly (P > 0.05) improve pod load compared with control. With pod evaluation index (Ipe), CPM treatments had higher Ipe value and this was significantly (P < 0.05) higher than other treatments and when compared with the control. The 1 %, 2% and 3% soap protected plots had Ipe value which were not significantly different (P > 0.05) when compared with the control. For seeds with feeding lesions, apart from CPM protected plots, all other plots did not significantly reduce feeding lesion compared with the control. The season effect on cowpea yield and yield related components under the application of native soap during the early and late seasons in Asaba is presented in Table 7. Grain yields in the early season were significantly (P <0.05) higher than the late season cowpea. Similar trend was encountered with respect to 100 seed weight, number of pods per plant, pod length, number of seeds per pod, aborted, and seed with feeding lesions. For pod load, there was no significant difference in both seasons, although, pod load was slightly better in the early than late. Pod damage followed the same trend on pod load. However, the cowpea pods had slightly more damage in the late than early pods. In the case of pod evaluation index, there was no significant difference between the two seasons; though Ipe value was slightly higher in the early season than 941

5 late. With wrinkled seeds per pod, significant difference did not exist between the two seasons. However, there were more wrinkled seeds in the late season than early. Seeds with feeding lesions were significantly higher in the early than late season. Table 4: Effect of application of native soap on the major insect pests of cowpea in the early and late seasons at Asaba. Early season Treatments CONTROL 1% 2% 3% CPM Aphis craccivora (rating)** Megalurothrips sjostedti (rating) 1.52 Flower bud thrips* (actual counting) Maruca vitrata* (actual counting) PSB** (actual counting) Late season CONTROL 1% 2% 3% CPM * Means of 20 flowers ** Number per 2 middle rows -Not significant Table 5: The seasonal effect of the application of native soap on the major insect pests of cowpea at Asaba. Treatments Aphis craccivora (rating) Megalurothrips sjostedti Flower bud thrips* (actual counting) Maruca vitrata* (actual Early Late LSD (0.05) (rating) counting) PSB** (actual counting) ** Number per 2 middle rows -Not significant 942

6 Table 6: Effect of native soap and cypermethrin on yield and yield related components from cowpea in the early and late seasons in Asaba Treatments Dry Grain yield (kg ha -1 ) 100 seeds wt(g) Number of pods/ plant (approx) Pod length (cm) Number of Pod load Pod damage Pod evaluation index Aborted Wrinkled Seeds with feeding lesions Early season CONTROL 1% 2% 3% CPM Late season CONTROL 1% 2% 3% CPM N.S - Not significant Table 7: The effect of early and late season on yield and yield related components from cowpea under native soap application at Asaba Season Dry Grain yield (kg ha -1 ) 100 seeds wt(g) Number of pods/ plant (approx) Pod length (cm) Number of Pod load Pod damage Pod evaluation index Aborted Wrinkled Seeds with feeding lesions Early Late Not significant 943

7 DISCUSSION Results from this study showed that Aphis craccivora was absent during the early season. This may be due to the following reasons: 1. Cowpea had not been in cultivation in the study area for several years; 2. The migratory activity of aphid could have possibly been hindered as rains were heavy and frequent in this season. Degri and Hadi (2000) reported from Bauchi the absence of Aphis craccivora on field cowpea under heavy rain fed condition. Similar reports on this insect have also been given by other cowpea researchers (Dina, 1982; Afun et al, 1991). The results indicated that at all the tested native soap concentration in the early season, M. sjostedti damage to cowpea can be prevented and this allows the crop to develop to maturity. Similarly, at 2% soap concentration, Maruca damage according to the study, was checked. In the late season experiment, native soap also at all the tested concentrations were effective against aphid and PSBs population. Against M sjostedti damage, soap was effective at 1% concentration. Furthermore, flower bud thrips population was highly reduced. The use of soap in the control of insect pests of crops is not a recent practice. Insects such as aphids on some fruits and grass house crops have been controlled with soft soap. Moreover, most small insects such as mealybugs and psyllids are susceptible to soaps. IITA (2002) had earlier shown the beneficial effects of soap spray in insect pest control in the improved cowpea variety IT90k and found yield of 516kgha -1 compared to 361 kgha -1 without insecticide (control). This study has demonstrated the insecticidal property in native soap in protecting cowpea insect pests - such as Aphis craccivora, M. sjostedti, Maruca vitrata and pod sucking bugs and the report here is in agreement with the findings of IITA (2002). During the late season experiment, M. vitrata was not affected at any of the soap concentrations. This may be due to the larvae wandering away from the leaf areas that were covered by the insecticide or possibly, the larvae remained hidden in their burrows and the insecticide could not touch them (Jackai, 1983). During the early season study, population of pod sucking bugs was generally low, an observation which agreed with the report of Dina (1982). The more population of PSBS in the cypermethrin plots as noted in the study was probably due to the more of cowpea pods available and exposed for PSBS attack after a reduced effect of cypermethrin. The significantly higher values recorded for A. craccivora, flower bud thrips and PSBs during the late cropping season compared to early, may be due to weather factors which favoured their establishment. Cowpea researchers had earlier reported on PSBs, in particular to be higher in the late season (IITA, 1983; Dina, 1982). On grain yield in the early season, the values suggested that native soap was an insecticide for pest control in cowpea production. In particular, 2% and 1% concentrations gave cowpea yields of - 57 kg ha -1 and kg ha -1 respectively. This work corroborated IITA (2002) report which gave a yield of 516kg ha -1 with soap spray in the Sudan Savannah, Nigeria. It was however observed that native soap had an inhibitory property by delaying and reducing copious flowering in cowpea. Probably yields would increase if this factor was eliminated. Local cowpea growers may prefer it to synthetic chemicals since this could save cost and pose less hazards to health. On yield related components, figures from the treatments were similar in value, suggesting that the treatments did not bring about variations to affect yields. Grain yields from all the soap treatments 1% (33.66 kg ha-1), 2% (15.11 kg ha -1 ), 3% (19.33 kg ha -1 ) during the late season were very low in Asaba. Apart from CPM (158kg ha -1 ) all other treatments had yields well below 50 kg ha -1. Probably the sudden high temperatures (28.0 o C) due to low rain (217.4mm) in the month of October, 2005 led to drying of leaves and this severely affected the photosynthetic ability of the plants. Thus application of chemicals was more or less a wasted effort. The data suggested that planting of cowpea should be done much earlier in this area for the crop to receive sufficient moisture. Most of the yield related components had poor values, probably because of the weather situation. Grain yields in the early ( kg ha -1 ) and late seasons (49.39 kg ha -1 ) showed that early grain yields were significantly higher than late yields at Asaba. The lower yield in the late seasons was due possibly to insufficient rainfall and rather high temperatures encountered at this period. This also affected yield related components. That is to say that most of the yield related components had better values in the early season than late. 944

