Whitefly Nymphs Research Articles

Parasitization by the wasp Eretmocerus mundus induces transcription of genes related to immune response and symbiotic bacteria proliferation in the whitefly Bemisia tabaci

BackgroundThe whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and the viruses it transmits, are a major constraint to growing vegetable crops worldwide. Although the whitefly is often controlled using chemical pesticides, biological control agents constitute an important component in integrated pest management programs, especially in protected agriculture. One of these agents is the wasp Eretmocerus mundus (Mercet) (Hymenoptera: Aphelinidae). E. mundus lays its egg on the leaf underneath the second-third instar nymph of B. tabaci. First instars of the wasp hatch and penetrate the whitefly nymphs. Initiation of parasitization induces the host to form a capsule composed of epidermal cells around the parasitoid. The physiological and molecular processes underlying B. tabaci-E. mundus interactions have never been investigated.ResultsWe used a cDNA microarray containing 6,000 expressed sequence tags (ESTs) from the whitefly genome to study the parasitoid-whitefly interaction. We compared RNA samples collected at two time points of the parasitization process: when the parasitoid first instar starts the penetration process and once it has fully penetrated the host. The results clearly indicated that genes known to be part of the defense pathways described in other insects are also involved in the response of B. tabaci to parasitization by E. mundus. Some of these responses included repression of a serine protease inhibitor (serpin) and induction of a melanization cascade. A second set of genes that responded strongly to parasitization were bacterial, encoded by whitefly symbionts. Quantitative real-time PCR and FISH analyses showed that proliferation of Rickettsia, a facultative secondary symbiont, is strongly induced upon initiation of the parasitization process, a result that supported previous reports suggesting that endosymbionts might be involved in the insect host's resistance to various environmental stresses.ConclusionThis is the first study to examine the transcriptional response of a hemipteran insect to attack by a biological control agent (hymenopterous parasitoid), using a new genomic approach developed for this insect pest. The defense response in B. tabaci involves genes related to the immune response as described in model organisms such as Drosophila melanogaster. Moreover, endosymbionts of B. tabaci appear to play a role in the response to parasitization, as supported by previously published results from aphids.

Bioassay Evaluation of the Entomopathogenic Fungi, Beauveria bassaina Vuellemin Against Eggs and Nymphs of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae)

This study was carried out to determine the lethal effect of the entomopathogenic fungi, Beauveria bassaina Vuell. on eggs, young and old nymphs of the whitefly, Bemisia tabaci Genn. Mortality percentage was significantly differed based on stage of B. tabaci and conidial concentrations of B. bassina. Average of the infection level to insect was very low particularly in eggs with only 4.49%, even with higher conidial concentrations (6 x 10(6) conidia mL(-1)). Whereas, it was higher with 1st and 2nd instars (42.045%) and 3rd and 4th instars (35.93%). Three parameters was assessed with B. tabaci eggs, namely; egg infection, egg hatchability and crawlers emergence. Egg mortality percentages averaged 1.2, 4.27 and 8.0% with fungal concentration 2 x 10(6), 4 x 10(6) and 6 x 10(6) conidia mL(-1), respectively. Daily infection percentages were varied depend upon the conidial concentration where the highest infection rate of eggs was occurred with 6 x 10(6), followed by 4 x 10(6) conidia mL(-1). Egg hatch was very high, while the mortality among the emerged crawlers was neglectable compared with the check. Efficiency of B. bassaina on whitefly nymphs also was varied based on the insect instar and fungal concentration. Mortality percentages were obviously higher to young nymphs (1st and 2nd instars) than to older ones (3rd and 4th instars). The results indicated that nymphs were highly susceptible to fungal treatment compared with eggs. Additionally, pathogenicity and virulence of B. bassaina against B. tabaci immatures was not indicated by LC50 only, but also, by the time in days (LT50) required to achieve 50% mortality of an insect.

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

AbstractWe 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.

