Colonization of tomato greenhouses by the predatory mirid bugs Macrolophus caliginosus and Dicyphus tamaninii

Colonization of tomato greenhouses by native predatory mirid bugs at the end of the spring cycle is common in the western Mediterranean area when no broad-spectrum insecticides are applied. Due to their polyphagy, these predators interact with pest populations and also with other natural enemies present in the crop. In this work we evaluate the abundance and timing of greenhouse colonization by these predators and their interaction with the greenhouse whitefly Trialeurodes vaporariorum, a key crop pest, and its introduced parasitoid Encarsia formosa. Although quite unpredictable, natural colonization of greenhouses by Macrolophus caliginosus and Dicyphus tamaninii, the two predominant species in our location, usually leads to the establishment of predator populations in the crop that subsequently prey on greenhouse whitefly. No preference for parasitized pupae was observed in greenhouse samples, while laboratory experiments revealed a marked tendency to avoid parasitoid pupae. In our area, IPM programs for greenhouse tomatoes and other vegetables should take advantage of the presence of this predator complex by allowing the immigration and establishment of its populations without disturbing them with highly toxic and non-selective insecticides.     

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.     

Influence of Hairiness ofGerbera jamesoniiLeaves on the Searching Efficiency of the ParasitoidEncarsia formosa

To characterize the relationship between the leaf surface ofGerbera jamesoniiHooker cultivars and the searching behavior of the parasitoidEncarsia formosaGahan on a leaf, the trichome density and shape were described, and the walking behavior was quantified. Leaf hair density varied from 80 to more than 1000 trichomes/cm²and the hair shape varied from single erect trichomes to tapestries of entangled trichomes above the leaf surface. The walking activity, speed, and pattern of the parasitoid were tested on leaves with different hair density and shape. In spite of the large differences in leaf surface structure, the walking activity was similar and around 75% on most cultivars. The walking speed was between 0.2 and 0.3 mm/s on all cultivars and was not significantly different from the speed on tomato. On hairless sweet pepper leaves the walking speed is much higher (0.73 mm/s), so the hairs onGerberaleaves do hamper parasitoid females and result in a strong reduction of the walking speed, but the variation in hair density and shape onGerberadoes not lead to differences in walking activity, pattern, and speed. It appears that the hairs ofGerberaare less of an obstacle forE. formosathan the stiff, large hairs occurring in a high density on cucumber, where the walking speed of the parasitoid is less than 0.2 mm/s. A rise of temperature of 5°C gave a significantly higher walking speed (0.39 mm/s) ofE. formosafemales on all cultivars tested. The relative straightness of the walking track was high and the same on all cultivars. Consequences of the results of the searching behavior ofE. formosaonG. jamesoniicultivars are discussed with respect to other host plants. As parasitoid walking speeds are the same onGerberaand tomato, and whitefly reproduction is also similar on these two host plants, we conclude that biological control of whiteflies onGerberais a realistic option. This conclusion is confirmed by the strong increase of commercial biological control onGerberawhich occurred during the past 5 years.     

Parasitism ofTrialeurodes ricini byEncarsia formosa: Level of parasitism,development time and mortality on different host plants

The effects of the host plant on the level of parasitism, development time and mortality ofEncarsia formosa Gahan parasitizing castor whitefly,Trialeurodes ricini Misra were studied. The level of parasitism varied significantly between host plants; ranging from an average high of 13/50T. ricini larvae parasitized per parasitoid per day on aubergine to an average low of 1.6/50 host larvae on potato. Development time ofE. formosa varied according to whitefly host plant; minimum average development time was 17.7 days on cotton. The mortality ofE. formosa was high on all host plants tested, and the type of host plant had no significant influence on mortality. Aubergine proved to be the most satisfactory laboratory plant for rearingE. formosa onT. ricini.     

