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Cold bath studies were conducted to examine the impacts of midgut content and fat body condition on supercooling points of adult boll weevils, Anthonomus grandis Boheman. The presence of solid food in weevil midguts significantly raised the supercooling points of weevils. Supercooling points of recently fed weevils with solid food present in their midguts ranged from −6.2 to −16.0°C, with a mean ± SD of −10.9 ± 1.9°C, whereas supercooling points of unfed weevils with empty midguts ranged from −10.2 to −20.2°C, with a mean ± SD of −16.0 ± 2.1°C. The mean supercooling point of weevils whose midguts contained colored traces of food from previous feeding was between those of recently fed weevils containing solid food and those having empty midguts. These findings indicate that the influence of feeding on supercooling points of weevils is related to the quantity and/or condition of midgut contents in weevils. No relationship was detected between the supercooling capabilities of weevils and amounts of hypertrophied fat bodies present for either fed or unfed weevils. Additionally, there was no significant difference in mean supercooling points between male and female weevils, and no relationship was detected between the supercooling points of weevils and their age. These results show that presence of food residues in the boll weevil midgut can have a significant effect on supercooling points of weevils, and indicate that the recent feeding history and midgut condition of weevils should be documented or at least considered in future supercooling and overwintering survival studies.

The response by five species of bark beetles to a range of verbenone doses were tested in bioassays using Lindgren funnel traps baited with attractant semiochemicals. The objective was to determine how these bark beetles respond to verbenone, a purported anti-aggregation pheromone of several economically significant bark beetle species. Catches of Dendroctonus ponderosae Hopkins, a species attacking live trees, were unaffected relative to a control trap (no verbenone) at release rates of 0.2 mg/24 h or less, but were significantly reduced at rates of 1.8 mg/24 h or more. Catches of Ips pini (Say) and I. latidens (LeConte), two opportunistic species normally attacking fresh, dead host material, were gradually reduced with increasing verbenone dose. Verbenone did not affect catches of Hylurgops porosus (LeConte) and Hylastes longicollis Swaine, two species normally associated with bark in contact with the ground, where saprophytic microorganisms quickly invade phloem tissue. The effect by verbenone on catches of the five species was consistent with differences in host-age preference. Catches of species requiring relatively fresh host tissue were reduced by verbenone, whereas catches of species accepting aged tissue were unaffected.

The response of bark beetle predators and woodboring beetles to the bark beetle anti-aggregation pheromone, verbenone, was tested in the field with multiple-funnel traps baited with attractant kairomones. Catches of the predators Thanasimus undatulus (Say), Enoclerus sphegeus (F.), Enoclerus lecontei (Wolcott) (Coleoptera: Cleridae), and Lasconotus complex LeConte (Coleoptera: Colydiidae) declined significantly with increasing release rates of verbenone. Lasconotus subcostulatus Kraus, and Corticeus praetermissus (Fall) (Coleoptera: Tenebrionidae) (in two of three experiments), showed no significant response to verbenone. In a third experiment, catches of C. praetermissus increased with verbenone dose. Likewise, catches of the striped ambrosia beetle, Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae), increased with verbenone dose in one experiment, but there was no effect in two other experiments. Verbenone had no effect on the response of Spondylis upiformis Mannerheim (Coleoptera: Cerambycidae). We hypothesize that predators specializing on early successional bark beetles are repelled by verbenone since this compound indicates a late stage attack. Generalist predators and woodborers either do not respond to verbenone at all, or they may be attracted by it.