Comparative studies of predation among feral, commercially-purchased, and laboratory-reared predators

The predatory activities of commercially-purchased adult Hippodamia convergens Guerin-Meneville and two laboratory-reared strains of adult Geocoris punctipes (Say) were compared with their feral counterparts. In single prey choice feeding tests, commercially-purchased and feral H. convergens were provided copious amounts of silverleaf whitefly, Bemisia argentifolii Bellows & Perring adults or eggs of pink bollworm, Pectinophora gossypiella (Saunders). Commercially-purchased H. convergens devoured more pink bollworm eggs and at a faster rate than the feral H. convergens. In contrast, feral H. convergens consumed more adult whiteflies and at a faster rate than commercial H. convergens. In multiple feeding choice tests, two distinctly different laboratory-reared strains and feral G. punctipes were provided a cotton leaf disk containing copious amounts of silverleaf whitefly eggs, nymphs, and adults. Virtually no predation was observed on whitefly eggs, but both laboratory strains of G. punctipes fed on more whitefly nymphs and adults than the feral G. punctipes. Moreover, both of the laboratory strains had a significantly faster feeding rate on adult whiteflies and spent significantly less time feeding on plant tissue than the feral strain. These results suggest that the augmentative biological control candidates retained their ability to prey on these selected prey items, even after being displaced from their overwintering site (H. convergens) or being reared in captivity (G. punctipes) for over 40 generations.

Host‐feeding of three parasitoid species on Bemisia tabaci biotype B and implications for whitefly biological control

AbstractParasitoids in the genera Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies through their reproductive as well as host‐feeding activities. The feeding capacities of female parasitoids of three species with different reproductive strategies [Encarsia sophia (Girault & Dodd), Encarsia formosa Gahan, and Eretmocerus melanoscutus Zolnerowich & Rose] on their host, sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were evaluated on cabbage in a single‐instar no‐choice experiment in the laboratory and a mixed‐instar choice experiment in the greenhouse. In both single‐ and mixed‐instar experiments, significant differences in host‐feeding capacities were found among the three parasitoid species. Encarsia sophia exhibited superior capacity of host‐feeding compared to E. formosa and E. melanoscutus. In the single‐instar experiment, parasitoids fed more on younger (smaller) hosts than older (larger) hosts. In the mixed‐instar experiments, all three parasitoid species exhibited a clear preference for feeding on older hosts compared to younger hosts. Total number of whitefly nymphs fed on by E. sophia was approximately three times that of the other two parasitoid species. Whitefly mortality accounted for by host‐feeding by E. sophia was up to 59.7%, and, thus, equivalent to parasitization. The significance of host‐feeding of E. sophia for biological control of B. tabaci is discussed.

Controle de mosca-branca com extratos vegetais, em tomateiro cultivado em casa-de-vegetação

Visando buscar métodos alternativos no controle da mosca-branca Bemisia tabaci (Gennadius) biótipo B em tomateiro, foram realizados testes de atratividade e preferência para oviposição em casa-de-vegetação, utilizando-se quatorze extratos aquosos a 3% (peso/volume). Os extratos foram preparados com partes de Azadirachta indica, Trichilia pallida,Chenopodium ambrosioides,Piper nigrum,Melia azedarach,Ruta graveolens,Ricinus communis,Mentha pulegium,Tagetes erecta,Eucalyptus citriodora,Cymbopogon nardus e Coriandrum sativum. Numa segunda etapa, os extratos mais eficientes em casa-de-vegetação foram observados em laboratório, a fim de avaliar o possível efeito sistêmico dos mesmos sobre ninfas da mosca-branca. Constatou-se que as plantas de tomateiro pulverizadas com extratos à base de folhas de M. pulegium e folhas e sementes de A. indica foram menos atrativas aos adultos do inseto. Plantas pulverizadas com extratos de folhas de A. indica e folhas + ramos de R. communis mostraram efeitos deterrentes à oviposição do inseto, reduzindo o número de ovos; em contrapartida, o extrato à base de folhas de C. nardus estimulou a oviposição da mosca-branca sobre as plantas. O uso dos extratos por via sistêmica não afetou o período de desenvolvimento (ovo-adulto) da mosca-branca; entretanto, a presença de extratos de sementes e folhas de A. indica e de folhas de M. pulegium provocou aumento significativo na mortalidade de ninfas de B. tabaci biótipo B.

