Characterization of alfalfa germplasm expressing resistance to silverleaf whitefly, Bemisia argentifolii

Abstract: Thirty‐eight plants were taken from a University of California alfalfa selection nursery for developing resistance to silverleaf whitefly, Bemisia argentifolii Bellows & Perring. Seventeen of the plants had low whitefly infestation and were categorized as ‘potentially resistant’; 21 of the plants had high whitefly infestation and were categorized as ‘presumed susceptible’. Plants were propagated vegetatively so that replicated measurements of whitefly performance could be made on each genotype. Two colonies of silverleaf whiteflies were used: one reared on alfalfa (alfalfa‐experienced whiteflies), and the other on cotton (alfalfa‐naive whiteflies). The effect of variation among alfalfa genotypes on whitefly performance was similar for both whitefly sources, although on all genotypes, the alfalfa‐experienced whiteflies generally performed better than their alfalfa‐naive counterparts. In greenhouse tests, fecundity of newly eclosed adults (over a 5‐day period) on the 17 potentially resistant genotypes was relatively consistent in being lower than fecundity on the presumed susceptible genotypes. However, in nymphal survival tests, the response on the 17 potentially resistant genotypes was not consistent. Nymphal survival (egg to adult) on some of these was very low, as expected, while nymphal survival on others was as high as on the presumed susceptible genotypes. Fecundity and nymphal survival data were not correlated for alfalfa‐naive whiteflies, and were only weakly correlated (r² = 0.13, d.f. = 32, P = 0.04) for alfalfa‐experienced whiteflies. Thirteen genotypes then were examined in the greenhouse in stage‐specific survival tests, where four genotypes demonstrated high resistance (<10% nymphal survival) and three demonstrated moderate resistance (11–34% survival) compared with the three presumed susceptible genotypes that were tested (51–73% survival). Most of the mortality on the resistant genotypes occurred in the first instar, while mortality was more evenly distributed across the life stages on the susceptible genotypes. Interestingly, if nymphs survived to second instar on the resistant genotypes, then their subsequent survival to adult eclosion was similar to survival of second instar to adult on susceptible genotypes. Six of the genotypes used in the greenhouse stage‐specific survival test also were evaluated in the field for nymphal survival, and these results were consistent with the greenhouse tests.     

Impact of greenhouse whitefly management on strawberry fruit quality

The greenhouse whitefly, Trialeurodes vaporariorum （Westwood）, is an important pest of strawberries in California, USA. The adults and nymphs feed on phloem sap of leaves to remove the photo-assimilates. The objective of this study is to test the impact of whitefly management with insecticides on strawberry fruit quality. Applications of imidacloprid, thiamethoxam, buprofezin and pyriproxyfen decreased the mean adult whitefly numbers by 2.80-, 2.17-, 1.69- and 1.39-fold, respectively, compared to the untreated control, Similarly, the mean numbers of first and second instar whiteflies were reduced 4.36-, 2.20-, 1.90- and 2.02-fold, respectively, while the mean numbers of third and fourth instars were reduced 5.48-, 2.28-, 2.71- and 1.43-fold, respectively, in plants treated with imidacloprid, thiamethoxam, buprofezin and pyriproxyfen. The mean soluble solids content in imidacloprid, thiamethoxam, buprofezin and pyriproxyfen treatments was 1.04-, 1.06-, 1.03- and 1.04-fold greater, respectively, than that in the control. The whitefly reduction enhanced the mean fruit titratable acidity by 4%-6%. Mean glucose levels in imidacloprid and thiamethoxam treatments were significantly higher than in other treatments. However, the whitefly management did not affect the mean fructose levels, lmidacloprid, thiamethoxam and pyriproxyfen treatments boosted the ascorbic acid levels by up to 4%. The impact of whitefly management on strawberry fruit nutrition and antioxidant capacity is discussed.     

