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The toxicity of a number of emamectin benzoate homologues and photodegradates to five species of Lepidoptera was investigated using diet and foliar bioassays. The emamectin benzoate homologues B1a and B1b were equally toxic in the diet and foliar assays to Spodoptera exigua (Hubner), Heliothis virescens (F.), Tricoplusia ni (Hubner), and Spodoptera frugiperda (J. E. Smith), within each of these species. Plutella xylostella (L.) was the most sensitive species to emamectin benzoate. The AB1a photodegradate of emamectin benzoate was as toxic as the parent compound in the diet assay. However, in the foliage assay AB1a was 4.4-fold less toxic to S. exigua than the parent compound. The MFB1a photodegradate of emamectin benzoate was as toxic as the parent compound to P. xylostella, and 3.1 to 6.2 times as toxic as the parent compound to the other species in the diet assay. The order of toxicity of the photodegradates were AB1a > MFB1a > FAB1a > 8,9-Z-MAB1a > PAB1a.

A diet-incorporation larval bioassay was developed to measure the response of codling moth, Cydia pomonella (L.), to the benzoylhydrazine insecticides tebufenozide and methoxyfenozide. The bioassay tested neonates and third, fourth, and fifth instars from a laboratory colony and neonates and fourth instars from a pooled population collected from five certified-organic apple orchards. Bioassays were scored after 6 and 14 d. No differences between the laboratory and field population were found for either insecticide. Significant differences were found in the response of third and fifth instars between the 6 and 14 d bioassays, primarily due to a high proportion of moribund larvae in the shorter assay. Larval age had a significant effect in bioassays and was more pronounced in 6- versus 14-d tests. Fifth instars were significantly less susceptible to both insecticides than other stages, while responses of third and fourth instars were similar. The response of neonates was significantly different from third and fourth instars to tebufenozide but not with methoxyfenozide in the 14-d test. Field bioassays excluded the use of fifth instars and were scored after 14 d. LC50s estimated for 18 field-collected populations varied five- and ninefold for tebufenozide and methoxyfenozide, respectively. The responses of all but six field-collected populations were significantly different from the laboratory strain. Five of these six populations were collected from orchards with no history of organophosphate insecticide use. The LC50 for methoxyfenozide of one field-collected population reared in the laboratory for three generations declined fourfold, but was still significantly different from the laboratory population. These data suggest that transforming current codling moth management programs in Washington from a reliance on organophosphate insecticides to benzoylhydrazines may be difficult.

A citrus leaf disk bioassay was developed to monitor the susceptibility of citrus rust mite, Phyllocoptruta oleivora (Ashmead), populations to abamectin. Disks from leaves of several citrus cultivars were equally suitable bioassay substrates, and there was no difference in mortality when mites were sprayed directly or exposed to dry abamectin residue. The concentration-response relationship was determined at intervals over 2 yr for a reference population of citrus rust mites that had been maintained in culture and never exposed to acaricides. Three diagnostic concentrations of abamectin were selected based on the response of the reference population and were used to test the susceptibility of 15 populations of mites from commercial citrus groves. Comparisons with the reference population showed reduced levels of susceptibility in some populations. Populations of citrus rust mites from 6 commercial groves were sprayed twice in 1997 with combinations of acaricides designed to exert different intensities of selection pressure from abamectin. None of these populations showed a change in their response to abamectin in pre- and postspray bioassays, although their susceptibility was usually less than that of mites from the susceptible reference population. Biweekly counts of rust mites on fruit in these 6 groves suggested that, relative to groves which received no abamectin or 1 abamectin spray, mite control was not adversely affected in the groves sprayed twice with abamectin. The bioassay method is discussed in relation to factors that affect the interpretation of results from its use, and factors that may affect the development of resistance to abamectin in citrus rust mite populations are presented. This study has provided baseline data with which the results of ongoing tests of the response of citrus rust mite populations to abamectin can be compared.

