Hugh A. Smith

A Survey of Syrphid Predators of Nasonovia ribisnigri in Organic Lettuce on the Central Coast of California

Abstract Organic lettuce, Lactuca sativa L., producers on California’s Central Coast rely on endemic syrphid flies (Diptera: Syrphidae) to suppress populations of Nasonovia ribisnigri Mosley (Homoptera: Aphididae) and other aphids affecting lettuce. Growers are using various forms of habitat manipulation to enhance biological control. We surveyed syrphids collected from organic romaine in and around the Salinas Valley from March through September 2005 to gain a better understanding of the species responsible for aphid suppression and to examine possible implications for biocontrol. The primary species of syrphid fly reared were Toxomerus marginatus (Say) (39%), Platycheirus stegnus (Say) (27%), Sphaerophoria sulfuripes (Thomson) (13%), and Allograpta obliqua (Say) (10%). Syrphus opinator Osten Sacken (2%), Toxomerus occidentalis (Curran) (1.3%), and Eupeodes volucris Osten Sacken (1%) were less common. Sphaerophoria pyrrhina Bigot, Scaeva pyrastri (L.), Platycheirus obscurus Say, Allograpta exotica Wiedemann, and Eupeodes americanus Wiedemann each made up <1% of the syrphids reared. T. marginatus and Sphaerophoria sulfuripes were commonly collected from romaine plants with few or no detectable aphids. P. stegnus was observed to deposit in clusters of eggs, and was only reared in significant numbers from highly infested fields. Approximately 5% of syrphid larvae overall were parasitized by either Diplazon sp. (Hymenoptera: Ichneumonidae) or Pachyneuron sp. (Hymenoptera: Pteromalidae).

Role of Syrphid Larvae and Other Predators in Suppressing Aphid Infestations in Organic Lettuce on California's Central Coast

Abstract Organic lettuce, Lactuca sativa L., growers on the Central Coast of California rely on conservation biological control to manage Nasonovia ribisnigri Mosley (Hemiptera: Aphididae) and other aphid pests of lettuce. In 2006, we carried out five replicated field trials to determine the importance of syrphid larvae in the suppression of N. ribisnigri and other aphids infesting organic romaine lettuce. We used Entrust, a spinosad-based insecticide approved for use on organic farms, to suppress syrphid larvae in aphid-infested romaine. Romaine treated with Entrust was unmarketable at harvest because of aphid infestation, whereas insecticide-free romaine was marketable. Syrphid larvae composed 85% or more of total predators in most trials, and they were the only predators consistently recovered from romaine that was infested with aphids early and largely aphid-free by harvest. The species mix of nonsyrphid predators varied from site to site. Applications of Entrust suppressed nonsyrphid predators in two trials, and so was an imperfect tool for selectively suppressing syrphid larvae. The relative importance of syrphid larvae and other predators in the conservation biological control of aphids in organic romaine is discussed. We conclude that syrphid larvae are primarily responsible for the suppression of aphids in organic romaine on California’s Central Coast.

Effect of Silver Reflective Mulch and a Summer Squash Trap Crop on Densities of Immature Bemisia argentifolii (Homoptera: Aleyrodidae) on Organic Bean

Abstract Polyethylene mulch with a reflective silver stripe and a yellow summer squash, Cucurbita pepo L., trap crop were tested alone and in combination as tactics to reduce densities of Bemisia argentifolii Bellows & Perring eggs and nymphs, and incidence of bean golden mosaic geminivirus on snap bean, Phaseolus vulgaris L. Egg densities were consistently higher on squash than on bean, but egg densities and virus incidence were not lower on bean grown with squash than on bean grown in monoculture. Silver reflective mulch reduced egg densities compared with bean grown on bare ground during the first week after crop emergence for 2 of the 3 yr that the study was conducted. However, egg suppression by silver mulch was not enhanced by the presence of a squash trap crop when both tactics were combined. The obstacles to suppressing B. argentifolii through the use of trap crops are discussed.

