John P. Sanderson

Greenhouse Trials of Aphidius colemani (Hymenoptera: Braconidae) Banker Plants for Control of Aphids (Hemiptera: Aphididae) in Greenhouse Spring Floral Crops

Abstract Banker plants with Aphidius colemani Viereck were tested in greenhouses in Massachusetts and New York for control of cotton aphid Aphis gossypii Glover, and green peach aphid Myzus persicae (Sulzer) on 2 spring flower crops, pansies (Viola tricolor hortensis) and Marguerite daisies (Argyranthemum hybrid). Banker plants consisted of pots of barley plants infested with the bird cherry-oat aphid Rhopalosiphum padi (L.), inoculated at the start of the crop with adults of A. colemani purchased from a commercial insectary. Initial trials were conducted in University of Massachusetts greenhouses containing flats of the crop plants. Sentinel plants in flats were infested uniformly with aphids, and particular greenhouses were subjected to the presence of banker plants or left as controls. Prior to University trials, a survey was conducted in commercial greenhouses in Massachusetts and New York to determine the frequency and species of aphid infestation in spring flower crops. After University trials, the efficacy of banker plants was tested in commercial greenhouses in both states. In surveys of commercial greenhouses, M. persicae was the most frequently detected species, accounting for 53% of all infestations. In University greenhouse trials, in absence of parasitism, A. gossypii increased fastest on daisy, followed by M. persicae on daisy, M. persicae on pansy, and A. gossypii on pansy. Parasitoid suppression of population increase was strongest for A. gossypii on daisy and poorest for M. persicae on pansy. The presence of 2 aphid species in the same greenhouse did not alter the level of biological control in our trial. In commercial greenhouses, banker plants failed to control M. persicae deployed on infested pansies as sentinel hosts. In the laboratory, a 12-h exposure to dried residues of pyriproxyfen or pymetrozine, insecticides commonly used to control aphids, reduced survival of A. colemani adults, compared to a water control (82% survival), to 71% and 53%, respectively. Adult parasitoid emergence from pesticide-treated aphid mummies was reduced from 68% for the controls to 56% for pyriproxyfen and 62% for pymetrozine.

Discovery and utilization of Bemisia argentifolii patches by Eretmocerus eremicus and Encarsia formosa (Beltsville strain) in greenhouses

The ability of two species of aphelinid parasitoids to find and attack Bemisia argentifolii was determined. Experiments were conducted with whitefly patches on single leaf poinsettia plants randomly distributed in canopies of four commercially grown poinsettia crops at an early and late stage of plant growth. Eretmocerus eremicus found experimental patches in canopies of small and large plants more quickly and frequently, and killed more nymphs following patch discovery than Encarsia formosa (Beltsville strain). E. eremicus exhibited a Type I functional response in small and large canopies while E. formosa (Beltsville strain) showed a Type II functional response in small canopies and a weak linear response in large canopies. In greenhouses treated with E. eremicus, canopy size increased 4.6× and nymphs per plant increased 14.2× between small and large canopy experiments. Consequently, area of search for this parasitoid increased 83%, number of wasps counted on patches decreased 74%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies. In greenhouses treated with E. formosa Beltsville strain, canopy size increased 7.3× and nymphs per plant increased 25.4× between small and large canopy experiments. Consequently for E. formosa Beltsville strain, area of search increased 11%, number of wasps counted on patches decreased 86%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies.

Developmental times and life table statistics of Aulacorthum solani (Hemiptera: Aphididae) at six constant temperatures, with recommendations on the application of temperature-dependent development models.

ABSTRACT Aulacorthum solani (Kaltenbach) (known as foxglove aphid or glasshouse potato aphid) is a pest of increasing economic importance in several agricultural crops worldwide, including greenhouse vegetables and ornamentals. Developmental rates and age-specific life tables for a North American population of A. solani on pansy (Viola × wittrockiana) (Gams.) were determined at six constant temperatures, and comparisons were made to previous studies of A. solani from differing geographic regions and host crops. On pansy, A. solani developed fastest at 25°C, passing through the four nymphal instars in an average of 6.9 d. The highest intrinsic rates of population increase (0.410 and 0.445) and shortest population doubling times (1.69 and 1.56 d) were recorded at 20 and 25°C, respectively. Average total fecundity remained high from 10 to 20°C (74–68 nymphs/adult); a significant decrease to 39 nymphs/adult occurred at 25°C. For calculating developmental thresholds, we present here a method of adjusting the lower developmental threshold (tmin) using estimates from nonlinear models to provide an improved estimate of the thermal constant (K, in degree-days). We also call attention to the necessity of using a simulation method to estimate the true upper developmental threshold (Tmax) and optimum developmental temperature (Topt) from the Lactin-2 model of temperature-dependent development.

