Shifting Nicotiana attenuata's diurnal rhythm does not alter its resistance to the specialist herbivore Manduca sexta

Arabidopsis thaliana plants are less resistant to attack by the generalist lepidopteran herbivore Trichoplusia ni when plants and herbivores are entrained to opposite, versus identical diurnal cycles and tested under constant conditions. This effect is associated with circadian fluctuations in levels of jasmonic acid, the transcription factor MYC2, and glucosinolate contents in leaves. We tested whether a similar effect could be observed in a different plant-herbivore system： the wild tobacco Nicotiana attenuata and its co-evolved specialist herbivore, Manduca sexta. We measured larval growth on plants under both constant and diurnal conditions following identical or opposite entrainment, profiled the metabolome of attacked leaf tissue, quantified specific metabolites known to reduce M. sexta growth, and monitored A/I. sexta feeding activity under all experimental conditions. Entrainment did not consistently affect NI. sexta growth or plant defense induction. However, both were reduced under constant dark conditions,as was M. sexta feeding activity. Our data indicate that the response induced by NI. sexta in N. attenuata is robust to diurnal cues and independent of plant or herbivore entrain- ment. We propose that while the patterns of constitutive or general damage-induced defense may undergo circadian fluctuation, the orchestration of specific induced responses is more complex.

Sex ratio of mirid populations shifts in response to hostplant co-infestation or altered cytokinin signaling

Herbivore species sharing a host plant often compete. In this study, we show that host plant-mediated interaction between two insect herbivores-a generalist and a specialist-results in a sex ratio shift of the specialist＇s offspring. We studied demographic parameters of the specialist Tupiocoris notatus（Hemiptera： Miridae）when co-infesting the host plant Nicotiana attenuata（Solanaceae） with the generalist leafhopper Empoasca sp.（Hemiptera： Cicadellidae）. We show that the usually female-biased sex ratio of T. notatus shifts toward a higher male proportion in the offspring on plants coinfested by Empoasca sp. This sex ratio change did not occur after oviposition, nor is it due differential mortality of female and male nymphs. Based on pyrosequencing and PCR of bacterial 16 S rRNA amplicons, we concluded that sex ratio shifts were unlikely to be due to infection with Wolbachia or other known sex ratio-distorting endosymbionts. Finally, we used transgenic lines of N.attenuata to evaluate if the sex ratio shift could be mediated by changes in general or specialized host plant metabolites. We found that the sex ratio shift occurred on plants deficient in two cytokinin receptors（irCHK2/3）.Thus, cytokinin-regulated traits can alter the offspring sex ratio of the specialist T.notatus.