Evidence for a new genetic variant in the <Emphasis Type="Italic">Bemisia tabaci</Emphasis> species complex and the prevalence of the biotype Q in southern Italy

The genetic diversity of Bemisia tabaci was investigated in Southern Italy using the mitochondrial cytochrome oxidase I (COI) gene as molecular marker and sampling whiteflies on cultivated plants, weeds and bushes. Phylogenetic analysis of COI sequences and restriction analysis of COI amplicons were used to genotype whitefly populations. A PCR-RFLP method based on digestion with the endonuclease ApoI was set up to identify the B. tabaci genetic variants so far recorded from the Mediterranean region. In general, biotype Q populations were most frequently collected (76.0% of all sampled populations). In greenhouse districts, 87.0% sampled populations were identified as biotype Q, and 13.0% were assigned to biotype B. Outside the greenhouse districts, the biotype B was never collected, whilst biotype Q populations were found on weeds and on plants cultivated in family gardens in different environments, also located in interior plains or in mountain areas distant from intensive cultivations of whitefly host plants. A new genetic variant unrelated to B and Q biotypes, which was named Ru, was collected on Rubus ulmifolius and grapevine. Phylogenetic analysis of COI sequences shown that Ru haplotypes form a well-supported clade sister to the clade including the Asian/Australian major genetic groups and the Italy major genetic group. The closest relative of the Ru clade (10.7% pairwise genetic distance) was the Italy group, with this latter so far including only the haplotypes of the T biotype. These results were discussed in the light of the recent B. tabaci species concept.     

Host range, distribution, and natural enemies of Bemisia tabaci ‘B biotype’ (Hemiptera: Aleyrodidae) in Turkey

The whitefly Bemisia tabaci (Gennadius) has caused notable damage to vegetable and cotton crops in the eastern Mediterranean region since about 1994, and has become particularly problematic in southern Turkey beginning in 2000. The development of squash silverleaf symptoms in Cucurbita species and the unprecedented high population levels in the region suggested that the B biotype, notable for the latter phenotypes, had been introduced. To test this hypothesis and determine the host distribution of the suspect introduced B biotype and its associated natural enemies, B. tabaci immature instars and adults, and the associated natural enemies were collected from cultivated and uncultivated plant species. From the southern Turkey collections, B. tabaci was found to colonize 152 species from 43 plant families. Of the plant species upon which B. tabaci was found to reproduce, 152 of them were reported as hosts of B. tabaci in Turkey. Five species of predators and two species of parasitoids were identified as natural enemies of the B biotype of B. tabaci in southern Turkey. Using the mitochondrial cytochrome oxidase I gene all B. tabaci were identified as the B biotype of the B. tabaci complex, at 96–100% shared identity with reference B biotype sequences. Results indicate that this invasive biotype has displaced the local Turkey-cotton haplotype that was known to occur previously in southern Turkey.     

Genetic variation and mtCOI phylogeny for Bemisia tabaci (Hemiptera, Aleyrodidae) indicate that the ‘B’ biotype predominates in Iran

Despite a large number of investigations on the molecular genetics and population structure of the whitefly Bemisia tabaci (Gennadius) complex, no such study had been conducted in Iran. The genetic variation of B. tabaci was examined using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) for 18 field collections from cucumber, eggplant, and tomato in four provinces of Iran. PCR amplification and restriction digestion with two enzymes detected 388 RFLP fragments, of which 16 fragments showed polymorphisms. Cluster analysis of these data placed all B. tabaci individuals within a single group, and there was no evidence for between- or within-population genetic variation. Phylogenetic (Clustal W) analysis of 42 B. tabaci mtCOI sequences (n = 21 field collections) from Iran, and a comparison with well-studied haplotype or biotype reference sequences available in public sequence databases, revealed that the Iranian B. tabaci populations were most closely related to the B biotype at 0–1.2% nucleotide identity. The B biotype is a well-known member of a sister clade from the Middle East–North African region of the world, owing to its nearly worldwide distribution and invasive characteristics. This report indicates that a single major haplotype of B biotype is prevalent in Iran and that its closest relative is the B biotype. Also, given the extent of known variation in the Middle East and African continent, data indicate somewhat surprisingly that the B. tabaci collections sampled in Iran had limited genetic variation and population substructure. Knowledge that the B biotype of B. tabaci predominates in Iran is important for designing effective pest management strategies given that biotypes of B. tabaci are known to differ greatly with respect to insecticide resistance, host range, virus–vector interactions, and other key biological characteristics.     

