Efficacy Assessment of the Nematode Steinernema carpocapsae and the Bacterium Bacillus thuringiensis in Control of Elm Leaf Beetle, (Xanthogaleruca luteola) under Laboratory Conditions

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Article Type:
Research/Original Article (دارای رتبه معتبر)
Abstract:
Background and Objectives

Elm leaf beetle (ELB), Xanthogaleruca luteola (Chrysomelidae), is one of the most serious and destructive pests of elm which is mainly suppressed by chemical pesticides. Concerning the prevalence of elm trees in urban green spaces and chemical control of elm and the consequent urban environmental pollution and natural enemy suppression, safe and eco-friendly tactics like biological control should be substituted for chemical control. Research carried out on biological control of ELB has suggested entomopathogenic nematodes (EPNs) as suitable and favorable candidate for the control of ELB. Regarding ELB integrated pest management, the combined use of EPNs and the bacteria Bacillus thuringiensis has been recommended. In the current study, the effect of different concentrations of the native isolate of Steinernema carpocapsae and the bacteria B. thuringiensis subsp. galleriae (Btg) either individually or in combination on ELB 2nd instar larvae and adult mortalities was tested under laboratory conditions.

Materials and Methods

Field-collected adults and larvae of ELB were exposed to in vivo-reared S. carpocapsae at 400 and 500 IJs/ml through leaf-bioassay. The elm leaves were floated for 30 sec. in 5‰ or 10‰ suspensions of Btg and air-dried before the assays. A replicate of either twenty 2nd instar larvae or twenty adults was introduced into small polystyrene boxes containing the treated leaves. The combination assays included these treatments: (a) S. carpocapsae 400 IJs/ml + Btg 5‰ (b) S. carpocapsae 500 IJs/ml + Btg 5‰ (c) S. carpocapsae 400 IJs/ml + Btg 10‰ (d) S. carpocapsae 500 IJs/ml + Btg 10‰. The corrected mortality rates were calculated by Abbott’s formula. Data were analyzed using General Linear Model, ANOVA in IBM SPSS and compared by Duncan’s test. Interaction between the nematode and bacterium was quantified through the formula of Robertson and Preisler.

Results

Pathogenicity of the native isolate of S. carpocapsae and Btg on 2nd instar larvae and adults of ELB was verified and mortalities, in general, were recorded in the range of 51.87-88.33%. Both the nematode- and bacteria-infected larvae and adults showed different pre- and post-mortem symptoms and signs. The results showed that there was no significant difference between the incurred mortalities of the studied nematodes and bacteria within each stage group of ELB except for one treatment (df=11, P<0.05). ELB larvae were more susceptible to the nematode and the bacteria in most treatments compared with the adults. Interaction between the tested bacterium and nematode was additive at all concentrations, and neither synergistic nor antagonistic effect was observed in the combined use of S. carpocapsae and Btg.

Discussion

Considering the higher susceptibility of ELB larvae to the studied nematode and bacterium compared with adults, their field application is recommended at the larval stages of ELB. The additive effect of B. thuringiensis and S. carpocapsae facilitates their combined use against ELB. Either of these entomopathogens could be simultaneously used as effective and safe management tools in the context of integrated pest management of ELB larvae.

Language:
Persian
Published:
Journal of Plant Protection, Volume:46 Issue: 1, 2023
Pages:
25 to 37
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