We documented patterns of species extirpation, shifts in species dominance, and rates of recolonization of litter-layer arthropod species following a catastrophic forest fire. The study site was located along the Rio Grande within the Bosque del Apache National Wildlife Refuge, Socorro County, NM, in a riparian forest dominated by cottonwood [Populus deltoides ssp. wislizenii (S. Watson) Eckenwalder] and salt cedar (Tamarix chinensis Loureiro). The forest-floor arthropod community was sampled with 18 pitfall traps during 1994–1997. The study site burned in June 1996, and the intense fire reduced the litter layer to mineral ash and killed all the above-ground portions of trees; salt cedar and some cottonwood trees began to stump-sprout shortly after the fire, and achieved heights of two m by October 1996. The prefire forest-floor arthropod community consisted of 80 species, dominated by spiders (Lycosidae, Gnaphosidae, Salticidae), beetles (Carabidae, Staphylinidae, Cryptophagidae, Tenebrionidae), isopods (Armadillidae, Porcellionidae) and crickets (Gryllidae). The surviving postfire arthropod community was dominated by generalist ants (Formicidae). The dominant cricket, Gryllus alogus Rehn (Orthoptera: Gryllidae), exhibited a rapid recovery in abundance following the fire, and the number of certain species that preferred open, bare-ground habitat [e.g., the tiger beetle Cicindela punctulata Olivier (Coleoptera: Carabidae)] increased on the burned site. During the 9 mo following the fire, 79 arthropod species were recorded from the fire site, 29 (37%) of which had not been recorded before the fire. Of the original prefire 80 arthropod species, 30 species (37%) were not recorded after the fire, and overall arthropod abundance was substantially reduced. The extirpated species were generally uncommon before the fire, while the more abundant species displayed more successful recolonization. These results suggest that wildfire in the Rio Grande riparian forest of New Mexico can have a substantial, short-term impact on abundance and species composition of the forest-floor arthropod community, and that both survivor activity and recolonization processes by dominant species can be rapid. Given the capacity for rapid recolonization by these arthropod species, the long-term recovery of the forest-floor arthropod assemblage will likely be driven by the postfire recovery rate of the plant community and eventual structure and composition of the forest floor litter layer.

The objective of this study was to determine if prescribed fire affects spider (Araneae) and carabid beetle (Carabidae) abundance, and whether the magnitude of this effect varies with time since fire. Within mixed conifer stands, nine understory fuels-reduction burns, ranging from <1 to 15 yr old, were compared with adjacent unburned sites. Pitfall traps were used to compare macroarthropod abundance over 5 mo. In total, 3,441 spiders in 24 families and >120 species, and 14,793 carabid beetles from 17 species, were identified from the samples. Seven spider families and five species of carabid beetles were abundant enough to be analyzed statistically. Four spider families were more abundant in unburned sites (Antrodiaetidae, Cybaeidae, Thomisidae and Linyphiidae) while three families were more numerous in burned sites (Lycosidae, Gnaphosidae and Dictynidae). Four of five carabid beetle species were more abundant in unburned sites [Pterostichus herculaneus Mannerheim, P. setosus Hatch, Scaphinotus rugiceps rugiceps (Horn) and Zacotus matthewsii LeConte]. There was no difference found for Omus cazieri van den Berghe. No differences in species richness or diversity (Simpson, Shannon-Wiener and Berger-Parker indices) were found for spiders or carabid beetles. Overall, the relationship between abundance and time since burning was weak, with marginal significance found only for Dictynidae and Gnaphosidae. We suggest that changes in foraging substrate, prey availability or microclimatic conditions since fire may have interacted with life history characteristics to influence the abundance of these organisms. Differences in fire intensities among years may have masked patterns in arthropod abundance associated with time since burning.

The influence of four constant temperatures (15, 20, 25, and 30°C) on development time and survivorship of Liriomyza trifolii (Burgess) and Liriomyza huidobrensis (Blanchard) was studied in laboratory experiments. L. huidobrensis required more time for embryonic development at 25 and 30°C, and less time at 15°C, compared with L. trifolii; at 20°C there were no differences between the two species. Larval development time for L. huidobrensis was longer than for L. trifolii at 20, 25, and 30°C. At 15°C no differences were detected. Pupal development of L. huidobrensis was always faster at 15, 20, and 25°C than that of L. trifolii. Total preimaginal development time was quicker at 15 and 20°C in L. huidobrensis than in L. trifolii; at 25°C no significant differences were found. Highest survival of L. trifolii (68%) occurred at 20°C, while that of L. huidobrensis (61%) occurred at 15°C. At 30°C no adults of L. huidobrensis emerged. The estimated lower threshold temperatures for egg, larva, pupa and total development of L. huidobrensis ranged between 7.3 and 8.1°C, and they were always lower than L. trifolii thresholds, which ranged between 9.9 and 10.7°C. The Logan model was used to describe the relationship between development rate and temperature. The quantification of development times presented in this study, combined with fecundity under different temperatures, could be incorporated into a phenological model that will aid in predicting population charges of leafminers.

