Integrated Management of Whitefly, Bemisia tabaci (Gennadius) and Potato Apical Leaf Curl Virus in India

This paper reviews the importance of Potato apical leaf curl virus (PALCV) in India, the biology of its major vector Bemisia tabaci and possible control measures of PALCV and B. tabaci. PALCV has appeared as a new problem in potato growing areas of northwestern plains of India. The first report of PALCV was made from Hissar around 2000. PALCV is a whitefly (B. tabaci) transmitted viral disease and the symptoms are manifested primarily in the form of upward or downward curling of leaves, with 40–75% infection being recorded in cultivars grown in the Indo-Gangetic Plains of India. B. tabaci is a polyphagous pest that feeds on numerous fibre (particularly cotton), food, vegetable and ornamental plants. B. tabaci produces many generations in a year and reaches high population densities. To check the disease incidence, whitefly suppression using imidacloprid either as seed treatment or as foliar application early in the season is recommended. To minimize within-field spread of viruses, removal of virus-infected plants is suggested. Application of mineral and vegetable oils has been found to inhibit virus transmission and possibly can help to avoid difficulties with insecticide resistance in whiteflies.     

Evaluation of common bean lines for their reaction to tomato yellow leaf curl virus-Ir2

Tomato yellow leaf curl virus (TYLCV) can cause an economically relevant disease in the major tomato growing regions, and no resistance has been identified in commercial and wild tomato cultivars in Iran. In the present study, 34 common bean lines were screened for their reaction to TYLCV-Ir2 under greenhouse conditions. The experiment was conducted in a randomized complete block design with three replications. Bean plants were inoculated at the first trifoliate stage with viruliferous whiteflies (Bemisia tabaci biotype B) and were then sprayed with an insecticide and maintained in whitefly-proof greenhouse. The inoculated plants were monitored for the development of symptoms and the presence of viral DNA by polymerase chain reaction (PCR) four weeks after inoculation. Results revealed that out of the 34 lines, five were resistant. These lines exhibited either no symptoms or very mild symptoms and no viral DNA was detected in them by PCR. Two lines, which showed no typical disease symptoms but contained viral DNA, were identified as tolerant to TYLCV-Ir2. The vector feeding preference for common bean lines was assessed. Results indicated a significant difference in adult whitefly numbers among bean lines but there was no relationship between the number of whiteflies and disease symptom severity. The resistance to TYLCY-Ir2 expressed in common bean lines may be useful as source of resistance for the development of resistant commercial common bean cultivars.     

Effectiveness of imidacloprid in combination with a root nitrogen fertilizer applied to tomato seedlings against Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly Bemisia tabaci (biotype B) is a worldwide pest of vegetables and field crops. We tested the efficacy of imidacloprid (IM) with a root fertilizer ‘Root Feed (RF)’ (9% N, 7% Ca, 1.5% Mg and 0.1% B) sub-irrigated in the growing medium against the whitefly on tomato. Tomato seedlings (3–4 true leaves) were treated with 0, 3, 6 or 12 mg active ingredient (a.i.) seedling⁻¹ of IM and with RF (0, 0.02, 0.04 or 0.08 ml seedling⁻¹). The efficacy of 12 mg IM seedling⁻¹ was further evaluated in the greenhouse for 60 days. The survival of B. tabaci adults, nymphs, and egg production were negatively affected by the treatments in a dosage-dependent manner. Treatment of 12 mg IM seedling⁻¹ caused >60% adult and nymph mortality 50 days after treatment (DAT). The active ingredient of IM in tomato leaves also increased with the increase of IM dosage. The RF exhibited a limited effect on B. tabaci. However, the mortality of whitefly adults and nymphs treated with RF (0.02 or 0.04 ml seedling⁻¹) positively interacted with IM, and was greater than IM alone. In the greenhouse, 12 mg IM seedling⁻¹ greatly reduced the number of whitefly adults and increased the dry weight of the tomato plants at 30 DAT. In conclusion, application of 12 mg IM seedling⁻¹ on tomato seedlings before transplanting effectively controled B. tabaci for up to 50 days, and the efficacy of IM combined with 0.02 ml RF seedling⁻¹ performed even better. This could be a cost-effective method for managing B. tabaci on tomato and other vegetables.     

