Population suppression of Bemisia tabaci (Hemiptera: Aleyrodidae) using yellow sticky traps and Eretmocerus nr. rajasthanicus (Hymenoptera: Aphelinidae) on tomato plants in greenhouses

We conducted three experiments for management of Bemisia tabaci (Gennadius) biotype ‘B’ on tomatoes under greenhouse conditions: (i) vertically placing yellow sticky cards either parallel or perpendicular to tomato rows at a rate of 1 per 3‐m row; (ii) releasing Eretmocerus sp. nr. rajasthanicus once at 30 adults/m² in the high whitefly density greenhouses (> 10 adults/plant), or twice at 15 adults/m² at a 5‐day interval in the low whitefly density greenhouses (< 10 adults/plant); and (iii) using combinations of yellow sticky cards that were placed vertically parallel to tomato rows and parasitoids released once at 30/m² in high whitefly density greenhouses or twice at 15/m² at a 5‐day interval in low whitefly density greenhouses. Our data show that yellow sticky cards trapped B. tabaci adults and significantly reduced whitefly populations on tomato. The yellow sticky cards that were placed parallel to tomato rows caught significantly more whitefly adults than those placed perpendicular to tomato rows on every sampling date. In the treatment where parasitoids were released once at 30/m² in high whitefly density greenhouses, the number of live whitefly nymphs were reduced from 4.6/leaf to 2.9/leaf in 40 days as compared with those on untreated plants on which live whitefly nymphs increased from 4.4/leaf to 8.9/leaf. In the treatment where parasitoids were released twice at 15/m² in low whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.1/leaf to 1.7/leaf in 20 days as compared with those on untreated plants on which numbers of live nymphs of B. tabaci increased from 2.2/leaf to 4.5/leaf. In the treatment of yellow sticky cards and parasitoid release once at 30/m² in high whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 7.2/leaf to 1.9/leaf, and in the treatment of yellow sticky cards and parasitoid release twice at 15/m² at a 5‐day interval at low whitefly density, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.5/leaf to 0.8/leaf; whereas the numbers of live nymphs of B. tabaci on untreated plants increased from 4.4/leaf to 8.9/leaf. An integrated program for management of B. tabaci on greenhouse vegetables by using yellow sticky cards, parasitoids and biorational insecticides is discussed.     

Biological properties,transmission, serological characterization and varietal susceptibility of an isolate of Papaya leaf curl virus affecting papaya crops in Eastern Uttar Pradesh,India

Papaya leaf curl disease (PLCD) was recorded with 5–35% incidence at six districts of Eastern Uttar Pradesh during survey. The characteristic symptoms observed were severe downward leaf curling, swelling of veins, twisting and reduction of petioles, inverted leaf bowls and stunted growth of the entire plant which bore only few small and distorted fruit. The virus isolate was identified as Papaya leaf curl virus (PaLCuV).The PaLCuV isolate was successfully transmitted by whitefly (Bemisia tabaci) but not by mechanical (sap) transmission on Carica papaya plants. Plants could be proved efficiently from infected to healthy C. papaya, Capsicum annuum, Lycopersicon esculentum, Nicotiana tabacum, Crotalaria juncea, Ageratum conyzoides, Zinnia elegans, Datura stramonium and Petunia hybrida. Symptomatic samples of these plants were tested with polyclonal antiserum of Tomato leaf curl New Delhi virus by DAC-ELISA test showed the positive relationship of the samples with geminivirus. On the basis of symptomatology, whitefly transmission, host range studies and serological relationship, the isolate was identified as whitefly transmitted geminivirus. To identify potential varietal resistances source to PaLCuV, five cultivars of C. papaya were tested against PaLCuV using whitefly insects to transmit the infection. Results revealed that two cultivars (Washington and Ranchi Dwarf) were found to be moderately resistant.     