Novel Chitinolytic Enzymes with Biological Activity Against Herbivorous Insects

The soil bacteria, Streptomyces albidoflavus, secretes endochitinases and chitobiosidases that are active over a broad range of pH (4–10). Ingestion of this mixture of chitinolytic enzymes significantly reduced the growth and development of Trichoplusia ni and significantly reduced survival of Myzus persicae, Bemisia argentifolii, and Hypothenemus hampei. Perfusion chromatography was used to separate endochitinases from chitobiosidases. The endochitinases had significantly greater biological activity against Bemisia argentifolii than the chitobiosidases. The utility of chitinolytic enzymes as regulators of populations of herbivorous insects is discussed.

Spatial scale of aggregation in three acarine predator species with different degrees of polyphagy

Aggregative responses by the predatory mites, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to spatial variation in the density of mobile stages of Tetranychus urticae (Acari: Tetranychidae) were studied over different spatial scales on greenhouse roses. Significant spatial variations in prey numbers per leaflet, per leaf, per branch or per plant were present in all experimental plots. None of the predator species responded to prey numbers per plant, and all searched randomly among plants. Within a plant, the oligophagous P. persimilis searched randomly among branches, but aggregated strongly among leaves within a branch and among leaflets within a leaf. The narrowly polyphagous T. occidentalis searched randomly among leaflets within a leaf and amond leaves within a branch, but aggregated strongly among leaflets or leaves within a plant. The boradly polyphagous A. andersoni searched randomly among leaflets within a leaf, a branch or a plant, and among leaves within a branch or a plant, but distributed themselves more often on branches with lower prey densities. Thus, specialist predators aggregate strongly at lower spatial levels but show random search at higher spatial levels, whereas generalist predators show random search at lower spatial levels but aggregate at higher spatial levels. This is the first empirical evidence demonstrating the relation between the degree of polyphagy and the spatial scale of aggregation. It is also concluded that both the prey patch size (i.e. grain) and predator foraging range (i.e. extent) are important for analyzing spatial scales of predator aggregation. The importance of studying spatial scale of aggregation is also discussed in relation to predator-prey metapopulation dynamics.

Biological control of Bemisia argentifolii (Hemiptera: Aleyrodidae) on poinsettia with inundative releases of Eretmocerus eremicus (Hymenoptera: Aphelinidae) : do release rates affect parasitism ?

The effectiveness of inundative releases of the parasitoid Eretmocerus eremicus n. sp. Rose & Zolnerowich for control of Bemisia argentifolii Bellows & Perring on poinsettia in replicated experimental greenhouses was determined. We evaluated two release rates of E. eremicus: a low release rate (one female per plant per week, released in two greenhouses, in spring 1995) and a high release rate (three females per plant per week, released in two greenhouses, in spring 1994), each over a 14 week growing season. Each release trial had either one (1995) or two (1994) control greenhouses in which B. argentifolii developed on poinsettia in the absence of E. eremicus . Life-tables were constructed for B. argentifolii in the presence and absence of E. eremicus by using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of whiteflies were also made. In the absence of E. eremicus , egg to adult survivorship of B. argentifolii on poinsettia was 75–81%. At the low release rate, egg to adult survivorship of B. argentifolii was 12% and parasitism was 34%. At the high release rate, egg to adult survivorship of B. argentifolii was 0.9% and parasitism was 10%. The average net reproductive rates (R o ) for populations of B. argentifolii in the absence of E. eremicus ranged from 20.5 to 26.1, indicating a rapidly increasing population density. Net reproductive rates for whitefly populations subject to parasitoid releases were 3.7 in the low release rate greenhouses, and 0.25 in the high release rate greenhouses, indicating substantially reduced B. argentifolii population growth. At week 14 of the trial, densities of immature whiteflies were lower in greenhouses at the low release rate when compared to the high release rate greenhouses. This was attributed to high levels of in-house reproduction by parasitoids at the low release rate.