The effect of nitrogen fertilizer applied to Euphorbia pulcherrima on the parasitization of Bemisia argentifolii by the parasitoid Encarsia formosa

More wasps of Encarsia formosa Gahan (Hymenoptera: Aphelinidae) were found on fertilized poinsettias, Euphorbia pulcherrima (Willd.) (Euphorbiaceae), than on non-fertilized plants. Parasitization of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) by E. formosa was higher on plants treated with calcium nitrate than with ammonium nitrate or on control plants. In a no-choice test, host feeding by E. formosa was higher when hosts were on fertilized plants than when hosts were on control plants. The nitrogen content of whitefly pupae reared on plants treated with ammonium nitrate was higher than those on calcium nitrate-treated plants.Variability in the parasitization of B. argentifolii by E. formosa appears to be due to host plant-mediated differences in the whiteflies. E. formosa may be influenced by the nutritional suitability of the host, which influences whether wasps continue to oviposit, feed, or disperse.     

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m⁻²/14 days), and a subsequent 3-month trial with high (100 m⁻²/week) and very high (1,000 m⁻²/week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50–100 juvenile and 50–70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50–70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10–100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.     

Host selection by the heteronomous hyperparasitoid Encarsia pergandiella: multiple-choice tests using Bemisia argentifolii as primary host

The ovipositional patterns of the heteronomous hyperparasitoid Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) in the presence of its primary host Bemisia argentifolii Bellows & Perring (Hemiptera: Aleyrodidae), and in the presence or absence of conspecific and heterospecific secondary hosts (Encarsia formosa Gahan andEretmocerus mundus Mercet; Hymenoptera: Aphelinidae) were examined to assess host species preferences. Host preferences by heteronomous hyperparasitoids may affect the relative abundance of co-occurring parasitoid species and may influence host population suppression by the parasitoid community. Four combinations of hosts were tested: (1) B. argentifolii, E. mundus, and E. formosa, (2) B. argentifolii, E. formosa, and E. pergandiella, (3) B. argentifolii, E. mundus, and E. pergandiella, and, (4) B. argentifolii, E. mundus, E. formosa, and E. pergandiella. Arrays of hosts (24) were constructed in Petri dishes using leaf disks, each bearing one host. Thirty arrays of each host combination were exposed to single females for 6 h. All hosts were dissected to determine number of eggs per host. Encarsia pergandiella parasitized E. formosa hosts as frequently as E. mundus hosts. However, E. pergandiella parasitized either of these heterospecific hosts more frequently than conspecific hosts in treatments including two secondary host species. When a third parasitoid species was included in host arrays, E. pergandiella parasitized conspecific hosts as frequently as heterospecific hosts. Developmental stage of the hosts did not significantly influence host species selection by E. pergandiella. Our results indicate that host selection and oviposition by heteronomous hyperparasitoids like E. pergandiella, vary with the composition of hosts available for parasitization, and suggest a preference for heterospecific over conspecific secondary hosts.     

Egg Size, Intrinsic Competition, and Lethal Interference in the Parasitoids Encarsia pergandiella and Encarsia formosa

Recent population dynamic theory predicts that disruption of biological control may occur when one parasitoid species' superiority in intrinsic competition is associated with a lower ability to find and exploit hosts (i.e., ability in extrinsic competition). One might expect such a trade-off, for instance, if parasitoids with larger (and fewer) eggs are more likely to prevail in intrinsic competition than species with smaller (and more numerous) eggs. We tested the idea that relative egg size could be used to predict the outcome of intrinsic competition in two closely related endoparasitoids, Encarsia pergandiella Howard and Encarsia formosa Gahan. Contrary to expectation, the parasitoid species with smaller eggs, E. pergandiella, prevailed in intrinsic competition, regardless of the order that hosts were exposed to the two species. In a literature survey, we found four studies of competing pairs of endoparasitoid species for which: (a) egg size estimates were available and (b) one species was consistently superior in intrinsic competition. In three of the four studies, the small-egged species prevailed in intrinsic competition, as we also found. Although E. formosa lost in intrinsic competition, this species negatively affected E. pergandiella's progeny production by host feeding on and killing hosts containing E. pergandiella eggs. E. formosa females also host fed on conspecific-parasitized hosts. As a mechanism of both intra- and interspecific interference competition, host feeding on parasitized hosts contradicts assumptions about the nature of interference competition in existing population dynamics models.     

