The silverleafwhitefly Bemisia tabaci biotype B is one of the most harmful insect pests for agricultural and vegetable crops. Beside the direct damage, it transmits pathogenic virus and induces plant physiological disorders, such as the squash silverleaf disorder. In this research we evaluated the development of leaf silvering in squash cultivars submitted to artificial infestation of B. tabaci biotype B. An experiment was conducted under field conditions, in Campinas, São Paulo State, Brazil, during the season 2003-2004. The germplasm (Cucurbita spp.) comprised of seven cultivars of summer squash and nine of bush squash. The experiment used a complete randomized blocks design, with 16 treatments (cultivars) and five replications. Each plot consisted of two plants. The artificial infestation was done when the plants emitted the third pair of leaves, by transplanting soybean plants infested with silverleafwhitefly between the squash plots. The leaf silvering was evaluated every two or three days, using a rating scale varying from 1 (no symptom) to 5 (leaves completely silvered). The highest level (5.0) was observed in ‘Baianinha’, ‘Golden Delight’, ‘Caravela’ and ‘Arlika’, while ‘novita’ (2.5), ‘Atlas’ (2.0) and ‘Atlanta AG-303’ (1.5) showed light symptoms, indicating that these have low sensibility to this physiological disorder.
Effect of sugar apple oil on the silverleafwhitefly. Sugar apple seeds emulsified oil at 0.5% caused 55.8% mortality of silverleafwhitefly nymphs in five days when sprayed on infested tomato leaves in the greenhouse (Table 1), against only 1.5% mortality in the control. Ten days after the spray, the mortality rates increased from 8.0% in the control to more than 90% when 0.5 or 0.25% oil treatments were used. The treatment with 0.125% oil also increased the mortality rate to 54.1%, more than 50% during the same period of time. Sugar apple seed oil was not phytotoxic to tomato plants even at the concentration of 0.5%. The mortality rates caused by β-cy fluthrin + imidacloprid were similar to those caused by 0.5 or 0.25% of sugar apple seed oil during the test period (Table 1).
The management of silverleafwhitefly in common beans has been carried out almost exclusively using synthetic insecticides from different chemical groups. However, there are several reports of resistance of whitefly populations to active ingredients, jeopardizing the effectiveness of this control tacti c (Horowitz et al. 2002; Alon et al. 2008; Houndete et al. 2010; Ma et al. 2010). More over, the abusive use of synthetic insecticides can negatively impact the environment, in particular the systemic insecticides that act by contact and ingestion (neonicotinoids based), cause undesirable effects on nontarget organisms, pollinators and natural enemies, as well as their leaching capacity in groundwater (Desneux et al. 2007; Furlan and Kreutzweiser 2015; Alford and Krupke 2017). Thereby, around the only control method used, it makes necessary search ing for new control strategies in an efficient and environmentally safe manner, according to the integrated pest management (IPM) precepts. The IPM is a dominant paradigm that guides most aspects of implementation of insect pest management, whose philosophy and history are well document ed (Perkins 1982; Kogan 1998; Pedigo 2002).
Among the plants of the Meliaceae family, A. indica presents a larger range of studies regarding the behavior of B. tabaci. According to Baldin et al. (2007), among the aqueous extracts sprayed on tomato plants that did not stimulate colonization by B. tabaci biotype B, the extract of neem seeds and leaves stood out with means of adults and eggs below 0.60 and 0.50, respectively, differing from the treatment with distilled water. Quintela &Pinheiro (2009) also reported reduced silverleaf whitely oviposition on leaves of common beans sprayed with aqueous extract of A. indica. However, in this study, the aqueous extract of neem seeds was classiied as neutral for host selection. These differences may be attributed to the methodologies used in the studies such as preparation, concentration, and source of material.