Evaluation of Orius majusculus and O. laevigatus as predators of Bemisa tabaci and estimation of their prey preference

The polyphagous predators Orius laevigatus and O. majusculus are common in several vegetable crops and are well-known biocontrol agents of thrips. The whitefly Bemisia tabaci is an important pest for some of these crops. The aim of the present study was to examine the potential of O. laevigatus and O. majusculus as biocontrol agents for B. tabaci when this whitefly coexists in a crop with the thrips Frankliniella occidentalis. Laboratory experiments were conducted to determine (1) the whitefly developmental stages accepted as prey by adults and nymphs of both Orius species, (2) the duration of the post-embryonic period when the only prey available were whitefly nymphs and (3) the preference of O. laevigatus and O. majusculus nymphs and adults for either B. tabaci or F. occidentalis. The results presented in this paper show that both O. laevigatus and O. majusculus are able to feed on whitefly eggs, nymphs and adults and that they can complete their respective preimaginal development with B. tabaci nymphs as their only available prey. When these predators were simultaneously presented with a choice of thrips larvae, whitefly eggs, whitefly nymphs and whitefly adults both species showed a clear preference for F. occidentalis, but at the end of the experiment O. majusculus adults have also killed up to 59% of the whitefly present. These results suggest than this Orius species could serve as an important biological control agent for use in crops in which B. tabaci and F. occidentalis occur together.

Greenhouse Pesticide Mixtures for Control of Silverleaf Whitefly (Homoptera: Aleyrodidae) and Twospotted Spider Mite (Acari: Tetranychidae)

This study assessed if tank mixing several commercially-available insecticides and miticides, in 2- and 3-way combinations, affects control of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and the twospotted spider mite, Tetranychus urticae Koch, under greenhouse conditions. Pesticides evaluated were acetamiprid, bifenazate, buprofezin, and chlorfenapyr with each applied at the label rate. Salvia × superba Stapf was artificially infested with silverleaf whiteflies, and African marigold, Tagetes erecta L., was infested with twospotted spider mites. Once infested, the plants were sprayed with the designated pesticide treatments. Plants were evaluated 7 and 14 d after treatment. Efficacy was based on percent mortality of silverleaf whitefly and twospotted spider mite nymphs per plant. The 2- and 3-way pesticide mixtures exhibited no antagonistic activity, based on percent mortality values of silverleaf whitefly nymphs 14 d after treatment, with most mixtures resulting in >75% mortality. Similarly, none of the pesticide mixtures appeared to be antagonistic in regards to controlling twospotted spider mite nymphs with ≥90% mortality 7 d after treatment for 4 of the mixtures, and 100% nymphal mortality for all the mixtures 14 d after treatment. Results from this study suggest that greenhouse producers may tank mix the evaluated pesticides without negatively affecting the control of either silverleaf whitefly or twospotted spider mite during crop production.

Life history of Eretmocerus melanoscutus (Hymenoptera: Aphelinidae) parasitizing nymphs of Bemisia tabaci Biotype B (Homoptera: Aleyrodidae)

