The whitefly, Bemisia tabaci (Gennadius) is documented as a major pest on soybean. It was reported that whitefly response towards its hosts and their cultivars varies, and is mediated through various host-related factors. Considering the significance of leaf morphological characteristics in influencing the host–whitefly responses, the present investigation was conducted in screen-house conditions to study the prevailing variations in leaf morphological characteristics of soybean genotypes and their role in governing the adult whitefly attractiveness and oviposition preference. In the multiple-choice test, the whitefly population (eggs, nymphs and adults) was found to be lowest in moderately resistant genotypes (SL 1028 and SL 1074) compared to highly susceptible (DS 3105) and susceptible genotypes (SL 688, SL 958 and SL 1113). The foliar trichomes were characterized using scanning electron microscopy and leaf area, leaf lamina thickness and leaf shape data were acquired using standard procedures. To determine the factors involved in the resistance/susceptible responses towards whitefly, Pearson correlation was applied between the morphological characteristics and the whitefly population. The results show that the leaf area, trichome density, trichome length and trichome angle showed a significant positive correlation with the whitefly population, whereas leaf lamina thickness was negatively correlated. Thus, for developing whitefly-resistant germplasm, breeders should choose genotypes having narrow and thick leaves with sparse, short and flat trichomes.

The Bemisia tabaci species complex is one of the most important pests of open field and protected cropping globally. Within this complex, one species (Middle East Asia Minor 1, B. tabaci MEAM1, formerly biotype B) has been especially problematic, invading widely and spreading a large variety of plant pathogens, and developing broad spectrum pesticide resistance. Here, we fit a CLIMEX model to the distribution records of B. tabaci MEAM1, using experimental observations to calibrate its temperature responses. In fitting the model, we consider the effects of irrigation and glasshouses in extending its potential range. The validated niche model estimates its potential distribution as being considerably broader than its present known distribution, especially in the Americas, Africa and Asia. The potential distribution of the fitted model encompasses the known distribution of B. tabaci sensu lato, highlighting the magnitude of the threat posed globally by this invasive pest species complex and the viruses it vectors to open field and protected agriculture.

The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important agricultural pests and virus vectors worldwide. Bemisia tabaci is considered a complex of cryptic species with at least 44 species. Among them, the species Middle East-Asia Minor 1 (MEAM1, formerly B biotype) and Mediterranean (MED, formerly Q biotype) are the most important, and they have attained global status. In Brazil, MEAM1 was first reported in the 1990s and is currently the predominant species in the country, meanwhile, MED was recently reported in the South and Southeast regions and was found to be mainly associated with ornamental plants. Currently, an increasing problem in the management of whitefly infestations in greenhouses associated with bell pepper was observed in São Paulo State, Brazil. The whiteflies were collected and identified based on a microsatellite locus (primer pair BEM23F and BEM23R) and the mitochondrial cytochrome oxidase I gene followed by restriction fragment length polymorphism analysis and sequencing. We observed that MED was the predominant species collected on bell pepper, but it was also found on tomato, cucumber, eggplant, and weeds grown in greenhouses. In open field, we found MED on tomatoes, bell peppers, and eggplants. In addition, MED was identified in Goiás State in association with ornamental plants. The begomovirus Tomato severe rugose virus and the crinivirus Tomato chlorosis virus was detected on bell pepper and tomato, respectively. Only MED specimens were found associated with the virus-infected plants. Moreover, we also investigated the endosymbionts present in the MED whiteflies. The collected populations of B. tabaci MED harbored a diversity of secondary endosymbionts, with Hamiltonella (H) found predominantly in 89 specimens of the 129 tested. These results represent a new concern for Brazilian agriculture, especially for the management of the newly introduced whitefly MED species, which must be implemented to limit the spreading and establishment of this pest in different crops in this country.