Foraging behaviour of the whitefly parasitoidEncarsia formosa on tomato leaflets

IndividualEncarsia formosa parasitoids were observed continuously until the parasitoids flew away, either on clean tomato leaflets, on leaflets with honeydew, or on leaflets with unparasitized and parasitized whitefly larvae. Encounters with unparasitized and parasitized whitefly larvae, and contact with honeydew arrested the parasitoids on the leaflet. The walking speed increased linearly from 0.179 to 0.529 mm/s between 15 and 25–30°C. The walking activity showed another relationship with temperature: it was below 10% at 15 and 18°C, and increased to about 75% at 20, 25 and 30°C. It was not affected by host encounters or by 1 to 4 ovipositions. The total handling time of hosts was between 1.8–21.8% of the total time on the leaflet. Self-superparasitism was not observed. Conspecific-superparasitism did occur in 14% of the encounters with hosts containing a parasitoid egg, but was not observed anymore when the parasitoid egg had hatched. Experienced parasitoids superparasitized as often as naive females. The foraging behaviour ofE. formosa from landing on a leaf until departure has now been quantified and is discussed.     

Comparison of Foraging Behavior, Interspecific Host Discrimination, and Competition of Encarsia formosa and Amitus fuscipennis

The foraging behavior of Amitus fuscipennis MacGown & Nebeker and Encarsia formosa Gahan was studied on tomato leaflets with 20 Trialeurodes vaporariorum (Westwood) larvae in the first or third stage. Ten of the whitefly larvae were previously parasitized and contained a conspecific or a heterospecific parasitoid egg or larva. The host type (host stage and/or previous parasitization) did not influence the foraging behavior of either parasitoid species. The residence time on these tomato leaflets was about 0.9 h for A. fuscipennis and 1.9 h for E. formosa. Amitus fuscipennis hardly stood still and fed little, while E. formosa showed extensive standing still and feeding. As a result, the time walking while drumming was similar for both parasitoid species. The numbers of host encounters and ovipositions per leaflet were similar for both parasitoid species. However, the residence time of A. fuscipennis was half as long as that of E. formosa so the rate of encounters and ovipositions was higher for A. fuscipennis. Amitus fuscipennis is more efficient in finding and parasitizing hosts under these conditions. The walking activity and host acceptance of the synovigenic E. formosa diminished with the number of ovipositions, but not those of the proovigenic A. fuscipennis. Encarsia formosa is egg limited, while A. fuscipennis is time limited because of its short life span and high egg load. Both parasitoid species discriminated well between unparasitized larvae and self-parasitized larvae, but discriminated poorly those larvae parasitized by a conspecific and did not discriminate larvae parasitized by a heterospecific. Self-superparasitism, conspecific superparasitism, and multiparasitism were observed for both parasitoid species. Superparasitism always resulted in the emergence of one parasitoid and multiparasitism resulted in a higher emergence of one parasitoid of the species that had parasitized first. The data suggest that A. fuscipennis is a good candidate for use in biological control of high-density spots of T. vaporariorum when we consider its high encounter and oviposition rate.     

