Physiological and Population Responses of Nilaparvata lugens after Feeding on Drought-Stressed Rice

Abstract

Drought stress greatly impacts insect development and population growth. Some studies have demonstrated increased reproductive capacity in drought-stressed insects; however, physiological changes in the brown planthopper (BPH), Nilaparvata lugens (Stål), during periods of drought are unclear. In this study, BPH fed on drought- stressed rice had lower population numbers than BPH feeding on non-stressed rice. Water content, osmotic pressure of hemolymph and total amino acid content of BPH were significantly lower when BPH fed on drought-stressed rice compared to the non-stressed control; however, glucose content and glutathione S-transferase (GST) activity were significantly higher in BPH fed on drought-stressed rice. The expression of Vitellogenin and Exuperantia in BPH fed on drought-stressed rice was higher than that in BPH feeding on non-stressed control plants. The size of myofibrils and the abundance of mitochondria in BPH flight muscles were significantly lower in BPH fed on drought-stressed rice compared to non-stressed plants. These results indicate that water management impacts the physiology of BPH, which may be useful in understanding the relationship between drought stress and this damaging herbivore.

Keywords: Nilaparvata lugens; biochemistry; drought stress; physiology; rice; ultrastructure of flight muscles.

Figure 1

Population changes in BPH fed on drought-stressed and non-stressed (control) rice plants for 7, 11, 15, 19, and 23 days. Data are expressed as means ± SE. * represents significant differences between drought-stressed and control treatments (PLSD test, p < 0.05).

Figure 2

Relative expression of NlVg, NlVas, NlMag and NlExu in female BPH after feeding on drought-stressed and non-stressed rice. Data represent means ± SE. * represents significant differences in relative expression (PLSD test, p < 0.05).

Figure 3

Morphology and ovary development in BPH fed on drought-stressed and non-stressed (control) rice. Panels (A,a) show morphology and ovary development in BPH feeding on non-stressed, control rice. Panels (B,b) show morphology and ovary development in BPH feeding on drought-stressed rice. (A,B) Body size was photographed with a Leica DMR connected to a Fuji FinePix S2 Pro digital camera (Wetzlar, Hesse-Darmstadt, Germany). Scale bar, 1 mm. (a,b) reproductive tracts from mated females; scale bar, 200 μm. Body size and ovaries from at least ten females were dissected and observed for each group.

Figure 4

Physiological and biochemical changes in BPH fed on drought-stressed and non-stressed rice for 23 days. Changes in (A) water content, (B) osmotic pressure of hemolymph, (C) glucose content, (D) total amino acid content, and (E) GST activity. Data indicate means ± SE. * represents significant difference between drought-stressed and non-stressed BPH at p < 0.05 (PLSD test).

Figure 5

Longitudinal and cross-sectional views of flight muscles in BPH adult females fed on drought-stressed and non-stressed rice. Longitudinal section of flight muscles in (A) non-stressed female adults and (B) drought-stressed female adults (×6270). Cross-sectional view of flight muscles in (C) non-stressed female adults and (D) drought-stressed female adults (×12,500). Abbreviations: MF—myofibril; Mt—mitochondria.

Figure 6

Changes in flight muscles of BPH adult females fed on drought-stressed and non-stressed rice: (A) sarcomere length; (B) percentage of mitochondrial volume in flight muscle fibers; (C) changes in the diameter of myofibrils; and (D) changes in the cross-sectional area of myofibrils. * represents significant differences at p < 0.05 (PLSD test).