Compatibility of an entomopathogenic fungus with a predator and a parasitoid in the biological control of greenhouse whitefly

An ongoing debate in biological control consists of whether interference between biological agents can disrupt pest control. This study investigated the outcome of interactions between the entomopathogen Beauveria bassiana with the whitefly predator Dicyphus hesperus and the parasitoid Encarsia formosa, as well as their effect on the control of the greenhouse whitefly Trialeurodes vaporariorum on greenhouse tomato crops. Our objective was to determine whether the generalist B. bassiana would disrupt biological control by interfering with D. hesperus or E. formosa. In experimental greenhouses, whitefly, parasitoid and predator populations were established, and over 27 days, tomato plants were sprayed with three applications of the B. bassiana based product BotaniGard® (5.13×10³ conidia/mm²) or water (control). Populations of greenhouse whitefly and biological control organisms were regularly monitored in control and B. bassiana-treated compartments. Overall, 10.6% of all whiteflies in treated compartments were infected, and 0.98% were both infected and parasitized. There were 31.7 and 22.3% fewer immature and adult whiteflies, respectively, on B. bassiana-treated plants relative to controls. Parasitism by E. formosa and predation by D. hesperus occurred at rates of 7.5 and 2.5%, respectively, in B. bassiana-treated compartments, and 5 and 6%, respectively in control compartments. Our study suggests that applications of B. bassiana for short-term biological control of greenhouse whiteflies are compatible with the concurrent use of E. formosa and D. hesperus on greenhouse tomato crops.     

Imidacloprid applications by subirrigation for control of silverleaf whitefly (Homoptera: Aleyrodidae) on poinsettia

The objective of this study was to determine whether silverleaf whiteflies, Bemisia argentifolii Bellows & Perring, on poinsettia, Euphorbia pulcherrima Willdenow ex Klotsch, can be controlled with imidacloprid applied by subirrigation. Different amounts of imidacloprid uptake by the growing medium were obtained by not watering the subirrigated plants for 0, 1, 2, or 4 d before the imidacloprid application. These treatments resulted in absorption of 12-175 ml of imidacloprid solution by the growing medium. These treatments were compared with untreated control plants and plants that were treated with a standard drench application (100 ml) to the top of the growing medium. All imidacloprid treatments resulted in a significant decrease in both the survival of adult whiteflies and number of immature whiteflies on the plants. Subirrigation treatments resulted in better control of adult and immature whiteflies than drench application. Withholding water for 2 or 4 d before the imidacloprid application by subirrigation improved control of immature whiteflies. This indicates that the application of imidacloprid to poinsettia by subirrigation is a practical and efficient method to control silverleaf whiteflies.     

Interactions of light intensity, insecticide concentration, and time on the efficacy of systemic insecticides in suppressing populations of the sweetpotato whitefly (Hemiptera: Aleyrodidae) and the citrus mealybug (Hemiptera: Pseudococcidae)

The impact of light intensity on the uptake and persistence of the systemic neonicotinoid insecticides, imidacloprid and dinotefuran, were evaluated in poinsettia (Euphorbia pulcherrima Willd.) and yellow sage (Lantana camara L.). Insecticide residues were measured in leaves sampled from the treated plants at four time intervals after treatment to determine the relationship between insecticide concentration and efficacy against two insect pests: sweetpotato whitefly, Bemisia tabaci Gennadius, and the citrus mealybug, Planococcus citri Risso. The insecticides were evaluated at their respective label rate and at the comparable label rate of the other insecticide under two different light environments: ambient and shade. The uptake of dinotefuran into yellow sage was more rapid at both treatment rates than both rates of imidacloprid, resulting in higher percent mortality of whitefly nymphs (89.8-100) compared with imidacloprid (14.1-89.2) across all 4 wk. Additionally, plants that received both rates of dinotefuran had fewer whitefly pupae (< 1.0) at week 4 compared with imidacloprid-treated plants (23.7-25.3). The uptake of dinotefuran into poinsettia plants was also more rapid and resulted in quicker and higher percent mortality of whitefly nymphs (89.5-99.6) compared with imidacloprid (14.1-89.2) across all 4 wk. However, despite efficient uptake, the efficacy of both systemic insecticides was less for citrus mealybug where percent mortality values were <50% among all the treatments across the 4 wk. The use of the two systemic insecticides evaluated in regards to pest management in horticultural cropping systems is discussed.     