Managing Meloidogyne incognita and Bemisia tabaci with thiacloprid in cucumber crops in China

Field trials were conducted to determine the potential use of thiacloprid for integrated Meloidogyne incognita and Bemisia tabaci B biotype control in cucumber (Cucumis sativus Linn.) in China. The following five treatments were evaluated: three thiacloprid doses (7.5, 15, and 30 kg ha⁻¹), an avermectin treatment (7.5 L ha⁻¹) and an untreated control. All thiacloprid application rates were effective for reducing the M. incognita and B. tabaci B biotype populations. M. incognita was reduced by 51.0%∼86.7% on 60th day and B. tabaci B biotype was reduced by about 37.2%∼95.3% within 21 days, respectively. In addition, greater thiacloprid doses resulted in fewer nematodes and whiteflies. Over two successive years, the cucumber plants that were treated with thiacloprid at a dose of 15 kg ha⁻¹ had the greatest plant height, plant vigor and marketable yield, which were 134.1 cm, 91, 1514.3 g plant⁻¹, respectively in 2010–2011 and 151.9 cm, 93, 1651.4 g plant⁻¹, respectively in 2011–2012. In addition, thiacloprid was superior to avermectin. The results of this study demonstrated that thiacloprid could be used in cucumber production for the integrated control of M. incognita and B. tabaci B biotype. Furthermore, a dose of 15 kg ha⁻¹ of thiacloprid was recommended for controlling nematode and whitefly populations according to the control effect and marketable cucumber yield.     

Management of Bemisia tabaci biotype B with botanical and mineral oils

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

Sudanese cotton and the whitefly: a case study of the emergence of a new primary pest

In the late 1970s the whitefly Bemisia tabaci (Gennadius) became the primary cotton pest in the Sudan, superseding the American bollworm Heliothis armigera (Hübner). DDT and a DDT/dimethoate combination were used to control the bollworm and, simultaneously, jassids and whiteflies. B. tabaci, a secondary pest at first, became resistant to dimethoate by frequent selections from 1964 onwards. At the same time, fertility stimulation occurred due to DDT residues on cotton plants. Finally, resistance reached a level so that the whitefly were not controlled by dimethoate, monocrotophos or other organophosphorus insecticides, and stimulation by DDT could exert its full effect. The consequence of this was a tremendous flare-up of the whitefly by 1980/81. This train of events was concluded from laboratory and field studies of the resistance patterns, as well as the acceleration effects from DDT residues on plants to the whitefly. A current hypothesis claiming that the problems arose from the elimination of beneficial insects through insecticide applications is reviewed in the light of experimental evidence and practical experience.     

Insecticide resistance in Bemisia tabaci biotype Q (Hemiptera: Aleyrodidae) from China

Dispersion of invasive biotypes of the tobacco whitefly, Bemisia tabaci, has led to protracted crop protection constraints in numerous countries over recent decades. These polyphagous, highly efficient vectors of plant viruses present an intractable problem as they frequently carry a diverse suite of insecticide resistance mechanisms. In many areas of China, native biotypes have been supplanted by the invasive and globally widespread biotype B since the 1990s. More recently, biotype Q has established, posing a new and more potent threat to agricultural production systems throughout the country. Insecticide resistance profiles for a range of Chinese B. tabaci strains covering biotypes B and Q were examined, to establish the potential for insecticides to play a pivotal role in biotype competition and ultimate displacement. Commonly used compounds including pyrethroids, neonicotinoids, abamectin and pyriproxyfen were targeted as widespread use is pre-requisite to drivers of population dynamics on a national scale.     

