Larva Crocidolomia binotalis adalah serangga hama penting pada tanaman kubis yang dapat merusak krop kubis sehingga dapat menurunkan hasil panen. Pengendalian C. binotalis menggunakan mikrobia telah dikembangkan untuk menggantikan peran insektisida kimia sintetik. Pada larva C. binotalis mati yang ditemukan saat pemeliharaan di Laboratorium Entomologi, Fakultas Biologi, UGM, diduga terdapat bakteri patogen yang berpotensi sebagai agensia pengendali hayati. Oleh sebab itu, perlu dilakukan proses skrining, isolasi, dan uji patogenisitas bakteri untuk mendapatkan agensia pengendali alternatif terhadap C. binotalis. Skrining, isolasi bakteri, dan pengujian bakteri patogen terhadap larva C. binotalis instar kedua dan ketiga dilakukan di Laboratorium Entomologi, Fakultas Biologi, UGM pada bulan Agustus 2013 – Mei 2014. Pengujian dilakukan secara acak lengkap dengan empat seri konsentrasi dan tiga kali pengujian menggunakan metode pencelupan daun. Jumlah kematian larva diamati selama 72 jam setelah perlakuan. Data mortalitas yang diperoleh dianalisis secara statistik menggunakan ANOVA dan DMRT. Nilai LC50 dan LC95 diperoleh dengan menggunakan Analisis Probit. Hasil penelitian menunjukkan bahwa diperoleh dua isolat bakteri yang bersifat patogen terhadap larva C. binotalis instar kedua dan ketiga, yaitu isolat SmLIIIR dan SmMI1. Kedua isolat bersifat lebih patogen terhadap larva C. binotalis instar ketiga daripada instar kedua dengan nilai LC50 berturut-turut sebesar 7,32x104 sel/ml dan 3,58x105 sel/ml sedangkan LC95 berturut-turut sebesar 1,02x109 sel/ml dan 7,20x1016 sel/ml.

Crocidolomia binotalis larvae is important insect pests on cabbage plants that can damage the crop of cabbage resulting reduce crop yields. Controlling of C. binotalis larvae using microbial agent have been developed to replace synthetic chemical insecticides. In C. binotalis dead larvae were found during rearing maintenance at the Entomology Laboratory, Faculty of Biology, Gadjah Mada University, allegedly use were contained potentially pathogenic bacteria for insect. Therefore, it is necessary to screening, isolation, and doing pathogenicity test to obtain an alternative control agents against C. binotalis. The use of second and third instar larvae of C. binotalis were done in Entomology Laboratory, Faculty of Biology, Gadjah Mada University in August 2013 - May 2014. The method was done using completely randomized design with four concentration series and three replication. The method used for pathogenicity test was leaf deep method. The mortality of tested larvae was observed for 72 hours after treatment. The mortality data obtained was analyzed statistically by using ANOVA and DMRT. The lethal concentration of 50% death larvae (LC50) and 95% death larvae (LC95) were analyzed by using Probit analysis. The results showed that the two isolates bacteria obtained are pathogenic to the second and third instar larvae of C. binotalis, were isolates SmLIIIR and SmMI1. Both isolates were more pathogenic against third instar larvae of C. binotalis than second instar larvae with the value of LC50 respectively were 7,32 x104 cells/ml and 3,58 x105 cells/ml, while the value of LC95 respectively were 1,02 x 109 cells/ml and 7,20x1016 cells/ml.

Kata Kunci : patogenisitas, Crocidolomia binotalis, bakteri patogen