A Maximum Dose Bioassay to Assess Efficacy of Key Insecticides Against Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae).

Loop-mediated isothermal amplification (LAMP) is a promising technique for detecting pest species used on the spot due to its simplicity and rapidity. The whitefly is regarded as a species complex encompassing over 44 cryptic species. These species are morphologically indistinguishable but exhibit notable differences in their biological traits. Among them, Bemisia tabaci MEAM1 and MED are the most invasive and devastating members. Accurately and quickly distinguishing between these two invasive whiteflies in the field directly affects the implementation of control measures. However, it is often difficult to directly distinguish between the two when they occur together in the field and require extensive specialist knowledge or instrumentation. However, one of the limitations of the current LAMP is that the reaction mixture requires cold chain, which is not ideal for the detection on the spot. To promote its actual application of LAMP on the spot, the LAMP methods to differentiate B. tabaci MEAM1 and MED were developed in the laboratory, and Trialeurodes vaporariorum was used as a negative control. Then the effect of the preservation condition (room temperature and low temperature) of the reaction mixture on the efficiency of LAMP was compared. The study showed that the application of B. tabaci MED- and MEAM1- LAMP reaction mixture can differentiate B. tabaci MEAM1, B. tabaci MED, and T. vaporariorum after low-temperature preservation for more than 24 h. Finally, we validated the method with temperature-controlled hot-water cup in the field and proved its effectiveness when applied to the field. The results demonstrated that the low-temperature preservation of reaction mixture provides available technical support for the application of LAMP on the spot.

Simple SummaryBemisia tabaci is a polyphagous pest with cryptic species that infest various agricultural crops worldwide. Among the cryptic species, MED and MEAM1 are the most invasive, causing large production losses due to the feeding and transmission of the virus. We aimed to analyze the influence of these insects on the physiology and biochemistry of tomato. We found that the cryptic species MED caused considerable reduction in CO2 assimilation rates, stomatal conductance, and instantaneous carboxylation efficiency. Furthermore, plants infested with MED showed high activity of the enzymes peroxidase and polyphenol oxidase, which are considered expressions of plant defense. In contrast, plants infested with MEAM1 showed low peroxidase activity, which may result in a less lignified feeding place.Infestation by Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) causes damage to tomatoes with production losses of up to 100%, affecting the physiological and biochemical aspects of host plants. The objective of this study was to analyze the influence of infestation of cryptic species of B. tabaci MED and MEAM1 on the physiological and biochemical aspects of tomato. Tomato plants ‘Santa Adélia Super’ infested with B. tabaci (MED and MEAM1), and non-infested plants were evaluated for differences in gas exchange, chlorophyll - a fluorescence of photosystem II (PSII), and biochemical factors (total phenols, total flavonoids, superoxide dismutase—SOD, peroxidase—POD, and polyphenol oxidase—PPO). Plants infested with B. tabaci MED showed low rates of CO2 assimilation and stomatal conductance of 55% and 52%, respectively. The instantaneous carboxylation efficiency was reduced by 40% in MED and by 60% in MEAM1 compared to the control. Regarding biochemical aspects, plants infested by MED cryptic species showed high activity of POD and PPO enzymes and total phenol content during the second and third instars when compared to control plants. Our results indicate that B. tabaci MED infestation in tomato plants had a greater influence than B. tabaci MEAM1 infestation on physiological parameters (CO2 assimilation rate (A), stomatal conductance (gs), and apparent carboxylation efficiency (A/Ci)) and caused increased activity of POD and PPO enzymes, indicating plant resistance to attack. In contrast, B. tabaci MEAM1 caused a reduction in POD enzyme activity, favoring offspring performance.