Abstract Eretmocerus melanoscutus Zolnerowich and Rose was originally imported from Thailand, and has been released in southern Texas, Arizona and California for biological control of Bemisia tabaci (Gennadius) biotype ‘B.’ Studies were conducted to determine biological parameters of E. melanoscutus , and evaluate its potential as a biological control agent of B. tabaci under laboratory conditions [26.7 ± 2 °C, 50–75% RH and a photoperiod of 14:10 (L:D) h]. E. melanoscutus successfully oviposited under all nymphal instars of B. tabaci on cabbage with the exception of late fourth instars. The females oviposited least under first instars (25.6 ± 3.2 eggs) and most under third instars (122.7 ± 9.6 eggs), followed by similar numbers of eggs under the second (95.6 ± 8.5 eggs) and early fourth instars (85.6 ± 6.9 eggs). Regardless of host stage parasitized, 93.4% adults emerged. Parasitoid development averaged 16.8 d from oviposition to adult emergence. Each female laid an average of 122.4 (±13.1) eggs during her lifespan or 11.2 ± 0.6 eggs per day. Mean longevity of adult females and males on plants with whitefly nymphs was 9.8 ± 0.9 and 13.2 ± 1.4 d, respectively. Of the offspring, 53.9% were females. The intrinsic rate of natural population increase ( r m ), net reproductive rate ( R o ), generation time ( T ), doubling time (DT), and the finite rate of increase ( λ ) of E. melanoscutus were estimated by life table analysis at 0.2175/d, 61.42 offspring, 19.0 d, 3.2 d, and 1.2429/d, respectively. These values are higher than those reported for B. tabaci on any host plant, indicating that E. melanoscutus has a great potential as a biological control agent of B. tabaci .

Intraguild interactions between an oligophagous predator, Delphastus catalinae (Coleoptera: Coccinellidae), and a parasitoid, Encarsia sophia (Hymenoptera: Aphelinidae), of Bemisia tabaci (Homoptera: Aleyrodidae)

The intraguild interactions between two natural enemies of Bemisia tabaci (Gennadius), an oligophagous predator, Delphastus catalinae (Horn), and a parasitoid, Encarsia sophia (Girault & Dodd), associated with predation, parasitization, host feeding, and suppression of B. tabaci populations were determined on cabbage under laboratory and greenhouse conditions. We conducted two laboratory experiments: a no-choice test of prey consumption by three larval instars and adult D. catalinae foraging for either whitefly fourth instar nymphs or whitefly nymphs containing second or third larval instar or pupal parasitoids of E. sophia; and a choice test, in which three larval instars or adult D. catalinae were allowed to forage for the above prey, presented simultaneously. We also conducted a mesocosm experiment under greenhouse conditions in which a low (20 females) or high (40 females) release of E. sophia adults, a low (6) or high (12) release of D. catalinae adults, a combined release with both predators and parasitoids at the low rate (20 parasitoids and 6 predators), and the experiments were performed on caged plants infested experimentally with whiteflies. In no-choice and choice experiments, predation was generally lower on the whitefly nymphs containing E. sophia pupae than on larval stages or on unparasitized whitefly nymphs. In choice tests, adult D. catalinae did not discriminate between prey types. In both choice and no-choice tests, second instar D. catalinae larvae tended to discriminate against whitefly nymphs containing parasitoid larvae, and the third and fourth instar predator larvae tended to attack less the whitefly nymphs containing parasitoid pupae than larvae. In the mesocosm experiment, the results indicate that D. catalinae did not avoid feeding on B. tabaci nymphs with larval stages of E. sophia and numbers of whitefly nymphs killed by E. sophia were lower in the presence of D. catalinae. However, whitefly immatures on cabbage leaves were significantly less abundant in each of the three treatments with the presence of D. catalinae as compared with treatments that did not include the predators.

Suitability of various prey types for the development of Propylea japonica (Coleoptera: Coccinellidae)

The relative suitability of three prey organisms, Bemisia tabaci (Gennadius) eggs, B. tabaci nymphs, and Myzus persicae (Sulzer), to the ladybird Propylea japonica (Thunberg) was evaluated under laboratory conditions. The larvae developed fastest when fed M. persicae, and slowest on B. tabaci eggs. When fed M. persicae, all larvae successfully developed into adult with a growth index (i.e., percent pupation/larval period in days) of 13.16 and development rate of 0.096. The longevity of starving adults was 4.7 ± 0.2 days. In contrast, when fed B. tabaci eggs, all larvae survived to the second instars, 56.7% of which survived to the third instars, 13.3% to the fourth instars; only 6.7% of larvae survived to the pupal stage and the pupae developed into abnormal adults that died shortly. When fed B. tabaci nymphs, all larvae survived and successfully developed into adults with a growth index of 10.71 and development rate of 0.083. The adult body mass was greater when larvae fed M. persicae, compared to adults eclosing from larvae fed B. tabaci nymphs. On the basis of these findings, the order of suitability of three prey organisms for P. japonica is M. persicae > B. tabaci nymph > B. tabaci egg. This is the first record that P. japonica can complete its development when feeding exclusively on whitefly nymphs.