Purification and Characterization of Indian Cassava Mosaic Virus

The Indian cassava mosaic virus (ICMV) was transmitted by the whitefly Bemisia tabaci and sap inoculation. ICMV was purified from cassava and from systemically infected Nicotiana benthamiana leaves. Geminate particles of 16–18 × 30 nm in size were observed by electron microscopy. The particles contained a single major protein of an estimated molecular weight of 34,000. Specific antiserum trapped geminate particles from the extracts of infected cassava and N. benthamiana plants in ISEM test. The virus was detected in crude extracts of infected cassava, ceara rubber, TV. benthamiana and N. tabacum cv. Jayasri plants by ELISA. ICMV appeared serologically related to the gemini viruses of Acalypha yellow mosaic, bhendi yellow vein mosaic, Croton yellow vein mosaic, Dolichos yellow mosaic, horsegram yellow mosaic, Malvastrum yellow vein mosaic and tobacco leaf curl.     

Effects of <Emphasis Type="Italic">Paecilomyces fumosoroseus</Emphasis> and <Emphasis Type="Italic">Encarsia formosa</Emphasis> on the control of the greenhouse whitefly: preliminary assessment of a compatability study

The effect of separate and combined activity of Paecilomyces fumosoroseus Wize (Brown and Smith) Trinidadian strain T11 and the parasitoid, Encarsia formosa Gahan, was assessed on populations of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), infesting Phaseolus vulgaris L. (French bean) and Pelargonium x domesticum (regal geranium) plants in replicate experiments. When infested bean and geranium plants were exposed to E. formosa for 2 days, and 4 days later sprayed with P. fumosoroseus blastospores, whitefly percent mortality was 99.5% and 75.5%, 94.6% and 59.4% for experiments 1 and 2, respectively. Treatment of infested bean plants with either E. formosa or P. fumosoroseus resulted in 87.8% and 78.7%, 73.1% and 97.0% whitefly mortality for experiments 1 and 2, respectively, while similar treatment of infested geranium plants resulted in 9.2% and 52.8%, 34.3% and 64.5% whitefly mortality for experiments 1 and 2, respectively. Our results support the use of E. formosa and P. fumosoroseus in combination in Experiment 1 for the treatment of whitefly infested P. vulgaris plants since a significant difference in mortality is observed than when either E. formosa or P. fumosoroseus is applied alone. However, in experiment 2, the combination treatment on P. vulgaris was no more effective than spraying P. fumosoroseus alone. On P. x domesticum plants, only P. fumosoroseus alone is needed for efficient control of the whitefly compared to the combination treatment. The relative timing of parasitoid oviposition and fungal infection are critical in determining the outcome of the interaction and are plant host dependent.     

Whiteflies Population and its Impact on the Incidence of Tomato Yellow Mosaic Virus in Venezuela

The heavy incidence of Tomato Yellow Mosaic Virus in Venezuela is related to the high population densities of its vector, the whitefly Bemisia tabaci Genn. The main factor affecting the population of the vector is the rainfall pattern; during the rainy season the populations are low but they increase rapidly in the drier months. A good correlation was found between the number of whiteflies trapped and the incidence of infested plants. It seems that in the low laying areas of the tropics the temperature does not have a marked effect on the whitefly population since it remains quite stable throughout the year.     

Density thresholds for Nesidiocoris tenuis (Heteroptera: Miridae) in tomato crops

Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) is common in vegetable crops of the Mediterranean area, with an increasing worldwide range of geographical distribution. This omnivore is a reputed predator of small arthropod pests, but also produces injuries on vegetative and reproductive plant parts. The aim was to estimate density thresholds based on N. tenuis and whitefly abundance for the management of N. tenuis in tomato crops. The assay was carried out in mesh-walled and plastic greenhouses in southern Spain during 2004 and 2007. The natural population dynamics of N. tenuis and whitefly were monitored, and impact on yield quantified. The economic injury level and intervention threshold were predicted based on the zoophytophagous response of N. tenuis and the yield compensation of tomato plants. The proportion of aborted flowers on the tomato plants was related directly to the abundance of N. tenuis and inversely to the interaction between the number of N. tenuis and the number of whitefly immatures. Over-compensation of fruit weight was predicted for flower abortion rates due to N. tenuis lower than 0.171. No yield reduction is expected for values <0.65 N. tenuis per leaf, independent of the whitefly abundance, nor for up to 5 N. tenuis and >26 whitefly immatures per leaf. For intermediate N. tenuis levels, the outcome depends on the prey density. The probability of N. tenuis producing yield loss in tomato crops increases at N. tenuis:whitefly ratios >0.168. Yield reduction is expected after N. tenuis population peaks, when whitefly numbers have been reduced.     

