The oriental fruit fly, Bactrocera dorsalis (Hendel), is a devastating pest of citrus fruits. After successful mating, adult females insert their eggs into the ripened fruit, resulting in moldy and rotten fruit and causing great economic losses for the citrus industry. In the field, flies initiate copulatory behaviors as twilight approaches, and decreasing light intensity in this period is the normal stimulus for copulation. In this study, ten light intensities ranging from 0–30 000 lux were set to identify the typical intensity that strongly regulates the copulation behavior of B. dorsalis. Three light intensities found to regulate the copulation behavior were then selected to verify their effects on adult male wing fanning and female chemotaxis towards 2,3,5-trimethylpyrazine (TMP). At last, strong light and complete darkness were artificially combined in the lab to verify whether they could prevent copulation to inform behavioral manipulation of oriental flies in the future. The results indicated that adult flies generally initiated copulatory behaviors at low light intensity (<1 000 lux). Stronger light significantly prevented copulation in proportion to intensity, with nearly no copulation events initiated when light intensity was above 20 000 lux. Both male wing fanning and female chemotaxis towards TMP were attenuated as light intensity became stronger. However, at 10 000 lux, males still fanned their wings to a certain extent while TMP completely lost its attractiveness to females. In the darkness, adults did not initiate any sexual behaviors, e.g., copulation, wing fanning, or chemotaxis to TMP. One hour of strong light (10 000 lux) combined with continuous darkness completely prevented mating. These results show that light condition is an essential factor for copulatory behaviors in the oriental fruit fly. Researchers could thus manipulate light conditions artificially or disrupt the molecular target in flies’ light transduction pathway to develop environmentally-friendly techniques to control this pest.
Compared with sole nitrate (NO3–) or sole ammonium (NH4+) supply, mixed nitrogen (N) supply may promote growth of maize seedlings. Previous study suggested that mixed N supply not only increased photosynthesis rate, but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization. However, whether this process depends on N absorption is unknown. Here, maize seedlings were grown hydroponically with three N forms (NO3– only, 75/25 NO3–/NH4+ and NH4+ only). The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO3– supply at 0–3 d, but was higher than under sole NO3– supply at 6–9 d. 15N influx rate under mixed N supply was greater than under sole NO3– or NH4+ supply at 6–9 d, although NO3– and NH4+ influx under mixed N supply were reduced compared to sole NO3– and NH4+ supply, respectively. qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO3– transporters in roots, such as ZmNRT1.1A, ZmNRT1.1B, ZmNRT1.1C, ZmNRT1.2 and ZmNRT1.3, or NH4+ absorption transporters, such as ZmAMT1.1A, especially the latter. Furthermore, plants had higher nitrate reductase (NR) glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO3– supply. The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth, especially for the reduction of NO3– by NR reductase. This research suggested that the increased processes of NO3– and NH4+ assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.
Super-absorbent polymers (SAPs) are widely used chemical water-saving materials, which play an active role in the accumulation of soil water and the improvement of soil structure. Little is known about their performance with repeated usage or about factors influencing their efficiency under alternate wetting and drying cycles. In this study, various concentrations of SAP (0, 0.1, 0.2 and 0.3%) in soil following three continuous wetting and drying cycles (T1, T2 and T3), were studied to determine effects on soil structure stability and hydro-physical properties. The results indicated that the SAP improved soil water supply capacity under conditions of mild drought (T2) and sufficient irrigation (T3) at concentrations of 0.2 and 0.3%, but a reduction was observed under severe drought conditions (T1), which was negatively correlated with the SAP concentration. The physical adsorption of the SAP by soil and the chemical connection between the SAP and soil mineral colloids as Si-O-Si bonds, -OH bonds and different crystalline silica were the important factors that directly lead to the reduction of water retention capacities of the SAP with alternating wet and dry conditions. Compared with the control, the soil liquid phase ratios of the SAP treatments were increased by 8.8–202.7% in the T1 and T2 cycles, which would have led to a decrease in the soil air phase ratios. After repeated wetting and drying cycles, the SAP treatments increased the amount of >0.25 mm soil aggregates and the contents of water-stable macro-aggregate (R0.25), and decreased the amount of <0.053 mm soil aggregates, especially with higher concentrations of the SAP. Increases in mean weight diameter (MWD) and geometric mean diameter (GMD), and declines in fractal dimension (D) and unstable aggregates index (ELT) were all observed with the SAP treatments, which indicated an improvement in soil stability and structure. It was concluded that the distribution and stability of soil aggregates and soil water supply capacity was closely related to SAP concentration, soil moisture condition and the interaction between the SAP and soil particles