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
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Date
2019-05-20
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Addis Ababa University
Abstract
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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Status, Abundance, Infestation, Sorghum, Biopesticides, C. Partellus