Integrating Spectroscopy with Potato Disease Management

Spectral phenotyping is an efficient method for the nondestructive characterization of plant biochemical and physiological status. We examined the ability of a full range (350 to 2,500 nm) of foliar spectral data to (i) detect Potato virus Y (PVY) and physiological effects of the disease in visually asymptomatic leaves, (ii) classify different strains of PVY, and (iii) identify specific potato cultivars. Across cultivars, foliar spectral profiles of PVY-infected leaves were statistically different (F = 96.1, P ≤ 0.001) from noninfected leaves. Partial least-squares discriminate analysis (PLS-DA) accurately classified leaves as PVY infected (validation κ = 0.73) and the shortwave infrared spectral regions displayed the strongest correlations with infection status. Although spectral profiles of different PVY strains were statistically different (F = 6.4, P ≤ 0.001), PLS-DA did not classify different strains well (validation κ = 0.12). Spectroscopic retrievals revealed that PVY infection decreased photosynthetic capacity and increased leaf lignin content. Spectral profiles of potato cultivars also differed (F = 9.2, P ≤ 0.001); whereas average spectral classification was high (validation κ = 0.76), the accuracy of classification varied among cultivars. Our study expands the current knowledge base by (i) identifying disease presence before the onset of visual symptoms, (ii) providing specific biochemical and physiological responses to disease infection, and (iii) discriminating between multiple cultivars within a single plant species.

Effect of insecticide management history on emergence phenology and neonicotinoid resistance in Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Emergence phenology and fitness attributes of several Colorado potato beetle, Leptinotarsa decemlineata (Say), populations were measured under field and greenhouse conditions. Anecdotal observations by producers and pest managers in many locations of the upper Midwest increasingly suggested that select populations of Colorado potato beetle were emerging over a longer period in the spring and were less sensitive to systemic neonicotinoids in cultivated potato. These changes in emergence phenology may be related to changes in systemic insecticide concentration over time. Specifically, a prolonged period of adult emergence in the spring increases the potential of low-dose chronic exposure to systemic neonicotinoid insecticides in potato. In 2010 and 2011, our objectives were twofold: 1) establish a common garden experiment to compare the emergence phenology of Colorado potato beetle populations uniquely managed with variable insecticide inputs, and 2) measure postdormancy fitness of emerged adult beetles from among these selected populations. Cumulative adult emergence was modeled with logistic regression. Results from this study found no clear evidence for direct relationships between phenology and management history or resistance. Differences in reproductive capacity, sex ratio, and body size were apparent in some instances. However, these results did not uniformly correspond to one specific form of potato pest management tested here. In this study, long-term reliance on systemic insecticides for Colorado potato beetle control did not serve as a strong predictor for variable life history for selected populations in Wisconsin.

Factors influencing aster leafhopper (Hemiptera: Cicadellidae) abundance and aster yellows phytoplasma infectivity in Wisconsin carrot fields

In Wisconsin, vegetable crops are threatened annually by infection of the aster yellows phytoplasma (AYp), the causal agent of aster yellows (AY) disease, vectored by the aster leafhopper, Macrosteles quadrilineatus Forbes. Aster leafhopper abundance and infectivity are influenced by processes operating across different temporal and spatial scales. We applied a multilevel modeling approach to partition variance in multifield, multiyear, pest scouting data sets containing temporal and spatial covariates associated with aster leafhopper abundance and infectivity. Our intent was to evaluate the relative importance of temporal and spatial covariates to infer the relevant scale at which ecological processes are driving AY epidemics and identify periods of elevated risk for AYp spread. The relative amount of aster leafhopper variability among and within years (39%) exceeded estimates of variation among farm locations and fields (7%). Similarly, time covariates explained the largest amount of variation of aster leafhopper infectivity (50%). Leafhopper abundance has been decreasing since 2001 and reached its minimum in 2010. The average seasonal pattern indicated that periods of above average abundance occurred between 11 June and 1 August. Annual infectivity appears to oscillate around an average value of 2% and seasonal periods of above average infectivity occur between 19 May and 15 July. The coincidence of the expected periods of high leafhopper abundance and infectivity increases our knowledge of when the insect moves into susceptible crop fields and when it spreads the pathogen to susceptible crops, representing a seasonal interval during which management of the insect can be focused.

