Richard K. Jansson

Pro-active Management of Beet Armyworm (Lepidoptera: Noctuidae) Resistance to Tebufenozide and Methoxyfenozide: Baseline Monitoring, Risk Assessment, and Isolation of Resistance

Abstract Susceptibility to tebufenozide and methoxyfenozide of beet armyworm [Spodoptera exigua (Hübner)] from the southern United States and Thailand was determined through exposure of first and third instars to dipped cotton leaves. Among the field populations evaluated, tebufenozide LC50 values for first and third instars, respectively, ranged from 0.377 to 4.41 and 4.37–46.6 μg (AI)/ml of solution. Methoxyfenozide LC50 values for first and third instars of field populations ranged from 0.058 to 0.487 and 0.601–3.83 μg (AI)/ml of solution. A Thailand field strain exhibiting reduced susceptibility to both compounds was subjected to intense laboratory selection for three nonconsecutive generations. At the LC50 and LC90, selected Thailand strains were 45–68 times and 150–1,500 times less susceptible to tebufenozide and 340–320 times and 120–67 times less susceptible to methoxyfenozide as first and third instars, respectively, when compared with the laboratory reference strain. Among the U.S. field populations evaluated, ones from Belle Glade, FL, and Florence, SC, were generally the most susceptible and ones from Maricopa and Parker, AZ, were the least susceptible. Selection of the Thailand field strain with tebufenozide reduced susceptibility to both compounds, and selection of Thailand strains previously pressured with either compound further reduced susceptibility to both, suggesting at least some commonality of resistance mechanism. Characterization of this resistance will provide information that will be helpful for pro-active management of resistance for this valuable group of insecticides.

Sampling range of male sweetpotato weevils (Cylas formicarius elegantulus) (Summers) (Coleoptera: Curculionidae) to pheromone traps: Influence of pheromone dosage and lure age

Studies were conducted to determine the effects of sex pheromone dosage and lure age on movement of male sweetpotato weevils (SPW),Cylas formicarius elegantulus (Summers), using mark-release-recapture techniques. SPW trap counts from various downwind distances were compared for dosages ranging from 0.01 to 10.0 μg and lure ages ranging from fresh (0 days old) to 64 days old. The percentages of male SPW recaptured decreased with an increase in release distance and decreased with a decrease in dosage at each corresponding distance. Most SPW were caught within the first 16-hr period. Slopes of percent recapture vs. release distance for the two higher dosages (10 μg and 1.0 μg) differed from those of the two lower dosages (0.1 and 0.01 μg) but did not differ from each other. Intercepts were similar among the three higher dosages. Slopes did not differ among the five lure ages examined. Intercepts differed between fresh (0 days old) and 24-day-old septa at 16 hr and between fresh (0 days old) and 34-day-old septa at 40 hr. Previous exposure to pheromone (conditioning) did not increase percentages of SPW recaptured. Results indicate that male SPW are capable of traversing distances of at least 280 m in 16 hr. The pheromone tested in this study appears to be effective at dosages lower than any other coleopteran sex-pheromone system. Incorporation of this pheromone into a SPW management system may effectively reduce the use of insecticides.

Efficacy of emamectin benzoate and Bacillus thuringiensis at controlling diamondback moth (Lepidoptera: Plutellidae) populations on cabbage in Florida

Emamectin benzoate (MK-244; Merck & Co., Rahway, NJ), used alone and alternated with Bacillus thuringiensis (Berliner) ssp. aizawai (Bta), Bta alone, and B. thuringiensis ssp. kurstaki (Btk) alone, were evaluated for control of diamondback moth, Plutella xylostella (L.), in head cabbage at three locations in Florida. Additional treatments unique to each location were also evaluated. Emamectin benzoate alone, Bta alone, emamectin benzoate alternated with Bta, and mevinphos were shown to be effective. Btk was less efficacious than Bta at two locations.

Effects of nitrogen and foliar biomass on population parameters of cabbage insects

The effects of different nitrogen (N) fertilization rates (0, 45, 90, and 168 kg N/ha), plant nitrogen concentration, and plant biomass on abundance and population growth of diamondback moth, Plutella xylostella (L.), cabbage looper, Trichoplusia ni (Hübner), cabbage budworm, Hellula phidilealis (Walker), imported cabbageworm, Artogeia rapae (L.), and cross‐striped cabbageworm, Evergestis rimosalis (Guenée), were investigated in Homestead and Sanford, Florida in 1987. The effects of these factors on the parasitization of P. xylostella were also examined. In Homestead, abundance of most insect pests and parasitized P. xylostella increased with an increase in the level of N applied and with an increase in plant biomass. Similar results were found in Sanford, although results were not consistently significant. Abundance of most insect pests was significantly positively correlated with plant N concentration. Multiple regression analyses indicated that foliar biomass was significantly more important than N fertilization rate and subsequent plant N concentration at predicting abundance of insect pests and parasitized P. xylostella on cabbage.