Vector and Host-Plant Relationships of the Leafhopper-Borne Maize Yellow Stripe Virus

Maize yellow stripe virus (MYSV), associated with tenuivirus-like filaments, is transmitted in a persistent manner by the leafhopper Cicadulina chinai. In this vector, MYSV acquisition and inoculation threshold times were 30 min each, latent period ranged from 4.5 to 8 days depending on temperature (14-25 °C), and retention periods were as long as 27 days. Up to 26 % of C, chinai collected from maize fields in Giza, Egypt, during September and October 1985 were naturally infective with MYSV. Two symptom-types (fine and coarse stripe) appeared on experimentally infected plants, usually on separate leaves of the same plant. However, these two symptom-types could not be isolated on separate plants through transmission by single C. chinai leafhoppers. MYSV was transmitted by nymphs and adults of C. chinai from maize to maize, wheat and barley, and from wheat to maize plants. Up to 6 % of the wheat plants examined in Naga Hamadi (Southern Egypt) in February 1986, were naturally infected. It is suggested that wheat, barley and possibly graminaceous weeds may serve as winter hosts or reservoirs for MYSV and its leafhopper vector in Egypt.     

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.     

Efficiency of some herbal pesticides on reproductive parameters of silverleaf whitefly,Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)

The silverleaf whitefly is one of the most important pests found commonly in Iran and in the world. The development of alternative methods instead of chemical applications is necessary in pest management for human health and environment protection. The objective of this research was to assess the effects of extracts of two medicinal plant species: Calotropis procera and Allium sativum, and a formulation containing azadirachtin on fecundity and fertility of the silverleaf whitefly, grown on greenhouse tomato plants. The effects were compared to that of pymetrozine, a synthetic insecticide. According to the results, there was a significant difference among treatments for all reproductive parameters. Gross fecundity rates for pesticides control, herbal extract control, C. procera extract, A. sativum extract, azadirachtin and pymetrozine were 184.75, 146.72, 80.11, 82.18, 63.06 and 55.96 eggs, respectively. These herbal extracts were effective against this pest and they can be the suitable choices for replacing these chemical insecticides.     

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of host plant Brassica species) and temperature on population increase of the cabbage whitefly Aleyrodes brassicae

Laboratory studies on the influence of host plant species on population growth of the cabbage whitefly Aleyrodes brassicae Walk. showed that greatest longevity occurred on mustard and lowest on turnip. Leaf age did not affect survival. At 20 or 25 °C the survival curves from mustard plants were shortened Slobodkin's type I whereas those from purple sprouts and turnip were typical of Slobodkin's type II. At 15 °C the survival curves from young leaves of all host plants were of Slobodkin's type I but those from mature leaves were of Slobodkin's type III except that of mustard which was of type I. Young leaves induced higher fecundities than mature leaves. Fecundity was highest on mustard followed by purple sprouts and turnip. This affected population rate such that, for example, daily r_m values on young leaves of mustard, purple sprouts, and turnip at 25 °C were 0.206, O.172, and 0.147, respectively.     