Comparison of biological parameters between the invasive B biotype and a new defined Cv biotype of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Hemiptera: Aleyradidae) in China

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a widely distributed and destructive agricultural pest on various host plants. The biology of two biotypes of B. tabaci: the invasive B and a new defined Cv biotype, on a range of host plants (hibiscus, laurel, poinsettia, collard, cucumber and tomato) were studied in the laboratory. Results revealed that the developmental periods of the B biotype immatures were not significantly different on the tested host plants except those between laurel and collard. The Cv biotype immatures developed significantly slower on cucumber and tomato than on the other plants. B. tabaci B biotype had the highest survivorship on collard (68.55%), and the lowest on laurel (33.24%), while the Cv biotype had the highest and lowest survivorships on laurel (61.63%) and tomato (36.74%). Host plants did not significantly affect the pre-ovipostion period regardless of biotype. The longest averaged longevity and highest fecundity of B biotype were both recorded on collard: 25.15 days and 143.0 eggs. The highest fecundity of Cv biotype was 196.49 eggs on laurel and its longest longevity was on hibiscus (19.62 days). The intrinsic rate of natural increase (r _m) of B biotype on the three vegetables were all higher than those on the three ornamentals whereas the r _m of Cv biotype on the three ornamentals were all higher that those on the three vegetables. Our research indicates that B. tabaci B and Cv biotypes have different host plant suitabilities. The three tested vegetables were more suitable for B biotype while the three tested ornamental plants were more suitable for Cv biotype. The potential mechanism for the different suitability of B and Cv biotypes on various host plants is also discussed.     

Host instar suitability of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Genn.) (Hom.: Aleyrodidae) for the parasitoid <Emphasis Type="Italic">Eretmocerus mundus</Emphasis> (Hym.: Aphelinidae)

Efficient use of parasitoids in pest control depend on the knowledge of the biological relationships between host and parasitoid. Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is one the most important natural enemies of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) that is found in fields and greenhouses in Adana, Turkey. Although more studies have been done to determine the relationships between E. mundus and B. tabaci, the differences among strains of E. mundus could have important biological concequences. In this study, biological characteristics of native population of E. mundus parasitization of B. tabaci (Q biotype) were determined using bean plants Phaseolus vulgaris (L.) at a constant temperature of 25 ± 1°C, relative humidity 70 ± 10% and 16:8 (L:D) photoperiod regimen. All B. tabaci nymphal instars were parasitized by E. mundus, but the mean number of daily-parasitized nymphs was highest in the second instars (15.3). In addition, second instar females had the shortest mean development time (15.2 days). Mean development times of parasitoids obtained from first, second, third and fourth B. tabaci instars varied from 15.2 to 16.2 days and 15.2 to 15.9 days for female and male, respectively. Proportion of female (♀/♂+♀) varied from first (0.53) to second (0.34) host instars. Impact of results on potential biological control of B. tabaci was discussed through conservation native natural enemies.     