SILVERLEAF WHITEFLY AND LEAFMINER MANAGEMENT ON SQUASH, SPRING 2006

Transplants were set 28 Mar, 1.5 ft apart within the row on 8-inch-high and 32-inch-wide beds of Myakka fine sand covered with white polyethylene mulch. Each plot consisted of a single 21 ft-long row spaced 11 ft end to end and 10 ft apart. Treatments were replicated four times in a randomized complete block design. Treatments were made as soil drenches in 4 ozs of water per plant on 28 Mar. The number of whitefly adults was counted weekly on one top leaf of the middle 10 plants in each plot. The numbers of eggs, and first instar and second to fourth instar whitefly nymphs were counted weekly on each of 4, 3.5 cm leaf disks per each of 10 leaves per plot. The number of Liriomyza leafmines was counted by each of two persons during a one minute search of each plot on 1 and 10 May.

Arabidopsis transcriptome changes in response to phloem-feeding silverleaf whitefly nymphs. Similarities and distinctions in responses to aphids.

Phloem-feeding pests cause extensive crop damage throughout the world, yet little is understood about how plants perceive and defend themselves from these threats. The silverleaf whitefly (SLWF; Bemisia tabaci type B) is a good model for studying phloem-feeding insect-plant interactions, as SLWF nymphs cause little wounding and have a long, continuous interaction with the plant. Using the Affymetrix ATH1 GeneChip to monitor the Arabidopsis (Arabidopsis thaliana) transcriptome, 700 transcripts were found to be up-regulated and 556 down-regulated by SLWF nymphs. Closer examination of the regulation of secondary metabolite (glucosinolate) and defense pathway genes after SLWF-instar feeding shows that responses were qualitatively and quantitatively different from chewing insects and aphids. In addition to the RNA profile distinctions, analysis of SLWF performance on wild-type and phytoalexin-deficient4 (pad4) mutants suggests aphid and SLWF interactions with Arabidopsis were distinct. While pad4-1 mutants were more susceptible to aphids, SLWF development on pad4-1 and wild-type plants was similar. Furthermore, although jasmonic acid genes were repressed and salicylic acid-regulated genes were induced after SLWF feeding, cytological staining of SLWF-infested tissue showed that pathogen defenses, such as localized cell death and hydrogen peroxide accumulation, were not observed. Like aphid and fungal pathogens, callose synthase gene RNAs accumulated and callose deposition was observed in SLWF-infested tissue. These results provide a more comprehensive understanding of phloem-feeding insect-plant interactions and distinguish SLWF global responses.

Manipulation of oviposition choice of the parasitoid wasp,Encarsia pergandiella, by the endosymbiotic bacteriumCardinium

Reproductive manipulations of hosts by maternally inherited bacterial endosymbionts often result in an increase in the proportion of infected female hosts in the population. When this involves the conversion of incipient males to genetic or functional females, it presents unique difficulties for symbionts invading hosts with sex-specific reproductive behaviours, such as the autoparasitic Encarsia pergandiella. In sexual forms of this species, female eggs are laid in whitefly nymphs and male eggs are laid in conspecific or heterospecific parasitoids developing within the whitefly cuticle. Further, eggs laid in the 'wrong' host do not ordinarily complete development. This study explored the role of a bacterial symbiont, Cardinium, in manipulating oviposition behaviour in a thelytokous population of E. pergandiella. Oviposition choice was measured by the number and location of eggs deposited by both infected and uninfected adult waSPS in arenas containing equal numbers of hosts suitable for the development of male and female waSPS. Uninfected waSPS included antibiotic-treated female waSPS and (untreated) daughters of antibiotic-treated female waSPS. The choices of waSPS in the thelytokous population treatments were compared with those of a conspecific sexual population. We found that offspring of antibiotic-cured thelytokous waSPS reverted to the behaviour of unmated sexual waSPS, laying their few eggs almost exclusively in hosts appropriate for male eggs. Infected thelytokous waSPS distributed their eggs approximately evenly between host types, much like mated sexual female waSPS. The antibiotic-treated female waSPS exhibited choices intermediate to waSPS in the other two treatments. The change in the observed behaviour appears sufficient to allow invasion and persistence of Cardinium in sexual populations. Lastly, our results suggest a reduction in host discrimination as a possible mechanism by which Cardinium influences this change.