Eradicating Bemisia tabaci Q biotype on poinsettia plants in the UK

The sweetpotato whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) continues to be a serious threat to crops worldwide. The UK holds Protected Zone status against this pest and, as a result, B. tabaci entering on plant material is subjected to a policy of eradication. Q biotype (Mediterranean species) is the predominant whitefly now being intercepted entering the UK. With increasing reports of neonicotinoid resistance in this biotype, it is becoming more problematic to control/eradicate. The current study evaluated sequential insecticide applications of a range of chemicals and two entomopathogenic fungi, Beauveria bassiana and Lecanicillium muscarium, applied within the first 21 days after potting poinsettia cuttings. All sequential treatment programmes tested eradicated Q biotype from poinsettia plants. The efficacy of chemicals and fungi against various Q biotype life-stages was also evaluated as individual treatments. Against the egg stage, abamectin (Dynamec), acetamiprid (Gazelle), refined petroleum spraying oil (Tri-Tek) and the physically acting product SB-Plant Invigorator all proved excellent. None of the products gave total control of second instar larvae. However, Agri-50E, B. bassiana, Tri-Tek and SB-Plant Invigorator all gave over 71% mortality. For adult control, B. bassiana and the oil based products (Addit, Tri-Tek and Spraying Oil) all produced 100% mortality. The work also demonstrated that B. bassiana offers better control of B. tabaci than L. muscarium. Investigating direct tank-mixing of the fungi with the chemical products proved that Majestic (physically acting product), spiromesifen (Oberon), Savona (physically acting product) and SB-Plant Invigorator significantly reduced germination of B. bassiana spores and so could not be recommended as mixes. Tri-Tek Oil, Spraying Oil, Addit, Dynamec and Gazelle showed best potential to be used as tank-mixes with over 90% B. bassiana spore germination following exposure to the test products for 24 h. A direct tank mix of L. muscarium with Tri-Tek allowed full fungal spore germination. The implications of the work in regards to continued protection of the UK horticultural industry from B. tabaci and overcoming insecticide resistance among biotypes are discussed.     

Effects of chlorfenvinphos on Bemisia tabaci Genn. and its parasites on cotton in the Sudan Gezira

Two large-scale field trials were carried out in consecutive cotton seasons to evaluate the effects of a chlorfenvinphos-based spray regime and a standard commercial spray regime on whiteflies (B. tabaci) and their parasites. During both trials B. tabaci was the dominant pest species and occurred in generally increasing numbers throughout October to January. The only abundant natural enemy of B. tabaci was an aphelinid parasite, Eretmocerus sp. This parasite occurred in very large numbers towards the end of the first cotton season but was less abundant in the following year. In both seasons, cotton fields treated with chlorfenvinphos had significantly lower populations of whiteflies than those treated with the standard commercial spray regime. In contrast, the percentage of parasitized whitefly scales and numbers of parasite adults was significantly higher in the chlorfenvinphos-treated fields. It is suggested that the better control of whiteflies achieved in fields sprayed with chlorfenvinphos is at least in part due to this greater conservation of natural enemies.     

Screening of mungbean germplasm against mungbean yellow mosaic India virus and its vector Bemisia tabaci

Yellow mosaic disease (YMD) caused by whitefly (Bemisia tabaci) transmitted mungbean yellow mosaic India virus (MYMIV) is an important constraint of mungbean in Pakistan. One hundred sixty-two mungbean genotypes from eight different geographic regions were evaluated for resistance to MYMIV and its whitefly vector B. tabaci. Resistance levels were assessed by visual scoring of symptoms in the field under natural conditions, in net-house by artificial transmission through whitefly and in greenhouse using graft inoculation for two consecutive years in 2008 and 2009. None of the tested genotypes was found to be disease free, while considerable variation in responses was observed among the genotypes and testing methods. All genotypes were found to be systemically infected in the field. In 2008, 32 genotypes were found to be resistant and 67 were moderately resistant with severity index (SI) values ranging from 1.0 to 1.4 and from 1.5 to 2.4, respectively. In 2009 34 genotypes were found to be resistant and 38 were moderately resistant with the same SI value ranges as in 2008, and the remaining genotypes were moderately susceptible to highly susceptible. However, only 35 genotypes were found to be moderately resistant with SI values of 1.5-2.4 and latent periods (LP) of 17-21 days when evaluated using artificial transmission through whiteflies. Similar results were obtained when these genotypes were evaluated using graft inoculation. Significant differences in adult whitefly densities among tested genotypes were also observed during both years but no correlation between the number of whiteflies and disease severity was observed. The results indicated that these genotypes did not have a high level of resistance against MYMIV, however, they may provide sources of partial resistance which can be exploited in the breeding programmes to develop mungbean genotypes resistant to MYMD or they can be used directly as varieties to manage MYMD after evaluation for acceptable agronomic characteristics, adaptation and stability in various regions.     