Evaluation of <Emphasis Type="Italic">Serangium parcesetosum</Emphasis> (Col.: Coccinellidae) for biological control of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> under greenhouse conditions

The cotton whitefly, Bemisia tabaci (Genn.) (Hom., Aleyrodidae) is increasingly a very important pest on many vegetables, field crops and ornamental plants. Therefore, controlling of this pest is still needed especially under glasshouse conditions. The specialist whiteflies’ predator, Serangium parcesetosum Sicard (Col., Coccinellidae) appears to have a great potential for the cotton whitefly control. In this study, the dynamic changes in B. tabaci populations in glasshouse cabins in response to S. parcesetosum were monitored. B. tabaci were introduced to cotton plants in three cabins in average of 50 adults per plant. One and two weeks later, adult females and males of S. parcesetosum were introduced at a rate of one female and one male per plant in the first and second cabins, respectively. The third cabin was considered as a control. The results showed that the mean number of whiteflies in the control cabin was found significantly higher than that of either when S. parcesetosum was introduced 1 or 2 weeks after the infestation with the whitefly. Also, the mean number of B. tabaci was significantly higher when the predator was introduced 2 weeks rather than 1 week after B. tabaci infestation. The maximum mean weekly number of whiteflies/plant was 192.3 in the second week, whereas it was 294.6 in the third week and 1136.4 in the fifth week, in first, second and control cabins, respectively. In the last experimental week, the mean weekly numbers were 74.7, 122.9 and 684.7 whiteflies/plant in the three cabins, respectively. S. parcesetosum has been successfully fed, reproduced and established its population on B. tabaci on cotton plants. The mean weekly number of the predatory individuals increased gradually with the progress of the experimental time. The results demonstrated that the maximum reduction percentage in B. tabaci population was 90.7 and 86.5% in the fifth week after B. tabaci infestation, when the predator was introduced 1 and 2 weeks after the infestation with the whiteflies, respectively. Nevertheless, it is speculated that an earlier release of S. parcesetosum would be more effective in the biological control of B. tabaci.     

Multiple invasions of Bemisia argentifolii into Australia and its current genetic connectivity across space

Detecting the number of invasions is crucial to understanding the process of invasion and perhaps the success of some invasive pest species. Detecting multiple invasions can be difficult using partial mitochondrial COI, however, due to lack of variation. To examine the post-invasion history of Bemisia argentifolii (also called B. tabaci Middle East-Asia Minor 1 and B biotype) in Australia and test for the presence of spatial genetic structure, we developed microsatellite loci based on the whole-genome sequence of B. argentifolii. We investigated gene flow among populations of B. argentifolii collected between 1995 and 2018, covering the time since the first detection in Australia (1994). Structure plots and PCAs of the microsatellite data revealed three clusters in 1995–1996, indicating multiple introductions. Since then, B. argentifolii has become a widespread single genetic population across the continent, with no geographic genetic structure in recent samples. The haplotype network generated from mitochondrial COI shows that Australian B. argentifolii mostly has the same haplotype as the invasive populations established elsewhere around the world. Analysis of the more recent samples showed that gene flow was high across regions, indicating movement of B. argentifolii across Australia is currently extensive. Undesirable traits and pathogens not already present in Australia, including insecticide resistance and plant viruses, could arrive with any new introductions of B. argentifolii and are likely to spread rapidly and be difficult to contain. This highlights the importance of biosecurity and continued quarantine measures to prevent new incursions, even when a species has already established.

     

Dynamics of resistance to organophosphate and carbamate insecticides in the cotton whitefly <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Hemiptera: Aleyrodidae) from Pakistan

Field populations of adult whiteflies, Bemisia tabaci, from Pakistan were monitored from 1992 to 2007 for their susceptibility to seven organophosphate and three carbamate insecticides using a leaf-dip method. Malathion, quinalphos and chlorpyrifos generally exhibited no or a very low level of resistance in B. tabaci over a 16-year monitoring period. Resistance to profenofos, triazophos, parathion-methyl and ethion was usually low to high up to 1995, and then it dropped to very low levels during 1996–2004. Resistance levels again picked up from low to moderate levels for triazophos during 2005–2007, for parathion-methyl during 2003–2007, and for ethion in 2006. Among carbamates, thiodicarb resistance was high during 1994–1996, which dropped to moderate levels in 1997 and 1998 and to very low levels during 1999–2001, but again increased from low to high levels during 2002–2007. Methomyl resistance was moderate in 1994 and 1995, which dropped to very low levels during 1996–2002, and then increased to low levels during 2003–2007. Butocarboxim resistance remained very low during 1994–2003 and then increased from low to high levels during 2004–2007. The insecticides exhibiting no, very low or low resistance, and no cross-resistance among themselves can be exploited in devising an insecticide resistance management strategy to combat whitefly resistance in the field.     