Whiteflies have distinct nymphal stages: their first stage is mobile, whereas the later immature stages are sessile. The developmental and structural changes of antennae and antennal sensilla in whiteflies during these stages have rarely been investigated. This paper describes the morphology of antennae and antennal sensilla in four nymphal stages of Aleurodicus dispersus based on scanning electron microscopy. There were significant differences found in shape and length of the antennae, and differences in type, number, morphological structure and distributional pattern of antennal sensilla in the four nymphal stages of A. dispersus. We found two types of sensilla on the antennae of first-instar nymph, three types on the third-instar nymphal antennae, four types on the second-instar and seven types on the fourth-instar nymphal antennae. Sensilla trichoidea (ST) and elevated sensilla placodea were found on the antennae of each nymphal stage, sensilla chaetica only occurred on the antennae of fourth-instar nymph. Sensilla furcatea occurred on the antennae of second- and third-instar nymphs, and sensilla basiconica were found on the antennae of second- and fourth-instar nymphs. In addition, there were sensilla campaniform and sensilla coeloconica found only on the antennae of fourth-instar nymph, whereas the ST of fourth-instar nymphs included sensilla trichoidea 1 and sensilla trichoidea 2. The possible functions of antennal sensilla are discussed. Our results contribute to a better understanding of the development of the olfactory system of whitefly nymphal stages, and provide a basis for further exploration of chemical communication mechanisms between whiteflies and host plants.

The cryptic species Middle East-Asia Minor 1 (MEAM1), formerly referred to as ‘B biotype’, of the whitefly Bemisia tabaci complex entered China in the mid 1990s, and the Mediterranean (MED) cryptic species, formerly referred to as ‘Q biotype’, of the same whitefly complex entered China around 2003. Field surveys in China after 2003 indicate that in many regions MED has been replacing the earlier invader MEAM1. The factors underlying this displacement are unclear. We conducted laboratory experiments and field sampling to examine the effects of insecticide application on the competitive interactions between MEAM1 and MED. In the laboratory, on cotton, a plant showing similar levels of suitability to both whitefly species, MEAM1 displaced MED in five generations when initial populations of the two species were equal and no insecticide was applied. In contrast, MED displaced MEAM1 in seven and two generations, respectively, when 12.5 and 50.0 mg l−1 imidacloprid was applied to the plants via soil drench. Field sampling indicated that in a single season MED displaced MEAM1 on crops heavily sprayed with neonicotinoid insecticides but the relative abundance of the two species changed little on crops without insecticide spray. We also examined the effects of host plants on the competitive interactions between the two species in the laboratory. When cohorts with equal abundance of MEAM1 and MED were set up on different host plants, MEAM1 displaced MED on cabbage and tomato in five and seven generations, respectively, but MED displaced MEAM1 on pepper in two generations. As field populations of MED have lower susceptibility than those of MEAM1 to nearly all commonly used insecticides including imidacloprid, insecticide application seems to have played a major role in shifting the species competitive interaction effects in favour of MED in the field across China. Host plants may also shape competition between the two species depending on the relative levels of plant suitability.

Organisms differ greatly in dispersal ability, and landscapes differ in amenability to an organism's movement. Thus, landscape structure and heterogeneity can affect genetic composition of populations. While many agricultural pests are known for their ability to disperse rapidly, it is unclear how fast and over what spatial scale insect pests might respond to the temporally dynamic agricultural landscapes they inhabit. We used population genetic analyses of a severe crop pest, a member of the Bemisia tabaci (Hemiptera: Sternorrhyncha: Aleyrodoidea: Aleyrodidea) cryptic species complex known as Middle East-Asia Minor 1 (commonly known as biotype B), to estimate spatial and temporal genetic diversity over four months of the 2006–2007 summer growing season. We examined 559 individuals from eight sites, which were scored for eight microsatellite loci. Temporal genetic structure greatly exceeded spatial structure. There was significant temporal change in local genetic composition from the beginning to the end of the season accompanied by heterozygote deficits and inbreeding. This temporal structure suggests entire cohorts of pests can occupy a large and variable agricultural landscape but are rapidly replaced. These rapid genetic fluctuations reinforce the concept that agricultural landscapes are dynamic mosaics in time and space and may contribute to better decisions for pest and insecticide resistance management.

