Sublethal concentrations of pymetrozine reduce Sogatella furcifera transmission of Southern rice black-streaked dwarf virus

A tyramine receptor gene LsTAR2 is involved in reproduction and feeding in the small brown planthopper Laodelphax striatellus

Tyramine (TA) is an important biogenic amine present in the central nervous system of insects, and mediates a variety of physiological and behavioral functions via tyramine receptors (TARs). However, TARs have not yet been characterized in planthoppers, and their physiological functions remain poorly understood in rice pests. Here, we cloned a tyramine receptor gene (LsTAR2) from the small brown planthopper Laodelphax striatellus, one of the most destructive rice pests. LsTAR2 shares high sequence identity with its orthologous receptors, and is closely related to its corresponding receptor groups. LsTAR2 transcript was expressed mostly in the egg stage and brain. RNAi-mediated knockdown of LsTAR2 significantly prolonged the preoviposition period and decreased the fecundity in females. Furthermore, LsTAR2 knockdown reduced the expression levels of vitellogenin (LsVg) in the fat body and ovary of L. striatellus, and changed the expressions of juvenile hormone (JH) and 20-hydroxyecdysone (20E) pathway genes. In addition, LsTAR2 knockdown significantly decreased the honeydew excretion of the adults, and affected the transcript levels of feeding-related neuropeptide signaling genes. These results provide critical information concerning the role of LsTAR2 in reproduction and feeding behavior in L. striatellus, and open the way for further investigations into novel strategies targeting TARs for pest control.

EPG Reveals Dinotefuran's Efficiency in Suppressing the Feeding Behavior of Frankliniella occidentalis on Kidney Bean Leaves

Western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is one of the serious damage pests on agricultural production globally. Dinotefuran is an effective insecticide to control this pest. This study compared the feeding behavior and feeding area of F. occidentalis on the kidney bean leaves under four treatments: F. occidentalis, whether treated with dinotefuran (DWFT) or untreated (CWFT), each fed on kidney bean leaves that were either treated with dinotefuran (DP) or untreated with dinotefuran (CP). (labeled as: DWFT-DP, CWFT-DP, DWFT-CP, and CWFT-CP (control), respectively). After 72 h, the LC50 and LC25 of dinotefuran against F. occidentalis were 39.018 mg L-1 and 20.441 mg L-1, respectively. The total number of probes, total time probing, the number and duration of noningestion probes and short-ingestion probes were significantly lower in DWFT-DP and CWFT-DP compared with the control, while the total duration of non-probing significantly increased, and a significant reduction in the number and total duration of long-ingestion probes was observed only in DWFT-DP. In contrast, there were few significant changes in the feeding behavior of F. occidentalis in DWFT-CP compared to control, with minimal effect on these electrical penetration graph parameters. Moreover, the feeding area of F. occidentalis decreased significantly by 39.20% and 48.58% in CWFT-DP and DWFT-DP than that in control, respectively. This study indicates that F. occidentalis feed on kidney bean leaves treated by sublethal concentrations of dinotefuran, and that their feeding behavior, ingestion, and feeding scars are impaired, and the effects are stronger in treated thrips than untreated ones.

Functional characterization of β-adrenergic-like octopamine receptors in planthopper reproduction and feeding

As an essential biogenic amine in invertebrates, octopamine (OA) regulates multiple physiological and behavioral processes via binding to octopamine receptors (OARs). The small brown planthopper Laodelphax striatellus is an important agricultural pest. However, little is known about OARs in L. striatellus. Herein, three β-adrenergic-like OARs (LsOA2s) were cloned, including LsOA2B1, LsOA2B2, and LsOA2B3. LsOA2s were expressed at the highest levels in egg stage and brain. Knockdown of LsOA2s significantly decreased the transcript levels of vitellogenin (LsVg) and Vg receptor (LsVgR), and reduced LsVg protein levels. LsOA2B2 knockdown shortened the oviposition period and inhibited the fecundity, while silencing LsOA2B1 and LsOA2B3 did not affect the reproduction performance including the preoviposition period, oviposition period, and fecundity. Ovary dissection indicated that LsOA2B2 knockdown decreased the ovary area and detained eggs. In addition, LsOA2s silencing prolonged the hatching period and reduced the hatching rate, and shortened the egg length on the fifth day of development. LsOA2B2 silencing also reduced egg width. Furthermore, LsOA2s knockdown decreased honeydew excretions of adults. Overall, these results provide evidence that LsOA2s play important roles in the reproduction and feeding behaviors of L. striatellus, and offer a reference for the exploration of potential molecular targets to control planthoppers.

Rice varietal resistance to the vector Sogatella furcifera hinders transmission of Southern rice black-streaked dwarf virus

BACKGROUND

The Southern rice black-streaked dwarf virus (SRBSDV) transmitted by Sogatella furcifera constitutes a threat to sustainable rice production. However, most rice varieties are highly vulnerable to SRBSDV, whereas the occurrence of the viral disease varies significantly under field conditions. This study aimed to evaluate the potential of rice varietal resistance to S. furcifera in reducing SRBSDV transmission.

RESULTS

Among the five rice varieties, Zhongzheyou8 and Deyou108 exhibited high resistance to S. furcifera, Baixiangnuo33 was susceptible, and TN1 and Diantun502 were highly susceptible. The S. furcifera generally showed non-preference for and low feeding on the Zhongzheyou8 and Deyou108 plants, which may explain the resistance of these varieties to S. furcifera. Transmission of SRBSDV by S. furcifera was significantly impaired on the resistant varieties, both inoculation and acquisition rates were much lower on Zhongzheyou8 than on TN1. The short durations of S. furcifera salivation and phloem-related activities and the low S. furcifera feeding amount may explain the reduced SRBSDV inoculation and acquisition rates associated with Zhongzheyou8. Spearman's rank correlation revealed a significant negative correlation between S. furcifera resistance and SRBSDV transmission among the tested varieties.

CONCLUSION

The results indicate that rice varietal resistance to the vector S. furcifera hinders SRBSDV transmission, which is largely associated with the host plant selection and feeding behaviors of the vector. The current findings shed light on the management of the SRBSDV viral disease through incorporation of S. furcifera resistant rice varieties in the management protocol. © 2024 Society of Chemical Industry.