Host preference and nymph performance of B and Q putative species of Bemisia tabaci on three host plants

Host selection is central to understanding the evolution of the interaction between herbivorous insects and host plants. Most studies on host selection of herbivorous insects are focused on the optimal oviposition theory which posits that the herbivores preferentially oviposit on plants that provide optimal conditions for offspring development (preference–performance hypothesis). However, the positive correlation between female oviposition preference and offspring performance is not always observed. Here, we determined the relationship between whitefly settling and oviposition preference and nymph performance of B and Q putative species of Bemisia tabaci on three host plants, cotton Gossypium hirsutum L., tomato Lycopersicum esculentum Mill, and poinsettia Euphorbia pulcherrima Wild. We further investigated whether nutritional and defensive chemistry of the three host species shaped whitefly settling and oviposition preference of both putative species. Foliar chemistry differed significantly among the three host species. Compared to cotton and tomato foliage, poinsettia foliage was 8?% lower in nitrogen, 60?% higher in carbohydrate, and 90?% higher in phenolic compounds, respectively. When given a choice, B and Q putative species of B. tabaci preferred settling on nutritionally superior tomato, whereas both putative species preferentially oviposited on nutritionally inferior poinsettia. Nymph survivorship of B and Q putative species was substantially reduced and nymph developmental duration (egg-to-adult) was markedly prolonged on poinsettia relative to those reared on cotton and tomato. Therefore, our results are consistent with the optimal foraging theory, rather than the optimal oviposition theory. Females of B and Q putative species of B. tabaci preferentially ovipositing on poinsettia may be a trade-off between nymph performance and the avoidance of natural enemy.     

Characterization of antibiosis and antixenosis to the whitefly silverleaf <Emphasis Type="Italic">Bemisia tabaci</Emphasis> B biotype (Hemiptera: Aleyrodidae) in several squash varieties

The objective of this study was to investigate the potential resistance mechanisms to Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) B biotype, in eight Cucurbita pepo varieties. Attractivity, oviposition preference, and nymphal development were evaluated under greenhouse and laboratory conditions. Variety Bianca was the least attractive to adult whiteflies in multi-choice tests. The whiteflies showed oviposition nonpreference (antixenosis) for Novita Plus, Bianca and Sandy in multi-choice test, and similar results were observed in no-choice tests with varieties Bianca, Novita, Caserta Cac and Sandy. Sandy expressed high antibiosis levels against whitefly nymphs, leading to 63.9% mortality. The high level of resistance in variety Sandy can serve as base for genetic improvement of C. pepo focusing on the development of resistant varieties to B. tabaci B biotype.     

Effect of sweetpotato whitefly, <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Homoptera: Aleyrodidae) infestation on eggplant (<Emphasis Type="Italic">Solanum melongena</Emphasis> L.) leaf

The nature of damage of sweetpotato whitefly, Bemisia tabaci (Gennadius) B biotype was investigated at the vegetative stage on eggplant (Solanum melongena L., family Solanasae, variety Baiyu) under laboratory conditions (temperature 25 ± 1°C, RH 70 ± 10% and photoperiod 12 h L:12 h D). The investigations were carried out after completing one generation of whitefly on the basis of morphology, physiology and anatomy of eggplant leaf. Significant differences were observed on three morphological parameters—leaf area, leaf fresh weight, and leaf dry weight. The reduction percentages of these three parameters were 26.6, 21.8 and 19.27%, respectively. Significant differences were also observed on two physiological parameters—chlorophyll content and rate of photosynthesis. The reduction percentages of these two parameters were 9.7 and 65.9%, respectively. There were no damaged tissue observed in the epidermis and mesophyll, but there were some damage tissue observed in the vascular bundle of infested leaf. There were no damaged vascular bundles observed in the control leaves. The non-damaged vascular bundles contained both xylem and phloem; while some damaged vascular bundles contained either xylem or phloem. Associated with the non-damaged vascular bundles on whitefly infested leaves were two settled whitefly nymphs apparently deriving nutrition from phloem sap. After one generation of whitefly infestation, the number of damaged and non-damaged vascular bundles of eggplant leaf was significantly different.     

