Toxicity of Bacillus thuringiensis Berl. KJ3P1 and DLM isolates towards pest of oil palm Oryctes rhinoceros [Coleoptera: Scarabaeidae]

Abstract

Oil palm plants are industrial plants that generate foreign exchange for Indonesia. Some obstacles are leading to production decrease. One of the important pests is Oryctes rhinoceros [Coleoptera: Scarabaeidae]. Both larval and imago stadia attack oil-palm in immature plants [IP] and mature plants [MP]. The method of controlling Oryctes often use chemical insecticides, in which continuously applications will cause residues in the environment and mortality of non-target insects. Therefore it is necessary to find an environmentally friendly control method that is easy, inexpensive and safe for the environment. The use of entomopathogenic bacteria Bacillus thuringiensis is an alternative. The study was aimed to study the toxicity of two B. thuringiensis isolates from the collection of Plant Protection Department, Faculty of Agriculture, Sriwijaya University [KJ3P1 and DLM isolate codes] on mortality of 3rd instar Oryctes larvae. Experiments were conducted at the Entomological Laboratory, Department of Plant Protection, Faculty of Agriculture, Sriwijaya University from March until May 2019. Bioinsecticide-based B. thuringiensis was made with 2 types of growth media, namely: 1] cow's bio-urine enriched with 5% molasses, and 2]. Rice washing water enriched with 5% molasses. Treatments were included: 1] DLM5 isolate, 2] KJ3P1 isolate, 3] commercial B. thuringiensis and 4]. without treatment [as control]. The test insects used were 25 individuals of 1st instar Oryctes larvae in each treatment. The results showed KJ3PI isolate that propagated in bio-urine media showed the highest production of B. thuringiensis [5.69 x 106 spores/ml], the highest mortality [76% ] and the lowest LT50 value [5.28 days] as well. The use of agricultural and livestock waste as a medium to multiply B. thuringiensis bacteria may produce high cell and spore production and can be used as bioinsecticides to control O. rhinoceros.