Interference competition between closely related alien and indigenous species often influences the outcome of biological invasions. The whitefly Bemisia tabaci species complex contains ≥28 putative species and two of them, Mediterranean (MED, formally referred to as the ‘Q biotype’) and Middle East-Asia Minor 1 (MEAM1, formally referred to as the ‘B biotype’), have recently spread to much of the world. In many invaded regions, these species have displaced closely related indigenous whitefly species. In this study, we integrated laboratory population experiments, behavioural observations and simulation modelling to investigate the capacity of MED to displace Asia II 1 (AII1, formally referred to as the ‘ZHJ2 biotype’), an indigenous whitefly widely distributed in Asia. Our results show that intensive mating interactions occur between MED and AII1, leading to reduced fecundity and progeny female ratio in AII1, as well as an increase in progeny female ratio in MED. In turn, our population cage experiments demonstrated that MED has the capacity to displace AII1 in a few generations. Using simulation models, we then show that both asymmetric mating interactions and differences in life history traits between the two species contribute substantially to the process of displacement. These findings would help explain the displacement of AII1 by MED in the field and, together with earlier studies on mating interactions between other species of the B. tabaci complex, indicate the widespread significance of asymmetric mating interactions in whitefly species exclusions.

The B and Q ‘biotypes’ of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) have been invading many parts of the world and causing severe damage to a range of crops. Recent phylogenetic analyses indicate that B and Q are cryptic species within the B. tabaci species complex. Although various attempts have been made to examine the reproductive compatibility between B and Q, few studies have tested the fertility of the F1 females and so the extent of possible gene flow remains unclear. In this study, we conducted a series of crossing experiments and behavioural observations to examine in detail the reproductive compatibility between the B and Q biotypes collected from Zhejiang, China, a region recently invaded by these whiteflies. Crossing experiments between the two biotypes using either single-pairs or small groups demonstrated that proportions of females in the F1 progeny were only 0–2% in the inter-biotype crosses compared to 58–68% in the intra-biotype treatments. Furthermore, all inter-biotype F1 females were sterile. Continuous video observations showed that B and Q adults very rarely copulated, and copulation occurred only when adults of opposite sex from different biotypes were enclosed in dense cohorts for a relatively long period of time. These data show that the B and Q biotypes examined in this study are completely isolated in reproduction. The isolation was due to mainly a copulation barrier, but post-copulation barriers were also involved.

Cotton leaf curl disease, a viral infection vectored by the whitefly Bemisia tabaci (Gennadius), is a major threat to the cotton industry in India and Pakistan. We examined the settling preferences of B. tabaci adults on infected versus healthy cotton plants under choice conditions. For experiments with plants at 20 and 35 days post-inoculation (DPI), whiteflies preferentially settled on healthy cotton plants after 8 and 1 h of release, respectively. Whiteflies, however, were unable to discriminate between virus-infected and healthy cotton plants at 5 DPI. Our results suggest that whiteflies' preference for healthy plants compared with diseased plants can lead to rapid virus spread in the field, resulting in higher crop losses.

Nesidiocoris tenuis (Reuter) (Hem. Miridae) is a native zoophytophagous predator of the Mediterranean region, and its populations colonize tomato crops when they are not heavily treated with insecticides. This generalist predator has a high capacity for controlling insect pests, and it is currently commercially produced and released in some areas to control Bemisia tabaci (Gennadius) (Hem. Aleyrodidae). However, its status as a pest and/or as beneficial is controversial. Therefore, the aim of this study was to evaluate the risk of damage to tomatoes in extreme conditions of prey scarcity, as well as high predator populations. Three predator densities were tested in a greenhouse cage experiment during a summer tomato crop. The crop did not display any negative effect caused by the predators during the first six weeks of interaction, independently of the density released. However, subsequently, the effect was dramatic, both on the vegetative growth of the plant and on the production of fruits. The reduction in vegetative growth was located at truss eight and it was expressed mainly by a lower number of leaves and a shorter length of the shoot above the truss. There was a significant reduction of yield with a lower number of fruits collected and a smaller mean weight, although this was not observable until truss seven. It seems that feeding on the plant by this mirid bug competed with the vegetative growth and fruiting processes of the plant in the extreme conditions of prey shortage maintained in our experiment.