Pre- and post-landing response of the parasitoid Encarsia formosa to whitefly hosts on Gerbera jamesonii

One of the factors that may complicate biological control of the greenhouse whitefly on Gerbera jamesonii by Encarsia formosa is the rosette shape of this ornamental, which differs from the vertical shape of most vegetable plants (cucumber, egg plant, tomato, etc.). Therefore, host-habitat location and the behaviour prior to landing on uninfested and infested leaves was studied. Attraction of E. formosa from a short distance by infested leaves could not be detected: the parasitoid females landed at random on uninfested and infested leaves. After the first landing, a redistribution of the wasps occurred on the leaves. After 24 h three times as many wasps were found on the infested leaves than on uninfested ones. In a dispersal experiment with four plants, E. formosa appeared to have no preference for landing on leaves of the medium age class, which is the age class on which most of the whiteflies in a suitable stage for parasitism occur. Twenty percent of the parasitoids were found on the plants 20 min after releasing them. These results were independent of the plant cultivar and the host density on the plants. In the course of 8 h, the number of E. formosa females recovered from plants increased linearly, and this increase was greater on plants where hosts were present and also greater on the plant cultivar with the lowest trichome density. After 24 h, the percentage of females was highest (56%) on plants with the highest host density. E. formosa females were arrested on leaves where hosts were present. Contrary to our expectation, the results from the two G. jamesonii cultivars that differed strongly in leaf hairiness were not significantly different in most experiments. Only at the high host density was parasitism found to be lower on the cultivar with the higher hair density. Parasitoids may walk on top of the `hair coverlet' of cultivars with high trichome density and, therefore, be hampered less than expected.     

Encarsia formosa parasitizing the Poinsettia-strain of the cotton whitefly,Bemisia tabaci, on Poinsettia: bionomics in relation to temperature

Adult longevity, developmental time and juvenile mortality ofEncarsia formosa Gahan (Hymenoptera:Aphelinidae) parasitizing the Poinsettia-strain ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on Poinsettia (Euphorbia pulcherrima Willd.) were investigated in laboratory experiments at three temperatures: 16 °C, 22 °C and 28 °C. Furthermore, the parasitoid's preference for different larval stages of the whitefly was determined at 24.5 °C. The lifespan ofE. formosa decreased with temperature from one month at 16 °C to nine days at 28 °C. A lower temperature threshold of 11 °C for adult development was found. The development of juvenile parasitoids inB. tabaci lasted more than two months at the lowest temperature, but was only 14 days when temperature was 28 °C. The lower temperature threshold for immature development was 13.3 °C, yielding an average of 207 day-degrees for the completion of development into adults. Juvenile mortality was high, varying from about 50% at 16 °C to about 30% at 22 °C and 28 °C.E. formosa preferred to oviposit in the 4th instar and prepupal stages ofB. tabaci followed by the 2nd and 3rd instars. The preference for the pupal stage was low. The parasitoid used all instars of the whitefly for hostfeeding, with no apparent differences between the stages. The average duration of the oviposition posture was four minutes. Demographic parameters were calculated from life tables constructed from the data. The intrinsic rate of increase (r _m) and the net reproductive rate (R ₀) increased with temperature from 0.0279 day⁻¹ at 16 °C to 0.2388 day⁻¹ at 28 °C and from about 12 at 16 °C to about 66 at 28 °C, respectively.     

Hyperparasitism behaviour of the autoparasitoid <Emphasis Type="Italic">Encarsia tricolor</Emphasis> on two secondary host species

Hyperparasitism by virgin female Encarsia tricolor was studied by direct observation of its behaviour when contacting two secondary host species (Encarsia formosa and E. tricolor) at different host stages (first and second larval stage, third larval stage, and pupal stage). The searching and hyperparasitism behavioural sequence of E. tricolor was independent of the host stage of the whitefly (Aleyrodes proletella), and was similar to several related primary parasitoid species. In experiments with equal numbers of secondary hosts, encounter frequencies were equal for both secondary host species in all developmental stages observed. However, rates of hyperparastism were different according to host stage and host species. Hosts in the late larval stages were most preferred for hyperparasitization and the heterospecific E. formosa was more preferred as a secondary host than the conspecific, E. tricolor, in particular from the prepupal stage onwards. The window of vulnerability, i.e., the duration of the period in which a secondary host is susceptible to hyperparasitism, was largely determined by the occurrence and rate of melanization after the onset of pupation. The duration of a successful hyperparasitization event was longer than one that failed. Superparasitism occurred only once in all cases. The potential effect of autoparasitoids on biological control programs and the consequences for selection and release of an effective, yet ecologically safe agent are discussed. Handling editor: Torsten Meiners.     