Efficacy of buprofezin, pyriproxyfen and spirotetramat against Bemisia tabaci MEAM1 nymphal field populations in Florida

The two common whitefly species, Bemisia tabaci (Gennadius) MEAM1 and Trialeurodes vaporariorum (Westwood), often co-occur on their host plants. The effect of host plant occupation by one species on later-arriving conspecific individuals or on the other competing species was examined. Resource preoccupied by T. vaporariorum had mostly negative effects on the life history parameters of later-arriving conspecifics. Red-eyed nymph and immature survival of T. vaporariorum decreased when resource was preoccupied by conspecifics, irrespective of the previous occupation scenario. However, resource preoccupied by T. vaporariorum had only minor detrimental effects on the performance of later-arriving B. tabaci MEAM1. In the opposite colonisation sequence, previous occupation by B. tabaci MEAM1 had no significant effects on the life history parameters of later-arriving conspecifics, but severe detrimental effects were observed on the performance of later-arriving T. vaporariorum. Total immature survival of T. vaporariorum decreased in both weak and strong previous occupation situations by B. tabaci MEAM1. The interspecific interactions between B. tabaci MEAM1 and T. vaporariorum were asymmetric, with B. tabaci MEAM1 being the superior competitor. This superiority could partially explain the rapid spread of B. tabaci MEAM1 in China.

Knowledge about host instar suitability of a parasitoid is critical to ensure bio-control efficacy. Studies were conducted to assess parasitizing and feeding behavior of a naturally occurring parasitoid, Eretmocerus hayati, on different instar nymphs of two invasive whiteflies, Bemisia tabaci (Gennadius) cryptic species MEAM1 and MED, in China. Er. hayati parasitized and fed on all nymphal stages of the two whiteflies, but preferred to parasitize 1st, 2nd and 3rd instar hosts of B. tabaci MEAM1 and 2nd instar hosts of B. tabaci MED. Parasitoids preferred to feed on earlier instar hosts of the two species. The preimaginal development times of parasitoids were the longest on 1st instar hosts, intermediate on 2nd and 3rd instars, and the shortest on 4th instars. The immature development time on B. tabaci MED hosts were slightly shorter than on MEAM1 ones. The highest parasitoid survivorships were on 4th instars, and the lowest were on 1st instars in both host species. The sex ratios of offspring remained stable at 0.5. Er. hayati could be a more suitable biological control agent for B. tabaci MED. Our results could provide guidance for indoor mass-rearing of Eretmocerus spp. for inundative release in the field, accelerating IPM programs against B. tabaci in China.

The tomato chlorosis virus (ToCV), transmitted by whitefly species of the genera Bemisia and Trialeurodes in a semipersistent manner, causes significant losses in solanaceous crops including tomato (Solanum lycopersicum) and sweet pepper (Capsicum annuum). Worldwide reports of natural and experimental infection of sweet pepper plants with ToCV are contradictory, raising the question of whether the critical factor determining infection is related to the susceptibility of sweet pepper cultivars or the genetics of virus isolates. In this work, ToCV isolates obtained from different hosts and geographical origins were biologically and molecularly analysed, transmitted by B. tabaci MEAM1 and MED, and the reaction of different sweet pepper cultivars was evaluated under different environmental conditions. Brazilian ToCV isolates from tomato, potato (S. tuberosum), S. americanum, and Physalis angulata did not infect plants of five sweet pepper cultivars when transmitted by B. tabaci MEAM1. Temperatures did not affect the sweet pepper susceptibility to tomato‐ToCV isolates from São Paulo, Brazil, and Florida, USA. However, sweet pepper‐ToCV isolates from Spain and São Paulo, Brazil, were transmitted efficiently to sweet pepper plants by B. tabaci MEAM1 and MED. Although the results indicated that ToCV isolates from naturally infected sweet pepper plants seem to be better adapted to plants of C. annuum, phylogenetic analyses based on the complete nucleotide sequences of RNA1 and RNA2 as well as the p22 gene did not reveal significant nucleotide differences among them. Additional studies are needed to identify intrinsic characteristics of ToCV isolates that favour infection of sweet pepper plants.

