Temporal and spatial progress of the diseases caused by the crinivirus tomato chlorosis virus and the begomovirus tomato severe rugose virus in tomatoes in Brazil

Efficient management of whitefly-borne diseases remains a challenge due to the lack of a comprehensive understanding of their epidemiology, particularly of the diseases tomato golden mosaic and tomato yellowing. Here, by monitoring 16 plots in four commercial fields, the temporal and spatial distribution of these two diseases were studied in tomato fields in Brazil. In the experimental plots these diseases were caused by tomato severe rugose virus (ToSRV) and tomato chlorosis virus (ToCV), respectively. The incidence of each virus was similar in the plots within a field but varied greatly among fields. Plants with symptoms for both diseases were randomly distributed in three of four spatial analyses. The curves representing the progress of both diseases were similar and contained small fluctuations, indicating that the spread of both viruses was similar under field conditions. In transmission experiments of ToSRV and ToCV by Bemisia tabaci MEAM1 (former biotype B), these viruses had a similar transmission rate in single or mixed infections. It was then shown that primary and secondary spread of ToCV were not efficiently controlled by insecticide applications. Finally, in a typical monomolecular model of disease progress, simulation of the primary dissemination of ToSRV and ToCV showed that infected plants were predominantly randomly distributed. It is concluded that, although the manner of vector transmission differs between ToSRV (persistent) and ToCV (semipersistent), the main dispersal mechanisms are most probably similar for these two diseases: primary spread is the predominant mechanism, and epidemics of these diseases have been caused by several influxes of viruliferous whiteflies.     

福建省露地及设施蔬菜烟粉虱越冬种群密度及耐寒性研究

2017年1月9—12日和2月21—24日，在南平建瓯、三明将乐、三明三元、福州闽侯、龙岩新罗以及漳州龙海等6个地区，调查了大棚和露地烟粉虱越冬寄主及种群密度，以期明确福建省露地及设施蔬菜烟粉虱越冬规律，为烟粉虱的综合治理提供理论依据。共记录烟粉虱越冬寄主6科16种，主要包括栽培蔬菜花椰菜、番茄、茄子以及阔叶类杂草龙葵、小飞蓬、辣子草和胜红蓟。在露地花椰菜上，烟粉虱越冬虫口密度1月份显著高于2月份；花椰菜采后残株上的越冬虫口密度显著高于莲座期和花球形成期。在温室大棚中，休耕大棚中越冬虫口密度显著高于生产大棚。无论是蔬菜还是杂草，温室大棚中的越冬虫口密度显著高于露地。烟粉虱各虫态均可在各地温室大棚和漳州露地越冬，而在南平和三明等温度较低的地区以卵和伪蛹在露地越冬。在蔬菜上发现越冬烟粉虱有MEAM1隐种和MED隐种，温室大棚中两隐种数量分别为57只和111只，温室大棚可能有助于MED隐种定殖。室内耐寒性测定证实卵和高龄若虫比低龄若虫以及成虫更耐寒，烟粉虱在花椰菜、龙葵和辣子草上的世代存活率分别为83.7%、79.3%和81.6%，世代发育历期分别为18.9 d、16.7 d和18.8 d，龙葵和辣子草是烟粉虱适宜的越冬杂草寄主。综上，烟粉虱可在福建省露地越冬，温室大棚加重了烟粉虱的发生为害。     

Management of Bemisia tabaci biotype B with botanical and mineral oils

While the toxic effects of neem, Azadirachta indica A. Juss, on Bemisia tabaci Genn. are well documented, few studies have evaluated other oils. We compared neem, sesame, citrus, castor, vegetable and mineral oils (1% v/v) to a chemical standard thiamethoxam (0.17 g A.I./L) against B. tabaci biotype B life stages on dry bean plants Phaseolus vulgaris L. under screenhouse conditions. Oils and thiamethoxam exhibited low ovicidal activity (<10% egg mortality). However, significant mortality occurred due to the residual activity to 1st instars that emerged from treated eggs. Overall, impacts of egg treatments were greatest for thiamethoxam (77% total mortality for eggs and 1st instars) compared with oils which were statistically similar (22–29% mortality). Larvicidal effect of oils (against 2nd instars) was greater than ovicidal effects. Highest nymphal mortality (>81%) was achieved with castor, sesame, citrus and neem oils, which was significantly greater than for thiamethoxam (65% mortality). Adult whiteflies were exposed to fresh and aged spray residues, rather than being sprayed directly. In this case, comparatively lower efficacy was achieved from oil treatments compared with thiamethoxam. While some mortality was observed from fresh residues of slow drying oils (up to 41% for castor oil), no significant control from any oil residues >3 days old was observed in our tests. The different route of exposure against adults likely reduced the effectiveness of oil treatments which act directly on the cuticle. In trials with viruliferous adult whiteflies exposed to fresh residues, none of the tested products completely prevented transmission of bean golden mosaic virus (BGMV). However, we noted reduced virus severity ratings from plants pre-treated with castor and citrus oil. We conclude that castor, sesame, citrus and neem oils have the potential to be used in whitefly management programs.     

烟粉虱的识别与鉴定技术

本文对烟粉虱的形态特征进行了详细描述,并对A、B两种生物型的超微结构特征进行了研究,提出鉴定这两种生物型的形态特征。此外,文中还就烟粉虱与温室白粉虱的区别特征进行了描述,并提出了烟粉虱的田间识别特征。