The influence of temperature on oviposition behavior, adult longevity, and fecundity on two Norwegian populations of the codling moth, Cydia pomonella (L.), was investigated within the range of 12.3–25°C. In addition, lower threshold temperatures (T₀) and degree-day (DD) requirements for three egg developmental stages are given. The results showed that the Norwegian populations of C. pomonella lay eggs at lower temperatures than reported previously from other countries. Eggs were deposited in ≈40% of the containers at an average temperature of 12.3°C. However, below 15°C, <40% of the population deposited eggs that developed to the black head stage. Preoviposition period was highly affected by temperature, and it was the only response for which population (West versus East) had a significant effect. At lower temperatures (≤15°C), the preoviposition period was markedly prolonged in both populations. The western population required ≈20 DDs more than the eastern population at a base temperature of 11°C, but these results remain to be validated with field data. Temperature had no significant effect on the realized fecundity per ovipositing female or the fertility of these eggs, and both responses were highly variable at all temperatures investigated. Mean fecundity was 11 eggs per female. All estimates of T₀ for the egg developmental stages were below 10°C, which suggests that the base temperature for egg development for the Norwegian populations of the codling moth is 1 or 2 degrees lower than 10°C.

Cryptolestes ferrugineus (Stephens) is often found in abundance in association with heating stored grain. Their mortality at high temperature and their distribution at optimum and hot temperatures are important information for insect control and for models of their distribution in grain bins. The lethal exposure times of the adults were determined at 42 ± 0.2–50 ± 0.2°C and 75 ± 5% RH. Insect mortality increased with increasing temperatures and exposure time. For each temperature, there was a cumulative period of thermal stress, and after the critical exposure time an additional few hours or minutes at that temperature would kill all of the adults. The mortality was 100% at 45°C in 78 h, at 47°C in 18 h, at 49°C in 4.5 h, and at 50°C in 3 h. At 50°C, insect mortality determined at 0 h was significantly different than that determined 12 h later after the insects had been moved to room temperature. A regression equation predicted insect mortality better than published models when temperatures were above 45°C. The net displacement of the adults in both vertical and horizontal directions at 27.5–52.5°C was determined in 100 by 100 by 1,000-mm wheat columns at 14.5 ± 0.3% moisture content with or without a 5°C/m temperature gradient. The adults responded to temperature gradients and the preferred temperature was from 30 to 36.5°C. There was no obvious boundary between preference and nonpreference temperatures for the adults. In horizontal wheat columns without a temperature gradient, the adults moved in both directions, and the distribution pattern gradually became more uniform when temperature increased but was under 42°C. At hot temperatures, adults could locate and move to the cooler area in <12 h; however, the adults could not move at 50°C. Geotaxis, temperature gradient, and the interaction between these two factors affected insect distribution and movement direction; and the geotaxis was more influential than temperature gradient at any condition in the vertical columns. A pattern for adult movement was suggested.