两种杀虫真菌制剂与低用量吡虫啉对温室粉虱的协同防效评价

在昆明市郊蔬菜基地4间大棚(5m×100m·间^-1)栽培的生菜上,用球孢白僵菌(Beauveriabassiana)和玫烟色拟青霉(Paecilomyces fumasonoseus)的纯孢子乳悬剂(有效含孢量10^10·ml^-1)及其与1％和3％(w／v)的吡虫啉10％WP的混配剂对温室粉虱(Trialeurodes vaporariorum)进行了协同药效试验,吡虫啉添加量仅相当于推荐用量的6．4％～9．5％和19．1％～28．6％,试验含6个菌剂处理、2个低用量吡虫啉处理和1个清水对照,各有3个小区(7m×5m·小区^-1)重复,随机区组排列,稀释1000倍的菌液(含孢量10^7·ml^-1)和吡虫啉液于生菜移栽后第11d首次喷雾,15d后喷第二次,首次用菌前调查初始粉虱密度,用菌后每隔5d调查活虫数和死虫数,从8月20日起历时30d,结果表明,连续2次用菌有效地控制了粉虱对当季大棚生菜的危害,各菌剂处理的最终相对防效和虫口减退率均达到95％以上,极显著地高于低用量吡虫啉处理,其中,玫烟色拟青霉制剂对粉虱的控制效果一般优于球孢白僵菌制剂,且与吡虫啉的添加量呈正相关,但是,各菌剂处理间控虫效果的差异主要发生在首次用菌后第5d和10d,此后差异逐渐缩小,至第二次用菌后第10d各菌剂处理间无显著差异,本试验结果表明,两种真菌的孢子乳悬剂均可用于温室粉虱的防治,添加微量吡虫啉可增强菌剂的防效。     

How predatory mites find plants with whitefly prey

We investigated the searching behaviour of two species of predatory mites, Typhlodromips swirskii (Athias-Henriot) and Euseius scutalis (Athias-Henriot), both known to feed on immature stages of the whitefly Bemisia tabaci Gennadius. When released in a greenhouse inside a circle of cucumber plants that were alternatingly clean or infested with immature whiteflies, the mites took several days to find plants. Both species were recaptured significantly more on plants with whiteflies. This suggests that the mites are able to discriminate between plants with and without whiteflies. The predators may either have been attracted to plants with whiteflies from a distance or arrested on plants with whiteflies. Typhlodromips swirskii that had previously fed on whitefly immatures on cucumber leaves were significantly attracted by volatiles from cucumber plants with whiteflies in a Y-tube olfactometer. This suggests that the mites use volatile cues to discriminate between infested and clean plants. However, this response waned rapidly; if predators, experienced as above, were starved for 3–4 h in absence of cucumber leaves, they no longer preferred volatiles of infested plants to clean plants. Furthermore, T. swirskii that had no experience with immature whiteflies on cucumber plants also did not prefer odours of infested plants to those of clean plants. Because the release experiment with this species in the greenhouse was done with inexperienced predators, this suggests that the aggregation of mites on plants with whiteflies was mainly caused by differential arrestment of mites on plants with prey and clean plants. For T. swirskii, this was in agreement with the finding that the fraction of predators on plants with prey increased with time to levels higher than 70%. A less clear trend was found for E. scutalis, for which the fraction of predators on plants with prey stabilized soon after release to levels from 54–70%. Hence, the predatory mites may find plants with prey by random searching, but they are subsequently arrested on these plants. An earlier study showed that 87% of all whiteflies released in a set-up as used here were recaptured within 1 day. Hence, the effectiveness with which predatory mites locate plants with whiteflies is low compared with that of their prey. We expect this to generate spatial patterns in the dynamics of predator and prey and this may have consequences for biological control of whiteflies with predatory mites.     

Host plants influence susceptibility of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to the entomopathogenic fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae)

We quantified the tritrophic effect of host plant on the susceptibility of the sweetpotato whitefly Bemisia tabaci (Genn.) to a fungal pathogen in the laboratory. Second-instar whiteflies reared on cucumber, eggplant, tomato and bean plants for six generations were exposed to conidial suspensions of Isaria fumosorosea isolate IF-1106. Our results did not detect differences in response (proportional survival or median lethal time, LT₅₀ days) among insect populations derived from different plants that were treated with 10⁷ conidia/ml. However, at concentrations ≤ 5×10⁶ conidia/ml, whiteflies reared on bean and tomato died significantly more quickly (i.e. LT₅₀ of 4–5 days) compared with cucumber and eggplant reared populations (5–7 days). Bean and tomato-reared populations were also more susceptible to mycosis (LC₅₀ ≈ 6 × 10⁵ conidia/ml) compared with those reared on cucumber (1.9 × 10⁶ conidia/ml) and eggplant (1.5 × 10⁶ conidia/ml). A separate study confirmed that this differential response of whitefly populations to I. fumosorosea was not explained by differences in deposition rate of conidia on leaf surfaces (i.e. a dosage effect). Our findings show that host plants affect the pathogenicity and virulence of a herbivore pathogen, but depend on the rate of exposure (inoculum) applied.     

