Sains Malaysiana 40(4)(2011): 311–316

In Vivo Production of Nosema bombycis Spores and their Efficacies against Diamondback Moth and Beet Armyworm Larvae in Laboratory Conditions

(Penghasilan Spora Nosema bombycis Secara In Vivo dan Keberkesanannya terhadap Larva Rama-rama Belakang Intan dan Ulat Ratus dalam Makmal)

Syarafina Ramli* & B.A.H. Zainal-Abidin

School of Biosciences and Biotechnology, Faculty of Science and Technology

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

A.B. Idris

School of Environmental Science and Natural Resources, Faculty of Science and Technology

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Diserahkana: 9 Disember 2009 / Diterima: 12 Ogos 2010

ABSTRACT

Diamondback moth (DBM), Plutella xylostella and beet armyworm (BAW), Spodoptera exigua are major insect pests of crucifer crops found worldwide. Since these pests are highly resistant to many chemical insecticides, using biological control agent(s) or biopesticides might be a good choice to overcome this problem. Nosema bombycis is a microsporidial pathogen with the potential to control insect pests. This study was aimed at producing N. bombycis spores in vivo and to test their efficacies against DBM and BAW in laboratory conditions. Production of this pathogen was carried out by feeding both DBM and BAW larval instars with artificial diet inoculated with viable spores of N. bombycis. Spore concentrations in the larvae were determined and accumulated. If a concentration of 1.56×10⁸ spores/mL was obtained, the production was continued. For laboratory efficacy tests, artificial diets with different spore concentrations namely 1×10⁴, 1×10⁵ and 1×10⁶ spores/μL were fed to different larval instar. Mortality rates were analysed using the Two-way ANOVA test. For both DBM and BAW, third instar showed the highest mean mortality rates and the mortality in each instars were significantly different (P<0.05). The concentration 1×10⁶ spores/μL caused the highest mean mortality rates and each concentration resulted in significantly different mortality (P<0.05). However, there was no interaction between both factors, where a combination of spore concentrations and instars did not show any significant differences (P>0.05). These results indicated that third instar larvae for both species and 1×10⁶ spores/μL treatments demonstrated the highest efficacy rates.

Keywords: Nosema bombycis; Plutella xylostella; Spodoptera exigua

ABSTRAK

Rama-rama belakang intan atau diamondback moth (DBM), Plutella xylostella dan ulat ratus atau beet armyworm (BAW), Spodoptera sp merupakan serangga perosak utama tanaman kubis di seluruh dunia. Masalah kerintangan serangga perosak ini terhadap insektisid kimia mendorong penggunaan biopestisid sebagai jalan penyelesaian. Nosema bombycis merupakan patogen mikrosporidia yang berpotensi untuk mengawal serangga perosak. Objektif kajian ini ialah menghasilkan spora Nosema bombycis secara in vivo dan mengkaji keberkesanannya mengawal DBM dan BAW dalam keadaan makmal. Bagi penghasilan spora, larva DBM dan BAW dijangkitkan dengan Nosema bombycis melalui diet buatan. Kepekatan spora dalam larva ditentukan dan hasil yang diperolehi adalah 1.56×10⁸ spora/mL, seterusnya penghasilan spora itu diteruskan. Keberkesanannya dalam makmal dikaji dengan menjangkitkan kepekatan spora yang berbeza, iaitu 1×10⁴, 1×10⁵ dan 1×10⁶ spora/μL kepada larva instar berbeza melalui diet buatan. Kadar mortaliti dianalisis menggunakan ujian ANOVA 2 Hala. Bagi kedua-dua DBM dan BAW, min kadar mortaliti yang tertinggi ditunjukkan oleh instar ketiga dan terdapat perbezaan kadar mortaliti yang beerti antara instar berlainan (P<0.05). Kepekatan 1×10⁶ spora/μL menyebabkan min kadar mortaliti yang tertinggi dan perbezaan beerti ditunjukkan pada kadar mortaliti kepekatan spora berbeza (P<0.05). Walau bagaimanapun, tiada interaksi antara kedua-dua faktor tersebut di mana gabungan kepekatan dan instar tidak menunjukkan perbezaan yang beerti (P>0.05). Hasil kajian tersebut menunjukkan instar ketiga kedua-dua spesies dan kepekatan spora 1×10⁶ spora/μL menyebabkan kadar keberkesanan yang paling tinggi.

Kata kunci: Nosema bombycis; Plutella xylostella; Spodoptera exigua

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*Pengarang untuk surat-menyurat; e-mail: eina_syara_fina@yahoo.com