Three methods for screening insecticides and acaricides were evaluated against select arthropod targets: tobacco budworm, Heliothis virescens (F.), beet armyworm, Spodoptera exigua (Hubner), Colorado potato beetle, Leptinotarsa decemlineata (Say), and the twospotted spider mite, Tetranychus urticae Koch. Methods varied in amounts of test solutions delivered and included a moderate pressure rotating spray tower that sprayed 50 ml of solution to runoff on 3 plant species, and 2 miniature volume assays; a low pressure, airbrush applicator that delivered 1 ml to both surfaces of individual leaves; and an agar-based artificial diet assay (Lepidoptera only) that delivered small aliquots (50 μl) of test solutions to the surface of the diet. Bioassays were compared using 2 avermectin insecticides, abamectin and emamectin benzoate, 2 pyrethroid insecticides, fenvalerate and lambda-cyhalothrin, 2 organophosphorous insecticides, mevinphos and trichlorfon, and 1 ecdysone agonist, tebufenozide. All 3 methods were comparable at estimating the sensitivity of arthropods to these compounds. Differences in lethal concentration values among assays were species specific. Variation among assays was more apparent with less potent compounds (e.g., organophosphorous compounds and tebufenozide) compared with more potent compounds (pyrethroids and avermectins) for H. virescens , whereas in S. exigua and T. urticae , lethal concentration values were comparable among bioassay types for most compounds tested. These data indicate that low volume bioassays were comparable to high volume bioassays at detecting and estimating insecticidal activity against a select panel of arthropod pests. The potential of miniature volume bioassays for use in insecticide discovery programs is discussed, with particular reference to screening programs that rely on sample collections that are available in limited quantities, such as natural product and combinatorial chemistry sources.

A petri plate (rapid) bioassay for monitoring abamectin susceptibility in twospotted spider mite, Tetranychus urticae Koch, populations was evaluated. Decision rules for classifying resistance were established by using abamectin-resistant and -susceptible populations. The assay was validated with field samples collected in California and Florida by comparing a leaf residual bioassay with the petri plate bioassay. The petri plate bioassay, using a discriminating concentration of 3 ppm, n = 100, and a decision rule to declare detection of resistance when mortality fell below 87%, can accurately identify abamectin-resistant and -susceptible populations. The petri plate assay is also a good predictor of the mortality in the leaf residual assay.

The entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All, S17, and S20 strains), S. feltiae (Filipjev) (= S. bibionis) (N27 strain), Heterorhabditis bacteriophora (Poinar) (HP88 strain), and Heterorhabditis sp. (Bacardis strain) were evaluated as biological control agents of the sweetpotato weevil, Cylas formicarius (F.), during two consecutive growing seasons in southern Florida. Two strains, S17 and S20, were genetically selected over 17 and 20 generations, respectively, for enhanced finding of the host scarab Popillia japonica Newman. Steinernematid nematodes were applied as aqueous suspensions. The heterorhabditid nematodes, tested only in the second year, were applied using cadavers of greater wax moth, Galleria mellonella (L.), infected with these nematodes. Abundance and damage of weevils differed among nematode treatments. In the first experiment, S. carpocapsae All and S17 were most efficacious at reducing weevil damage and produced the highest percentages of marketable roots. In the second experiment, the heterorhabditid nematode, HP88, was most efficacious at reducing weevil damage to storage roots. All of the steinernematids, except S20 applied at a high rate (7.9 billion infective juveniles per ha), produced comparable percentages of marketable roots but were less efficacious than HP88. In the first experiment, S. carpocapsae All and S17 persisted poorly, whereas S. feltiae N27 persisted for >160 d after application. In the second experiment, most nematodes were recovered at moderate levels for >120 d after application; however, only Heterorhabditis sp. Bacardis was consistently recovered at high levels for >230 d after application.

