Browsing by Author "Nega, Adem"

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    Studies on the Status of Chilo Partellus (Swinhoe) (Lepidoptera: Crambidae) and its Natural Enemies, and the Effect of Botanicals and Cow Urine Against the Pest and Natural Enemies
    (Addis Ababa University, 2019-05-20) Nega, Adem; Getu, Emana (Professor)
    The exotic stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is the most important pest of sorghum in East Africa. The insect infests sorghum crop throughout its growth stages. It has also been recorded and documented from wild host plants. C. partellus has several native and exotic natural enemies. Field and laboratory studies were conducted to know the status of C. partellus and its natural enemies and assess the efficacy of botanicals and cow urine against C. partellus and their effect on the natural enemies. Surveys were conducted in 2016/17 and 2017/18 in three districts and nine farmer fields of Kalu, Bati and Dawa Chefa districts, Ethiopia. Sampling was done both randomly and purposively. Analysis of variance (ANOVA) was carried out to determine if there were any significant differences across the locations and between the plant growth stages. Laboratory evalution of plant and animal-based insecticides and optimum concentration on C. partellus was conducted in 2016. The experiment was laid out in completely randomized design in three replications for each rate. The rates were 2g, 2.5g, 3g of powder and 1ml, 1.5ml and 2ml w/v of the solutions. The most effective biopesticides were further tested in 2017 in farmer’s field. The trial was designed in a randomized complete block design in factorial arangment in three replications. The treatments were at two levels of frequencies (2 & 3 times application) and three rates of powder (1g, 2g and 3g) and three rates of solution (5%, 10% and 15%). The study revealed that C. partellus constituted 90.3 & 91.2% on sorghum and 45.4 & 69.2% on wild hosts in 2016/17 and 2017/18, respectively. Significant differences were observed among the host plants and sorghum growth stages. In sorghum, C. partellus density were found to be significantly higher than on wild hosts (P<0.05). Relatively higher numbers of larvae (5.02±0.5) per plant were recorded from Bati at seedling stage and the lowest; (3.32±0.3) was from Kalu. Significant difference was observed in incidence of C. partellus (F=11.8; d.f.=2;P<0.008). C. partellus was significantly (F=60.3;d.f.=2; P<0.000) different at the three plant growth stages across the locations. Similarly, significant (F=24.75; d.f.=2;P<0.001) difference was recorded at vegetative stage in terms of exit holes. Natural enemies’ abundance showed significant difference among sorghum growth stages. C. flavipes (Cameron) recorded abundantly at maturity stages of sorghum. The highest number (0.48) was recorded from Bati at the vi maturity stage with the relative abundance of 33.8%. Cotesia flavipes parasitism varied across the locations and host growth stages. The highest (61.5%) parasitism was recorded from Bati at maturity in both seasons. Ants were highly abundant at maturity and lower at early stages at Bati, while (83.7%) relative abundance was recorded from Kalu. Earwigs were highly abundant in Dawa Chefa district, while the maximum number was found from Bati at maturity stage with the relative abundance of 26.3%. Laboratory study showed that Millettia ferruginea seed powder and aqua extract caused 100% mortality at the highest rates after 24 hrs exposure. Cow urine, Phytolacca dodecandra aqua extract and its mixture with cow urine were found effective. Results of field trial showed that all pesticides formulations significantly (P<0.01) reduced C. partellus damage at the highest rates with two times applications compared to untreated check. Likewise, their effect on the main natural enemy of C. partellus was minimal. C. partellus was found attacking by several natural enemies at each stages of sorghum, thus it is suggested that use of plant and animal-based insecticide can be regarded as suitable alternative to synthetic insecticides for the management of C. partellus in the field.
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    Study on Ovicidal, Larval Settlement, Feeding and Oviposition Deterrence Effects of Seed Kernel Powder Extracts of Birbira, (Milletia ferruginea) on Diamondback moth, (Plutella. xylostella L.) (Lepidoptera: Plutellidae)
    (Addis Ababa University, 2002-06) Nega, Adem; Seyum, Emiru(PhD)
    Solvent extractions having different polarities with different doses prepared from birbira tree seeds, Milletia ferruginea (Hochst) Baker. This study was carried out to assay the ovicidal, larval settlement, feeding and oviposition deterrence effects on Diamondback moth (Plutella xylostella L.). Leaf dipping method was used to run both assays by using the extracts from birbira seed kernel powder in water (w/v): 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.4 mg/ml. In the assays significantly higher larval mortality was recorded on leaves treated with polar than the non polar and Chloroform extracts. Days to the 1st larval mortality was observed within a day after the exposure of the 3rd instar larvae on treated leaves with different solvent extracts of birbira except the Water. Days to the last mortality were observed on the 14th days on all extracts. Days to the highest larval mortality were significantly higher for Water, Acetic acid and Acetone, extracts at 0.8, 0.6 and 0.4 mg/ml; respectively for the other extracts it was significantly higher at the higher rates of application. In the control most larvae pupated on 8th day. Acetone prevented pupation at the higher rates, Water, Acetic acid, Chloroform and Hexane allowed fewer larvae to pupate, and in contrast more number of larvae was pupated in Toluene extract at all the rates. Significantly small numbers of adults were emerged at the higher rates of Water, Acetic acid and Acetone than the others. Adults took longer time to emerge from pupae on Chloroform, Toluene and Hexane extracts at the higher rates. Eggs unhatchability was higher at 0.4 mg/ml and increased at the rate of 1.4 mg/ml for polar extracts. However, significant eggs unhatchability was recorded only at the higher rates for the non polar extracts. Oviposition deterrence was significantly lower at the lower rates of Water, Acetic acid and Acetone full deterrence was recorded at the higher rates, in contrast Toluene and Hexane showed least deterrence effect even at the higher rates of application. The number of eggs oviposited in the inner surface of the Petri dishes were higher at all the rates except for Water, Acetone and Chloroform extracts. Numbers of eggs deposited in the inner walls of the cages were higher at 0.6 and 1.4 mg/ml for Water and at 0.4 and 1.4 mg/ml for Hexane. Small numbers of larvae were settled on non polar solvent extracts. Mortality caused by extracts with Water, and Acetone was very high, and have much smaller LC50 values. In contrast the LC50 was higher for the other extracts and caused significant larvae kill only at the higher rates. Thus, results of this study indicate that M. ferrugginea has a good possibility for controlling P. xylostella (L.).