Similar results as indirect selection were found by Oliveira et al. (2012), selected genotypes with the highest trichome density and found levels of resistance to the moth Tuta absoluta that were much higher than those exhibited by susceptible controls, and treatment BPX-367D-238-02 was particularly effective. Maluf et al. (2007) found similar results of indirect selection for resistance to the red spider mite T. urticae. This finding indicates that a correlation exists between trichome density and silverleafwhitefly oviposition; that is, the higher the glandular trichome density, the lower the level of oviposition (Tables 3 and 4). Oriani, Vendramim and Vasconcelos (2011) found genotypes with very high antixenosis with regard to oviposition associated with the presence of type IV glandular trichomes. According to Aragão, Dantas and Benitas (2000), who identified and quantified foliar trichomes in tomato specimens, leaflets with the highest concentrations of 2-TD were associated with the highest glandular trichome densities. However, that correlation was not perfect because the measurement of glandular trichome density is associated with sampling error and does not consider possible differences in the concentration of allelochemicals in each trichome.
Segregating populations were developed for the study described. The parents used to develop these populations were S. galapagense (LA1401) and S. lycopersicum (TOM-684). LA1401 is a wild accession characterized by a high level of acylsugars, the presence of type IV trichomes, and resistance to insects (JOUY, BORDAT; BESSIERE, 1992, LUCATTI et al., 2013). Previous studies at UFLA/Hortiagro demonstrated resistance of LA1401 to the silverleafwhitefly Bemisia tabaci biotype B (= Bemisia argentifolii) (data not shown). TOM-684 (susceptible to insects) is a proprietary fresh-market tomato inbred line from Hortiagro Sementes S.A. A cross was initially obtained between the line TOM- 684 (female parent) and the accession LA1401 (male parent), thus obtaining the F1 generation. F1 plants were self-pollinated to obtain the F2 generation and backcrossed with the parental accession TOM-684 to obtain the backcross BC1 [=(F1 x TOM-684)]. Segregating progeny and parental accessions were phenotyped for the density and type of trichomes (LUCKWILL, 1943). The F2 population was used to identify QTLs associated with trichomes, and the F1BC11 backcross population was used to validate these QTLs. Tomato plants were grown in a greenhouse in a completely randomized design, with parents included as replicated checks. Experiments consisted of 20 plants from each parental line, 20 plants from the F1, 140 individuals from the F2. For the backcross120 individuals were included.
groups were formed (Table 1). The hybrid PE 001 had the longest incubation period, in comparison to F1 011, F3 008. The wild accession FLA 003 ranked into the group of genotypes with the lowest incubation periods. The intermediary group included the genotypes F2 015, F4 002, 'Ecuador 72' and 'Cigana Preta'. These incubation values are higher than the reported one – 6.5 days on the cassava cultivar Cascuda – by Gazola et al. (2009), for the same species of whitefly, at 25±3ºC. The hybrid PE 001 stood out from the others because, on this genotype, the higher values of the insect-egg incubation time increased the time for the whitefly to complete its cycle.
All kanamycin resistant lines showed the amplification of Figure 3. In-vivo bioassay of transgenic and control plants with whitefly. Control and transgenic lines challenged with freshly emerged adult whiteflies. (A) Whiteflies colonizing on control plant while the transgenic lines show protection, lower panel shows enlarged view of upper panel (B) The surviving number of insects were counted after 5, 10 and 15 days. The count of whitefly and percent population reduction was plotted for each of the selected lines. Bars = number of insects; lines = population reduction over control. Data shown are average of six plants of each line (3experimental setups 62 plants/setup) 6 standard deviation. Asterisk indicates significant difference in treatments (transgenic plants) compared to control (dsasal) plants (Student’s t-test, *p,0.05,**p,0.01).