Studies were conducted to develop a pheromone trap monitoring system for the sweetpotato weevil, Cylas formicarius (F.), in sweet potato, Ipomoea batatas (L.) Lam., in the southern United States. The current studies examined the effects of lure type, age, and their duration in cold storage on weevil collections in traps. We also characterized release rates of pheromone off soxhlet-extracted and nonextracted rubber septa. Most commercially prepared (matrix sheet system) lures and methylene chloride-extracted rubber septa did not differ in their attractiveness to C. formicarius when loaded with 10 μg of pheromone, but they did differ when loaded with 100 μg of pheromone. Traps baited with extracted rubber septa caught more weevils than those baited with matrix sheet lures. In another experiment, weevil counts did not differ among traps baited with rubber septa that were soxhlet-extracted with methylene chloride and those not extracted for septa obtained from two commercial suppliers. Regression parameter estimates from log10 release rate (ng/h) on log10 dosage did not differ among soxhlet-extracted and non extracted rubber septa obtained from one of the suppliers and extracted septa obtained from the other supplier. Lure age, however, did affect attractiveness to C. formicarius . The percentage of weevils caught per night decreased with an increase in lure age for ages between 0 and 80 d. However, nonextracted lures from one of the suppliers can probably be used for monitoring for at least 2 mo in the fleld. Soxhlet-extracted lures from the other supplier lost their attractiveness more rapidly; hence, a shorter replacement time of between 1 and 2 mo is probably sufficient. Time in cold storage did not affect the attractiveness of soxhletextracted rubber septa. Septa loaded with 10 μg of synthetic sex pheromone, sealed in air tight vials and stored in a refrigerator at 5 ± 1°C for >2.2 yr, were as attractive as those stored for only 90 d. The importance of these data in a pheromone trap monitoring program for this weevil is discussed.

Within-root mortality of sweetpotato weevil, Cylas formicarius (F.), by six strains of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae ( Steinernema carpocapsae \[Weiser\] \[= Neoaplectana carpocapsae, Steinemema Feltiae \] All and Mexican strains; Steinernema feltiae \[Filipjev\] \[= Steinemema bibionis \] N-27 strain; Steinernema glaseri [Steiner]; Heterorhabditis bacteriophora Poinar [= Heterorhabditis heliothidis] HP88 strain; and Heterorhabditis sp. FL2122 strain [an un-described nematode isolated in Florida]) was tested in several buried-root bioassays. The ability of nematodes to locate and kill weevils, and the location within the root where infection occurred, were measured. In addition, mortality of the weevils in roots that were artificially infested in the laboratory was compared with mortality in naturally infested roots from the field using two concentrations of one nematode ( s. carpocapsae Mexican strain). In general, the heterorhabditid nematodes caused higher levels of mortality within the root than the steinernematids. Heterorhabditis sp. FL2122 strain killed the highest proportion of weevils in the shortest period of time. Similar differences among nematodes were seen in the inner portion (½ radius) of the storage roots, as well as ill the outer portion. Although weevil mortality in the artificially infested roots was greater than in the naturally infested roots, the trends in mortality were similar; we observed increased mortality in the nematode treatments compared with the control and no difference in mortality between the two nematode concentrations.

Ten entomopathogenic nematode species or strains in the families Stein-ernematidae and Heterorhabditidae-Steinernema carpocapsae (Weiser), Agriotos, All, Breton, Italian, and Mexican strains; Steinernema feltiae (Filipjev), N27 strain; Steinernema intermedia (Poinar); Heterorhabditis bacteriophora , Poinar, HP88, and North Carolina strains; and an unidentified Heterorhabditis sp. FL2122 strain-were compared in the laboratory against the sweetpotato weevil, Cylas formicarius (F.). Although all nematodes tested could kill sweetpotato weevils, there were differences among the nematodes. Larval LC50S were low for most nematodes tested (< 10 infective juveniles per insect). The heterorhabditid nematodes included the most virulent nematode (unidentified Heterorhabditis sp. FL2122 strain), and the least virulent nematode ( H. bacteriophora North Carolina strain). Heterorhabditid nematodes were more pathogenic to pupae than were steinemematid nematodes. Weevil adults were the least susceptible stage to nematode infection. With the exception of S. carpocapsae All strain, adult mortality was < 6% for all nematodes. Adult mortality by All strain ranged from 25 to 60% depending on the nematode concentration applied. Male weevils accounted for 96-100% of the adult mortality by All strain. Larval mortality from nematode infection increased significantly over a 4-d period for all nematodes with the exception of S. feltiae , which caused high mortality within 24 h. Heterorhabditid nematodes produced Significantly more infective juveniles per cadaver than did steinernematid nematodes. The importance of these data for selecting suitable nematodes for biological control of the sweetpotato weevil is discllssed.