Factors affecting the attack rate of Bemisia tabaci on cucumber

The objective of this work was to determine the effects of rainfall, temperature, predators, parasitoids, plant age, leaf chemical composition, levels of leaf nitrogen and potassium, besides density of leaf trichomes, on attack intensity of Bemisia tabaci biotype B on the Cucumis sativus. An increase in the number of whitefly adults and nymphs per leaf was observed with plant aging. A higher number of whitefly adults per leaf and eggs cm-2 was verified in the apical part than in the middle and bottom part of the plants canopy. However, the higher number of whitefly nymphs was observed in the mid-part than in the apical and bottom part of the plant canopy. The incidence of whitefly nymphs was negatively affected with foliar nitrogen. Pentacosane and octacosane positively affected whitefly adults and the first compound also affected the nymphs of this pest species.

Effect of <I>Melia azedarach</I> L. Extract on <I>Bemisia argentifolii</I> (Hemiptera: Aleyrodidae) and Its Biocontrol Agent <I>Eretmocerus rui</I> (Hymenoptera: Aphelinidae)

We studied the effects of Melia azedarach L. fruit extracts on survival of Bemisia argentifolii Bellows and Perring nymphs and the parasitoid Eretmocerus rui Zolnerowich and Rose and on whitefly oviposition under laboratory conditions. In an experiment to determine toxicity to second-instar nymphs of aqueous extracts of three different sources of M. azedarch, survival of treated nymphs was significantly lower than survival of untreated control nymphs. In a second experiment to determine the effect of combined treatments involving extract application and exposure to parasitoids, the number of emerged whiteflies was significantly higher from control plants than from any of the combined treatments. Successful parasitism was the lowest when adult parasitoids were introduced after dipping second instars in the extract and when whitefly nymphs were dipped in extract 2 d after parasitism. However, the level of parasitism in parasitized nymphs dipped in extracts 4 and 8 d after parasitism was comparable with that of the control. The number of dead whitefly nymphs in combined treatments declined as the age of whitefly nymphs at application increased, with a concomitant increase in successful parasitism. Combined application of plant extract and parasitoids had an additive effect on whitefly nymphal mortality. In a test of whitefly oviposition, there was no significant difference in number of eggs laid on plants treated with extracts and on control plants. However, significantly fewer whiteflies emerged from eggs laid on treated plants than on control plants, indicating that M. azedarach extracts had affected egg development. Thus, M. azedarach fruit extract and the parasitoid E. rui are compatible and may contribute to lower whitefly populations in an integrated pest management program.

Economic injury level and sequential sampling plan for Bemisia tabaci in outdoor tomato

Abstract: This work aimed to determine the economic injury levels and to establish sequential sampling plans for nymphs and adults of the whitefly Bemisia tabaci Genn. (Sternorrhyncha: Aleyrodidae) in tomato fields. Densities of nymphs and adults, as well as crop yield were evaluated in 13 commercial tomato fields to determine the economic injury levels. The whitefly nymphs were sampled by direct counting in a leaf from the lower part of the canopy and the adults were sampled by beating an apical leaf against a white plastic tray. The sequential sampling plan was based on data collected in eight commercial tomato fields. The validation of the sequential sampling plan was carried out based on the curves of operational characteristics and average sample numbers. The decisions reached with the conventional and the sequential sampling plans in 21 commercial fields were compared for the intended validation of the sequential plan. The economic injury levels were four nymphs per leaf and one adult per tray. The decisions taken based on the sequential sampling plan were similar to those obtained through the conventional sampling plan. Most of the decisions taken with the sequential sampling plan were obtained through the minimum number of seven samples per field for nymphs and 11 samples per field for adults, with reductions of 84.44% and 54.17% in the number of samples required to reach a decision with the sequential sampling plan compared with the conventional sampling plan.