In recent years, there has been an increased interest in Europe and in the USA in grafting watermelon onto bottle gourd, Lagenaria siceraria (Mol.) Standl. In this study, genetic diversity and relationships were examined [using 236 sequence-related amplified polymorphism markers] among 56 United States plant introductions (PIs) of L. siceraria and PIs of important cucurbit crops [including Cucurbita maxima Duchesne (winter squash), Cucurbita pepo L. (squash and pumpkin), Citrullus spp. (watermelon), Cucumis melo L. (melon) and Cucumis sativus L. (cucumber)]. The analysis showed that L. siceraria is distinct and has similar genetic distances to the cucurbit species examined herein. The L. siceraria PIs were assembled into two major clusters. One cluster includes groups of PIs collected mostly in South Asia (India) and a few PIs collected in the Mediterranean region and in Northeast Africa. The second cluster includes groups of PIs collected mainly in Southern Africa and in North, Central and South America, and PIs collected in China, Indonesia and Cyprus. All L. siceraria PIs in this study were susceptible to the southern root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Sandground]. However, several PIs, among them a group of closely related PIs collected in Mexico and Florida, were less infected with southern RKNs. All L. siceraria PIs were infested with whiteflies [Bemisia tabaci (Gennadius)], while several PIs were less infested than others and need further evaluation and selection for developing breeding lines that may be less appealing to this pest. Most of the PIs that showed resistance to zucchini yellow mosaic virus and tolerance to powdery mildew were collected in India and belong to the same phylogenetic groups (PGs). Experiments with L. siceraria PIs representing different PGs showed similar grafting compatibility with watermelon. Findings from this study should be useful for the development of superior L. siceraria rootstock lines with enhanced resistance to diseases and insect pests of cucurbit crops.

Omnivory involves numerous feeding relationships and a complex web of interactions. When using omnivores in biocontrol, these interactions need to be understood to maximize feeding on the target species and minimize non-target interactions. Dicyphus hesperus is used along with Encarsia formosa for biocontrol of whiteflies in greenhouse tomato crops. Dicyphus hesperus is a generalist omnivore which feeds on all components of the system. To quantify these interactions, stable isotope analysis was used to identify trophic position with nitrogen isotopes (δ15N) and plant sources with carbon isotopes (δ13C). Feeding trials were used to establish baseline isotopic data for D. hesperus and their diet, including Verbascum thapsus, an alternative plant food. Cage trials were used to monitor population abundances and the isotopic signature of D. hesperus. In feeding trials, D. hesperus were enriched relative to their food, suggesting an elevated trophic position. However, large amounts of isotopic variation were found within all diet components, with only V. thapsus exhibiting a distinct signature. In cage trials, the average δ15N and δ13C of the omnivore declined over time, coinciding with declines in total available prey, though it may be confounded by changes in temperature. The range of δ13C, but not the range of δ15N, also declined over time. This suggests a change in the plant source within the diet, but also some unquantified variability within the population. We suggest that diet variability exists within D. hesperus populations, declining as prey become less abundant.