In both the winter and rainy seasons, whitefly infes- tations were higher at 25 and 32 DAE and decreased until the last sampling date (60 DAE). Our results agree with those of Jesus et al. (2010), who evaluated resistance of common bean genotypes to B. tabaci biotype B and found that the infestation was higher during the initial stages of plant development. Similar results were found by Tosca- no et al. (2002) and Campos et al. (2005) when assessing whitefly oviposition in tomato and cotton. In our study, at 25-32 DAE, plants of different cultivars were at growth stages V4 (third trifoliate open and plain) to R5 (first flo- ral raceme in lower nodes, pre-flowering) (Fernandez et al., 1986). In this period, whiteflies are likely to encoun- ter the best conditions for development, such as suitable chemical and morphological plant features (Walker and Perring, 1994). Studies should be conducted to further investigate these observations, since a similar condition was observed in tomato (Toscano et al., 2002) and cotton (Campos et al., 2005). Higher energy accumulation at this stage of development in plants with subsequent nutrient possibly shift from leaves to flowers and to fill pods and seeds (Marschner, 1995), which may explain population decline from this period to the last sampling date.
In addition to direct mortalities caused by acute concentrations of insecticides, some biological traits of target pests may be also affected by sublethal doses. The cotton whitefly, Bemisia tabaci (Hem: Aleyrodidae) is an important pest of a wide variety of agricultural crops across the world. The control of B. tabaci largely relies on wide application of chemical insecticides. In this study, we analyzed the life table parameters to evaluate the sublethal effect of three plant-derived insecticides (Fumaria parviflora (Fumariaceae), Teucrium polium (Lamiaceae), and Thymus vulgaris (Lamiaceae)) and two chemical insecticides (pymetrozin and neemarin) on B. tabaci. The whiteflies were allowed to oviposit on plants infected with each of the five insecticides using leaf-dip method. The data were analyzed using the age-stage two-sex life table. We found significant differences in the gross reproductive rate (GRR), the net reproductive rat (R 0) , the intrinsic rate of increase (r)
Whitefly chitin hydrolysis: About 20 µL crude enzyme (0.08 U mg −1 protein) of each chitinase was used to hydrolyze whitefly exoskeleton. Microscopic observation showed that whitefly exoskeleton were thinned out. Chitinases of the isolates made the exoskeleton getting thinner after 3 days treatment. Treatment of chitinase showed significantly different than that of control on whitefly exoskeleton. The treated exoskeletons were become more transparent than that of control particularly on the effect of I.21 crude chitinase (Fig. 5).
ABSTRACT - The toxicity of thiamethoxam and imidacloprid to Podisus nigrispinus (Dallas) nymphs, and their efficacy against whitefly and cotton aphid were studied. Thiamethoxam and imidacloprid were 217.6 and 223.4 and 1435.2 and 346.8 times more toxic (LC 90 ) by ingestion than by residual contact to 2nd- and 5th-instar nymphs of this predator, respectively. Nymphs caged on potted cotton plants and treated with either insecticide at 1 mg (a.i.) per plant or more had lower survival than those on untreated plants, up to day 52 after treatment. Thiamethoxam and imidacloprid reduced field survival of P. nigrispinus compared to untreated plants up to nine days after treatment. Thiamethoxam and imidacloprid showed significant control of whitefly in comparison with untreated plants up to 40 days after treatment in potted plants. Whitefly population had low density over time in the field with no differences between treatments and only at day 64 higher whitefly population was observed on untreated plants and plants treated with 0.5 mg (a.i.) of thiamethoxam per plant. Plots treated with thiamethoxam and imidacloprid at doses over 1 mg (a.i.) per plant retained aphid infestation lower than 10% up to 61 days of plant age. Untreated and treated plants with 0.5 mg of thiamethoxam showed infestation of 68.7 and 31.2%, respectively, at this time. Thiamethoxam and imidacloprid used in cotton for whitefly and aphid control aiming P. nigrispinus preservation can be more successful when they are used at doses bellow 1 mg (a.i.) per plant due to shorter residual effect.
Antibiosis. Treatments did not affect the duration of the egg stage of B. tabaci biotype B. However, significant differences occurred in the development of first to fourth instar nymphs and in the duration of the total whitefly cycle, when feeding on cucumber plants treated with calcium silicate and BTH, regardless of the application method. All application methods of calcium silicate and BTH caused a significant increase in the duration of the developmental period of second to fourth instar nymphs, as compared to the control. For first instar nymphs, the application of BTH and BTH with calcium silicate delayed molting to the second nymphal instar by more than 70% (Table 3).
