Effects of two pesticides, TZP and JGM, on reproduction of three planthopper species, Nilaparvata lugens Stål, Sogatella furcifera Horvath, and Laodelphax striatella Fallén.

Three planthopper species, the brown planthopper (BPH), Nilaparvata lugens Stål, the white-backed planthopper (WBPH), Sogatella furcifera Horvath, and the small brown planthopper (SBPH), Laodelphax striatella Fallén, often co-occur in rice grown regions of China. The present investigation examined effects of two pesticides, triazophos (TZP) and jinggangmycin (JGM) (a fungicide), on reproduction of BPH, WBPH, and SBPH. The results showed that TZP stimulated the fecundity of the three planthopper species. Interestingly, JGM stimulated the fecundity of BPH but suppressed the fecundity of WBPH. In addition, TZP and JGM had a significant effect on the preoviposition period (PVD), the oviposition period (OPD), and the longevity of adult females (LAF) of BPH and WBPH. Based on these findings, to avoid resurgence occurrence of planthoppers, we suggest that the application of TZP should be banned in rice fields, that JGM should be used to control rice sheath blight at the early growth stages of rice (with WBPH occurrence and without BPH occurrence).

Comparisons of topical and spray applications of two pesticides, triazophos and jinggangmycin, on the protein content in the ovaries and fat bodies of the brown planthopper Nilaparvata lugens Stål (Hemiptera:Delphacidae).

The pesticide-induced stimulation of reproduction in pests is one of the most important mechanisms of pest resurgence. There have been numerous reports on the insecticide-induced stimulation of reproduction. However, the relationship between pesticide application method and pest resurgence (stimulation of reproduction) has received little attention. Here, we studied the effect of two treatment methods, triazophos (TZP) and jinggangmycin (JGM), on the protein content in the ovaries and fat bodies of the brown planthopper (BPH) Nilaparvata lugens Stål. The results showed that pesticide treatment methods significantly affected the protein content in the ovaries and fat bodies of BPH. In addition, grand means (means of main effect) of the protein content at 2 and 3 days after emergence (2 and 3 DAE) for foliar sprays was significantly higher than that observed after topical treatments, which increased by 23.9% (from 1.42 to 1.76) and 8.82% (from 4.42 to 4.81), respectively. No significant differences on the protein content in the ovaries and fat bodies for the JGM topical treatment were observed compared with controls. However, the protein content for JGM foliar sprays was significantly higher than that for the controls. The protein contents in both topical and spray treatments of TZP were significantly higher than those of the controls. Ovarian protein is mainly yolk protein. There is a positive correlation between ovarian protein content and the number of eggs laid. These findings show that foliar spray of the pesticides promotes the resurgence of BPH. Therefore, the foliar spray of some pesticides, such as JGM, should be avoided for the control of pests, which is the sideeffects of the fungicide on non-target insect pests' occurrence.

Impact of Day Intervals on Sequential Infestations of the Rice Leaffolder Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae) and the White-Backed Rice Planthopper Sogatella furcifera (Horváth) on Rice Grain Damage.

The present study illustrates that different day intervals (DIs) between the sequential infestations of two pest species, the rice leaffolder (RLF) Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) and the white-backed rice planthopper (WBPH) Sogatella furcifera Horváth (Hemiptera: Delphacidae), have a significant impact on the rice yield loss rate (YLR) and on the carbohydrate contents of rice plants. For WBPH release after RLF release (WRARR), the YLR decreased with the increasing DIs, and the YLR at the 24 DI was significantly lower compared to that at the 6 and 12 DIs and had a minimum value for a simultaneous infestation of the two pest species (SITS). In contrast, for RLF release after WBPH release (RRAWR), the YLR at the 24 DI had a maximum value and was significantly higher compared to that at the 6 and 12 DIs and the SITS. These findings indicate that damaged rice plants gradually recover, with an increase in the DI for WRARR. The above results were demonstrated by biochemical tests. Therefore, the sequential infestation of the two pest species and their DIs should be considered for integrated pest management (IPM) and control strategies for rice pests.

Heat-dependent fecundity enhancement observed in Nilaparvata lugens (Hemiptera: Delphacidae) after treatment with triazophos.

The brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is a serious pest of rice crops in the temperate and tropical regions of Asia and Australia, and it is also a classic example of an insecticide-induced resurgent pest. Brown planthopper outbreaks have been reported to be closely associated with pesticide application. Previous studies have shown that the insecticide triazophos enhances thermal tolerance and fecundity in brown planthopper. However, the effects of triazophos and high temperature on reproductive capacity have not been studied in high temperature-conditioned reciprocal pairs of adult males and females. The present experiments showed that triazophos enhanced the reproductive capacity of brown planthopper under high temperature (34°C). The number of eggs laid by females treated with 40 ppm triazophos at 34°C approximately doubled compared with untreated insects. Furthermore, the triazophos-induced fecundity enhancement at 34°C was significantly greater than that at 26°C, and the number of eggs laid for mating pair of adult males at 34°C with adult females under 34°C (♂(34) × â™€(34)) were significantly greater than that of adult males at 26°C (♂(26) × â™€3(4)), suggesting that this insecticide enhances the resistance of brown planthopper to high-temperature stress. Insecticide-induced enhancement of reproductive capacity in brown planthopper under high temperatures should be of great concern, and it has important implications for forecasting future brown planthopper outbreaks as well as the pesticide-selection process.