8 CONCLUSION The study suggests that (1) native soap is an effective bio-pesticide against cowpea insect pests (2) more grain yield could be obtained if the inhibitory factor in native soap is removed; local cowpea growers may prefer it to synthetic chemicals, since this could save cost and pose less hazards to health. REFERENCES Afun, J.V.K., Jackai, L.E.N. and Hodgson, C.J. (1991) Calendar and monitored insecticide application for the control of cowpea pests. Crop Protection 10: Alabi, O.Y., Odebiyi, J.A. and Jackai, L.E.N. (2003) Field evaluation of cowpea cultivars (Vigna unguiculata (L) Walp.) for resistance to flower bud thrips (Megalurothrips sjostedti Trybom) Thysanoptera: Thripidae) International Journal of Pest Management. 49 (4), Anderson, J. W. (1985) Cholesterol lowering effects of canned beans for hypercholestrolmic, Med. Clin. Res. 33(4), 871. Arnason, J.T., Philogene, B.J.R. and Morand, P. (eds) (1989) Insecticides of plant origin. ACS Symposium Series No. 387, American chemical society. Washington, D.C. USA. 213 pp. Aykroyd, W.R. and Doughty, J. (1982). Legumes in Human Nutrition. FAO. Nutrition Studies 19, FAO, Rome. Ayoade, K.A. (1975) Recent trends in chemical control of the insect pest complex of cowpea in Western Nigeria. In: Proc. IITA collaborators' meeting on Grain Legume Improvement, 9-13 June, International Institute of tropical Agriculture, Ibadan, Nigeria., pp Dina, S. O. (1982) Interactions between rate, spray interval and number of applications of the synthetic pyrethroid Decis in Cowpea (Vigna unguiculata) pest control. J. Agric, Camb Ejiga, N.O. (1979) The efficiency of the indigenous food grain marketing systems in Nigeria, Savannah Dec., 8 (2), FOS (1995) Annual Abstract of statistics, Lagos, Nigeria. IITA (1984) Annual Report for Ibadan, Nigeria. IITA (2002) Improving and intensifying cereal-legume systems in the moist and dry savannas of the West and Central Africa. Annual Report IITA, Ibadan pp 23. Jackai, L. E. N. (1983) Efficacy of insecticide applications at different times of day against the legume pod borer, Maruca vitrata (Fab) (Lepidoptera: pyralidae) on cowpea in Nigeria. Protection Ecology Jackai, L.E.N. and Daoust, R.A. (1986). Insect pests of cowpeas. Annual Review of Entomology Jackai, L.E.N. and Singh, S.R. (1988) Screening Techniques for Host Plant Resistance to Insect Pests of cowpea. Tropical Grain Legume Bulletin 35: Jackai, L.E.N., J.M.F. Roberts and S.R. Singh (1988). Cowpea seed treatment with carbosulfan: potential for control of seedling pests. Crop Protection Vol. 7, December 1988, Litsinger, J.A., Quirino, C.B., Lumaban, M.D. and Bandong, J.P. (1977) Grain Legume Pest Complex of Three Phillipine Rice-Based Cropping System. Cropping Program, IRRI. Los Banos. Philippines, 39. Okigbo, B.N. (1978) Grain legumes in the agriculture of the tropics. In Pests of Grain legumes Ecology and control (Edited by Singh S.R. Van Emden H.E. and Taylor T.A) Academic Press, Inc., New York. Olatunde, J.A. Odebiyi, Chiang, H.S. and Jackai, L.E.N. (1991) Identification of sources of resistance in cowpea, Vigna unguiculata L. Walp. to Clavigralla tomentosicollis. Stal. (Hemipera: Coreidae) Insect Sci. Applic., 12 (4), Omongo, C. A., Adipala, E., Ogenga Latigo, M. W., Kyamanywa, S. (1997) Insecticide application to reduce pest infestation and damage on cowpea in Uganda. Afri. Plant Prot. 4 (2), Rachie, K.O. (1985) Introduction. P. xxi xxviii. In: S.R. Singh and K.O. Rachie (eds). Cowpea research, production and utilization. Wiley New York. Remison, S.U. (1978e) Cowpea agronomy works at National Cereals Research Institute. Paper presented at the 1st National meeting. On development of package. Recommendations for legume crops at N.C.R.I, Ibadan, 7-8 February. Taylor, T.A. (1964). The field pest problems on cowpea. (Vigna sinensis L.) in Southern Nigeria, Grower Producer3 (2). 945