The effect of season on the levels of predation by the ladybird <Emphasis Type="Italic">Serangium parcesetosum</Emphasis> Sicard (Coleoptera: Coccinellidae) on the cotton whitefly <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Genn.) (Homoptera: Aleyrodidae), a serious pest of eggplants

The whitefly Bemisia tabaci is a serious pest of eggplants, especially those grown undercover in polytunnels and greenhouses. Due to increasing levels of resistance of B. tabaci to a wide range of insecticides, there is now an urgent need to explore other non-chemical methods of control. In this study, Serangium parcesetosum, a ladybird, was evaluated as a possible biological control agent of B. tabaci’s winter and spring populations which infests eggplants grown undercover in Turkey. It was found that in winter, S. parcesetosum failed to control B. tabaci, even when the ladybird population was augmented six times over the course of the experiment. This contrasted with that observed in spring when, with only one introduction of the ladybird, control of the pest was gained within 3 weeks after release. In spring, the B. tabaci population in the cages receiving two and four S. parcesetosum adult per plant showed 56 and 53% reduction, respectively. The percent reduction in B. tabaci population rose to 98.6 and 98.3% in both cages, respectively, by the end of experiment. It is suggested that release of S. parcesetosum against B. tabaci during spring months may be offered as an alternative solution to increase implementation of biologically based B. tabaci management. In winter other biological control agents are needed and these need to be further explored.     

Influence of host plant species of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) on some of the biological and ecological characteristics of the entomophagous Serangium parcesetosum Sicard (Col., Coccinellidae)

The entomophagous Serangium parcesetosum Sicard (Col., Coccinellidae) is an effective predator of some whitefly species. However, information on the influence of the preys host plant species on its biological and ecological characteristics is still lacking in the literature. Therefore, the current study focuses on the possible influence of three greenhouse and two field host plant species of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) on the number of eggs laid by S. parcesetosum. In addition, because of the economic importance and widespread planting of cucumber in greenhouses and cotton in the field, these plants were selected for further investigation into the development, mortality, longevity and reproduction of S. parcesetosum at a high temperature in the laboratory. Results showed that S. parcesetosum was able to lay eggs on all five host plant species of B. tabaci, whether greenhouse or field plants. However, among the three greenhouse plant species studied, S. parcesetosum females laid the highest number of eggs on cucumber followed by tomato and then sweet pepper. Of the two field plant species, significantly higher numbers of eggs were laid on tobacco than on cotton. S. parcesetosum could develop either on cucumber or on cotton as preferable host plant species for B. tabaci. There were significant differences in mean developmental duration of larval instars of the same sex between both host plant species; the duration was significantly shorter on cucumber than on cotton. There were no significant differences for mean total developmental duration from egg to adult emergence between both host plant species within the same sex; females showed a mean of 15.9 days and males of 15.1 days on cucumber, while on cotton the means were 17.2 days for females and 16.2 days for males. Total mortality percentage of S. parcesetosum during development from egg to adult stage was lower on cucumber than on cotton, 20.6 and 23.8%, respectively. Longevity of S. parcesetosum varied according to host plant species and sex with a mean of 63.4 days for females and 50.3 days for males on cucumber, and 92.4 days for females and 52.5 days for males on cotton. On cucumber, mean period of oviposition of S. parcesetosum was significantly longer than on cotton. Mean total fecundity was significantly higher on cucumber than on cotton, with means of 97.7 and 31.0 eggs/female, respectively.     