Effect of imidacloprid on the sivlerleaf whitefly, Bemisia argentifolii Bellows and Perrring (Homoptera: Aleyrodidae), and whitefly parasitism

Bioassays were conducted under greenhouse conditions to determine the effect of imidacloprid on adult and nymphal stages of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and parasitism by Encarsia formosa (Gahan). A flowable formulation (24Oglitre^-1) of imidacloprid at six rates (0.09, 0.04 and 0.02 g a.i. litre^-1 pot volume for experiments 1 and 2; 0.009, 0.004, and 0.002 g a.i. litre^-1 pot volume for experiment 3) was evaluated. After a 48 h exposure to treated plants, high mortality of adult whitefly (>94%) was observed. Adults exposed to poinsettias treated 150 days earlier also had significantly greater mortality (>79%) than the adults on control plants. When exposed to treated plants for only 6 h, >65% of adults were killed. All three rates of imidacloprid caused >97% mortality of immature whiteflies by day 19. When treated plants were continually exposed to adult whiteflies, immature mortality was 100% for the three higher rates of imidacloprid up to and including 88 days after treatment. During the same time, emerging adults were reduced significantly. Immatures reinfested on plants treated 161 days earlier, incurred 80% mortality at the higher rate 0.09 g a.i. litre^-1 pot volume and 38% mortality at 0.02 g a.i. litre^-1 pot volume. At lower treatment rates, results varied. At 0.009 g a.i. litre^-1 of pot volume, mean percentage whitefly mortality (65%) 25 days after treatment was significantly higher than the controls; however, whitefly mortality at 0.004 and 0.002 g a.i. litre^-1 pot volume was not significantly different from controls or plants treated with the higher rate. Parasitoids could develop to the adult stage on whiteflies infesting imidacloprid treated plants. Parasitism occurred at low levels (< 10%), doe to high levels of whitefly mortality on treated plants. No phytotoxicity was observed for any treatment throughout the length of the trials that lasted through flowering.     

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.     

Zoophytophagy in the plantbug Nesidiocoris tenuis

1 The zoophytophagy of Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) was characterized in relation to prey availability and environmental factors by: (i) monitoring its population dynamics in tomato greenhouses; (ii) analysis of the influence of N. tenuis and whitefly density, temperature and humidity on the intensity of N. tenuis plant feeding; and (iii) laboratory assays under controlled conditions to determine the intensity of plant feeding in relation to prey availability, temperature and humidity. 2 A negative relationship was found between plant feeding and predated whiteflies in tomato greenhouses. Plant feeding was directly related to N. tenuis density and temperature and inversely related to whitefly density. The significance of prey availability and temperature was corroborated in laboratory assays. The intensification of plant feeding at low prey density indicates switching from zoophagy to phytophagy as prey become scarce. 3 Nesidiocoris tenuis showed a typical predator dynamic in relation to variance in prey density. Populations increased after whitefly outbreaks and decreased after whitefly had been depleted. The rapid decrease of N. tenuis populations after whitefly decreased, however, suggests that plants are a poorer nutrient source than whitefly for this species.     

Resistance to Tomato leaf curl New Delhi virus in Cucurbita spp.

Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus (family Geminiviridae) first reported in India and its neighbouring countries. ToLCNDV severely affects zucchini crop (Cucurbita pepo) in the main production areas of Southern Spain since 2012. This emerging begomovirus is a serious threat to this and other cucurbit crops. Breeding resistant cultivars is the most promising method for disease control, but requires the identification of sources of resistance in the Cucurbita genus. In this work, we screened for ToLCNDV resistance a large collection of Cucurbita spp. accessions, including landraces and commercial cultivars of the main cultivated species, C. pepo, Cucurbita moschata and Cucurbita maxima and wild species. The screening was performed using mechanical and whitefly inoculation. The level of resistance was assessed by scoring symptom severity and by measuring the virus content with quantitative polymerase chain reaction in selected genotypes. Diversity in the response was observed within and among species. Severe symptoms and high viral amounts were found at 30 days after mechanical and whitefly inoculation in C. pepo, in all accessions belonging to the Zucchini morphotype and to other morphotypes of both subspecies, pepo and ovifera, and even in the wild relative Cucurbita fraterna. C. maxima was also highly susceptible. This species showed characteristic symptoms of leaf decay and intense yellowing, different from those of mosaic, curling and internode shortening found in C. pepo. The only species showing resistance was C. moschata. Four accessions were symptomless or had some plants with only mild symptoms after three independent rounds of mechanical inoculation with different inoculum sources. Two of them also remained symptomless after virus inoculation with viruliferous whiteflies. ToLCNDV was detected in these asymptomatic accessions at 15 and 30 days post inoculation, but viral amounts were much lower than those found in susceptible genotypes, suggesting a high level of resistance. The symptoms in the susceptible accessions of this species were also different, with a characteristic leaf mottling, evolving to a severe mosaic. The newly identified C. moschata resistant accessions are good candidates for breeding programmes to avoid the damage caused by ToLCNDV.     