Lethal and sublethal effects of a novel cis-nitromethylene neonicotinoid insecticide, cycloxaprid, on Bemisia tabaci

Begomoviruses cause losses in several crops around the world. Whiteflies of the Bemisia tabaci cryptic species MEAM1 and MED are efficient vectors of begomoviruses. MEAM1 has been the predominant species in Brazil since the mid‐1990s. MED was detected in Brazil in 2014, and since then, high insect infestations have been reported, mainly in greenhouse production of solanaceous crops. In this study, we compared the transmission efficiency of the begomoviruses tomato severe rugose virus (ToSRV) and tomato rugose mosaic virus (ToRMV) to tomato (Solanum lycopersicum) and bean golden mosaic virus (BGMV) to common bean (Phaseolus vulgaris) by a population of MEAM1 and four populations of MED. B. tabaci MEAM1 efficiently transmitted ToSRV and ToRMV to tomato and BGMV to common bean. B. tabaci MED populations did not transmit ToSRV and ToRMV to tomato. Only one population of B. tabaci MED transmitted BGMV with an efficiency of 3%. PCR analysis indicated that B. tabaci MED can acquire ToSRV, ToRMV and BGMV after a 24 h acquisition access period. Furthermore, some greenhouse tomato plantings from São Paulo state were surveyed for the presence of viruses and whiteflies, and B. tabaci MED were predominant, whereas begomoviruses were absent. Our results demonstrate that populations of MED from São Paulo state are inefficient vectors of begomoviruses, being able to acquire the virus but not transmit it to plants. Understanding this interaction is important and suggests that the spread of B. tabaci MED could change the epidemiological scenario of begomoviruses in areas where this insect predominates.

Whiteflies are important agricultural pests of several crops and cause great economic losses, mainly by the transmission of plant viruses. Among the different species of whiteflies, Trialeurodes vaporariorum and Bemisia tabaci MEAM1 (B biotype) transmit the crinivirus Tomato chlorosis virus (ToCV). Previous studies report that virus‐infected plants can influence the attractiveness and the behaviour of different species of whiteflies. In this study, we evaluated the number of eggs, egg hatching rate and emergence of adults of both T. vaporariorum and B. tabaci MEAM1 on ToCV‐infected and healthy tomatoes. In addition, ToCV transmission assays were conducted with both whitefly species. ToCV infection did not influence the number of eggs or egg hatching rate of T. vaporariorum; whereas the emergence of adults was reduced by 37.3% on ToCV‐infected tomatoes. By contrast, ToCV‐infected tomatoes strongly affected the B. tabaci MEAM1 egg hatching rate and emergence of adults with reductions of 41.8% and 92.4%, respectively. Regarding virus transmission, T. vaporariorum transmitted ToCV with lower efficiency (35.7%) than B. tabaci MEAM1 (78.6%). Our data suggest that the performance of T. vaporariorum is less affected than that of B. tabaci MEAM1 when feeding on ToCV‐infected tomato plants.

Tomato golden mosaic disease, caused by the tomato severe rugose virus (ToSRV), is one of the most serious tomato diseases. ToSRV is transmitted by the whitefly Bemisia tabaci MEAM1, from a wide range of hosts. Introducing ToSRV in commercial fields probably can occur by transporting the virus from distant locations. However, our hypothesis is that the inoculum causing epidemic development might be related to nearby sources. This study evaluated the short‐range flight distance of B. tabaci MEAM1 (marked with detectable proteins and powder dye), through recaptures in yellow sticky traps, and the transmission of ToSRV by viruliferous B. tabaci MEAM1 to tomato plants placed at increasing distances from a release point. Evaluated whiteflies reached a maximum of 30 m from the release point, and no ToSRV‐infected tomato plants were detected at greater distances. These findings reinforce the suspicion that the epidemic‐supporting source of ToSRV inoculum must be close to commercial cultivation areas. About the efficacy of the type of markers used, of the two protein sources tested (pasteurized chicken egg‐white albumin and commercial soy‐based extracts as sources of albumin and lecithin, respectively), albumin was considered easier to detect. Marking with these proteins or with two dyes (blue or pink) did not affect B. tabaci MEAM1 mortality, although field tests showed that fewer marked than unmarked insects were recaptured. Dye marking was considered more practical because of the ease of detection. The study validates a new tool to understand the movement of B. tabaci MEAM1, based on different marking methods.