Genetic diversity of Quercus glandulifera var. brevipetiolata populations in three forest communities with different succession stages

In order to understand the relationship between population succession and its genetic behavior, random amplified polymorphic DNA (RAPD) technique was used to analyze the genetic diversity of Quercu glandulifera var. brevipetiolata populations in three forest communities with different succession stages (coniferous forest, coniferous and broad-leaved mixed forest, evergreen broad-leaved forest). The results showed that 145 repetitive loci were produced in 60 individuals of Q. glandulifera using 11 primers, among which 120 loci were polymorphic, and the total percentage of polymorphic loci was 82.76% with an average of 64.14%. Estimated by the Shannon information index, the total genetic diversity of the three populations was 0.4747, with an average of 0.3642, while it was 0.3234, with an average of 0.2484, judged from the Nei index. Judged from percentage of polymorphic loci, Shannon inform at ion index and Nei index, the genetic diversity followed a decreasing order: coniferous forest > broad-leaved mixed forest > evergreen broad-leaved forest. Analysis of molecular variance (AMOVA) showed that 69.73% of the genetic variance existed within populations and 30.27% of the genetic variance existed among populations. The coefficient of gene differentiation (GST) was 0.2319 and the gene flow (N _m) was 1.6539. The mean of genetic identity among populations of Q. glandulifera was 0.8501 and the mean of genetic distance was 0.1626. The genetic identity between the Q. glandulifera population in the coniferous forest and that in the coniferous and broadleaved mixed forest was the highest. UPGMA cluster analysis based on Nei’s genetic distance showed that the population in the coniferous forest gathered with that in the coniferous and broad-leaved mixed forest firstly, then with that in the evergreen broad-leaved forest. The genetic structure of Q. glandulifera was not only characteristic of the biological characteristics of this species, but was also influenced by the microenvironment in different communities. __________ Translated from Journal of Northwest Forestry University, 2008, 23(1): 18–22 [译自: 西北林学院学报]     

Combining banker plants to achieve long-term pest control in multi-pest and multi-natural enemy cropping systems

Banker plants increase biological pest control by supporting populations of non-pest arthropod species, used as alternative hosts or prey by natural enemies. Due to the specificity of trophic interactions, banker plants may not efficiently promote natural enemies with different ecologies. Yet in most cropping systems, different pest species are present together and require different biocontrol agents to efficiently control them. In the present study, we tested the combined use of two banker plants and their associated prey/host to enhance populations of the specialist parasitoid Encarsia formosa targeting the main tomato pest Bemisia tabaci, and a polyphagous ladybird Propylea japonica targeting the secondary pest Myzus persicae in tomato crops. In a laboratory and a greenhouse experiment, we measured the abundances of these four species using the Ricinus communis—Trialeurodes ricini banker plant system alone, in combination with the Glycines max—Megoura japonica system, or in absence of banker plants. We found that the first banker plant system enhanced populations of E. formosa, resulting in increased suppression of B. tabaci populations and the suppression of their outbreak in both our laboratory and greenhouse experiment. Conversely, abundances of P. japonica were not affected by this first system, but were significantly increased when the second was present. This resulted in increased control of M. persicae populations and the suppression of their early and late outbreaks. Our study demonstrates the potential for combined banker plants to provide long-term, sustainable control of multiple pests by their target natural enemies in complex agroecosystems.

