Abstract
Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is an important pest of stone and pome fruits. Growers usually depend on chemical insecticides to control this pest, but demand for more environmentally-friendly means of controlling pests is increasing. At least 91 plant extracts have been reported to be effective against other lepidopterans, but their acute toxicity against G. molesta has rarely been studied. Among these 91 materials, we assessed the residual toxicity of 32 extracts against first instar larvae (< 5 h old) of G. molesta in the laboratory. Nicotiana tabacum L., used at the concentration of 2 mg/ml, showed the highest corrected mortality (92.0%) with a lethal time (LT50) value of 12.9 h. The extract was followed in its efficacy by Allium sativum L. (88.0%), Zanthoxylum piperitum (L.) De Candolle (70.0%), and Sapindus mukorossi Gaertner (65.0%), when mortality was assessed at 20 h after exposure. Against adult fruit moths (< 5 d old), N. tabacum also showed the highest corrected mortality among tested extracts, being 85 and 100% in adult females and males, respectively, at 168 h after exposure. However, there was no synergistic effect of the combined application of any of the top four extracts in either laboratory or greenhouse assays. Oviposition by G. molesta on peach twigs was reduced 85–90% when N. tabacum was applied at 4 ml/ twig compared to control (methanol), demonstrating that N. tabacum may have potential for use as a botanical insecticide against G. molesta.
Highlights
Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is a serious pest of fruit trees in the temperate regions, worldwide [1,2,3,4]
Among the 32 plant extracts tested, Nicotiana tabacum L., Allium sativum L., and Zanthoxylum piperitum (L.) De Candolle showed the highest mortality on first instar larva (Table 3)
The LT50 value of Sapindus mukorossi Gaertner was 17.5 h (χ2 = 10.04, df = 5, P = 0.074), which was significantly higher than N. tabacum or A. sativum
Summary
Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is a serious pest of fruit trees in the temperate regions, worldwide [1,2,3,4]. Effect of plant extract on Grapholita molesta resistance is a serious threat to the fruit industry [6], and G. molesta has developed resistance to 14 insecticides including 10 organophosphates [8]. As many of these insecticides are neurotoxins, they have some potential to be harmful to non-target organisms, including people and domestic animals [4]. To avoid such risks, new pest management tactics need to be developed for the management of G. molesta. Due to their less residual toxicity, lower development cost, and general safety to people, plant extracts have the potential to be effective alternatives for control of pest insects [9]
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