Survival of the parasitoidEncarsia formosa after treatment of parasitized greenhouse whitefly larvae with fungal spores ofAschersonia aleyrodis

The interaction between the entomopathogenic fungusAschersonia aleyrodis and the parasitoidEncarsia formosa on greenhouse whitefly as a host organism was studied, in particular, the survival of the parasitoid after treatment of parasitized hosts with fungal spores. The mean number of parasitized black pupae per parasitoid produced at 25°C was significantly reduced after spore treatment in the first three days following parasitization. Spore treatment four, seven or ten days after parasitization resulted in a mean number of parasitized pupae not significantly different from the number of black pupae in the control. The rather sudden change from low to high survival of parasitized hosts when treated with spores four days after parasitization in spite of high numbers of infected unparasitized larvae, coincided with the hatching of the parasitoid larva from the egg inside the host. Possible reasons for this decrease in susceptibility to infection after parasitoid egg hatch, such as induced changes in host cuticle or haemolymph, are discussed. Parasitoids emerged from treated hosts did not show differences in reproduction compared with parasitoids emerging from untreated hosts. Both natural enemeies of whitefly are compatible to a great extent.     

Temperature dependent functional response ofEncarsia formosa parasitizing the Poinsettia-strain of the cotton whitefly,bemisia tabaci, on Poinsettia

The control efficiency and performance ofEncarsia formosa Gahan (Hymenoptera: Aphelinidae) as influenced by the density of its host, the Poinsettia-strain ofBemisia tabaci Gennadius (Homoptera: Aleyrodidae), were investigated by laboratory experiments on Poinsettia (Euphorbia pulcherrrima Willd.).E. formosa showed a Type II functional response to fourth instar larvae ofB. tabaci, the response plateau increasing with temperature. A response model for randomly searching parasitoids incorporating temperature-dependent handling time and temperature-independent search rate was in accordance with the results, and gave an estimated search rate of 0.033 leaf·hour⁻¹ and handling times of 1.54, 2.86 and 20.1 h at 28°C, 22°C and 16°C, respectively. From the latter, the maximum number of hosts that can be parasitized at the three temperatures are 10.4, 5.6 and 0.8 larvae per day (provided the light period is 16 h). The number of hosts with ovipositor punctures was higher than the number of parasitized hosts, especially at 22°C and 28°C, implying thatE. formosa refrains from laying eggs in some of the hosts examined with the ovipositor. About 31% of the punctured larvae did not contain any eggs. Superparasitism occured during the experiment presumably originating from young, inexperienced parasitoids. Individual larvae were occasionally punctured several times, also by non-superparasitizingE. formosa. The resulting distribution of ovipositior holes was random, indicating thatE. formosa on the basis of antennal testing is unable to determine if a larva has previously been examined with the ovipositor. Almost fifty percent of the punctures were not followed by egg-depositions. Besides parasitizationE. formosa used hosts as food source. The number of hostfed larvae was independent of density, but varied with temperature being highest at 28°C (0.12 hostfed larvae per parasitoid per day).     