POTENCY, SPECTRUM AND RESIDUAL ACTIVITY OF FOUR NEW INSECTICIDES UNDER GLASSHOUSE CONDITIONS

Abstract The toxicities of four classes of insecticides, emamectin benzoate (avermectin), chlorfenapyr (pyrrole), fipronil (phenylpyrazole), and tebufenozide (benzoylhydrazide) were compared using an artificial diet assay and a residual efficacy assay against several species of Lepidoptera. Emamectin benzoate was consistently the most toxic insecticide; it was 20- to 64,240-times more toxic than the other compounds tested. The LC90 values for emamectin benzoate ranged from 0.0050 to 0.0218 ug/ml for six species of Lepidoptera. Similarly, chlorfenapyr displayed consistent toxicity to all species, with LC90 values ranging from 1.9 to 4.6 ug/ml. The toxicities of fipronil and tebufenozide varied among the species tested. Fipronil LC90 values varied 501-fold (range, 0.64 to 321.3 ug/ml), while tebufenozide toxicity varied 113-fold (range, 0.24 to 27.1 ug/ml) among species tested. In residual efficacy tests conducted in the glasshouse, all compounds were effective (i.e., >90% mortality) at controlling Heliothis virescens on garbanzo bean at projected field rates and at 1/10 of projected field rates with fipronil and emamectin benzoate. Emamectin benzoate, chlorfenapyr and tebufenozide were effective at controlling Spodoptera exigua on sugar beet at projected field rates. However, mortality with fipronil was reduced to 20% or less at 7 to 14 days after treatment. All compounds at projected field use rates were effective against Trichoplusia ni on cabbage, although tebufenozide was the only compound effective at 1/10 of projected field rate for 14 days after treatment. However, tebufenozide was ineffective against Plutella xylostella at projected field use rates on cabbage while emamectin benzoate, chlorfenapyr, and fipronil were effective. The potential of these compounds for arthropod pest management are discussed.

Efficacy of Solid formulations of Emamectin Benzoate at Controlling Lepidopterous Pests

Six solid formulations of emamectin benzoate (three impregnated powder blends, two dry powder blends, and one soluble granule) were compared with an emulsifiable concentrate (EC) formulation for their residual efficacy at killing tobacco budworm, Heliothis virescens (F.) (= Helicoverpa virescens (F.)), and beet armyworm, Spodoptera exigua (Hubner), in glasshouse tests. Two trials were conducted. Emamectin benzoate was applied to plants at two rates in each trial (8.4 and 0.084 g ai/ha in the first trial; and 8.4 and 0.84 g ai/ha in the second trial). The first trial was conducted in a glasshouse; in the second trial, plants were treated in the glasshouse and moved outdoors for the duration of the study. In the first trial, all three impregnated powder blends, one dry powder blend, and the EC formulation were comparable in their effectiveness at controlling both targets when applied at the high rate (8.4 g ai/ha). At the low rate, efficacy at controlling H. virescens did not differ among formulations, whereas the two powder formulations provided the longest residual efficacy against S. exigua. In the second trial, one impregnated powder blend, two dry powder blends, a soluble granule, and the EC formulation were comparable in their effectiveness at killing both species up to 10 days after application when applied at the high rate (8.4 g ai/ha). At the low rate (0.84 g ai/ha), one powder formulation was consistently more effective at controlling S. exigua, whereas no formulation consistently outperformed all others at controlling H. virescens. Two field studies demonstrated that two dry powder blend formulations were very effective and comparable to the EC formulation at controlling Helicoverpa zea (Boddie), Keiferia lycopersicella (Walsingham), and S. exigua on tomato. These data demonstrate that solid formulations of emamectin benzoate have potential for control of Lepidoptera. The importance of a solid formulation for emamectin benzoate is discussed.