Cardinium infection alters cotton defense and detoxification metabolism of its whitefly host

Field monitoring revealed that the infection ratio of the bacterial symbiont Cardinium in the whitefly (Bemisia tabaci MED) was relatively low in northern China. However, the role of this symbiont and the symbiont–whitefly–host plant interaction mechanism are poorly understood. We investigated the influence of Cardinium on the competitiveness of the host whitefly and the physiological interaction between the host plants and host whiteflies. Cardinium-infected whiteflies were displaced by uninfected whiteflies after 5 generations, which showed that Cardinium infection reduced whitefly competitiveness. The defense response genes of cotton significantly decreased under infestation by infected whiteflies compared to uninfected whiteflies. The expression of detoxification metabolism genes, especially the uridine 5ʹ-diphospho-glucuronyltransferase and P450 genes, in infected whiteflies significantly decreased. These results demonstrated that Cardinium could inhibit the defense response of the host plant and decrease the detoxification metabolism ability of the host whitefly. The reduced competitiveness of infected whiteflies may be associated with the inhibition of the whitefly detoxification metabolism by Cardinium, resulting in the reduced performance of infected whiteflies. However, Cardinium infection can suppress plant defenses, which may benefit both infected and uninfected whiteflies when they coexist. This research illustrates the symbiont–whitefly–host plant interaction mechanism and the population dynamics of the whitefly.     

A model of greenhouse whitefly Trialeurodes vaporariorum (Westwood) population development and management on Camarosa variety strawberry plants

A deterministic parameterized model of development of a greenhouse whitefly (Trialeurodes vaporariorum) population on field grown strawberry plants (Fragaria × ananassa) is presented (var. Camarosa). The model calculates the timing of the physiological development of individual whiteflies and population size as a function of temperature, mortality, oviposition, and plant condition using parameters from the literature and field observations from California. Simulated dynamics of a T. vaporariorum population accurately reflected the observed population development in an untreated strawberry field, and its response to applications of pyriproxyfen and imidacloprid under production conditions in central coastal California. It was validated with an independent field observation where both imidacloprid and pyriproxyfen were applied at different periods of strawberry plant development. These results present an opportunity to predict effects of management strategies targeting T. vaporariorum populations on variety Camarosa strawberry plants.     

Field Evaluation of Amitus bennetti (Hymenoptera: Platygasteridae), a Parasitoid of Bemisia argentifolii (Hemiptera: Aleyrodidae), in Cotton and Bean

Field cage experiments were conducted in Riverside, California to quantify the impact of releases of the parasitoid Amitus bennetti Viggiani & Evans on mortality of the whitefly Bemisia argentifolii Bellows & Perring. Single-row 50-m-long plots were planted with either cotton or bean. Cages were erected over the plants in each row, and adult whiteflies were released into the cages. Approximately 10 days later, adult parasitoids were released. Marked individual whiteflies were scored every 4 days for 6 weeks. Paired life tables were then constructed from census data from release and control cages over a single whitefly generation. Total whitefly mortality in release cages (71% in bean, 61% in cotton) was significantly greater than in control cages (25% in bean, 34% in cotton). The marginal rate for mortality attributable directly to the parasitism was 0.535 in the bean plots and 0.201 in the cotton plots. In addition, other mortality was greater in the release plots, possibly reflecting death of parasitized hosts before larval parasitoids could complete development. Parasitism was the greatest mortality factor in the study.     

Demographic analyses of organophosphate-resistant and susceptible strains of greenhouse whitefly, Trialeurodes vaporariorum, on three cotton cultivars

Laboratory experiments were conducted using organophosphate-resistant and susceptible strains of greenhouse whitefly, Trialeurodes vaporariorum Westwood, to assess age-specific vital rates in individually-held adults, and development and survival in preadults on three cotton cultivars at 27±1 °C, 50±10% RH, and a photoperiod of 16:8 (L:D). Female whiteflies lived longer than males, with a maximum life expectancy of 29 days. Heaviest egg laying occurred at ages between 7 and 18 days when individual whiteflies laid > 10 eggs/day. Greenhouse whitefly populations doubled weekly, with stable age distribution of 63% eggs, 28% larvae, 5% pupae, and 4% adults. Analysis of various life history parameters that combine aspects of survival, developmental rates, and fecundity indicated no consistent differences in reproductive fitness between the two greenhouse whitefly strains. Of the three cotton cultivars tested, Pima S-6 was most susceptible, Acala SJ-2 was intermediate and Gumbo 500 was most resistant to greenhouse whitefly. Resistance of Gumbo 500 was expressed as slower developmental rates, reduced survival to adulthood, lower reproductive rates, and lower intrinsic rate of increase.     