The aim of this study was to develop and optimize silverleaf bioassay, esterase analysis and PCR-based techniques to distinguish quickly and reliably biotype B of the whitefly, Bemisia tabaci (Gennadius), from Indian indigenous biotypes. Zucchini and squash readily develop silverleaf symptoms upon feeding by the B biotype, but they are not readily available in Indian markets. A local pumpkin variety ‘Big’ was, therefore, used in silverleaf assay, which developed symptoms similar to those on zucchini and squash and can be used reliably to detect B biotype. Analysis of non-specific esterases of B and the indigenous biotypes indicated both quantitative and qualitative differences in esterase patterns. Two high molecular weight bands were unique to B biotype and they occurred in abundance. These esterases were used to develop quick and field-based novel detection methods for differentiating B from the indigenous biotypes. Development of these simple and cost-effective protocols has wider application as they can be potentially used to identify other agricultural pests. Mitochondrial cytochrome oxidase I gene sequences and randomly amplified polymorphic DNA (RAPD) polymorphisms, generated using the primer OpB11, were also found useful for detecting B. tabaci biotypes. A B biotype-specific RAPD band of 800 bp was sequenced, which was used to a develop sequence characterized amplified region (SCAR) marker. The SCAR marker involved the development of B biotype-specific primers that amplified 550 bp PCR products only from B biotype genomic DNA. Silverleaf assay, esterases, RAPDs or a SCAR marker were used in combination to analyse whitefly samples collected from selected locations in India, and it was found that any of these techniques can be used singly or in combination to detect B biotype reliably. The B biotype was found in southern parts of India but not in the north in 2004–06.

The sweet potato whitefly, Bemisia tabaci, harbors Portiera aleyrodidarum, an obligatory symbiotic bacterium, as well as several secondary symbionts including Rickettsia, Hamiltonella, Wolbachia, Arsenophonus, Cardinium and Fritschea, the function of which is unknown. Bemisia tabaci is a species complex composed of numerous biotypes, which may differ from each other both genetically and biologically. Only the B and Q biotypes have been reported from Israel. Secondary symbiont infection frequencies of Israeli laboratory and field populations of B. tabaci from various host plants were determined by PCR, in order to test for correlation between bacterial composition to biotype and host plant. Hamiltonella was detected only in populations of the B biotype, while Wolbachia and Arsenophonus were found only in the Q biotype (33% and 87% infection, respectively). Rickettsia was abundant in both biotypes. Cardinium and Fritschea were not found in any of the populations. No differences in secondary symbionts were found among host plants within the B biotype; but within the Q biotype, all whiteflies collected from sage harboured both Rickettsia and Arsenophonus, an infection frequency which was significantly higher than those found in association with all other host plants. The association found between whitefly biotypes and secondary symbionts suggests a possible contribution of these bacteria to host characteristics such as insecticide resistance, host range, virus transmission and speciation.

The two most widespread biotypes of Bemisia tabaci (Gennadius) in southern Europe and the Middle East are referred to as the B and Q-type, which are morphologically indistinguishable. In this study various DNA markers have been developed, applied and compared for studying genetic diversity and distribution of the two biotypes. For developing sequence characterized amplified regions (SCAR) and cleaved amplified polymorphic sequences (CAPS) techniques, single random amplified polymorphic DNA (RAPD) fragments of B and Q biotypes, respectively, were used. The CAPS were investigated on the basis of nuclear sodium channel and the mitochondrial cytochrome oxidase I genes (mtCOI) sequences. In general, complete agreement was found between the different markers used. Analysis of field samples collected in Israel for several years, using these markers, indicated that the percentage of the Q biotype tends to increase in field populations as time progresses. This may be attributed to the resistance of the Q biotype to neonicotinoids and pyriproxyfen and the susceptibility of the B biotype to these insecticides.

The parasitism of Bemisia tabaci (Gennadius) was evaluated on three horticultural crops in the Nicaraguan dry tropic: tomato, Lycopersicon esculentum Mill; squash, Cucurbita argyrosperma (Huber); and sweet pepper, Capsicum annuum L. Parasitoid species were identified and their abundance recorded on the three crops. The study was carried out during both the rainy and dry seasons between 2001 and 2002. The nymphs of B. tabaci were counted weekly and parasitism rates evaluated. During the rainy season, the predominant parasitoids in squash and tomato crops were Encarsia pergandiella Howard and E. nigricephala Dozier. Parasitism rates of 17 and 10% were recorded for squash and tomato, respectively. In sweet pepper, the parasitoid species were E. pergandiella, E. nigricephala, E. desantisi Viggiani and Amitus sp. with a parasitism rate of 12%. During the dry season, the parasitoids in squash were E. pergandiella and E. nigricephala with a parasitism rate of 57%. Encarsia pergandiella was the only species noted in tomato with a parasitism rate of 58%, while in sweet pepper the species noted were E. pergandiella and E. nigricephala, with a 42% rate of parasitism. The abundance of parasitoids remained stable during both sampling seasons. Our results suggest that the parasitism rate is independent of B. tabaci densities. This is the first mention of E. pergandiella, E. nigricephala, E. desantisi and Amitus sp. as parasitoids of B. tabaci in Nicaragua.