Comparison of Searching Behaviour of Two Aphelinid Parasitoids of the Greenhouse Whitefly, Trialeurodes vaporariorum under Summer vs. Winter Conditions in a Temperate Climate

Searching behaviour of two aphelinid parasitoids, Encarsia formosa Gahan and Eretmocerus eremicus Rose and Zolnerowich, was compared in a controlled environment under simulated summer [high light intensity (83 ± 1 W/m²), and 24 ± 1°C] and winter [low light intensity (11 ± 0.5 W/m²), and 20 ± 1°C] greenhouse conditions on tomato leaflets, with and without a single 3rd instar whitefly host, Trialeurodes vaporariorum (Westwood), within a 4-cm tomato leaflet arena. Residence time of both parasitoid species was longer on infested leaflets vs. clean leaflets, and longer under winter than summer conditions. When parasitoids encountered a host on infested leaflets, residence time increased. In all cases, residence time of E. formosa was longer that of E. eremicus. Proportion of time spent searching (i.e. antennating leaf surface while walking or standing still) was longer on clean vs. infested leaflets for both E. formosa and E. eremicus. Walking speed by E. eremicus on clean leaflets was faster than E. formosa under both summer and winter conditions. Host handling time and proportion of host acceptance did not vary among parasitoids. These findings suggest that E. eremicus could be more efficient in host finding on tomato leaflets than E. formosa over all seasons, especially in the winter when natural light is limiting and where daylight temperatures are ≥20°C.     

Poinsettia (Euphorbia pulcherrima Willd Ex Koltz) Cultivar-Mediated Differences in Performance of Five Natural Enemies of Bemisia argentifolii Bellows and Perring, n. sp. (Homoptera: Aleyrodidae)

Laboratory evaluations of five natural enemies of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, n. sp., were conducted to determine their potential as biological control agents in greenhouse poinsettia ranges. Adult longevity, prey consumption or host feeding and parasitism rates, and parasitoid emergence were measured for one predator, Delphastus pusillus LeConte, and four parasitoids, Encarsia formosa Gahan, Encarsia luteola Howard, Encarsia pergandiella Howard, and Encarsia transvena (Timberlake), as possible indicators of efficacy. Characterization of each parameter was performed on two poinsettia cultivars: the first, ′Annette Hegg Brilliant Diamond,′ has trichome densities on the leaf undersurfaces approximately 15% less than the trichome densities on the leaf undersurfaces of the second cultivar, ′Lilo.′ Adult longevity varied significantly between natural enemies (ranging from an average high of 85.2 days for female D. pusillus feeding on B. argentifolii nymphs to an average low of 2.8 days for the Canada colony of E. formosa), but not between cultivar. Prey consumption and oviposition by D. pusillus varied between prey type (nymphs consumed > eggs consumed) and poinsettia cultivar (′Annette Hegg Brilliant Diamond′ > ′Lilo′). Host feeding, parasitism and total number of B. argentifolii nymphs killed varied significantly among Encarsia spp., but no single wasp performed better than the rest across all three parameters. Host feeding, parasitism, and total number of nymphs killed were greater on ′Annette Hegg Brilliant Diamond′ than on ′Lilo′ and this difference was consistent among the four parasitoid species. Among parasitoid species differences in percentage emergence were consistent between the two poinsettia cultivars with emergence from parasitized nymphs on ′Lilo′ being greater than emergence on ′Annette Hegg Brilliant Diamond.′ Results from these evaluations suggest that the probability of achieving successful augmentative biological central will be greater on poinsettia cultivars with fewer trichomes. In addition, achieving biological control is likely to be difficult with releases of E. transvena, but a greater chance for success may be possible through releases of D. pusillus when whitefly densities are high or through releases of E. formosa (Beltsville colony) or mated E. pergandiella independent of whitefly densities.     