     

Characterization of antibiosis to the silverleaf whitefly Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) in cowpea entries

The silverleaf whitefly, Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae), is considered one of the most important pests of cowpea (Vigna unguiculata L. Walp.), limiting the productivity of this crop worldwide. Chemical control is still the main strategy for the management of populations of this insect. However, due to the harmful effects of pesticides on the environment and to humans, less injurious alternatives have been investigated. Along this line, the use of resistant genotypes can be a valuable tool for the control of the silverleaf whitefly. In this paper, we investigate some biological aspects of B. tabaci biotype B confined on 14 genotypes of cowpea. We evaluated the incubation period, egg viability, duration of nymphal stages, total duration of the juvenile phase, instar mortality and total mortality of the immature stage. The genotype MNC 99-541 F21 exhibited antibiosis against the whitefly, prolonging the lifecycle of the insect. The genotypes Canapu, BRS-Urubuquara and TE97-304 G-4 also exhibited antibiosis, causing high nymphal mortality. These results may help in breeding programmes to develop cowpea lines with resistance to B. tabaci biotype B.     

Prey consumption preferences of<Emphasis Type="Italic"> Serangium parcesetosum</Emphasis> Sicard (Col., Coccinelidae) for different prey stages,species and parasitized prey

Serangium parcesetosum Sicard (Col., Coccinellidae) is considered one of the important predators of whiteflies. However, knowledge about its preferences for different prey stages, species and parasitized prey is still lacking in the literature. The present work investigated the preferences of S. parcesetosum for different stages of B. tabaci, different prey species and B. tabaci parasitized by Encarsia formosa Gahan (Hym., Aphelinidae) by prey consumption at different temperatures in the laboratory. Results showed that L₂ and L₄ predatory instars of S. parcesetosum preferred puparia to nymphs and eggs of Bemisia tabaci (Genn.) (Hom., Aleyrodidae). The mean daily prey consumption was 5.1–9.0, 4.5–6.2 and 3.6–4.3 by L₂ and 6.4–9.7, 5.5–8.5 and 2.5–7.5 by L₄ for puparia, nymphs and eggs, respectively. Adult females, however, indicated a significantly greater preference for both puparia and nymphs, consuming a daily mean of 6.4–7.5 puparia and 5.1–6.7 nymphs, but only 3.0–4.7 eggs. At 18 and 30 °C, all S. parcesetosum stages tested significantly preferred B. tabaci and Trialeurodes vaporariorum Westwood (Hom., Aleyrodidae) over the other three prey species offered. At both temperatures, all predatory stages preferred B. tabaci to T. vaporariorum, the L₂ instar at 18 °C, showing significantly more preference for B. tabaci than T. vaporariorum. In contrast, very few individuals were consumed from Aphis gossypii Glover (Hom., Aphididae), Frankliniella occidentalis (Pergande) (Thys., Thripidae) and Tetranychus urticae Koch (Acari, Tetranychidae). At 18 °C, a daily mean of 7.5–8.0, 6.6–9.0 and 6.7–8.1 B. tabaci as well as 5.3–6.4, 5.4–7.8 and 5.6–6.3 T. vaporariorum was consumed by L_2, L₄ and adult females, respectively, while at 30 °C, L₂, L₄ and adult females consumed a mean of 9.3, 8.8–9.7 and 8.3–9.7 B. tabaci/day as well as 8.3–9.0, 7.8–9.1 and 5.5–8.4 T. vaporariorum/day, respectively. S. parcesetosum L₂ and L₄ instars as well as adult females and males at both studied temperatures showed a significant tendency to avoid B. tabaci puparia after 5 days of parasitism by E. formosa and preferred to feed on unparasitized whiteflies. At 18 °C, the mean daily consumption was 8.7 and 0.2 (L₂), 11.1 and 0.6 (L₄), 12.1 and 1.0 () as well as 10.5 and 0.2 (), while at 30 °C the means were 15.9 and 0.5 (L₂), 19.8 and 1.0 (L₄), 18.9 and 1.2 () as well as 17.4 and 0.6 () from unparasitized and parasitized B. tabaci puparia, respectively.This paper is gratefully dedicated to Prof. Dr. W Schwenke on his 83rd birthday, 22 March 2004     

Adult attractiveness and oviposition preference of Bemisia tabaci biotype B in soybean genotypes with different trichome density