Potential of Field Corn as A Barrier Crop and Eggplant as A Trap Crop for Management of Bemisia Argentifolii (Homoptera: Aleyrodidae) on Common Bean in North Florida

Trap crops and barrier crops are among the cultural control methods promoted for management of Bemisia argentifolii Bellows & Perring, particularly for small farmers in the tropics. In 1996 eggplant, Solanum melongena L., was tested as a trap crop, and in 1996 and 1997 corn, Zea mays L., was tested as a barrier crop for management of B. argentifolii on bean, Phaseolus vulgaris L. In 1996 treatments were compared by sampling immature B. argentifolii on bean leaves. Neither egg nor nymphal densities were reduced by eggplant or corn treatments in 1996. In the 1997 corn barrier trial plot size was increased and the orientation of barrier row to wind direction was evaluated. A dust-and-release procedure was used to measure entry of greenhouse-reared adult B. argentifolii into experimental plots. Counts from yellow sticky traps in 1997 indicated that migration by adult whiteflies into plots was determined primarily by air currents and was only marginally influenced by the presence of a corn barrier. The results indicate that barrier crops and certain trap crops may have limited value for whitefly management.

Effect of Intercropping Common Bean with Poor Hosts and Nonhosts on Numbers of Immature Whiteflies (Homoptera: Aleyrodidae) in the Salamá Valley, Guatemala

Abstract Intercropping with poor and nonhosts was tested as means to reduce densities of whitefly eggs and nymphs on common bean (Phaseolus vulgaris L.) in central Guatemala during dry and rainy seasons. Row and mixed intercrop field designs were used, with pesticides evaluated on a subplot level in the row-intercrop test. Tomato (Lycopersicon esculentum Mill.) was also evaluated in the mixed-intercrop test. Intercropping failed to reduce whitefly densities, although interpretation of data was difficult because of high variability among samples and reduced crop quality in some intercrop and pesticide treatments. Imidacloprid effectively reduced whitefly densities, but imidacloprid combined with intercropping offered no advantage over imidacloprid in monoculture. Laundry detergent and vegetable oil were tested as less-toxic inexpensive alternatives to pesticides under monocropped and intercropped conditions during the dry season, but failed to provide protection against whiteflies or other sucking insects. Trialeurodes vaporariorum Westwood was the predominant whitefly species in the area. Bemisia tabaci (Gennadius) on bean comprised ≈10% of the total whitefly population at the end of the dry season, 46% in the middle of the rainy season, when overall populations were lowest, and 1.15% toward the end of the rainy season. Encarsia pergandiella Howard was the predominant whitefly parasitoid throughout the study, and the only parasitoid reared from whitefly nymphs on bean in the dry season. Members of the Encarsia meritoria species complex and Amitus fuscipennis MacGown & Nebeker were recovered from tomato during the rainy season. Parasitoid diversity increased in the rainy season on tomato intercropped with roselle (Hibiscus sabdariffa L.) and corn (Zea mays L.) compared with tomato grown in monoculture. Intercropping with poor and nonhosts did not reduce whitefly densities on bean in an economically significant manner under high, intermediate, or low whitefly populations levels in either the dry or rainy season.

Nitrogen accretion in soil and biomass production by three Prosopis species.

Trunk circumferences and canopy diameters of Prosopis glandulosa, P. chilensis and P. alba, and soil nitrogen under and between the trees were measured in a seven-year-old plantation at the University of California, Riverside. P. glandulosa had the smallest biomass of the three species. However, the nitrogen concentration of the soil under P. glandulosa was higher than under the other two species. Presumably more nitrogen is cycled through the leaves of this species rather than invested in wood production, where it would be sequestered. The soil nitrogen accumulation under P. glandulosa was significantly higher (total and subsurface) than that measured in soil taken between trees. The soil nitrogen content under P. chilensis and P. alba was not significantly different than that between the trees. These results indicate that the choice of woody legume in an agroforestry system will depend on its intended use. The most efficient nutrient cycling is not necessarily associated with the best biomass production.

