Assessing the pathogenicity of gut bacteria associated with tobacco caterpillar Spodoptera litura (Fab.)

Abstract

The symbiotic relationship between insects and gut microbes contributes to their fitness by serving immense range of functions viz. nutrition and digestion, detoxification, communication and reproduction etc. However, this relationship between insect and gut microbes varies from mutualistic to pathogenic. Gut microbes become pathogenic when the healthy normal microbial composition is perturbed leading to the death of insect host. Spodoptera litura (Fab.) is a polyphagous pest that causes significant damage to many agricultural crops. The management of this pest primarily depends upon chemical insecticides which have resulted in development of resistance. Thus in search for alternative strategies, culturable gut bacteria isolated from S. litura were screened for insecticidal potential. Among these Serratia marcescens and Enterococcus mundtii induced higher larval mortality in S. litura. The mortality rate increased from 32 to 58% due to S. marcescens at concentrations ranging from 2.6 × 108 to 5.2 × 109 cfu/ml and 26 to 52% in case of E. mundtii due to increase in concentration from 4.6 × 108 to 6.1 × 109 cfu/ml. Both the bacteria negatively affected the development, nutritional physiology and reproductive potential of insect. The results indicated a change in gut microbial composition as well as damage to the gut epithelial membrane. Invasion of gut bacteria into the haemocoel led to septicaemia and ultimately death of host insect. In conclusion both these gut bacteria may serve as potential biocontrol agents against S. litura.

Effectiveness of Bacillus thuringiensis (Bt) application in controlling mortality of Spodoptera litura on rice plants (Oryza sativa L.)

“…This is indicated by LC50 values of 97.74 g and 70.32 g, respectively, while LC90, 147.60 g and 122.21 g, respectively, are suspected of causing test insects' death (Table 1). According to Zulfiana et al and Devi et al [6,24], B. thuringiensis given to S. litura larvae can cause mortality and increase mortality by 100% at 10 HSA doses of 30 g.mL -1. The mechanism of action of B. thuringiensis when entering the body of pests is to produce proteins that will interfere with/neutralize the digestive system of insects so that they cannot process food in the stomach.…”

Microbial Community Changes in Silkworms Suspected of Septicemia and Identification of Serratia sp.

“…Microbial community analysis is a powerful tool in disease research [20]. In a previous similar study of the intestinal microbial community of insects, numerous microorganisms were found to live in the intestines of healthy insects, with the balance disrupted under specific environmental conditions, resulting in disease onset [21,22]. According to Koch's postulates, microbial community analysis is used in disease diagnosis because the initial condition of a disease-causing pathogen is "dominant" [23].…”

Comparative genomics of pesticide-degradingEnterococcussymbionts ofSpodoptera frugiperda(Lepidoptera: Noctuidae) leads to the identification of two new species and the reappraisal of insect-associatedEnterococcusspecies

“…However, there are associations in which they were reported to establish pathogenic interactions with lepidopteran host larvae [32][33][34]. In Spodoptera, Enterococcus faecalis has been shown pathogenic to Spodoptera exigua [35], and Enterococcus mundtii [36] and Enterococcus cloacae [37] to Spodoptera litura.…”