Indirect effect of elevated CO2 concentration on Bemisia tabaci MEAM1 feeding on Bt soybean plants

The development of herbivore insects is influenced by the quality of their host plants. Elevated CO₂ alters plant metabolism, which may change the nutritional quality of the plant, modifying the life history and feeding behaviour of herbivore insects. Understanding how insect pests respond to increasing CO₂ concentration is essential for predicting the impact of the pest on food security. In this study, we investigated the effects of elevated CO₂ (eCO₂) on the life history and feeding behaviour of the MEAM1 species of Bemisia tabaci on a Bt soybean cultivar. We found that eCO₂ increased the egg to adult development time and reduced the reproductive responses (fecundity and fertility) of B. tabaci. The whitefly B. tabaci that fed on the soybean plants grown under eCO₂ conditions was negatively influenced by several traits related to the host plant resistance, such as the time spent on phloem sap ingestion. Furthermore, we evaluated the changes in the C:N concentration and plant morphology of the Bt plants. The biomass (weight of leaves and stems) of the Bt soybean plants grown under eCO₂ conditions was significantly increased, and the elevated C:N ratio in the phenological stage V6 (i.e. when the plants had six trifoliate leaves developed) was the most pronounced difference in the Bt soybean plants subjected to eCO₂ treatment. Taken together, our results indicate that Bt plants cultivated under eCO₂ inhibit B. tabaci feeding, which can reduce whitefly infestations of the soybean fields.     

Resistance to Bemisia tabaci biotype B of Solanum pimpinellifolium is associated with higher densities of type IV glandular trichomes and acylsugar accumulation

Advances in tomato breeding for pest resistance have been achieved via gene introgression from wild Solanum (section Lycopersicon) species (Solanaceae). Ninety‐nine F₃ families derived from an interspecific cross using as parental lines Solanum lycopersicum L. ‘LAM‐148' (susceptible standard) and Solanum pimpinellifolium L. ‘TO‐937‐15’ (multiple pest resistance accession with type IV glandular trichomes and acylsugar accumulation) were evaluated for their resistance against the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B in free‐choice and no‐choice tests for oviposition and adult colonization. The parental lines and eight F₃ families with contrasting levels of resistance against the whitefly were selected and investigated in additional assays, which included the estimation of trichome densities and foliar acylsugar levels. The F₃ families BTR‐302 and BTR‐331 exhibited low amounts of eggs of whitefly and transgressive segregation for type IV glandular trichome density with values greater than that of TO‐937‐15 plants. However, the tested families did not surpass the total foliar acylsugar content found in TO‐937‐15. BTR‐331 exhibited low colonization in the free‐choice test and it was the least preferred F₃ family in the no‐choice test. The higher resistance levels of BTR‐331 were associated with a positive combination of higher type IV trichome density and higher acylsugar levels. Some F₃ families displayed reduced fruit set due to the presence of flowers with style exertion of the antheridial‐cone. Fruit weight at harvest stage of the selected families (from 4.9 to 14.5 g) was lower than that of LAM‐148 (139.5 g) but higher than that of TO‐937‐15 plants (1.3 g). Therefore, although difficult to reach due to the simultaneous segregation of many polygenic traits, the combination of high B. tabaci resistance levels with superior horticultural traits is feasible. These results confirm TO‐937‐15 as a source of biotype B resistance. From the breeding standpoint, the genetic similarity between S. lycopersicum and S. pimpinellifolium would allow a more efficient resistance introgression by facilitating recombination and minimizing the potentially undesirable linkage drag associated with this trait.