Seasonal patterns of aster leafhopper (Hemiptera: Cicadellidae) abundance and aster yellows phytoplasma infectivity in Wisconsin carrot fields

In Wisconsin, vegetable crops are threatened annually by the aster yellows phytoplasma (AYp), which is obligately transmitted by the aster leafhopper. Using a multiyear, multilocation data set, seasonal patterns of leafhopper abundance and infectivity were modeled. A seasonal aster yellows index (AYI) was deduced from the model abundance and infectivity predictions to represent the expected seasonal risk of pathogen transmission by infectious aster leafhoppers. The primary goal of this study was to identify periods of time during the growing season when crop protection practices could be targeted to reduce the risk of AYp spread. Based on abundance and infectivity, the annual exposure of the carrot crop to infectious leafhoppers varied by 16- and 70-fold, respectively. Together, this corresponded to an estimated 1,000-fold difference in exposure to infectious leafhoppers. Within a season, exposure of the crop to infectious aster leafhoppers (Macrosteles quadrilineatus Forbes), varied threefold because of abundance and ninefold because of infectivity. Periods of above average aster leafhopper abundance occurred between 11 June and 2 August and above average infectivity occurred between 27 May and 13 July. A more comprehensive description of the temporal trends of aster leafhopper abundance and infectivity provides new information defining when the aster leafhopper moves into susceptible crop fields and when they transmit the pathogen to susceptible crops.

Effects of landscape composition and rotation distance on Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) abundance in cultivated potato

Knowledge of the Colorado potato beetle's, Leptinotarsa decemlineata (Say), relationship to previous potato crops has contributed to the development of a pest management strategy focused upon crop rotation. Previous investigations revealed that potato rotations exceeding 0.4 km were effective in reducing colonization in current season potato. The current study examines the relationship between beetle abundance in potato (Solanum tuberosum L.) and distance from multiple, previous year potato fields in Wisconsin, and integrates information about the influence of natural habitats adjacent to previous season potato. Colorado potato beetle count data were collected in 1998 and 2008 and distance to previous potato, field areas, and landscape classes were estimated using maps from 1997 and 2007. Poisson regression was used to relate counts to combinations of distance and local landscape characteristics calculated for all fields within 1,500 m of sampled potato. In 1998, beetle counts measured in current season potato declined significantly with increasing distance from previous potato fields and field size did not influence these counts. However, there was no relationship between beetle abundance and distance to prior year potatoes in 2008. In both years, increased proportions of surrounding habitats, previously described as preferred for diapause sites (e.g., wooded field boundaries), did not relate significantly to counts. However, grassland habitat was negatively correlated with counts. Results indicate that distance from previous potato remains an important factor to reduce the magnitude of colonization. This analysis further suggests that certain landscape components (e.g., grassland) may influence infestation, which may be useful for refining future integrated pest management programs.

Response of wild bees (Hymenoptera: Apoidea: Anthophila) to surrounding land cover in Wisconsin pickling cucumber

Cucumber (Cucumis sativus L.) is among the plants highly dependent on insect-mediated pollination, but little is known about its unmanaged pollinators. Both domestic and wild bee populations in central Wisconsin pickling cucumber fields were assessed using a combination of pan trapping and floral observations before and during bloom. Together with land cover analyses extending 2,000 m from field centers, the relationship of land cover components and bee abundance and diversity were examined. Over a 2-yr sample interval distributed among 18 experimental sites, 3,185 wild bees were collected representing >60 species. A positive association was found between both noncrop and herbaceous areas with bee abundance and diversity only during bloom. Response of bee abundance and diversity to land cover was strongest at larger buffers presumably because of the heterogeneous nature of the landscape and connectivity between crop and noncrop areas. These results are consistent with previous research that has found a weak response of wild bees to surrounding vegetation in moderately fragmented areas. A diverse community of wild bees is present within the fields of a commercial cucumber system, and there is evidence of floral visitation by unmanaged bees. This evidence emphasizes the importance of wild pollinators in fragmented landscapes and the need for additional research to investigate the effectiveness of individual species in pollen deposition.

