S. Lyon

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.

COMPATIBILITY OF SPINOSAD WITH PREDACIOUS MITES (ACARI: PHYTOSEIIDAE) USED TO CONTROL WESTERN FLOWER THRIPS (THYSANOPTERA: THRIPIDAE) IN GREENHOUSE CROPS

Abstract Releases of predacious mites are recommended for use in greenhouse flower crops for suppression of western flower thrips, Frankliniella occidentalis (Pergande). Control from predacious mites alone, however, is not adequate and must be supplemented with the use of insecticides. The principal material currently used by growers in the northeastern United States for western flower thrips control is spinosad (Conserve®). In laboratory tests on direct toxicity, we found that fresh residues (2 h) of this material were not toxic to motile stages of Neoseiulus (=Amblyseius) cucumeris (Oudemans) (74 vs 78% survival for the treated group and the untreated water controls, respectively), the principal species of predacious mites used for control of western flower thrips, but did lower survival of Iphiseius degenerans (Berlese) (56 vs. 73% survival for the treated group and the untreated water controls, respectively). There were no differences for either species from exposure to older (24 h) residues. In contrast, using the same assay we observed 10 and 3% survival of first instar and adult western flower thrips. We found no indication of that either mite species was repelled by freshly dried (2 h post application) residues of this compound. Spinosad did, however, reduce oviposition of mites when confined in glass vials with pollen, a water source, and pesticide-treated foliage. Oviposition in the first 24 h period after confinement was not affected but in the second and third days, it was reduced by 48 and 76% for N. cucumeris and 41 and 70% for I. degenerans, compared with oviposition in the same periods by mites in untreated vials. These data indicate that the use of spinosad may not be compatible with releases of these predacious mites in a western flower thrips suppression program.

ASSESSMENT OF COST AND PERFORMANCE OF ERETMOCERUS EREMICUS (HYMENOPTERA: APHELINIDAE) FOR WHITEFLY (HOMOPTERA: ALEYRODIDAE) CONTROL IN COMMERCIAL POINSETTIA CROPS

Releases of Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) at release rates of 3.0-7.5 females per plant per week successfully suppressed whitefly populations on commercial poinsettia (Euphorbia pulcherrima Willd. ex Koltz.) crops in fall of 1996 at four Massachusetts commercial producers. At two sites, the whitefly populations consisted exclusively of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and at the other two sites exclusively of silverleaf whitefly, Bemisia argentifolii Bellows and Perring. Parasitoids were received from commercial suppliers and monitored weekly to determine the sex ratio of newly emerged adults, as well as the rate of adult emergence. Commercially produced pupae were 48.1% ( 2.2 SE) female and had 58.1% ( 3.6 SE) emergence under greenhouse conditions. Plants from the four biological control greenhouses in this trial at the time of sale of the crop had an average of 0.55 ( 0.28 SE) nymphs per leaf. Chemically-protected poinsettias offered for sale at eight local retail outlets had an average of 0.16 ( 0.09 SE) nymphs per leaf. Final whitefly densities in both biological control and insecticide-treated greenhouses were acceptable to consumers. An average of 6.8 insecticide applications was applied to suppress whiteflies in chemical control greenhouses in this trial, compared to 1.7 in the biological control greenhouses. Use of biological control was 27 fold more expensive, costing

COMPARATIVE COST OF CHEMICAL AND BIOLOGICAL WHITEFLY CONTROL IN POINSETTIA: IS THERE A GAP?

2.14 per plant compared to

EFFECT OF PARASITOID RELEASE PATTERN ON WHITEFLY (HOMOPTERA: ALEYRODIDAE) CONTROL IN COMMERCIAL POINSETTIA

0.08 for chemical control. Cost of biological control was inflated by three factors: (1) an incorrectly high estimate by one grower of number of plants per greenhouse, (2) an unusually long production period (23 weeks) for one grower, and (3) miscommunication with the insectary concerning manner of filling orders to compensate for reduced percentage of emergence of adult parasitoids from ordered parasitized nymphs. Control of these cost-inflating factors would allow some reduction in the cost of the use of this parasitoid, but not to levels competitive with current pesticides. This study is the first to demonstrate the ability of E. eremicus releases to suppress T. vaporariorum populations in commercial poinsettia crops and parasitism of T. vaporariorum by E. eremicus was 7.5-fold higher (ave. 24.8% parasitism of fourth instar nymphs in pooled seasonal samples) than that observed in B. argentifolii (ave. 3.3%).

Biological control of invasive plants in the Eastern United States.

Abstract Cost is the principal constraint on the use of biological control against whiteflies in poinsettia (Euphorbia pulcherrima Willd. ex Koltz.) crops in the United States. Here we show that a new, lower release rate of the whitefly parasitoid Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae), 0.5 females per plant per week, maintains whiteflies (Bemisia argentifolii Bellows and Perring) at harvest below the economic threshold of 2 live nymphs + pupae per leaf, when used in combination with two mid-crop applications of the insect growth regulator fenoxycarb (Precision®). Cost of this program (for 16.5 cm dia single stem pots, with 30,000 plants under protection) varies from 21 to 34 cents per plant for the season, for cropping periods from 12 to 18 weeks. Shipping costs are calculated and included in estimated costs. These values compare favorably to the real cost of whitefly chemical control incurred by Massachusetts poinsettia growers in fall of 2000, which was 14 cents for a 16.5 cm dia single stem pot, with a range of 1 to 40 cents. Programs consisting of a single application of the systemic insecticide imidacloprid alone cost 12 cents per pot per season.This difference between 21 cents for the biological control program and 14 cents for the chemical control program is the smallest yet reported for biological control of whiteflies in poinsettia.

Compatibility of Insect Growth Regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for Whitefly (Homoptera: Aleyrodidae) Control on Poinsettias I. Laboratory Assays

Under commercial poinsettia production conditions we compared two patterns of parasitoid release for the aphelinid whitefly parasitoid Eretmocerus eremicus Rose and Zolnerowich. We compared the currently used pattern of a fixed weekly release number (3 females per plant per week) to an experimental pattern in which more parasitoids were released early in the crop (wks 1-8), followed by a lower number (wks 9-17), with the seasonal release average still being 3 female parasitoids per plant per week. We further compared the outcome of these two treatments (fixed and variable) to a low release rate (1 parasitoid per pl per wk) of Encarsia formosa Gahan, an aphelinid parasitoid widely used for whitefly control in greenhouse crops. In control cages without parasitoid releases, whitefly nymphal densities reached 15-32 live nymphs per leaf, which was 7 to 16-fold greater than the acceptable level at crop harvest. In cages in which parasitoid releases were made, whitefly nymphal densities were suppressed 99.8%, 96.8% and 50.9% by fixed-rate E. eremicus, variable-rate E. eremicus, and low-rate E. formosa treatments, respectively. In greenhouse populations, the final densities of live whitefly nymphs per leaf were significantly higher in the E. formosa treatment than the two E. eremicus treatments. Releases of low numbers of E. formosa provided commercially acceptable control in only one of two greenhouses. There was no difference between the fixed and variable release rate treatments of E. eremicus, indicating that whitefly suppression was not increased by concentrating the release of this parasitoid early in the crop.