Cytoplasmic incompatibility and multiple symbiont infection in the ash whitefly parasitoid, Encarsia inaron

Terrestrial arthropods are commonly infected with maternally inherited symbionts that cause reproductive incompatibilities between hosts with differing infection status. Such symbionts can have major effects on the efficacy of a biological control program if releases are comprised of mixtures of differentially infected individuals. In this study, the ash whitefly parasitoid, Encarsia inaron (Hymenoptera: Aphelinidae) from Arizona was surveyed for the presence of heritable bacterial symbionts; experiments were also performed to test for two phenotypes known to be caused by Encarsia symbionts—cytoplasmic incompatibility and changes in oviposition behavior and host use. E. inaron has successfully reduced ash whitefly to non-pest status in all three locations it has been released (California, Arizona, and North Carolina) and is also notable as one of the only Encarsia species that is not autoparasitic, with both male and female wasps developing as primary parasitoids of whiteflies. We show that E. inaron is infected with both Wolbachia and Cardinium. While there was no effect of the symbionts on oviposition behavior or host use, crosses between doubly infected male wasps and uninfected females resulted in a severe reduction in the number of female offspring; male offspring production was unaffected. This study thus serves as a further warning that ascribing a phenotype to a symbiont with confidence depends on eliminating the possibility of a mixed infection, and establishes E. inaron as a useful model for dissecting Wolbachia–Cardinium interactions.     

Testing for non-target effects of spiromesifen on <Emphasis Type="Italic">Eretmocerus mundus</Emphasis> and <Emphasis Type="Italic">Orius laevigatus</Emphasis> under greenhouse conditions

Spiromesifen is a novel insecticide/acaricide belonging to the new chemical class of spirocyclic phenyl-substituted tetronic acids, and it is especially active against whiteflies and tetranychid spider mite species. In the biologically based integrated pest management (IPM) programs in vegetable crops in southeastern Spain, the key natural enemies include the parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) for sweetpotato whitefly control, and the minute pirate bug, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) for western flower thrips control. Side effects of spiromesifen on E. mundus and O. laevigatus, were evaluated by laboratory studies and field trials in commercial greenhouses under IPM programs. Results indicate that spiromesifen had favourable selectivity to O. laevigatus and E. mundus and would complement biological control of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) by E. mundus. Handling editor: Patrick De Clercq     

Establishment of papaya banker plant system for parasitoid, Encarsia sophia (Hymenoptera: Aphilidae) against Bemisia tabaci (Hemiptera: Aleyrodidae) in greenhouse tomato production

The silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), is a key pest of tomato (Solanum lycopersicum L.) and other vegetable crops worldwide. To combat this pest, a non-crop banker plant system was evaluated that employs a parasitoid, Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) with whitefly, Trialeurodes variabilis (Quaintance) (Hemiptera: Aleyrodidae), as an alternative host for rearing and dispersal of the parasitoid to the target pest. (a) Multi-choice and no-choice greenhouse experiments were conducted to determine host specificity of T. variabilis to papaya (Carica papaya L.) and three vegetable crops including tomato, green bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L.). The result showed that papaya was an excellent non-crop banker plant for supporting the non-pest alternative host, T. variabilis, whose adults had a strong specificity to papaya plants for feeding and oviposition in both multi-choice and no-choice tests. (b) The dispersal ability of E. sophia was investigated from papaya banker plants to tomato and green bean plants infested with B. tabaci, as well as to papaya control plants infested with T. variabilis; and (c) the percent parasitism by E. sophia on T. variabilis reared on papaya plants and on B. tabaci infested on tomato plants was also evaluated. These data proved that E. sophia was able to disperse at least 14.5 m away from papaya plants to target tomato, bean or papaya control plants within 48–96 h. Furthermore, E. sophia was a strong parasitoid of both T. variabilis and B. tabaci. There was no significant difference in percent parasitism by E. sophia on T. variabilis (36.2–47.4%) infested on papaya plants or B. tabaci (29–45.9%) on tomato plants. Thus, a novel banker plant system for the potential management of B. tabaci was established using papaya as a non-crop banker plant to support a non-pest alternative host, T. variabilis for maintaining the parasitoid to control B. tabaci. The established banker plant system should provide growers with a new option for long-term control of B. tabaci in greenhouse vegetable production. Ongoing studies on the papaya banker plant system are being performed in commercial greenhouses.