Crop and Non-Crop Plants as Potential Reservoir Hosts of Alfalfa mosaic virus and Cucumber mosaic virus for Spread to Commercial Snap Bean

Diseases caused by aphid-transmitted viruses such as Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV) have increased in snap bean (Phaseolus vulgaris) in the Midwestern United States. Plants immediately surrounding agricultural fields may serve as primary virus inocula for aphids to acquire and transmit to bean crops. The project objectives were to (i) identify potentially important AMV and CMV reservoirs among naturally infected plants and (ii) determine the relationship between the virus inoculum potential (VIP) in adjacent crop field margins and virus incidence in P. vulgaris. From 2006 to 2008, surveys were conducted to quantify the virus incidence and percentage cover (2008 only) of plants present within 5 m of the P. vulgaris crop. In all, 4,350 individual plants representing 44 species were assayed, with overall AMV and CMV incidences averaging 12 and 1.5%, respectively. A VIP index was developed and used to rank the importance of virus-susceptible plants in adjacent field margins. The overall VIP index for AMV in field margins was weakly associated with AMV incidence in P. vulgaris and no relationship was observed between local CMV inoculum and P. vulgaris incidence, suggesting that factors additional to local inoculum sources may influence CMV epidemics in P. vulgaris.

Detection and variability of aster yellows phytoplasma titer in its insect vector, Macrosteles quadrilineatus (Hemiptera: Cicadellidae)

The aster yellows phytoplasma (AYp) is transmitted by the aster leafhopper, Macrosteles quadrilineatus Forbes, in a persistent and propagative manner. To study AYp replication and examine the variability of AYp titer in individual aster leafhoppers, we developed a quantitative real-time polymerase chain reaction assay to measure AYp concentration in insect DNA extracts. Absolute quantification of AYp DNA was achieved by comparing the amplification of unknown amounts of an AYp target gene sequence, elongation factor TU (tuf), from whole insect DNA extractions, to the amplification of a dilution series containing known quantities of the tuf gene sequence cloned into a plasmid. The capabilities and limitations of this method were assessed by conducting time course experiments that varied the incubation time of AYp in the aster leafhopper from 0 to 9 d after a 48 h acquisition access period on an AYp-infected plant. Average AYp titer was measured in 107 aster leafhoppers and, expressed as Log10 (copies/insect), ranged from 3.53 (+/- 0.07) to 6.26 (+/- 0.11) occurring at one and 7 d after the acquisition access period. AYp titers per insect and relative to an aster leafhopper chromosomal reference gene, cp6 wingless (cp6), increased approximately 100-fold in insects that acquired the AYp. High quantification cycle values obtained for aster leafhoppers not exposed to an AYp-infected plant were interpreted as background and used to define a limit of detection for the quantitative real-time polymerase chain reaction assay. This method will improve our ability to study biological factors governing AYp replication in the aster leafhopper and determine if AYp titer is associated with frequency of transmission.

Effects of citrus and avocado irrigation and nitrogen-form soil amendment on host selection by adult Homalodisca vitripennis (Hemiptera: Cicadellidae)

Host plant water status is thought to influence dispersal of the xylophagous leafhopper Homalodisca vitripennis Germar, especially where plants are grown under high evaporative demand. Preference by adult H. vitripennis for plants grown under different water deficit and nitrogen form fertilization regimens was studied under laboratory conditions. Leafhopper abundance and ovipositional preference were studied on potted 'Washington navel' orange and 'Haas' avocado in cage choice tests, and feeding rate was estimated using excreta produced by insects confined on plants. A similar study compared responses to citrus treated with 1:1 and 26:1 ratios of fertigated nitrate-N to ammonium-N. The insects were more abundant, oviposited, and fed significantly more on surplus-irrigated plants than on plants under moderate continuous deficit irrigation except avocado feeding, which was nearly significant. Plants exposed to drought became less preferred after 3 and 7 d in avocado and citrus, respectively. Citrus xylem fluid tension at this point was estimated at 0.93 MPa. A corresponding pattern of decline in feeding rate was observed on citrus, but on avocado, feeding rate was low overall and not statistically different between treatments. No statistical differences in abundance, oviposition, or feeding were detected on citrus fertigated with 26:1 or 1:1 ratios of nitrate-N to ammonium-N. Feeding occurred diurnally on both plant species. Discussion is provided on the potential deployment of regulated deficit irrigation to manage H. vitripennis movement as part of a multitactic effort to minimize the risk of disease outbreaks from Xylella fastidiosa Wells et al. in southern California agriculture.

