Abstract
BackgroundUnder laboratory and greenhouse conditions, the virulence of 2 isolates of Thai indigenous entomopathogenic nematodes (EPNs) in controlling the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera; Noctuidae), was demonstrated. Six EPNs dosages were tested against 2 larval instars of FAW under the laboratory conditions, while 2 different concentrations were tested under the greenhouse conditions.ResultsThe results of a laboratory experiment revealed that 2 Thai indigenous EPNs isolates (Heterorhabditis indica isolate AUT 13.2 and Steinernema siamkayai isolate APL 12.3) were efficient against the FAW, 2nd and 5th larval instars. Six different nematode concentrations (50,100, 150, 200, 250 and 300 infectious juveniles (IJs) ml−1) were evaluated, and all were proven to be effective, with the mortality rate associated with concentration. Inoculated larvae in the 2nd instar was more vulnerable than that in the 5th instar. H. indica isolate AUT 13.2 was more destructive than S. siamkayai isolate APL 12.3. The greatest mortality rate of 2nd instar larvae was 83% when H. indica AUT 13.2 was applied at the concentration of 250 IJs ml−1, and 68% when the nematode S. siamkayai APL 12.3 was used at the concentration of 300 IJs ml−1. At 250 IJsml−1, the highest mortality rate of the 5th instar larvae was 45% for H. indica AUT 13.2 and 33% for S. siamkayai APL 12.3, respectively. To customize the concentration and volume of nematodes suspension evaluated in the greenhouse settings, the most sensitive stage of FAW and the optimum concentration that caused the highest mortality were used. The concentrations of both indigenous nematodes’ isolates were 20,000 and 50,000 IJsml−1 per pot, respectively, and the results showed that the mortality rates were lower than that in the laboratory. FAW mortality rate was the highest (58%) in case of the nematode H. indica isolate AUT 13.2, against (45%) in case of S. siamkayai isolate APL 12.3, at the 50,000 IJs ml−1 concentrations.ConclusionsThe study revealed the 2 Thai indigenous EPNs isolates (H. indica isolate AUT 13.2 and S. siamkayai isolate APL 12.3) were capable of controlling the FAW in both laboratory and greenhouse environments. The 2 Thai EPNs showed the potential to be considered as a biological control agent.
Highlights
Under laboratory and greenhouse conditions, the virulence of 2 isolates of Thai indigenous entomopathogenic nematodes (EPNs) in controlling the fall armyworm (FAW), Spodoptera frugiperda
After 48 h, death rate of the larvae was observed. It was influenced by the EPN isolates applied and the densities of Infective Juveniles (IJs) used
When using the highest concentration of 300 IJs m l−1, S. siamkayai isolate APL12.3 delivered the highest mortality percentage of 67.5%, which was non-significantly different from the density at 250 IJs ml−1
Summary
Under laboratory and greenhouse conditions, the virulence of 2 isolates of Thai indigenous entomopathogenic nematodes (EPNs) in controlling the fall armyworm (FAW), Spodoptera frugiperda The pest is causing considerable economic losses in Africa (De Groote et al 2020) This pest was first detected in Thailand in December 2018, in a few sub-districts of Kanchanaburi and Tak provinces in the west of the country, near the Myanmar border (IPPC 2018). This insect is a polyphagous pest that has been documented to impact over 353 plant species from 76 plant families (Montezano et al 2018). It burrows into the growing point (bud, whorl, etc.), leading "dead heart," wilting and death of the unfurled leaves (Day et al 2017)
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