Effects of manipulating spray-application parameters on efficacy of the entomopathogenic fungus Beauveria bassiana against western flower thrips, Frankliniella occidentalis, infesting greenhouse impatiens crops

Abstract The effects of various spray application parameters on the efficacy of a clay-based wettable powder formulation of Beauveria bassiana strain GHA conidia against western flower thrips, Frankliniella occidentalis, were evaluated in a series of greenhouse tests. With the aim of optimizing spray application methods to maximize biopesticide efficacy, a series of independent experiments was conducted that varied four spray parameters: application interval, rate, volume, and spray-program timing. Impatiens crops infested with western flower thrips were treated with (1) multiple sprays at the rate of 5×1013 conidia in 935 L aqueous carrier ha−1 applied at 3-, 5-, and 7-day intervals, (2) weekly sprays at rates of 5×1013, 1×1014, and 2.0×1014 conidia in 935 L carrier ha−1, (3) weekly sprays at a rate of 2.0×1014 conidia in volumes of 935, 1870, and 3740 L water ha−1, and (4) multiple sprays at the rate of 2.0×1014 conidia in 3740 L carrier ha−1 applied at 5-day intervals in spray programs initiated before versus after the onset of flowering. Pollen-bearing impatiens flowers were sampled twice weekly to estimate thrips population density, and adult female and second-instar thrips were collected 24 h post application for determination of acquired dose (conidia/insect). Numbers of conidia inoculated onto thrips increased with increasing spray frequency and volume. Dose was unexpectedly not directly correlated with application rate when volume was held constant, suggesting that thrips avoided concentrated spray residues. Statistically significant thrips population reductions relative to controls were achieved only when three to four sprays were applied at the highest label rate in the highest volume at < 7-day intervals. Applications against thrips infesting young, preflowering impatiens crops were not consistently more effective than applications in older crops. The most effective treatment programs reduced pest populations by 30–40% compared to untreated controls; this slowed, but did not stop, the growth of pest populations. Results indicate that use of fungi for thrips management will require integration with other control agents.

Pathogenicity of conidia-based preparations of entomopathogenic fungi against the greenhouse pest aphids Myzus persicae, Aphis gossypii, and Aulacorthum solani (Hemiptera: Aphididae)

Seeking new isolates of entomopathogenic fungi with greater virulence against greenhouse aphid pests than those currently registered in North America for control of these insects, single-dose screening assays of 44 selected fungal isolates and 4 commercially available strains were conducted against first-instar nymphs of Myzus persicae and Aphis gossypii. The assays identified a number of Beauveria and Metarhizium isolates with virulence equal to or greater than that of the commercial strains against the nymphal aphids, but none exhibited exceptionally high virulence. Virulence of Isaria isolates was unexpectedly low (<31% mortality at doses>1000conidia/mm(2)). In dose-response assays, Beauveria ARSEF 5493 proved most virulent against M. persicae and A. gossypii; however, LC50s of this isolate did not differ significantly from those of B. bassiana commercial strain JW-1. Dose-response assays were also conducted with Aulacorthum solani, the first reported evaluations of Beauveria and Metarhizium against this pest. The novel isolate Metarhizium 5471 showed virulence⩾that of Beauveria 5493 in terms of LC25 and LC50, but 5493 produced a steeper dose response (slope). Additional tests showed that adult aphids are more susceptible than nymphs to fungal infection but confirmed that infection has a limited pre-mortem effect on aphid reproduction. Effects of assay techniques and the potential of fungal pathogens as aphid-control agents are discussed.

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

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

Biological control of Bemisia argentifolii (Hemiptera: Aleyrodidae) on poinsettia with inundative releases of Eretmocerus eremicus (Hymenoptera: Aphelinidae): does varying the weekly release rate affect control?

The effectiveness of varying weekly release rates of the parasitoid Eretmocerus eremicus Rose & Zolnerowich for control of Bemisia argentifolii Bellows & Perring on poinsettias was determined. Two variable release rate strategies for E. eremicus were evaluated: a low–high and a high–low release regimen. In the low–high treatment, one female parasitoid was released per plant per week for seven weeks, then the release rate was increased to five female parasitoids per plant per week for the remaining seven weeks of the trial. In the high–low treatment, five female parasitoids per plant per week were released for the first seven weeks, then the release rate was reduced to one female parasitoid per plant per week for the final seven weeks of the trial. Both release rates averaged three female parasitoids per plant per week. Life-tables were made for B. argentifolii in the presence and absence of parasitoids. In the absence of E. eremicus , egg to adult survivorship for B. argentifolii was 65%. In low–high release greenhouses, average egg to adult survivorship for B. argentifolii was 6% and parasitism was 28%. In high–low greenhouses, average egg to adult survivorship for B. argentifolii was 5% and parasitism was 16%. Average net reproductive rates for B. argentifolii in the absence of parasitoids was 17 indicating a rapidly increasing population. Net reproductive rates were 1.46 and 1.24 for low–high and high–low release greenhouses, respectively, indicating substantially reduced B. argentifolii population growth. At week 14 of the trial, densities of live nymphs and pupae were lower in high–low greenhouses when compared to low–high greenhouses. Better whitefly control is achieved with inundative releases of E. eremicus when this natural enemy acts as a predator as opposed to a parasitoid.