Spatial Analysis of Almond Leaf Scorch Disease in the San Joaquin Valley of California: Factors Affecting Pathogen Distribution and Spread

Almond leaf scorch (ALS) disease has emerged as a serious threat to almond (Prunus amygdalus) production areas throughout California's San Joaquin Valley. This disease is caused by the xylem-limited bacterium Xylella fastidiosa, and this pathogen is transmitted by xylophagous insects including sharpshooter leafhoppers (Hemiptera: Cicadellidae) and spittlebugs (Hemiptera: Cercopidae). Among four orchards surveyed, enzyme-linked immunosorbent assay (ELISA) and bacterial isolation followed by polymerase chain reaction (PCR) were equally effective in detecting X. fastidiosa from ALS-symptomatic trees. Disease incidence varied among almond cultivars in each orchard, with the highest mean incidence and most severe symptoms frequently encountered in 'Sonora'. X. fastidiosa isolates consisted of mixtures of grape or "G-genotype" and almond or "A-genotype" strains present in surveyed orchards. The X. fastidiosa G-genotypes characterized from each orchard were associated with the most severely affected 'Sonora' trees in three of the four orchards. Both ordinary runs and simple randomization analyses revealed aggregations of ALS in three of the four orchards. Clusters of ALSaffected trees frequently occurred in the outermost orchard rows. Plots of semivariance in ALS incidence over distance varied in shape and magnitude among cultivars. Semivariance increased over distance in 'Sonora' and 'Carmel', indicating spatial dependence or aggregations of incidence best fit by a combination of spherical and linear models. These results document both random and aggregate patterns of ALS spatial distribution in selected orchards and further illustrate how cultivar susceptibility influences the distribution patterns of ALS incidence. Following the recent introduction and establishment of the glassy-winged sharpshooter, Homalodisca coagulata, the impact upon the epidemiology and spread of ALS is unknown.

Seasonal dispersal patterns of Frankliniella fusca (Thysanoptera: Thripidae) and tomato spotted wilt virus occurrence in central and eastern North Carolina

The seasonal abundance and temporal pattern of Frankliniella fusca Hinds dispersal were monitored from 1996 to 2000 at 12 locations in central and eastern North Carolina. The predominant vector species of tomato spotted wilt virus (TSWV) captured across all locations was F. fusca (98%). The temporal patterns of F. fusca dispersal observed during spring seasons varied among locations in all years except 2000. Regression analysis estimated that times of first flight in the spring seasons varied among locations, whereas flight duration intervals were similar. Temporal patterns of F. fusca captured varied significantly between aerial traps placed 0.1 and 1.0 m above the soil surface. Fewer total thrips were captured at 0.1 m, although thrips dispersal occurred earlier and over a greater time interval compared with 1.0-m traps. Temporal patterns of TSWV occurrence differed among locations in the spring seasons of 1999 and 2000, whereas patterns of virus occurrence were similar during the fall seasons. Patterns of F. filsca dispersal and subsequent TSWV occurrence were synchronous at locations in 1999 and 2000 where the greatest number of TSWV lesions was recorded. Knowledge of the temporal patterns of F. fiasca dispersal and TSWV occurrence may be a useful indicator for describing the time when susceptible crops are at highest risk of TSWV infection.

The Role of Weed Hosts and Tobacco Thrips, Frankliniella fusca, in the Epidemiology of Tomato spotted wilt virus