Resistance to whitefly (Bemisia tabaci) in cotton (Gossypium hirsutum) in the Sudan

Over the past 10–15 years, the cotton whitefly (Bemisia tabaci Genn.) has caused severe damage to cotton in many tropical countries. Effects of three leaf-hair densities (LHD) (high, moderate and low) and three leaf shapes (LS) (normal, okra and super okra) on whitefly numbers were examined in the Sudan in 1982. Resistance was conferred by low LHD and okra or super okra LS, with significant reductions in numbers of whitefly adults per leaf and adults, scales and pupae per unit area. Adults per leaf were lowest on the most resistant line, ORS-13 (exotic Gossypium hirsutum cv., low LHD/okra LS) throughout the season. Pupal parasitism was significantly higher on this line than on a hairy plant of normal leaf shape. Honeydew causing stickiness of lint was reduced to acceptable levels on resistant lines. Leaf shape influenced the microclimate, in that relative humidity was lower and temperature was slightly higher in the canopy of Sudac-K than in Barac (67)B. Fewer whiteflies on Sudac-K may be due to a more adverse microclimate for whitefly and improved host-searching conditions for adult parasites. A breeding programme in the Sudan should be maintained for selection of field-resistant varieties.     

Effect of Cardinium Infection on the Probing Behavior of Bemisia tabaci (Hemiptera: Aleyrodidae) MED

Facultative endosymbionts can affect the growth, physiology, and behavior of their arthropod hosts. There are several endosymbionts in the invasive whitefly Bemisia tabaci Mediterranean (MED, Q biotype) that influence host fitness by altering stylet probing behavior. We investigated the probing behavior of B. tabaci MED infected with the facultative endosymbiont Candidatus Cardinium hertigii (Cardinium (Sphingobacteriales: Flexibacteraceae)). We generated genetically similar Cardinium-infected (C^*+) and uninfected (C^-) clonal sublines and analyzed the probing behavior of newly emerged adult on cotton (Malvales: Malvaceae), Gossypium hirsutum L., using electropenetrography (EPG). The C^- subline demonstrated a longer duration of E2 (2.81-fold) and more events of E2 (2.22-fold) than the C^*+ subline, indicating a greater level of sustained ingestion of plant phloem. These findings provide insight into the fitness costs (fitness of a particular genotype is lower than the average fitness of the population) of the Cardinium-infected B. tabaci.     

Understanding the dynamics of neonicotinoid activity in the management of Bemisia tabaci whiteflies on poinsettias

The relative efficacies of registered label rates for foliar and soil drench treatments of imidacloprid and dinotefuran at preventing the establishment of Bemisia tabaci B biotype whitefly populations on newly infested poinsettia plants were evaluated. Pesticide levels within and on plant leaves were monitored for 10 weeks by ELISA and LC/MS in an effort to better understand the dynamics of neonicotinoid activity against this insect and to estimate insecticide concentrations needed to kill the nymphal and adult stages. While all treatments proved equally effective as a remedial measure for the control of the resident adult populations, thereby accomplishing the objective of foliar contact treatments, the dinotefuran soil drench application was the only treatment that provided multi-generational control of Bemisia populations.     

Combining reflective mulch and host plant resistance for sweetpotato whitefly (Hemiptera: Aleyrodidae) management in watermelon

A study was conducted to evaluate the use of reflective mulch and host plant resistance for the management of the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in watermelon [Citrullus lanatus var. lanatus (Thunberg) Matsum & Nakai]. Whitefly abundance data were collected under both greenhouse (caged and uncaged) and field conditions. Consistently, a reflective mulch (also called silver or metallic) treatment resulted in a lower incidence of adult whiteflies as compared with a standard black mulch treatment. Moreover, two whitefly resistant Citrullus colocynthis (L.) Schrad genotypes, which are wild relatives of cultivated watermelon, reduced whitefly populations as compared with standard watermelon. There was generally no interaction between the mulch and genotype variables. No effect of mulch color was observed on sticky card capture of Delphastus catalinae (Horn), a whitefly predator, or on capture of an Eretmocerus sp. whitefly parasitoid in caged trials, which suggests no adverse effect on these natural enemies when using reflective mulch. Overall whitefly populations were relatively low during four seasons of field trials (2006–2009). Results from this study suggest that a combination of using reflective mulch and host plant resistance can additively suppress whitefly infestations, which have particular importance in the fast-growing organic vegetable production industry.     