Impact of Bemisia whiteflies (Homoptera: Aleyrodidae) on alfalfa growth, forage yield, and quality

A 3-yr project was initiated in 1993 to examine the effects of insecticides and sustained whitefly, Bemisia argentifolii Bellows & Perring [aka. B tabaci Gennadius (Strain B)], feeding on alfalfa plant growth and vigor in greenhouse cage studies, and to determine the impact of natural Bemisia whitefly populations on alfalfa forage yields and quality in a large-plot field experiment. Alfalfa plant growth and vigor after exposure to imidacloprid and a mixture of fenpropathrin and acephate insecticides did not differ from untreated plants in the greenhouse. Consequently, foliar and soil applied insecticides were used to manipulate whitefly densities on alfalfa plants to measure whitefly feeding effects on plant growth and forage yield. Heavy whitefly densities on untreated alfalfa plants in the greenhouse resulted in significant reductions in relative growth rates and net assimilation rates as compared with imidacloprid-treated plants that were maintained relatively whitefly-free. Reductions in alfalfa plant growth measured between infested and treated plants were proportional to whitefly densities. Field plot results derived from three crop seasons were relatively consistent with our greenhouse trials. Both experimental approaches clearly showed that alfalfa plants exposed to high densities of whitefly immatures and adults grew at a significantly slower rate and produced less foliage. As a result of reduced growth rates, alfalfa maturity in the naturally infested plots was estimated to be approximately 7-10 d behind managed plots. Delays in maturity resulted in significant reductions in forage yields of 13-18% during August-September harvests when whitefly populations reached peak abundance. Whitefly feeding stresses also effected hay quality through the reduction of crude protein content and contamination of foliage with honeydew and sooty mold. The status of the Bemisia whiteflies as an economic pest to alfalfa is clearly evident from these studies, but the damage potential of whiteflies in the southwestern United States appears to be restricted to one or two harvest periods during the summer coinciding with peak adult populations and their dispersal from alternate host crops.     

Non-consumptive effects of the predatory beetle Delphastus catalinae (Coleoptera: Coccinellidae) on habitat use patterns of adult whitefly Bemisia argentifolii (Hemiptera: Aleyrodidae)

This study examined habitat use patterns by adult whiteflies, Bemisia argentifolii Bellows and Perring, in response to predators, Delphastus catalinae (Horn), at different spatial scales. When female whiteflies were confined to small arenas with leaf discs from which they could not escape, whiteflies significantly delayed settling on leaf discs when predators were present compared to when no predators were introduced. The presence of D. catalinae altered the vertical distribution of adult whiteflies (sex ratio = 1:1) on cucumber plants; adult whiteflies moved upward faster over time within the plant canopy when predators were present mainly on the lower leaves of the plants compared to whiteflies on plants without predators. Most D. catalinae remained in the lower parts of the plants during the experiment. Therefore, we inferred that female whiteflies more quickly moved to the upper plant strata to reduce the risk of predation of their progeny; this would induce subsequent movement of males seeking mates. Introduction of D. catalinae onto a cucumber plant with high whitefly density did not cause increased dispersal of adult whiteflies (sex ratio = 1:1) into neighboring uninfested plants. The results indicate that predator-avoidance behaviors by adult B. argentifolii differed at different spatial scales. The predator-avoidance behavior may have a negative impact at the within-plant scale by inducing more whiteflies to move into upper plant strata. However, the effect of predators on the among-plant dispersal of whiteflies was not significant.     