The citrus (or orange) spiny whitefly, Aleurocanthus spiniferus (Quaintance) (Hemiptera: Aleyrodidae), is an important pest of various economic crops such as citrus and tea, causing severe economic losses. However, the population genetics of A. spiniferus is poorly understood, both in China and in other countries. To improve our knowledge of the population structure and genetic variation of this species, 10 polymorphic microsatellite loci for A. spiniferus were developed and characterized using FIASCO (Fast Isolation by AFLP of Sequences Containing Repeats). Our results showed that the polymorphic information contents (PIC) of all 10 loci were greater than 0.5, showing a high degree of polymorphism. The number of alleles ranged from 12 to 27 across 60 individuals from 6 populations. In addition, the expected heterozygosity (HE) and the observed heterozygosity (Ho) ranged from 0.851 to 0.958 and from 0.621 to 0.850, respectively. Interestingly, all loci deviated from the Hardy-Weinberg equilibrium, although - according to our study - they were not affected by the species' specific reproductive strategy, and thus must be related to other unknown factors. Furthermore, linkage disequilibrium analysis revealed that C19-2 and D14, and also I20 and F12 showed linkage disequilibrium. Cross-species amplification was also tested in 5 closely related whitefly species (Aleurodicus disperses Russell, Pealius mori (Takahashi), Aleuroclava aucubae (Kuwana), Bemisia tabaci (Gennadius) MEAM1 and B. tabaci MED) in this study. Nine pairs of primers were successfully amplified at different levels except for F12. In particular, A21-2, D14, F13-2, and F42-2, coupled with I20 were successfully amplified across all the above species. Consequently, the 10 loci identified here can be used to study the population genetic structure of A. spiniferus and other closely related whitefly species.

Sugar transporters (STs) play pivotal roles in the growth, development, and stress responses of phloem-sucking insects, such as the whitefly, Bemisia tabaci. In this study, 137 sugar transporters (STs) were identified based on analysis of the genome and transcriptome of B. tabaci MEAM1. B. tabaci MEAM1 encodes a larger number of STs than other selected insects. Phylogenetic and molecular evolution analysis showed that the 137 STs formed three expanded clades and that the genes in Sternorrhyncha expanded clades had accelerated rates of evolution. B. tabaci sugar transporters (BTSTs) were divided into three groups based on their expression profiles across developmental stages; however, no host-specific BTST was found in B. tabaci fed on different host plants. Feeding of B. tabaci adults with feeding diet containing dsRNA significantly reduced the transcript level of the target genes in B. tabaci and mortality was significantly improved in B. tabaci fed on dsRNA compared to the control, which indicates the sugar transporters may be used as potential RNAi targets for B. tabaci bio-control. These results provide a foundation for further studies of STs in B. tabaci.

Performance of Bemisia tabaci MEAM1 on soybean and resistance traits of cultivars

The level of midgut penetration of two begomoviruses affects their acquisition and transmission by two species of Bemisia tabaci

The whitefly (Bemisia tabaci), an important invasive pest that causes severe damage to crops worldwide, has developed resistance to a variety of insecticides. Carboxylesterases (COEs) are important multifunctional enzymes involved in the growth, development, and xenobiotic metabolism of insects. However, systematic studies on the COEs of B. tabaci are scarce. Here, 42 putative COEs in different functional categories were identified in the Mediterranean species of B. tabaci (B. tabaci MED) based on a genome database and neighbor-joining phylogeny. The expression patterns of the COEs were affected by the development of B. tabaci. The expression levels of six COEs were positively correlated with the concentration of imidacloprid to which B. tabaci adults were exposed. The mortality of B. tabaci MED adults fed dsBTbe5 (67.5%) and dsBTjhe2 (58.4%) was significantly higher than the adults fed dsEGFP (41.1%) when treated with imidacloprid. Our results provide a basis for functional research on COEs in B. tabaci and provide new insight into the imidacloprid resistance of B. tabaci.