Use of fluorescence to determine reduction in Bemisia tabaci (Hemiptera: Aleyrodidae) nymph feeding when exposed to cyantraniliprole and imidacloprid through systemic applications

The Bemisia tabaci whitefly is an important pest of many agricultural crops. Direct feeding by this pest can cause physiological plant symptoms including irregular ripening in tomatoes and silverleaf disorder in squash. In addition, B. tabaci can transmit more than 100 plant viruses that cause severe diseases that affect crop yield and quality. Insecticides are often applied to control this pest and they may be applied to the foliage and/or to the soil. Insecticides that kill quickly or cause feeding cessation reduce the damage caused by B. tabaci on the host plant most effectively. In this study fluorescence was used to assess B. tabaci feeding and to determine the effect of systemically applied insecticides on feeding by the pest. Cyantraniliprole (Verimark™) and imidacloprid (AdmirePro^®) produced a rapid reduction in B. tabaci feeding. At 24 h after a systemic application, the percentage of whitefly nymphs still feeding in plants treated with cyantraniliprole (anthranilic diamide) and imidacloprid (neonicotinoid) were 19% and 33%, respectively. Both products showed a good reduction in insect feeding and since they have different modes of action they should be considered as rotational partners for B. tabaci control in areas where there is no resistance to neonicotinoid insecticides. While the fluorescein sodium salt cannot be used to trace the uptake of insecticides, it has been shown to reliably demonstrate feeding cessation of whitefly nymphs after foliar and systemic applications of insecticides.     

Lethal and sublethal effects of buprofezin and imidacloprid on Bemisia tabaci (Hemiptera: Aleyrodidae)

The sweetpotato whitefly, Bemisia tabaci (Gennadius), has become a major threat to agriculture worldwide. The development of insecticide resistance in B. tabaci has necessitated the exploration of new management tactics. The toxicity of imidacloprid and buprofezin to various life stages of B. tabaci was determined in the laboratory. Also, the sublethal effects of both insecticides were studied on demographic and biological parameters of B. tabaci. Both insecticides were very toxic against first stage larvae of the pest with LC₅₀ values of 1.0 and 19.3 ppm for buprofezin and imidacloprid, respectively. Toxicities decreased between successive stages (LC₅₀ values ranging from 1.0 to 2854.0 ppm). The LC₅₀ values of imidacloprid for adult males, females and eggs were 11.8, 71.6 and 151.0 ppm, respectively. Buprofezin had no significant effect on adults and eggs. The sublethal concentration of imidacloprid had no significant effect on demographic and biological parameters of B. tabaci but the maximal value for the mean generation time (T) (18.8 day) was observed in imidacloprid treatment. Buprofezin significantly decreased stable population and biological parameters of B. tabaci except it did not decrease the rate of population increase or the sex ratio of offspring.     

Evaluation of a modified sticky card to attract Bemisia tabaci (Hemiptera: Aleyrodidae) and a behavioural study on their visual response

Sticky cards with a yellow circle in black background originally developed to attract anthophilous thrips were also found to attract whiteflies. The potential of the new sticky cards for capture of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) was evaluated in oriental melon greenhouses in comparison with ordinary rectangular yellow sticky cards. Two types of the new sticky card (24W × 39L cm) were designed to contain either two large yellow circles (18D cm) or two small yellow circles (13D cm) in a black background on both sides. In each greenhouse, 18 sticky cards of each type were installed. The cards with small circles captured 1.8 times more B. tabaci per unit area than the rectangular yellow sticky cards. In the examination of on-site flight activity of B. tabaci, the cards with large circles attracted 70% of the B. tabaci that took off from the plant canopy. The card with small yellow circles captured 49% and the rectangular yellow sticky card captured 32%. In laboratory behavioural studies, sticky cards with different backgrounds and shapes were attached inside acrylic cages and B. tabaci on tomato leaves were released. Yellow sticky cards with a black background were 2.1 times more attractive than sticky cards with a green background, and triangular-shaped yellow sticky cards with a black background attracted 1.5 times more B. tabaci than those with squares. In conclusion, sticky cards with yellow circles in a black background attracted more B. tabaci per unit area than ordinary rectangular yellow sticky card, and thus could be an improvement for monitoring or managing B. tabaci.     

