Information from the abstract
Background: The fall armyworm, S. frugiperda, is a globally threatening insect pest of agricultural crops, including in Thailand. Symbiotic bacteria in the genera Xenorhabdus and Photorhabdus, which are derived from entomopathogenic nematodes, can produce diverse bioactive compounds with insecticidal activities. However, no study on Thai isolates of these symbiotic bacteria against S. frugiperda has been reported, leading to a significant gap in local biopesticide development. Methods: Two symbiotic bacterial isolates, X. miraniensis (bMH16.1_TH) and P. akhurstii (bSBR11.1_TH), were isolated from Thai entomopathogenic nematodes and cultured in LB broth at 108 CFU/mL. Three bacterial fractions, i.e., whole-cell suspension, cell supernatant, and cell pellet, were prepared from each isolate. Insecticidal bioassays were conducted by topical application on second- and fifth-instar larvae of S. frugiperda (10 larvae × 5 replicates per treatment, CRD). Larval mortality was recorded daily for seven days, and median lethal time (LT50) was calculated. Data were analyzed by two-way ANOVA with Duncan’s Multiple Range Test (p < 0.05). Results: The results indicated that both bacterial isolates caused significantly higher larval mortality than controls across all treatments (p < 0.05). X. miraniensis (bMH16.1_TH) showed higher virulence, achieving ~80% mortality of second-instar larvae within 24 h and 100% by day three. Whole-cell suspensions consistently produced the fastest and highest mortality with the lowest LT50 values in both larval stages. Second-instar larvae were significantly more susceptible than fifth-instar larvae. The shortest LT50 was recorded in second-instar larvae treated with X. miraniensis supernatant at 0.616 days, while fifth-instar larvae generally showed higher LT50 values across all treatments. Conclusions: Our comparative study demonstrated that the insecticidal efficacy varied between the two symbiotic bacterial isolates and among their fractions. Whole-cell suspensions of X. miraniensis (bMH16.1_TH) produced the highest larval mortality and the smallest LT50 values, particularly against early-instar larvae. These findings demonstrated that local symbiotic bacteria are promising candidates to be developed as sources of biopesticides against this insect pest. In addition, characterizing active insecticidal compounds, evaluating field efficacy, and assessing safety to non-target organisms need to be further studied to support integration of these biopesticides in sustainable pest management programs.
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Related topics: Entomopathogenic Microorganisms in Pest Control · Insect symbiosis and bacterial influences · Insect Resistance and Genetics
Thai researcher and institutional participation
Wandee Wattanachaiyingcharoen · Aunchalee Thanwisai · Apichat Vitta · Patcharapun Wanitsumran · Supawan Pansri · Det Wattanachaiyingcharoen · Naresuan University
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