Bemisia tabaci consists of a complex of morphologically indistinct biotypes, varying with respect to their host ranges and ability to transmit plant viruses. Biotype “B” has increased in importance at every growing season in soybean crops in Brazil. The objective was to evaluate B. tabaci biotype B infestations in 24 soybean genotypes, including cultivars of expression for planting and the main sources of insect resistance. The study was performed in a greenhouse with evaluations for adult attractiveness and oviposition preference (free-choice test); these parameters were correlated with trichome density. Three evaluations were carried out, and counts were obtained for number of adults, eggs, and trichomes on the abaxial surface of the leaves. The experimental design consisted of randomized blocks (192 plots). In all three evaluations, “Coodetec 215” was the most attractive to adults; the least attractive cultivars were “IAC 18” (first); PI 274453, “IAC 18,” and D 75-10169 (second); and “IAC 24” (third). As to oviposition preference, “Coodetec 215” showed the highest mean in all evaluations; the lowest means corresponded to “IAC 18” (1st); PI 274453 (2nd); and PI 274453 and L1-1-01 (3rd). No significant correlation was observed between trichome density and oviposition preference and adult attractiveness. Considering all parameters and focusing on commercial germplasm, “IAC 24,” as well as “BRS Barreiras,” “IAC 18,” “IAC 17,” and “IAC 19” can be indicated for planting in regions and/or seasons where B. tabaci biotype B is a problem for soybean production or even in properties where other crops affected by this whitefly are grown simultaneously with soybean or after this legume is grown.     

Plant-derived essential oils affecting settlement and oviposition of Bemisia tabaci (Genn.) biotype B on tomato

The silverleaf whitefly Bemisia tabaci (Genn.) biotype B (Hemiptera: Aleyrodidae) is an economically important pest of tomatoes Solanum lycopersicum (L.), causing irregular ripening on fruits and transmitting several plant pathogenic geminiviruses. The management of this pest is commonly based on repetitive spraying with synthetic pesticides, causing serious environmental damages and increase of resistance by insect population. In the present study, essential oils from the leaves of Artemisia camphorata Vill., Ageratum conyzoides L., Foeniculum vulgare Mill., Lippia alba (Mill.) N. E. Br., Plectranthus neochilus Schltr., and Tagetes erecta L. were investigated for their possible repellent and oviposition-deterrent effects against B. tabaci biotype B on tomato. In a multi-choice assay, P. neochilus essential oil was the most active repellent and oviposition deterrent. Essential oils of A. conyzoides and T. erecta significantly deterred the female B. tabaci biotype B from laying eggs on treated tomato leaflets compared with the control. (E)-Caryophyllene (30.67 %) and the monoterpenes α-pinene (15.02 %) and α-thujene (11.70 %) were identified as the major constituents of the essential oil of P. neochilus. Our findings demonstrated the potential of essential oil of P. neochilus and other oils in the reduction of settlement and oviposition of B. tabaci biotype B on tomato.     

Biological control of<Emphasis Type="Italic"> Bemisia tabaci</Emphasis> Biotype “B” (Homoptera: Aleyrodidae) by introduction,release and establishment of<Emphasis Type="Italic"> Eretmocerus hayati</Emphasis> (Hymenoptera: Aphelinidae)

For the biological control Bemisia tabaci (Genn.) Biotype B (Homoptera: Aleyrodidae) , about 200,700 individuals of the imported parasitoid Eretmocerus hayati Zolnerowich and Rose (Hymenoptera: Aphelinidae) were released during 2000 and 2002 on different host plants in Egypt. The average parasitism rates in different governorates on Lantana camara, Gossypium barbadence (cotton), Helianthus annus (soybean) and Solanum melongena (eggplant) were 10.3 and 14%, 16 and 11.4%, 12.9 and 8.7%, 18 and 13% during 2001 and 2002, respectively. The population of E. hayati correlated significantly with the buildup of the whitefly population in all three governorates, which indicated the establishment of the E. hayati parasitoid on these economically important crops in Egypt.