Greenhouse tomatoes, Solanum lycopersicum, are severely attacked by whiteflies, which are small sucking insects of the Aleyrodidae family (order Hemiptera). Two main species are recognized, Bemisia tabaci Gennadius and Trialeurodes vaporariorum Westwood. The greenhouse whitefly T. vaporariorum, a cosmopolitan species, has been reported in South America in Brazil, Chile, Colombia, Ecuador, Guiana, Peru, Uruguay, Venezuela and Argentina (Arnal et al 1993, Basso et al 2001, Lourenção et al 2008). It is the most common and abundant whitefly in Argentine horticultural greenhouse crops, especially infesting tomato plants (Viscarret 2000, Polack 2005).
resistance in T. vaporariorum. The response of TV8pyrsel after only three generations of selection demonstrated a very potent resistance to this insecticide. Interestingly, pyriproxyfen is not registered for use in Germany. The moderate resistance found in TV8 could be due to either cross-resistance between pyriproxyfen and a different class of insecticides or transfer of whitefly infested plant materials from regions were pyriproxyfen is used for whitefly control. However, selection of TV8 with pyriproxyfen did not result in enhanced resistance to other compounds belonging to major insecticides classes used for whitefly control, such as neonicotinoids, tetronic acid derivatives and pyrethroids (Figure 1). This leads to the conclusion that the resistance identified in this strain is due to European or global plant trade.
Recently emerged males and females fed with whitefly eggs laid on each tomato genotype were indi- vidually placed in plastic cages (16 cm in height and 13 cm in diameter). The cage had a plastic lid with a 6 cm diameter hole that was covered with an anti-aphid screen to allow airflow into the cage. The leaves were placed in a 5-cm-long plastic hose filled with distilled water attached to the inner wall of the cage. Until their death, the insects were daily fed ad libitum with whitefly eggs laid on soybean leaves. Females were confined with two or three males over 24 h for mating, after which the males were removed. For evaluation purposes, the leaves were observed under a stereoscopic microscope, and the daily oviposition and male and female survival were determined.
The tests were conducted in a greenhouse in Jaboticabal, SP, Brazil in 1999/2000. The wild genotypes of Lycopersicon pennellii (LA 716), L. hirsutum f. glabratum (PI 134417), L. hirsutum (PI 127826 and PI 127827) were provided by EMBRAPA Hortaliças, Brasília- DF; the commercial genotypes (L. esculentum) were obtained from the companies Agroflora (Bruna VFN hybrid) and Hortec (Santa Clara open pollination cultivar). The insects used in the experiments were obtained from a pool of whitefly individuals captured at the Entomology section of Instituto Agronômico de Campinas (IAC). They were kept in cages measuring 2.0 x 3.0 m at the bottom, and 2.0 m in height, manufactured out of an iron frame covered by anti-aphid screen. Soybean, cabbage and drunkard’s dream plants were placed inside the cage and replaced as necessary.
Whitefly adults and nymphs settle on the underside of the cotton leaves to feed themselves. The insects suck large vol- umes of phloem sap, rich in sucrose, but they have low con- centrations of essential amino acids (TERRA; FERREIRA, 2009). Amino acids are important for performing the insect’s physiological processes and need to be concentrated. For this, excess water is withdrawn by the filter chamber present in its digestive system and excreted along with sugars in the form of mela, which is deposited on the cotton leaves or plume. This substance is used as a substrate for growing saprophytic fungi such as Capnodium, followed by the fumagine that reduces the photosynthetic area of the leaves. Both honeydew and sooty mold contaminate the fiber and reduce its quality, rendering it unsuitable for the textile industry. ARAÚJO; BLEICHER (2004) report that the crop’s critical period to attack from whiteflies is starting from the emergence of the plants until the appearance of the first buds.