Fig 1.
A phototaxis switch of the wandering larvae.
A two-choice test in laboratory. Light avoidance indexes (LAI) were assessed for second-instar (SI), third-instar (TI) and foraging fourth-instar (FI) larvae (D1-D4 indicates day 1 to day 4 after ecdysis) at an interval of a half day, and from 4.0 to 6.0 days at an interval of six hours.
Fig 2.
Involvement of JH signal in control of phototaxis switch.
20E pulse was prematurely generated by feeding of 20E (A); 20E signal was reduced by knockdown of an ecdysteroidogenesis gene SHD (B), the 20E receptor gene EcR (C), and a signaling gene HR3 (D). ILP signal was inhibited by silencing of ILP2 (E). JH titer was increased by feeding of JH (F), knockdown of AS-C, JHEH1 and JHDK (G); JH pathway was repressed by silencing of JHAMT and Met (H). Larvae having ingested PBS (CK) and dsegfp were set as blank and negative controls. Light avoidance indexes (LAI) were calculated at each testing time point from 72 to 138 hours after ecdysis. Significant differences between blank control (CK) and treatments at each tested time point are indicated by different letters (P < 0.05).
Fig 3.
PTTH signal promotes light avoidance of the wandering larvae.
PBS (CK), dsegfp, dsPTTH, 20E and dsPTTH+20E were dietarily introduced to the larvae. LdPTTH mRNA level (three repeats) (A), light avoidance index (LAI) (D), rate of larvae that had buried in soil per day (RLB) (E), and accumulated RBP (ARLB) (F) were determined at each testing time point demonstrating in Fig. LdPHM mRNA level and 20E titer (B) were tested at day 1 of the fourth-instar larvae. Pupation rate (C), rate of pupae at the soil surface (RPS) (G, H), average depths from pupation site to soil surface (DS) (I), and rate of pupae that had constructed pupation chambers (RPC) (J) were measured at the end of the experiment (P<0.05). Significant differences between blank control larvae (CK) and treatments are indicated by different letters (P<0.05).
Fig 4.
Disturbance of both PTTH and JH signals causes no additive effects on light avoidance.
The larvae have fed on dsegfp, dsegfp+JH, dsPTTH, dsPTTH+JH and dsPTTH+JH+20E; dsegfp, dsegfp+dsAS-C, dsPTTH, dsPTTH+ dsAS-C and dsPTTH+dsAS-C+20E; dsegfp, dsegfp+dsJHAMT, dsPTTH, dsPTTH+dsJHAMT and dsPTTH+ dsJHAMT+20E; or dsegfp, dsegfp+dsMet, dsPTTH, dsPTTH+dsMet and dsPTTH+ dsMet+20E for three days. Significant differences in light avoidance index (LAI) (A-D), accumulated rate of larvae that had buried in soil (ARLB) (E-H) at each testing time point, rate of pupae on the soil (RPS) (I-L) through a two-week experiment period to those in control (dsegfp-fed) were indicated by different letters (P < 0.05).
Fig 5.
PTTH signal affects photo transduction to promote light sensing.
Dsegfp+20E, dsPTTH+20E, dsTrpA1+20E and dsPTTH+dsTrpA1+20E were dietarily introduced to the larvae. Significant differences in transcript abundance of LdPTTH and LdTrpA1 (A), light avoidance index (LAI) (B), accumulated rate of larvae that had buried in soil (ARLB) (C) at each testing time point, and rates of pupae on the soil (RPS) (D) through a two-week experiment period to those in control (dsegfp+20E-fed) were indicated by different letters (P<0.05). (E) A model depicting the hormonal cascade regulating the light avoidance of the wandering larvae (see text for details).