Transmitting Plant Viruses Using Whiteflies

Whiteflies, Hemiptera: Aleyrodidae, Bemisia tabaci, a complex of morphologically indistinquishable species⁵, are vectors of many plant viruses. Several genera of these whitefly-transmitted plant viruses (Begomovirus, Carlavirus, Crinivirus, Ipomovirus, Torradovirus) include several hundred species of emerging and economically significant pathogens of important food and fiber crops (reviewed by^9,10,16). These viruses do not replicate in their vector but nevertheless are moved readily from plant to plant by the adult whitefly by various means (reviewed by^{2,6,7,9,10,11,17}). For most of these viruses whitefly feeding is required for acquisition and inoculation, while for others only probing is required. Many of these viruses are unable or cannot be easily transmitted by other means. Therefore maintenance of virus cultures, biological and molecular characterization (identification of host range and symptoms)^3,13, ecology^2,12, require that the viruses be transmitted to experimental hosts using the whitefly vector. In addition the development of new approaches to management, such as evaluation of new chemicals¹⁴ or compounds¹⁵, new cultural approaches^1,4,19, or the selection and development of resistant cultivars^7,8,18, requires the use of whiteflies for virus transmission. The use of whitefly transmission of plant viruses for the selection and development of resistant cultivars in breeding programs is particularly challenging⁷. Effective selection and screening for resistance employs large numbers of plants and there is a need for 100% of the plants to be inoculated in order to find the few genotypes which possess resistance genes. These studies use very large numbers of viruliferous whiteflies, often several times per year.Whitefly maintenance described here can generate hundreds or thousands of adult whiteflies on plants each week, year round, without the contamination of other plant viruses. Plants free of both whiteflies and virus must be produced to introduce into the whitefly colony each week. Whitefly cultures must be kept free of whitefly pathogens, parasites, and parasitoids that can reduce whitefly populations and/or reduce the transmission efficiency of the virus. Colonies produced in the manner described can be quickly scaled to increase or decrease population numbers as needed, and can be adjusted to accommodate the feeding preferences of the whitefly based on the plant host of the virus.There are two basic types of whitefly colonies that can be maintained: a nonviruliferous and a viruliferous whitefly colony. The nonviruliferous colony is composed of whiteflies reared on virus-free plants and allows the weekly availability of whiteflies which can be used to transmit viruses from different cultures. The viruliferous whitefly colony, composed of whiteflies reared on virus-infected plants, allows weekly availability of whiteflies which have acquired the virus thus omitting one step in the virus transmission process.     

Probing and feeding characteristics of the greenhouse whitefly in association with host-plant acceptance and whitefly strains

Host-plant and whitefly strain effects and their interactions on the probing and sap feeding of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), have been investigated in this study using the DC-EPG (Electrical Penetration Graph) technique. Whiteflies generally displayed fewer but longer probes on highly acceptable cucumber than on less acceptable tomato. Both whitefly strains, the T(omato)-strain and the C(ucumber)-strain, showed a significantly lower number of phloem phases on cucumber than on tomato. However, the duration of total phloem phases achieved by either of the whitefly strains on these two host plants was not significantly different. These data indicate that a more continuous phloem feeding has occurred on cucumber plants. Indeed, the percentage of phloem feeding time after the first sustained phloem phase (longer than 15 min) was higher on cucumber for the C-strain whiteflies. When comparing these two whitefly strains, the T-strain whiteflies probed less frequently but longer than the C-strain whiteflies did on both host plants. Also, the T-strain whiteflies displayed a longer duration of total phloem phases on tomato. An interaction between the whitefly strain and plant effects was detected on a parameter, which showed that whiteflies probed significantly longer before reaching the first phloem phase on the host plants that had been previously experienced. In conclusion, both plant species and whitefly strains affect whitefly's probing and feeding behaviour, though plant effects are much stronger.     

Host plant evaluation behaviour of Bemisia tabaci and its modification by external or internal uptake of imidacloprid

The behaviour of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) was observed on leaves of cotton, Gossypium hirsutum L., to study the process of host plant evaluation. Seven distinct behavioural elements were identified and recorded for a period of 20 min after initial contact with leaves. The behaviour of the whiteflies was observed on untreated leaves or on leaves treated with either foliar or systemically applied imidacloprid. Thus, contact with imidacloprid by whiteflies was either via the external cuticle or by ingestion, allowing determination of the effect of uptake route on host evaluation behaviour. Analysis of behavioural sequences and comparison of latencies, frequencies and durations of elements of behaviour between treatments revealed that host evaluation behaviour was similar on untreated and foliar treated leaves, but markedly different on those treated systemically. After their first probe, whiteflies on systemically treated leaves were much more active, spending significantly greater time walking and dabbing the labium tip onto the leaf surface. There was also a 50% reduction in the total time spent probing into systemically treated leaves, compared to the other treatments. This effect was the result of a shorter mean probe duration, and no effect of treatment was found on the frequency of probing. Pre-oviposition behaviour was significantly more common on the systemically treated leaves, although the number of eggs laid was similar on all treatments. These results also show that the host evaluation phase of adult female B. tabaci was dominated by probing. The behavioural sequence that leads to probing was affected significantly by imidacloprid when ingested, but not by direct contact with this compound on the leaf surface. The wider implications for the mechanisms of whitefly–host plant interactions are discussed.     

