Insecticidal activity and cuticle degrading enzymes of entomopathogenic fungi against Plutella xylostella (Lepidoptera: Plutellidae)

• Main Authors: Chui-Chai N., Krutmuang P., Nalumpang S., Mekchay S., Khanongnuch C., Chanbang Y.
• Format: Article
• Published: Chiang Mai University 2015
• Subjects: Multidisciplinary
• Online Access: http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=84872226353&origin=inward; http://cmuir.cmu.ac.th/handle/6653943832/38034
• Institution: Chiang Mai University

Fourteen isolates of Beauveria spp. and eleven isolates of Metarhizium spp., entomopathogenic fungi, were selected to screen for entomopathogenic efficiency to control 2nd instar larvae of diamondback moth, Plutella xylostella. The median lethal times (LT50) were estimated at 108 conidia ml-1 concentration and revealed to be distinguishable into two groups. A first group comprised the 5 higher efficacy isolates (BCC4810, BCC4849, BCC17599, Bb.5335 and Bb.2637) with a LT50 ranging from ca. 25 to 35 h, while the second group comprised the 5 lower efficacy isolates (BCC1707, BCC1858, BCC12636, BCC14841 and BCC22353) with a LT50 ranging from ca. 73 to 145 h. The highest efficacy of Beauveria sp. and Metarhizium sp. were Bb.5335 and BCC4849 with the 96-h lethal concentration (LC50) of 2.66×106 and 3.11×105 conidia ml-1, respectively. All isolates were preliminary investigated for chitinase production on 15% (w/v) colloidal chitin agar. Eight of ten isolates were positive and the highest clear zone was detected in BCC17599, while 2 isolates, BCC14841 and Bb.2637, were negative. In addition chitinase production in liquid culture showed that Bb.5335 was the greatest chitinase activity at the 11-day cultivation. Further study revealed that all 8 positive isolates produced protease since 1 day of cultivation and chitinase activity tended to rise up after the highest protease activity. Moreover, chitinase and protease activities were associated with the insecticidal activities. Metarhizium isolates showed higher insecticidal efficacy and hydrolytic enzyme activities than in Beauveria isolates. We suggested that the insecticidal effects of entomopathogenic fungi could be associated with cuticle hydrolytic enzyme activity.