Studies were conducted to develop a pheromone-trap monitoring system for sweetpotato weevil, Cylas formicarius (Fabricius), in the southern United States. Effects of trap type and pheromone dose on weevil collections in traps baited with synthetic sex pheromone were studied in four states: Florida, Texas, North Carolina, and Louisiana. A plastic funnel trap and the Universal moth trap (Uni-trap) were more efficacious at collecting C. formicarius males than a screen-cone boll weevil trap. More weevils were consistently caught in the former two trap types than in the latter trap when trap counts were high (average > 60 weevils per trap per night for both the Uni-trap and the plastic funnel trap) than when trap counts were low (average < 60 weevils per trap per night). The plastic funnel trap was more efficient (72.8%) than the Uni-trap (58.0%) at capturing marked male weevils released at the base of the traps; however, these traps were equally effective at preventing adults from escaping (2% escape) and were superior to the screen-cone boll weevil trap (43% escape). Trap counts increased (although not consistently significantly) with an increase in pheromone dose between 1 microgram and 1 mg. The importance of these data for monitoring C. formicarius in the southern United States and the Caribbean basin is discussed.

The effects of planting date and mowing interval of the summer cover crop consisting of a sorghum-sudangrass hybrid on the abundance of wireworms, Melanotus communis (Gyllenhal), Conoderus rudis (Brown), C. amplicollis (Gyllenhal), and C. falli Lane, and subsequent damage to tubers in the following potato crop were investigated during two consecutive growing seasonsin southern Florida. Eight summer cover crop management programs were evaluated: cover crop planted early (within 38 d after potato harvest) and late (75-89 d after harvest) and mowed at 3-, 6-, or 9-wk intervals; cover crop planted early and not mowed (standard summer management program); and mechanical fallow. In both years, planting date affected wireworm abundance and damage to potato. In the 1st yr, wireworm larvae were 14.2–33.7 and 19–45 times more abundant in plots planted with early cover crop than in those planted with late cover crop and in those fallowed, respectively. Wireworms were 1.3-2.0 times more abundant in plots planted with late cover crop than in plots mechanically fallowed. Similar results were found during the 2nd yr. Mowing interval did not consistently affect wireworm abundance. Wireworm damage to potato tubers was affected by planting date. Percentages of wireworm injury and damage to tubers were 6.6-9.6 and 1.8-6.7 times greater in potatoes that followed early-planted cover crops than in those that followed late-planted cover crops or mechanical fallow in the firstand second year, respectively. Crop loss due to wireworms was $1,808–$2,084 and $1,298–$3,386 per hectare higher in plots planted with early cover crop than in those planted with late cover crop in the firstand second year, respectively. Thus, delaying the planting date of the summer cover crop resulted in a reduction in wireworm abundance and associated crop loss in the following potato crop.

Sampling programs for the sweet potato weevil, Cylas jormicarius elegantulus (Summers), were developed for 0.2-ha and 0.4-ha plots of sweet potato ( Ipomoea batatas (L.) Lam.). Taylor’s power law was fit to data on spatial dispersion of sweet potato weevil, and results were used to develop relationships between numbers of sample units and levels of precision for selected mean densities per plant. Results were similar whether the sample unit was the whole plant or a region from 15 cm below to 10 cm above the crown. Total numbers of weevils in the whole-plant samples were linearly related with numbers in the subsample (region from 15 cm below to 10 cm above the crown). Spatial statistics indicated that weevil populations were aggregated. The numbers of plant samples (whole-plant or region of plant) needed to estimate weevil populations reliably were too high and required too much time to be practical. A sequential sampling program that might decrease sampling time and effort was developed to classify populations into critical densities.

The entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (= H. heliothidis Khan, Brooks, & Hirschmann) (HP88 strain) and Steinernema (=Neoaplectana ) carpocapsae Weiser (All and G-13 strains) were evaluated as biological control agents of the sweet potato weevil, Cylas formicarius elegantulus (Summers). In Petri dish bioassays, all three strains were pathogenic to larvae and pupae of C. f. elegantulus . The LD50 values of C. f. elegantulus larvae were 2.6, 2.9, and 3.4 infective juveniles per insect for ‘All,’ ‘G-13,’ and ‘HP88,’ respectively. The LD50 values of pupae were 4.9, 5.9, and 4.8 infective juveniles per insect for these three nematodes, respectively. Virulence did not differ among strains or between life stages within each strain. Under simulated field conditions, ‘G-13’ was most efficacious at killing weevil larvae within infested sweet potato ( Ipomoea batatas (L.) Lam.) roots followed in decreasing order by ‘HP88’ and ‘All’ nematodes. Efficacy in killing pupae within roots did not differ among the three nematodes or between life stages for each nematode. Field applications of ‘HP88’ and ‘All’ nematodes were more effective than chemical insecticides at reducing weevil densities on plants. ‘HP88’ nematodes were more effective than ‘All’ nematodes and chemical insecticides at reducing weevil damage to fleshy roots.

Susceptibility to tebufenozide and methoxyfenozide of beet armyworm [Spodoptera exigua (Hubner)] 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 microg (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 microg (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.

Laboratory and field experiments were conducted to determine the potential importance of deco fol in the management of Colorado potato beetle (COB), Leptinotarsa decemlineata (Say). Laboratory experiments determined the effects of dicofol-treated (0.37 and 0.55 g [AI]/liter) and non treated potato, Solarium tuberose tuberose L. cv. Pang, foliage on survivorship and egg mass production of CPR. Corresponding field experiments determined the effects of deco fol on abundance and damage of COB and subsequent yield of potato. Survivorship and egg mass production of COB were significantly lower on dicofol-treated than on non treated foliage. Females produced 0.55 ± 0.03 egg masses per female per day on non treated foliage compared with zero or nearly zero egg masses per female per day on foliage treated with 0.37 and 0.55 g (AI)/liter of dicofol, respectively. In the field, abundance and damage of COB were significantly lower on dicofol-treated plants than on non treated plants. Tuber yields of dicofol-treated plants were 3.4-5.9 times greater than those of non treated plants, comparable to those of plants treated with the current insecticide standard for COB management in New Jersey. The potential of deco fol in COB management programs is discussed.

Thermal requirements for preimaginal development of Edovum puttleri Grissell (EP) were determined under constant temperatures in the laboratory and under variable conditions in commercial eggplant, Solanum melongena L., fields. Parasitism of the Colorado potato beetle, Leptinotarsa decemlineata (Say), by EP was quantified in commercial eggplant fields. Under constant temperatures, EP required ca. 237 ± 6 degre-days (DD) above a base temperature of 10.2°C to complete preimaginal development. The wasp required ca. 253 ± 2 DD to emerge from parasitized egg masses that were pinned to the undersurface of leaves of potted eggplant plants. In commercial fields, thermal requirements for development were more variable and ranged from 223 to 279 DD. EP parasitized 71–91% of all egg masses. Within an egg mass, EP parasitized 23–25% of all eggs and killed an additional 44–54% of all eggs by probing. EP emerged from ca. 80–85% of all parasitized eggs. Two- to 4-fold more females than males emerged.