Reliable molecular identification of nine tropical whitefly species

The identification of whitefly species in adult stage is problematic. Morphological differentiation of pupae is one of the better methods for determining identity of species, but it may vary depending on the host plant on which they develop which can lead to misidentifications and erroneous naming of new species. Polymerase chain reaction (PCR) fragment amplified from the mitochondrial cytochrome oxidase I (COI) gene is often used for mitochondrial haplotype identification that can be associated with specific species. Our objective was to compare morphometric traits against DNA barcode sequences to develop and implement a diagnostic molecular kit based on a RFLP‐PCR method using the COI gene for the rapid identification of whiteflies. This study will allow for the rapid diagnosis of the diverse community of whiteflies attacking plants of economic interest in Colombia. It also provides access to the COI sequence that can be used to develop predator conservation techniques by establishing which predators have a trophic linkage with the focal whitefly pest species.     

Impacts of two conventional insecticides on different stages of Encarsia inaron Walker parasitizing the whitefly,Trialeurodes vaporariorum Westwood under greenhouse condition

In this research, for the first time, compatibility of imidacloprid and pyriproxyfen was assayed with both pupa and adult stages of Encarsia inaron Walker parasitizing Trialeurodes vaporariorum Westwood. First, the insecticides were sprayed on bean plants containing the parasitoid pupae, thenceforth, survival of the adult parasitoid was evaluated 24 h post-exposure to fresh, 1-, 4-, 7-, 14-, and 21-day-old residues of them on bean leaflets in Petri dishes. Both insecticides significantly reduce E. inaron adult emergence. Mortality of the parasitoid pupa in treatment with imidacloprid (69.7%) was significantly higher than mortality with pyriproxyfen (28.6%). Pyriproxyfen was non-toxic to the adult parasitoid when residues were dried in fresh and aged through the experiment, while in the same condition, imidacloprid significantly killed the adult parasitoids up to 7 days after application. Results have been discussed on the potential compatibility of the insecticides with E. inaron in an integrated pest management (IPM) approach.     

Attraction of Trialeurodes vaporariorum and Bemisia argentifolii to eggplant, and its potential as a trap crop for whitefly management on greenhouse poinsettia

Trap cropping, though promising, has had little evaluation in greenhouses. This study evaluated eggplant, Solanum melongena L. (Solanaceae), as a trap crop for two whitefly species, Trialeurodes vaporariorum (Westwood) and Bemisia argentifolii Bellows & Perring (both Hemiptera: Aleyrodidae), on greenhouse poinsettia, Euphorbia pulcherrima Willd. ex Koltz (Euphorbiaceae). Because the two whitefly species co‐occur in greenhouses, a common trap crop for both whiteflies is desirable. When adults were provided a choice between eggplant and poinsettia in a cage, 60% of B. argentifolii and 98% of T. vaporariorum were observed on eggplant after 3 days. However, when adults were given eggplant after first settling on poinsettia, only 38% of B. argentifolii were later found on eggplant, whereas 95% of T. vaporariorum moved to eggplant. In a greenhouse experiment, eggplant did not affect either the spatial distribution or density of adult B. argentifolii on poinsettias. In contrast, eggplant changed the spatial distribution of T. vaporariorum within 3 days by attracting and retaining the adults. However, the attractiveness of eggplant did not result in a reduced number of T. vaporariorum on poinsettias compared with poinsettias in monoculture. Adult T. vaporariorum mortality was high on poinsettias and this likely caused adult density on poinsettias in monoculture to decrease as fast as that under trap cropping. A simulation model was developed to examine how adult whitefly mortality on poinsettia influences trap cropping effectiveness. When whitefly mortality was high, simulated densities were similar to the experimental data. This reveals an unexpected factor, pest mortality on the main crop, that can influence the relative effectiveness of trap cropping. Our results indicate that eggplant will not work unilaterally as a trap crop for B. argentifolii. For T. vaporariorum, attraction to eggplant might be useful as a trap crop system when whitefly mortality on the main crop is not high.