Systemic toxicity of spinosad to the greenhouse whiteflyTrialeurodes vaporariorum and to the cotton leaf wormSpodoptera littoralis

When spinosad was administered at the stem base of tomato plants grown in rockwool, the main substrate used in greenhouses in northern Europe, it was taken up by the roots and transported to the leaves. Laboratory toxicity experiments showed that systemically applied spinosad, at doses as low as 2 mg active ingredient per plant, gave excellent control of nymphs of the greenhouse whiteflyTrialeurodes vaporariorum, but was less toxic to adults. The toxicity of spinosad on Homoptera has not been documented yet and a dose-response relationship was established. The persistence of toxicity was at least 22 days for whitefly nymphs. A dose-response relationship of systemically applied spinosad was also determined on third-instar larvae of the cotton leaf wormSpodoptera littoralis; a dose of 5 mg per plant consistently killed all larvae. The persistence of systemically applied spinosad reached up to 45 days after treatment. Systemically applied spinosad was harmless to the parasitic waspEncarsia formosa.

Biology of a thelyotokous biotype of Eretmocerus mundus (Hymenoptera: Aphelinidae) on Bemisia tabaci (Homoptera: Aleyrodidae)

Abstract Thelyotokous biotype of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae), a parasitoid of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was recently recorded in northern Iran. Reproductive biology of this biotype was studied as part of an evaluation of its potential for biological control of B. tabaci. The parasitoid deposited more eggs under 2nd and 3rd nymphal instars than 1st or 4th instars. Adult females fed honey, with no access to whitefly nymphs, lived significantly longer (13.6 ± 4.7 d) than those given access to nymphs, but not fed honey (7.6 ± 2.21 d). Lifetime fecundity averaged 81.7 ± 26.9 female progeny per female parasitoid, ranging from 11–132. Daily fecundity, measured as the number of whitefly nymphs parasitized by per female each day for 10 d, averaged 18.06 ± 3.95 for the first 6 d of life, and then declined to < 11. Developmental time from oviposition to parasitoid emergence was significantly shorter in the 3rd instar of the host (15.9 ± 1.06 d) than in the 1st instar (18.7 ± 2.3 d), but not in the 2nd instar (16.4 ± 1.3 d).

Host-parasitoid interactions relating to penetration of the whitefly, Eretmocerus mundus

It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal instars of the sweet potato whitefly, Bemisia tabaci (Biotype B), with 3rd instars being the preferred hosts. The parasitoid lays its egg on the leaf underneath the host nymph. First instars hatch and later penetrate the whitefly. Previous studies have shown that the initiation of parasitoid penetration induces the host to form a cellular capsule around the parasitoid. As described here, females never oviposited once the 4th instar whitefly nymph had initiated adult development. First instar E. mundus larvae were observed under 2nd, 3rd and 4th instar whitefly nymphs, however, penetration did not occur until the whitefly had reached the 4th instar. The non-penetrating E. mundus larva almost always induced permanent developmental arrest in its 4th instar whitefly host and also caused a reduction in whole body host ecdysteroid titers. Therefore, unless there is a peak in molting hormone titer in the area local to penetration, it appears that the induction of capsule formation is not due to an increase in ecdysteroid titer. As the capsule formed around the penetrating parasitoid, host epidermal cells multiplied and became cuboidal and columnar, and relatively thick layers of new cuticle were deposited within the developing capsule, particularly near its ventral opening. The newly formed host cuticle was thinner in the dorsal part of the capsule and appeared to be absent at its apex. These results provide new information regarding the timing and dynamics of parasitoid oviposition and egg hatch as related to larval penetration, parasitoid-induced changes in whitefly development, molting hormone titers and the process of capsule formation.