Residual Effects of New Insecticides on Egg and Nymph Densities of Bemisia tabaci (Hemiptera: Aleyrodidae)

ABSTRACT The residual effects of 4 new insecticides (cyazypyr, flupyradifurone, pyrifluquinazon, and sulfoxaflor) and 2 registered insecticides (pymetrozine and a combination of zeta-cypermethrin and bifenthrin) on egg and nymph densities of Bemisia tabaci biotype B were evaluated at 3, 7 or 14 days after treatment (DAT) of the tomato seedlings with insecticides. Whole plant egg and nymph counts were taken weekly for 3 wk after the introduction of whitefly adults. The study was repeated 3 times. Egg densities tended to be statistically higher at 14 DAT than 3 or 7 DAT in the zeta-cypermethrin/bifenthrin and pymetrozine treatments. The other materials demonstrated greater efficacy than zeta-cypermethrin/bifenthrin and pymetrozine on 14 DAT. Egg densities were very low in all insecticide treatments compared to untreated plants at 3 and 7 DAT. Egg densities on plants treated with cyazypyr, flupyradifurone, pyrifluquinazon, and sulfoxaflor were statistically similar within a given DAT interval for most trials. Treatment effects on nymph densities were similar to treatment effects on egg densities. Cyazypyr, flupyradifurone, pyrifluquinazon, and sulfoxaflor represent distinct modes of action, and should contribute to future integrated pest management and integrated resistance management plans for B. tabaci on tomato.

New insecticides for management of tomato yellow leaf curl, a virus vectored by the silverleaf whitefly, Bemisia tabaci.

ABSTRACT. Greenhouse studies using a randomized complete block design were carried out to evaluate the effect of six insecticides on transmission of Tomato yellow leaf curl virus (TYLCV) by the silverleaf whitefly, Bemisia tabaci biotype B Gennadius (Hemiptera: Aleyrodidae) to tomato, Lycopersicon esculentum (Miller) (Solanales: Solanaceae), seedlings that were inoculated with whiteflies from a TYLCV colony in cages 3, 7, or 14 d after treatment with insecticide. The purpose was to reveal differences in residual efficacy of four materials that are nearing registration for use on tomato—cyazypyr, flupyradifurone, pyrafluquinazon, and sulfoxaflor—and to compare them with two established insecticides, pymetrozine and a zeta-cypermethrin/bifenthrin combination. Differences in efficacy were expected because these six materials represent five distinct modes of action and both contact and systemic materials. Percentage of tomato seedlings expressing virus symptoms tended to be lowest in seedlings treated with flupyradifurone. The zeta-cypermethrin/bifenthrin insecticide demonstrated comparable efficacy to flupyradifurone in some trials at 3 and 7 d after treatment inoculations, but not the 14 d after treatment inoculation. Pyrafluquinazon was not statistically different from cyazypyr or sulfoxaflor in percentage of plants with virus symptoms in any trial. Percentage virus in the cyazypyr and sulfoxaflor treatments was not statistically different in the 3 and 7 d after treatment inoculations. Among seedlings treated with insecticide, percentage with virus symptoms tended to be highest in the seedlings treated with pymetrozine.

Effect of Insecticide Rotations on Density and Species Composition of Thrips (Thysanoptera) in Florida Strawberry (Rosales: Rosaceae)

