Abstract
Voracious feeding, trans-continental migration and insecticide resistance make Spodoptera litura among the most difficult Asian agricultural pests to control. Larvae exhibit strong circadian behavior, feeding actively at night and hiding in soil during daytime. The daily pattern of larval metabolism was reversed, with higher transcription levels of genes for digestion (amylase, protease, lipase) and detoxification (CYP450s, GSTs, COEs) in daytime than at night. To investigate the control of these processes, we annotated nine essential clock genes and analyzed their transcription patterns, followed by functional analysis of their coupling using siRNA knockdown of interlocked negative feedback system core and repressor genes (SlituClk, SlituBmal1 and SlituCwo). Based on phase relationships and overexpression in cultured cells the controlling mechanism seems to involve direct coupling of the circadian processes to E-boxes in responding promoters. Additional manipulations involving exposure to the neonicotinoid imidacloprid suggested that insecticide application must be based on chronotoxicological considerations for optimal effectiveness.
Highlights
Voracious feeding, trans-continental migration and insecticide resistance make Spodoptera litura among the most difficult Asian agricultural pests to control
S. litura last instar larvae exhibited a daily rhythm in locomotion and feeding during days 1–3 under LD (12 h light: 12 h dark) with the acrophase at midnight, ZT 18, and the trough at ZT 6 (Fig. 1a, b, Supplementary Data 4)
To provide a more convincing demonstration of a circadian fluctuation in the expression of SlituClk, SlituBmal[1], SlituPer, SlituTim, and SlituCwo, we extended the time for continuously checking the transcript levels in the brain under LD and DD conditions to 72 h at 3 h intervals (Fig. 3, Supplementary Data 1, 2)
Summary
Trans-continental migration and insecticide resistance make Spodoptera litura among the most difficult Asian agricultural pests to control. 1234567890():,; Spodoptera litura belongs to the family Noctuidae, sonamed because larvae feed and adults fly at night This insect is called “night thief” in Japan, because the voracious feeding of the late instar larvae is intense at night, while, in contrast, they cryptically hide in the soil during the day. This species is highly polyphagous, ranging over 120 host plants (https://www.cabi.org/isc/datasheet/44520). The feeding and digestion of another congener, S. littoralis, are reported to be linked with circadian rhythms[15], as are larval activity and feeding in Heliothis virescens, another noctuid pest[16] This may be a common feature with S. litura, which exhibits similar circadian processes. Whether the circadian network mechanism is shared in effecting downstream larval behavioral rhythms or insect adaptation to various host plants and related circumstances remains unknown
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