The sweet potato whitefly Bemisia tabaci (Gennadius) is a pest of diverse agricultural systems worldwide, owing to its capacity to transmit viruses, both intraspecific and host-associated variations. In Ghana, it is the only known arthropod vector for cassava-infecting begomoviruses (Geminiviridae). Two genetic variants of B. tabaci, previously characterized by RAPD–PCR and subsequently reared on cassava and okra, were allowed access to five weed species in order to examine host preference and suitability: Amaranthus retroflexus, Chromolaena odorata, Desmodium tortuosum, Euphorbia heterophylla and Malvastrum coromandelianum. Overall, the duration of the life cycle ranged between 16.5 and 26.3 days and survival rates were 0–27.5%. The population from field-infested okra reproduced and developed to maturity on C. odorata, D. tortuosum and E. heterophylla. Both populations produced male and female progeny. Amaranthus retroflexus and M. coromandelianum were considered poor hosts for both populations, due to the low fecundity and survival of eggs, pupae and adults. The rearing host did not significantly (P>0.05) influence survival on subsequent hosts in either case. The host-restriction of the population collected from cassava was not corroborated here, based on the demonstrated ability of the Ghanaian cassava population to complete its life cycle on D. tortuosum and E. heterophylla. It was estimated that B. tabaci could achieve 13–22 generations per year in Ghana. Removal of C. odorata, D. tortuosum and E. heterophylla from the vicinity of susceptible crops is recommended.

Bionomics, morphometric measurements and partial mitochondrial cytochrome oxidase I gene (mtCOI) sequences were examined for a population of Bemisia afer (Priesner & Hosny) (Hemiptera: Aleyrodidae) collected from cassava in Uganda. The development of the eggs, first to fourth instar nymphs and adults required respectively, 12, 31 and 10 days, with a total life duration of approximately 53 days on the cassava cultivar Ebwanateraka. Each female laid one egg per day for 13 days and about 40% of the eggs failed to develop into adults. The male: female sex ratio was 1:4. The length and width of the four nymphal instars were positively correlated (correlation coefficient=0.97). Females were bigger than males and the sexes differed significantly based on body length (P<0.001) and width (P<0.001). Overlaps in their body sizes, however, makes sex assignment based on size alone unreliable. The B. afer population shared 68% mtCOI sequence (817 nucleotides) identity with a cassava Bemisia tabaci population (Namulonge) from Uganda. This is the first study on B. afer fecundity and morphometrics, and the variability that might exist in this species is discussed.

A major cause of yield loss in cassava, Manihot esculenta Crantz in tropical Africa is African cassava mosaic virus, transmitted by the whitefly, Bemisia tabaci (Gennadius). Investigations into the epidemiology of the disease and the ecology of the insect vector at the Kenya coast demonstrated that the serious loss of yield caused by the virus could be greatly reduced if simple changes in husbandry practices were adopted. The regular rogueing of infected plants greatly reduced the incidence of African cassava mosaic virus.

Spatial dispersion of the nymphs of the jassid, Amrasca biguttula biguttula (Ishida), and the adults of the whitefly, Bemisia tabaci Genn. on F414, a Gossypium hirsutum variety, was systematic in Ludhiana (Punjab). Both the jassid and the whitefly displayed no definite pattern along the height of the plant, though a maximum number of whiteflies were recorded at middle canopy (21–40 cm from bottom). Sample sizes of 10–15 plants, selected in a statistically linear fashion represented populations of jassid nymphs and adult whitefly on all four varieties. Sampling jassid nymphs by visual counting and whitefly by split-cage were the most suitable sampling methods for local cotton growers among the various methods compared.