Brightness mediates oviposition in crepuscular moth, Grapholita molesta

Abstract

Plant colouration is known to be used by some nocturnal flower-visiting insects to foraging among colourful flowers in dim light. However, it remains unknown whether crepuscular species possibly reliably discriminate plant colouration (i.e. colour and/or brightness) for oviposition even driven by challenges of variably light conditions and similar leaf colouration. Here, we explored this question in the oriental fruit moth Grapholita molesta, a major pest of stone fruits worldwide, using coloured squares under changing illuminants (1000, 100, 1 and 0.01 mW/m 2 ). G. molesta female preferred to oviposit on green and orange over yellow, red, blue and purple with a lower discrimination at starlight (0.01 mW/m 2 ), whereas the preferential brighter white can be discriminated clearly from those achromatic grey and black at all tested light intensities. When both cues were presented in conflicting for oviposition, the moths were more attracted to brightness than colour cues irrespective of light intensity they are exposed to. Interestingly, there was a decrease in the reflectance between young and old leaves of P. persica at similar wavelengths between 500 and 550 nm, providing an apparent brightness. Ovipositing females preferred the brighter light green over the dark green. Our results indicate that as a more reliable cue, brightness of leaves rather than colour plays a more important role for mediating crepuscular moth G. molesta to lay eggs on young leaves in microhabitats in changing light environments. We discuss that the brightness oriented in oviposition task in complex orchards is relevant to leaf apparency.

Achromatic Cues Are Important for Flower Visibility to Hawkmoths and Other Insects

“…For several species-groups, however, it is still unknown which type of photoreceptor is most important for achromatic signal detection (Table 1). Presumably, the use of achromatic cues also plays a role in detecting oviposition sites for herbivorous insects (Prokopy et al, 1975;Blake et al, 2020;Yang et al, 2020).…”

Oviposition site selection in the crepuscular moth, Grapholita molesta: does light matter?

“…As such, gravid females can discriminate volatiles emitted from host plants from those of non‐host plants, from those of different host plant species, and even from plants of different developmental stages (Piñero & Dorn, 2009; Najar‐Rodriguez et al, 2013). When a female moth senses a plant species, the similar volatile chemicals released between sunny and shaded sites become less distinguishable, so visual rather than olfactory cues are believed to be more important in short‐range preference determination (Yang et al, 2020). In this study, G. molesta significantly preferred to lay eggs in the light even when exposed to dark conditions with attractive odor stimuli.…”

“…However, vision may be crucial for G. molesta females to discriminate potential oviposition sites within a plant species. A recent study has demonstrated that G. molesta can modify their oviposition behavior in response to brightness in dim light (Yang et al, 2020). However, whether or not the preference for sunny sites can be guided by light in dim or variable light conditions is unclear.…”

Baculoviruses hijack the visual perception of their caterpillar hosts to induce climbing behaviour thus promoting virus dispersal

“…One face of the apparatus was illuminated with white LED light (9 W, c. 500 lux) and the other five sides were left in darkness (Figure S1C). The spectrum of the LED light ranged from 400 to 700 nm (Yang et al, 2020). Experimental larvae (n = 3 replicates of 30 larvae each) were held in darkness for 30 min prior to testing and then placed in the central arena of the apparatus.…”