Wild plant species were systematically sampled to characterize reproduction of thrips, the vector of Tomato spotted wilt virus (TSWV), and natural sources TSWV infection. Thrips populations were monitored on 28 common perennial, biennial, and annual plant species over two noncrop seasons at six field locations across North Carolina. Sonchus asper, Stellaria media, and Taraxacum officianale consistently supported the largest populations of immature TSWV vector species. The tobacco thrips, Frankliniella fusca, was the most abundant TSWV vector species collected, comprising over 95% of vector species in each survey season. Perennial plant species (i.e., Plantago rugelii and Taraxacum officianale) were often only locally abundant, and many annual species (Cerastium vulgatum, Sonchus asper, and Stellaria media) were more widely distributed. Perennial species, including P. rugelii and Rumex crispus, remained TSWV infected for 2 years in a small-plot field test. Where these perennial species are locally abundant, they may serve as important and long-lasting TSWV inoculum sources. In random surveys across 12 locations in North Carolina, TSWV infection was documented by double antibody sandwich enzyme-linked immunosorbent assay in 35 of 72 (49%) common perennial (N = 10), biennial (N = 4), and annual (N = 21) plant species across 18 plant families. Estimated rates of TSWV infection were highest in Cerastium vulgatum (4.2%), Lactuca scariola (1.3%), Molluga verticillata (4.3%), Plantago rugelii (3.4%), Ranunculus sardous (3.6%), Sonchus asper (5.1%), Stellaria media (1.4%), and Taraxacum officianale (5.8%). Nine plant species were determined to be new host recordings for TSWV infection, including Cardamine hirsuta, Eupatorium capillifolium, Geranium carolinianum, Gnaphalium purpureum, Linaria canadense, Molluga verticillata, Pyrrhopappus carolinianus, Raphanus raphanistrum, and Triodanis perfoliata. Our findings document the relative potential of a number of common annual, biennial, and perennial plant species to act as important reproductive sites for F. fusca and as acquisition sources of TSWV for spread to susceptible crops.

Overwintering of Frankliniella fusca (Thysanoptera: Thripidae) on Winter Annual Weeds Infected with Tomato spotted wilt virus and Patterns of Virus Movement Between Susceptible Weed Hosts

ABSTRACT Overwintering of tobacco thrips, Frankliniella fusca, was investigated on common winter annual host plants infected with Tomato spotted wilt virus (TSWV). Populations of tobacco thrips produced on TSWV-infected plants did not differ from those produced on healthy plants, whereas populations varied greatly among host plant species. The mean per plant populations of F. fusca averaged 401, 162, and 10 thrips per plant on Stellaria media, Scleranthus annuus, and Sonchus asper, respectively, during peak abundance in May. Adult F. fusca collected from plant hosts were predominately brachypterous throughout the winter and early spring, but macropterous forms predominated in late spring. Weed hosts varied in their ability to serve as overwintering sources of TSWV inoculum. Following the initial infection by TSWV in October 1997, 75% of Scleranthus annuus and Stellaria media retained infection over the winter and spring season, whereas only 17% of Sonchus asper plants remained infected throughout the same interval. Mortality of TSWV-infected Sonchus asper plants exceeded 25%, but mortality of infected Stellaria media and Scleranthus annuus did not exceed 8%. TSWV transmission by thrips produced on infected plants was greatest on Stellaria media (18%), intermediate on Scleranthus annuus (6%), and lowest on Sonchus asper (2%). Very few viruliferous F. fusca were recovered from soil samples collected below infected wild host plants. Vegetative growth stages of Stellaria media, Sonchus asper, and Ranunculus sardous were more susceptible to F. fusca transmission of TSWV than flowering growth stages, whereas both growth stages of Scleranthus annuus were equally susceptible. In a field study to monitor the spatial and temporal patterns of virus movement from a central source of TSWV-infected Stellaria media to adjacent plots of R. sardous, the incidence of infection in R. sardous plots increased from <1% in March to >42% in June 1999. Infection levels in the Stellaria media inoculum source remained high throughout the experiment, averaging nearly 80% until June 1999 when all Stellaria media plants had senesced. Dispersal of TSWV from the inoculum source extended to the limits of the experimental plot (>37 m). Significant directional patterns of TSWV spread to the R. sardous plots were detected in April and May but not in June. R. sardous infections were detected as early as March and April, suggesting that overwintering inoculum levels in an area can increase rapidly during the spring in susceptible weed hosts prior to planting of susceptible crops. This increase in the abundance of TSWV inoculum sources occurs at a time when vector populations are increasing rapidly. The spread of TSWV among weeds in the spring serves to bridge the period when overwintered inoculum sources decline and susceptible crops are planted.