Abstract Feeding by Frankliniella (Thysanoptera: Thripidae) thrips causes economic damage to strawberry (Fragaria ananassa Duchesne; Rosales: Rosaceae) crops in Florida and in other production regions worldwide. Resistance to spinosyn insecticides, particularly in Frankliniella occidentalis (Pergande), is a major concern for strawberry and other crops. Experiments were carried out in 2014 and 2015 to evaluate the effect of 6 insecticide programs on the numbers and species composition of thrips attacking strawberry on a season-long basis in Florida. Five insecticide programs included spinetoram applied once, twice, or 3 times in the rotation, alternated with acetamiprid, cyantraniliprole (Cyazypyr®), novaluron, sulfoxaflor, and/or tolfenpyrad. Also included in the treatments were bifenthrin and a non-treated check. Thrips densities were sampled weekly in flowers, and in both flowers and fruits in 2015, 2 d after treatment applications. The primary thrips species recovered from strawberry flowers and fruit was Frankliniella bispinosa Morgan. Other species included F. occidentalis, Frankliniella schultzei (Trybom), Scirtothrips dorsalis Hood, Scolothrips sp., Thrips spp. (all Thripidae), and Haplothrips gowdeyi (Franklin) (Phlaeothripidae), Frankliniella bispinosa was controlled by all insecticide programs. Numbers of F. occidentalis thrips were not reduced by any spinetoram-based rotation relative to the control in either year. Repeated applications of bifenthrin increased numbers of F. occidentalis thrips relative to the control each year, and increased numbers of F. schultzei thrips relative to the control in 2014. The thrips predator Orius sp. (Hemiptera: Anthocoridae) was not observed in the bifenthrin treatment and was rare in other treatments. Insecticide rotations in Florida strawberry appear to shift the species composition from F. bispinosa to F. occidentalis and other insecticide-tolerant species including F. schultzei. Thrips damage to strawberries may be due to the species that is least susceptible to control rather than the species that is most abundant early in the cropping season. However, the relative importance of various stages or species has yet to be critically determined.

Combining Novel Modes of Action for Early-Season Management of Bemisia tabaci (Hemiptera: Aleyrodidae) and Tomato Yellow Leaf Curl Virus in Tomato

Abstract Management of Tomato yellow leaf curl virus (TYLCV) in Florida tomato involves destroying inoculum sources, using reflective mulches to repel the vector, growing TYLCV-tolerant varieties, and using insecticidal control. Three new insecticides with distinct modes of action were evaluated for management of Bemisia tabaci (Gennadius) and the whitefly-transmitted TYLCV. Chemicals were applied in paired combinations during the first 5 weeks after transplanting. Flupyradifurone (Sivanto) and cyantraniliprole (Cyazypyr™) are systemic insecticides that can be applied to soil or foliage and pyrifluquinazon is a translaminar material for foliar application. In order to determine optimal combination of chemicals with different modes of action for early-season whitefly control and virus suppression, systemic materials were soil-applied at-plant followed by foliar applications of a material with a distinct mode of action. Dinotefuran (Venom) was included as a standard at-plant material for comparison. Field trials were carried out using a split plot design with insecticide programs as main plot treatments which were split into plots covered under a floating row cover for the first 2 weeks after planting or left uncovered. The intention of the row cover treatment was to compare the degree of protection offered by at-plant treatments when the crop was exposed to virus immediately after transplanting to exposure two weeks after transplanting, and to determine if any at-plant treatment were comparable to mechanical exclusion of the vector. In fall 2012, when virus pressure was moderate, end of season virus incidence was lower than the untreated control in all chemical treatments except dinotefuran drench alone or followed by cyantraniliprole. Percentage virus in these 2 treatments were not significantly different from the untreated plots as of 5 weeks after transplanting in both fall trials (2012 and 2013). During both fall trials, percent virus was numerically lowest each week in either the flupyradifurone or flupyradifurone followed by pyrifluquinazon treatments, although the differences from other treatments were not always statistically significant. In spring 2013, when virus pressure was negligible, yield was higher in plots treated with dinotefuran followed by cyantraniliprole than in other treated plots, with the exception of flupyradifurone followed by cyantraniliprole. Row cover treatments were only partially successful, and did not indicate that any at-plant treatment was comparable to mechanical exclusion of the vector. Integration of new materials into insecticide recommendations and resistance management plans for Florida tomato (Solanum lycopersicum L.) production are discussed.