Comparison of single and multiple releases of Heterorhabditis bacteriophora Poinar (Nematoda: Heterorhabditidae) for control of Cylas formicarius (Fabricius) (Coleoptera: Apionidae)

Abstract Single and multiple releases of the entomopathogenic nematode, Heterorhabditis bacteriophora Poinar (= H. heliothidis Khan, Brooks, and Hirschmann) (HP88 strain), were evaluated for controlling populations and damage of the sweetpotato weevil, Cylas formicarius (Fabricius), during two consecutive growing seasons in southern Florida. Sweet potato, Ipomoea batatas (L.) Lam., plants were treated with one, two, or three applications of H. bacteriophora in a Krome very gravelly loam soil. Weevil population reduction and damage in nematode-treated sweet potato plots were compared with that in plots treated with monthly applications of chemical insecticides and in nontreated plots. Persistence of nematodes in soil was assessed at various times after release by baiting soil samples with greater wax moth larvae, Galleria mellonella (L.). Applications of H. bacteriophora did not consistently reduce weevil abundance, but did consistently reduce damage to sweet potato storage roots compared with nontreated plants. Weevil densities and damage did not differ between plants treated with one, two, or three applications of H. bacteriophora , suggesting that a single, early season release of this nematode was adequate for managing this weevil. Weevil damage on plants treated with chemical insecticides was intermediate to that on nematodetreated and nontreated plants. H. bacteriophora persisted in soil for over 130 and 250 days after application in the first and second experiment, respectively.

Biological approaches for management of weevils of root and tuber crops: a review.

Several weevils attack root and tuber crops. These include: Cylas formicarius (Fabricius), C. puncticollis (Boheman), C. brunneus (Fabricius), Euscepes postfasciatus (Fairmaire), E. porcellus Boheman, Alcidodes dentipes (Oliver), Parisacalles guadalupensis (Hust.), and Parisacalles sp. on sweet potato, Ipomoea batatas (L.) Lam.; Premnotrypes spp. on potato, Solanum tuberosum L.; and Palaeopus dioscoreae Pierce on yam, Dioscorea spp.. Few studies have evaluated biological control agents of these weevils. All known natural enemies, biological control agents, and other biorational approaches, such as sex pheromone, used against these weevils for their management are reviewed. In addition, the future of these approaches for managing these weevils is discussed.

Evaluation of food baits for pre-plant sampling of wireworms (Coleoptera: Elateridae) in potato fields in southern Florida

Experiments were conducted during two consecutive growing seasons to evaluate food baits for pre-plant sampling of wireworms that attack potato in southern Florida. Wireworm species studied were: Melanotus communis (Gyllenhal), southern potato wireworm, Conoderus falli Lane, C. amplicollis (Gyllenhal), and C. rudis (Brown). Baits evaluated were hybrid sweet corn seed, hybrid sorghum-sudangrass seed, a 1:1 mixture of corn and sorghum-sudangrass seed, a whole sweet corn ear, potato seed pieces, a 1:1 mixture of oatmeal and corn flake, rolled oats, and carrots. In the first year, numbers of wireworm larvae did not differ between food bait and soil samples for most food baits tested. Melanotus communis larvae were most numerous in the oatmeal-corn flake and sorghum-sudangrass seed baits. Conoderus spp. larvae were most numerous in the sorghum-sudangrass seed and corn ear baits. In the second year, M. communis larvae were more numerous in food baits than in soil samples, and more numerous in the oatmeal-corn flake and rolled oat baits than in other food baits. Numbers of Conoderus spp. larvae did not differ between food bait and soil samples nor among food baits. In addition to attracting more wireworms, oatmeal-corn flake and rolled oat baits had some of the shorter processing times. The use of one of these two baits is currently recommended for pre-plant sampling of wireworms in potato fields in southern Florida.

Development of a Novel Soluble Granule Formulation of Emamectin Benzoate for Control of Lepidopterous Pests

Six solid formulations of emamectin benzoate (one wettable powder (WP) blend, one wettable dispersible granule (WG), and four soluble granules (SG)) were compared with an emulsifiable concentrate (EC) formulation for their residual effectiveness at controlling tobacco budworm, Heliothis virescens (F.), beet armyworm, Spodoptera exigua (Hubner), and cabbage looper, Trichoplusia ni (Hubner), in three glasshouse tests. Emamectin benzoate was applied to plants at two rates in each trial (8.4 and 0.084 g ai/ha). Results from the glasshouse studies showed that most formulations were comparable at controlling all lepidopterous pests tested. Four field trials conducted in Florida confirmed that all formulations were comparable in their effectiveness at controlling populations of lepidopterous pests on vegetables, including diamondback moth, Plutella xylostella (L.), on cabbage, southern armyworm, Spodoptera eridania (Cramer), on pepper, and T. ni and S. exigua on celery. These studies identified a novel SG formulation of emamectin benzoate that was comparable to the EC formulation in its effectiveness at controlling lepidopterous pests, but superior to the EC in terms of safety to man and the environment. This novel SG formulation is currently being developed for control of lepidopterous pests on a variety of crops.