Inoculation of Tomato Spotted Wilt Virus into Cotton

Tomato spotted wilt virus (TSWV) is an economically important virus of many crops throughout the world. Cotton, Gossypium hirsutum L., has previously been demonstrated to be susceptible to TSWV (1). During the fall of 1996, cotton was assayed as a potential host of TSWV, as it is an important early season host of thrips vectors of TSWV. Four commercial cotton varieties (DP 20, DP 52, DP 5409, and HS 46) were screened for susceptibility to four isolates of TSWV: two from tobacco, one from pineapple, and one from dahlia. Greenhouse-grown plants in the first true leaf stage were inoculated mechanically. Mean percent infection ranged from 20 to 33% (x = 27%) across all cotton varieties screened against all virus isolates 21 days post-inoculation. TSWV was recovered through mechanical inoculation from double antibody sandwich-enzyme-linked immunosorbent assay (DAS ELISA) positive cotton leaves in 83% of indicator plants, Emilia sonchifolia (L.) DC. ex Wight. Individual cotton plants testing TSWV ELISA positive were held for an additional 28 days with 4% of these again testing virus positive. The four cotton varieties were tested in the cotyledon, one-leaf, and four-leaf stages for susceptibility to tobacco thrips, Frankliniella fusca Hinds, transmission of one TSWV isolate from tobacco. First instar thrips were obtained from an avirulent colony. Mean percent infection among all varieties assayed was 10, 63, and 5%, respectively, for the three developmental stages. Cotton appears to be most susceptible in the one-leaf developmental stage with potential to serve as a source for TSWV spread to other crops. Reference: (1) G. L. Schuster and R. S. Haliwell. Plant Dis. 78:100, 1994.

Efficacy of three synthetic pyrethroids against three mosquito species in Arkansas and Louisiana

Adult mortality of Anopheles quadrimaculatus, Culex quinquefasciatus, and Aedes sollicitans was observed following ultra-low-volume (ULV) exposure to Responde, Permanone 31-66 RTU, and Scourge. Permanone 31-66 RTU (1:2.13, permethrin:PBO) and Scourge (1:3, resmethrin:PBO) were applied at 0.00175 lb AI/acre, while Responde (1:3, prallethrin:PBO) was applied at 0.001 lb AI/acre, and all were evaluated at 100, 200, and 300 ft. downwind of application. Significant mortality differences (P < or = 0.05) were observed among all compounds at 15 min and at 1, 12, and 24 h posttreatment against An. quadrimaculatus and Cx. quinquefasciatus. Responde exhibited significantly greater (P < or = 0.05) control (knockdown) against An. quadrimaculatus at both 15 min and 1 h posttreatment than did Permanone 31-66 RTU or Scourge; however, some recovery occurred by 12 h posttreatment. At 15 min posttreatment, Responde and Scourge were significantly (P < or = 0.05) more effective against Cx. quinquefasciatus than Permanone 31-66 RTU except at 300 ft. downwind, where Scourge was significantly (P < or = 0.05) more effective than either compound. No significant mortality differences (P < or = 0.05) were observed among the 3 compounds at 15 min, 1 h, 12 h, and 24 h posttreatment when tested against Ae. sollicitans. No significant mortality differences (P < or = 0.05) were observed between the 1:3 and 1:5 (prallethrin: piperonyl butoxide) formulations of Responde at any time posttreatment when tested against Ae. sollicitans.

Laboratory and field plot bioassay of Bacillus sphaericus against Arkansas mosquito species

Bacillus sphaericus was evaluated in laboratory bioassays against larvae of 7 Arkansas mosquito species and in rice field plots against a single mosquito species. Laboratory-tested species included Aedes aegypti, Ae. albopictus, Ae. vexans, Anopheles punctipennis, Culex quinquefasciatus, Cx. restuans, and Psorophora columbiae. Field plot bioassays were evaluated against Ps. columbiae only. The laboratory formulation tested demonstrated activity against all 7 species. Mortalities were observed at 24 and 48 h posttreatment. Twenty-four-hour LC50 results ranged from 0.84 to 15.04 international toxic units (ITU)/ml for all species and 48-h LC50 results ranged from 0.38 to 9.27 ITU/ml. Twenty-four-hour LC90 results ranged from 1.90 to 48.21 ITU/ml for all species, whereas 48-h LC90 results ranged from 1.30 to 33.83 ITU/ml. Subsequent field plot evaluations yielded control at both dosages (0.45 and 0.9 g/ ha) during the initial 48-h exposure period. Mortalities at 48 h posttreatment for both dosages were 87 and 90%, respectively. Posttreatment mortalities never exceeded 16.7% after 24 h and none were significantly different from control mortality (P < or = 0.05).