Field evaluation of yield effects on the U.S.A. heirloom sweetpotato cultivars infected by Sweet potato leaf curl virus

The incidence of Sweet potato leaf curl virus (SPLCV), a Begomovirus, on sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae), in South Carolina, U.S.A. has increased rapidly in recent years. This is likely due to the use of infected propagating materials and the increasing population of its vector, the sweetpotato whitefly, Bemisia tabaci (Gennadius). In this study, we demonstrated in field experiments that SPLCV infection reduced the yields of most heirloom sweetpotato lines relative to the yields of non-infected plants. Real-time polymerase chain reaction (PCR) technology specific to several common sweetpotato viruses was used to determine the virus infection status in 69 selected accessions of heirloom sweetpotato lines. Meristem tip culture technology was used to regenerate virus-free plants from these materials. To ensure the virus-free status, each mericlone was evaluated using real-time PCR and graft bio-indexing on the indicator species, Ipomoea setosa Ker Gawl. Mericlones of 27 cultivars were found to be free of the viruses. The 27 cultivars were included in a field test to determine the effect of SPLCV infection on yield. Yields of virus-free plants of the cultivars ranged from 10 to 80% greater than the yields of SPLCV-infected plants. However, the yield differences between virus-free and infected plants were diminished in the second year of the field experiment due to a rapid re-infection by SPLCV. These results demonstrate the importance of using certified, virus-tested seed roots or cuttings. The rapid re-infection of the virus-tested sweetpotato plants with SPLCV observed in these studies suggests that management of the whitefly population should be a critical element in control of this important virus.     

Sampling and management of Bemisia tabaci (Genn.) biotype B in Australian cotton

Data on seasonal population abundance of Bemisia tabaci biotype B (silverleaf whitefly (SLW)) in Australian cotton fields collected over four consecutive growing seasons (2002/2003–2005/2006) were used to develop and validate a multiple-threshold-based management and sampling plan. Non-linear growth trajectories estimated from the field sampling data were used as benchmarks to classify adult SLW field populations into six density-based management zones with associated control recommendations in the context of peak flowering and open boll crop growth stages. Control options based on application of insect growth regulators (IGRs) are recommended for high-density populations (>2 adults/leaf) whereas conventional (non-IGR) products are recommended for the control of low to moderate population densities. A computerised re-sampling program was used to develop and test a binomial sampling plan. Binomial models with thresholds of T=1, 2 and 3 adults/leaf were tested using the field abundance data. A binomial plan based on a tally threshold of T=2 adults/leaf and a minimum sample of 20 leaves at nodes 3, 4 or 5 below the terminal is recommended as the most parsimonious and practical sampling protocol for Australian cotton fields. A decision support guide with management zone boundaries expressed as binomial counts and control options appropriate for various SLW density situations is presented. Appropriate use of chemical insecticides and tactics for successful field control of whiteflies are discussed.     

Cross-resistance, inheritance and stability of resistance to acetamiprid in cotton whitefly, Bemisia tabaci Genn (Hemiptera: Aleyrodidae)

The cotton whitefly Bemisia tabaci, (Genn.) is an important pest of field crops, vegetables and ornamentals worldwide. Neonicotinoids are considered an important group of insecticides being used against B. tabaci for several years. B. tabaci has developed resistance to some of the compounds of the group. This study was designed to investigate if the selection of B. tabaci with acetamiprid would give a broad-spectrum of cross-resistance and to genetically classify the resistance. At G₁ a low level of resistance to acetamiprid, imidacloprid, thiamethoxam, thiacloprid and nitenpyram was observed with resistance ratios of 3-fold, 8-, 9-, 6- and 5-fold, respectively, compared with a laboratory susceptible population. After selection for eight generations with acetamiprid, resistance to acetamiprid increased to 118-fold compared with the laboratory susceptible population. Selection also increased resistance to imidacloprid, thiamethoxam, thiacloprid, nitenpyram, endosulfan and bifenthrin but no change in susceptibility to fipronil was observed. Furthermore resistance in a field population was stable in the absence of acetamiprid selection pressure. Genetic crosses between resistant and susceptible populations indicated autosomal and incompletely recessive resistance. Further genetic analysis suggested that resistance could be controlled by a single factor. The high level of cross-resistance and stability of incomplete resistance in the field population is of some concern. However, lack of cross-resistance between acetamiprid and fipronil or unstable resistance in the resistant population could provide options to use alternative products which could reduce acetamiprid selection pressure.