Developmental stages of peach, plum, and apple fruit influence development and fecundity of Grapholita molesta (Lepidoptera: Tortricidae).

Host plant attributes are essential factors determining the population dynamics of herbivorous insects. The developmental stage of host plants, in particular, may affect the biology of Grapholita molesta (Busck), a possibility that has rarely been examined. Here we assessed the effect of developmental stage of plum, peach, and apple fruits on the development and fecundity performance of G. molesta, along with an examination of the firmness and sugar content of the fruits. Among the fruits collected earliest (May 31), plum and apple were better food sources for G. molesta compared to peach in terms of development, reproduction, and life table parameters. However, despite the higher sugar content in peach, G. molesta larvae showed a lower rate of fruit penetration in peach, probably due to fruit firmness. In the later-collected fruit (June 25), both peach and apple were better than plum, as peach and apple were softer and had higher sugar content. Nevertheless, the penetration rate of larva was still low in peach probably due to pubescence on the fruit surface. Although the plum fruits in the later collection date were softer with higher sugar content, there was a negative impact on the development and reproduction because fruits started to liquefy earlier. In conclusion, the developmental stage of fruits with changes in fruit firmness or sugar content affected the development and reproduction of G. molesta, and apple would be the best food source.

Development and fecundity performance of Grapholita molesta and Grapholita dimorpha (Lepidoptera: Tortricidae) on different immature fruits.

Both Grapholita molesta (Busck) and Grapholita dimorpha Komai (Lepidoptera: Tortricidae) are important pests of pome and stone fruits. Mature fruits of peach and plum have been tested as food sources for G. molesta, but no studies have examined the suitability of immature fruits, which are the fruit stage more likely to be available for the spring populations of both G. molesta and G. dimorpha. Thus, we evaluated immature fruits of peach, plum, and apple as food sources by assessing their effects on biological and behavioral attributes of these moths in the laboratory. Immature fruits were collected in May and June of 2016 and again in 2017. The first-instar larvae of G. molesta preferred either peach or plum, which showed exit rates of mature larvae of 81.0 and 100.0% for the two fruits, respectively. On peach, development time was shorter, and fecundity was lower than plum. However, G. dimorpha preferred plum and apple, showing the lowest fruit-boring rate and lowest mature larval exit rate on peach, from which only one female moth emerged but produced no eggs. In conclusion, it seems that at the immature fruit stage, plum and apple are better food sources for both G. molesta and G. dimorpha than is peach.

Extract of Nicotiana tabacum as a potential control agent of Grapholita molesta (Lepidoptera: Tortricidae).

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.