Efficacy of a 1:1 and 1:5 mixture of technical permethrin and piperonyl butoxide against Anopheles quadrimaculatus and Psorophora columbiae

Anopheles quadrimaculatus and Psorophora columbiae adults were treated with a 1:1 and 1:5 mixture of technical permethrin and piperonyl butoxide. These mixtures (0.00075 lb AI/acre) at 100, 200, and 300 ft. downwind of application killed a similar (P < or = 0.05) percentage of Ps. columbiae ranging from 45.1 to 68.8% and 85.7 to 100.0% after 1 and 24 h posttreatment, respectively. Similar results were obtained at 1 and 24 h posttreatment against An. quadrimaculatus (0.00075 lb AI/acre) where percentage mortality ranged from 42 to 62% and 63 to 78% after 1 and 24 h posttreatment, respectively. At 24 h posttreatment, significantly more mortality (P < or = 0.05) occurred in An. quadrimaculatus than in Ps. columbiae for both the 1:1 and 1:5 formulations above, except at 100 ft. downwind. A higher dosage against An. quadrimaculatus (0.001 lb AI/acre) resulted in a higher mean mortality at 1 h posttreatment (45.1-79.1%) and 24 h posttreatment (59.2-86.0%) than at the lower dosage. A 25% increase in permethrin (0.001 lb AI/acre) vs. a 400% increase in piperonyl butoxide alone gave increases in mortality of 30.4% vs. 8.6%, respectively.

Evaluation of aerial and ground-applied adulticides against mosquito species in Arkansas and Louisiana

Mosquitoes were subjected to ultra-low volume (ULV) aerial applications of permethrin synergized with piperonyl butoxide (Biomist 30:30. Biomist 31:66) and Cythion and ULV ground applications of permethrin synergized with piperonyl butoxide (Biomist 30:30. Biomist 12:60), resmethrin (Scourge), and sumithrin (Solo 40-OS and Duets 8.8-OS). Permethrin compounds tested aerially against Anopheles quadrimaculatus were not significantly different. Biomist 30:30 tested aerially against Culex quinquefasciatus did provide significantly greater mortality compared to Cythion. Biomist 30:30 and Biomist 31:66 tested aerially against An. quadrimaculatus at 1 h did not provide a significant difference up to 600 ft. (182.9 m). Both products ground tested at 24 h revealed nonsignificant results. Biomist 30:30 and Biomist 12:60 ground tested against Cx. quinquefasciatus at 1 h did not provide a significant difference at 100 ft. (30.5 m) or 200 ft. (61.0 m); however, significantly greater mortality was observed at 300 ft. (61.0 m) and 600 ft. (91.4 m). At 24 h no significant mortality differences were observed at 300 ft. (61.0 m) and 600 ft. (91.4 m). Anopheles quadrimaculatus and Psorophora columbiae were treated with a 1:1 mixture of Solo 40-OS and Duet 8.8-OS (sumithrin+piperonyl butoxide). Significant mortality differences (P < or = 0.05) between species at 1 h posttreatment occurred at 300 ft. (91.4 m).

Assessment of Anopheles quadrimaculatus response to permethrin and resmethrin by topical application

Topical applications with field-captured mosquitoes provided LD50 estimates ranging from 13.3 to 20.0 ppm for permethrin and 8.5 to 18.9 ppm for resmethrin in the Stuttgart, AR, area in 1993. Mosquitoes collected from the abatement area appeared to be more susceptible to resmethrin than those from outside the area (8.5 ppm vs. 18.9 ppm). The observed difference was not great enough to be of concern from an economic or control standpoint. The data provided a firm baseline for future assessment of changes in susceptibility to these 2 materials. Mosquitoes collected in Walnut Ridge, AR, were susceptible to permethrin and resmethrin within the same range as the Stuttgart populations, but the limited number of observations preclude firm LD50 estimates.