Efficacy of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) against the striped flea beetle, Phyllotreta striolata

Abstract

The striped flea beetle, Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae), is an economically important pest on crucifer vegetables worldwide. Twenty isolates of entomopathogenic nematodes (EPNs) (Rhabditida: Steinernematidae and Heterorhabditidae) were evaluated against soil-dwelling stages of the flea beetle in the laboratory. The corrected mortalities and reproduction rates at a concentration of 36 infective juveniles (IJs) cm -2 surface area of sand against third instars of the pest greatly differed among the tested isolates, ranging from 6.7% to 100%. When tested over a range of temperatures from 15°C to 35°C, 25°C was found to be the optimal temperature for four selected nematode isolates (Steinernema carpocapsae All, Steinernema pakistanense 94-1, Heterorhabditis indica LN2 and H. indica 212-2) to infect the third instar and reproduce in the cadavers. S. pakistanense 94-1 and H. indica 212-2 showed markedly greater heat-tolerance compared to S. carpocapsae All and H. indica LN2. Corrected mortalities and reproduction rates increased as the concentration of IJs increased from 4 to 36 IJs cm -2 . The LC 50 values of S. carpocapsae All, S. pakistanense 94-1, H. indica LN2 and 212-2 were 17.1, 15.5, 6.5 and 5.9 IJs cm -2 , respectively. The third instars larvae and pupae of P. striolata were more susceptible to the four nematode isolates than the first and second instars. Higher pathogenicity and greater heat tolerance and reproduction potential makes H. indica 212-2 the most promising candidate for the biological control of P. striolata under the field conditions of South China.

Differential susceptibility of pine weevil, Hylobius abietis (Coleoptera: Curculionidae), larvae and pupae to entomopathogenic nematodes and death of adults infected as pupae

“…The susceptibility of Chrysomelidae is sometimes higher in the larval stage (Saleh et al 2009), sometimes in the pupal stage (Xu et al 2010) and which stage is more susceptible is sometimes dependent on temperature (Yang et al (2001) and Khatri-Chhetri et al (2011) found that pupae were more susceptible than larvae to EPN. Ramos-Rodríguez et al (2006) found EPN were less efficacious against pupae and adults than larvae of Tribolium castaneum.…”

Field evaluation of entomopathogenic nematodes for biological control of striped flea beetle, Phyllotreta striolata (Coleoptera: Chrysomelidae)

“…Although H. indica was expected to yield better control than S. carpocapsae in the field because of its reported higher virulence (lower LC 50 ) and higher activity (higher reproduction rate and good performance at different temperatures) against the younger larval instars of P. striolata in the laboratory (Xu et al 2010), no clear difference in efficacy was observed in the present field study. Although in the first experiment, less adult flea beetles emerged from soil treated with S. carpocapsae All than after treatment with H. indica LN2, no differences were noted in the second experiment.…”

“…Both S. carpocapsae and H. indica were also deemed to be promising biocontrol agents against P. striolata in laboratory screening experiments (Xu et al 2010). In the latter study, both EPNs caused over 80 % mortality of P. striolata third instars, with LC 50 -values of 17.1 and 6.5 IJs cm -2 , respectively, and were able to infect all soil-dwelling stages of the pest except for the first instars in the case of S. carpocapsae.…”

“…Damage caused by the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), was reduced when EPNs were applied during sowing of corn (Toepfer et al 2008). A prophylactic strategy could also be attempted to control the early larval stages of P. striolata by application of EPNs when early stages of the pest are present in the field as they proved susceptible to the nematodes (Xu et al 2010).…”

“…However, control was not always satisfactory in the field (Wei and Wang 1993). In order to select more effective nematode isolates for the biological control of the striped flea beetle, several EPN isolates, including local isolates from Southern China, were screened for their efficacy against the different instars of the pest at different temperatures and concentrations of infective juveniles (IJs) (Xu et al 2010). The findings from the latter laboratory study indicated that Steinernema carpocapsae Weiser and Heterorhabditis indica Poinar, Karunaka and David yielded more than 90 % larval mortality at 36 IJs cm -2 and affected both the larval and pupal stages of the striped flea beetle.…”