Visual cues of oviposition sites and spectral sensitivity of Cydia strobilella L

Fine Structure of the Visual System of Arge similis (Hymenoptera, Argidae)

External morphology and ultrastructure of the visual system of Arge similis (Vollenhoven, 1860) adults were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Each compound eye contains 2022 ± 89 (mean ± SE) facets in males and 2223 ± 52 facets in females. Arge similis has an apposition kind of compound eye composed of a cornea, a crystalline cone of four cone cells, and a centrally fused rhabdom made up of the rhabdomeres of eight large retinular cells. Each crystalline cone is surrounded by primary and secondary pigment cells with black spherical screening pigment granules measuring 0.60 ± 0.02 and 0.41 ± 0.01 μm in diameter, respectively. Based on our findings, the compound eye of A. similis can be expected to exhibit high adaptability to light intensity changes.

Foliage Intensity is an Important Cue of Habitat Location for Empoasca onukii

For many herbivorous insects, vision is more important than olfaction in the prealighting stage of host habitat location. Tea leafhoppers, Empoasca onukii (Hemiptera, Cicadellidae), are serious pests that preferentially inhabit the tender leaves of tea plants across China. Here, we investigated whether tea leafhoppers could distinguish foliage colors associated with different leaf ages and use this visual cue to guide suitable habitat location from short distances. Similar to honeybees, the adult E. onukii has an apposition type of compound eye, and each ommatidium has eight retinular cells, in which three spectral types of photoreceptors are distributed, with peak sensitivities at 356 nm (ultraviolet), 435 nm (blue), and 542 nm (green). Both changes in spectral intensity and hue of reflectance light of the host foliage were correlated with varying leaf age, and the intensity linearly decreased with increasing leaf age. Behavioral responses also showed that adult E. onukii could discriminate between the simulated colors of host foliage at different leaf ages without olfactory stimuli and selected the bright colors that strongly corresponded to those of tender leaves. The results suggest that, compared with the spectral composition (hue), the intensity of light reflectance from leaves at different ages is more important for adult leafhoppers when discriminating host foliage and could guide them to tender leaves at the top of tea shoots.

Do Grapholita funebrana Infestation Rely on Specific Plum Fruit Features?

The effective control of the plum fruit moth, Grapholita funebrana (Lepidoptera: Tortricidae) still represents a difficult challenge for organic plum farming. Little information is available on the susceptibility of plum cultivars to this moth pest. We investigated the roles of several fruit parameters (i.e., shape, volume, hardness, fruit colour, and physiochemical properties) on the susceptibility of four different plum cultivars (Angeleno, Friar, President and Stanley) to G. funebrana attack. Field data demonstrated the importance of some fruit parameters (i.e., elongation index, sugar degree, titratable acidity, cover colour percentage) on susceptibility to G. funebrana infestation. Under laboratory conditions, colour and shape had a significant role in determining the time spent on false fruits, i.e., female moths preferred yellow and rounded fruits over elongated red or green fruits. Angeleno (yellow and rounded fruits) and Stanley (green and elongated fruits) were the most and least susceptible cultivars, respectively. Overall, this study adds useful knowledge about plum cultivar susceptibility to G. funebrana. Information reported here may be useful to improve integrated pest management strategies both in conventional and organic orchards because the use of less susceptible cultivars may reduce insecticidal treatments, limiting the development of resistance in target insects and the harmful side effects on beneficial species.