Field data collected from the major citrus-producing regions of Florida over the past 5 yr indicate that the introduction of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), has increased in abundance while the formerly dominant Cycloneda sanguinea (L.) has declined. What is known of the diet breadth, habitat preferences, and thermal thresholds for development of these two species indicates considerable niche overlap. The larger H. axyridis has many intrinsic advantages over C. sanguinea, including higher fecundity and fertility, and a lower rate of larval cannibalism. In laboratory tests, adults and larvae of H. axyridis consumed eggs of C. sanguinea more readily than vice versa. All H. axyridis adults provided with either a conspecific or a heterospecific second-instar larva killed and ate it, whereas only 15% of C. sanguinea adults consumed a second-instar larva of H. axyridis over a 24-h period. Larvae of H. axyridis were more aggressive against larvae of C. sanguinea in laboratory tests than vice versa; even when H. axyridis larvae were paired with a C. sanguinea larva 2 d older and two to three times as large, they won 67% of contests. In choice tests, larvae of both species preferred to feed on dead C. sanguinea larvae than on dead H. axyridis larvae. Larvae of H. axyridis were capable of completing development exclusively as intraguild predators on C. sanguinea larvae, whereas the reverse was not true. The data suggest that H. axyridis is a highly evolved interspecific competitor, whereas C. sanguinea is adapted more to intraspecific competition and has few defenses against H. axyridis. Competitive displacement of C. sanguinea by H. axyridis appears to be in progress in the citrus ecosystem in Florida.

It is well recognized that host-specialized folivores prefer to feed on young in comparison to old leaves. However, the capacity of young leaf feeders to track specific leaf developmental stages has not been clearly demonstrated. Using three insect folivores and two plant species, we show that nitrogen (N) fertilization changes leaf development and that herbivores track these changes in leaf development. Nicotiana tabacum L. and Populus deltoides Bartram were fertilized at two and three rates of N addition, respectively. Plants with high rates of N supply had faster growth, greater leaf area, and faster leaf initiation rates than plants receiving low rates of N supply. Most important, all N addition treatments changed the position on the stem where leaves reached 95% full expansion; with leaves on plants receiving high rates of N addition reaching 95% full expansion further from the stem apex (e.g., leaf position 5 versus leaf position 3). Feeding assays with Trichoplusia ni Hubner on N. tabacum, and Plagiodera versicolora Laicharting and Chrysomela scripta F. on P. deltoides showed that these insect species preferred to feed on leaves at a specific degree of leaf expansion. This preference was exhibited independent of leaf position and N addition rate.

The red sunflower seed weevil, Smicronyx fulvus LeConte, is a pest of sunflower in the northern and central Plains sunflower production regions. Weevil larvae feed and develop in the sunflower achene dropping to the soil to overwinter. A total of 630 parasitoids emerging from seed weevil larvae recovered from North and South Dakota and Minnesota from 1991 to 1995 was identified as Triaspis aequoris Martin, a solitary koinobiont endoparasitoid. The mean parasitization rate for the red sunflower seed weevil by T. aequoris ranged from 2.5 to 24.2% per year. There was an increase in the percentage parasitization as overall weevil populations decreased over years. In Nebraska, percent parasitization by T. aequoris, the only species recovered, increased with increasing densities of S. fulvus between 1993 and 1995. Patterns of emergence for both red sunflower seed weevil and T. aequoris were similar in two locations in North Dakota. Oviposition pattern in seeds in the sunflower head showed decreasing density toward the center, but T. aequoris parasitization was equal throughout the head. Triaspis aequoris, an egg-larval parasitoid, effectively searched for and attacked weevil eggs as soon as weevil oviposition had begun in the field. Date of planting studies showed that damage from weevils increased as seeding of fields was delayed, but parasitization of weevil larvae was similar among all dates. Activity by T. aequoris may have contributed to the decline of the red sunflower seed weevil from North and South Dakota and Minnesota. Lower densities of weevils also may account for the reduction in the diversity of parasitoid species of this weevil. The parasitoid appears to be well adapted to its host, efficiently parasitizes the red sunflower seed weevil and is amenable for use with some pest management strategies in cultivated sunflower.

The spatial distribution of immature stages of the cranberry fruitworm, Acrobasis vacinii Riley, and cherry fruitworm, Grapholitha packardii Zeller was studied in Michigan blueberry farms. Single blueberry plants or individual clusters of fruit were compared as sampling units. Distributions of eggs and larvae at each sampling date were described by fitting data to either Poisson (random) or negative binomial (aggregated) distributions, and by calculating parameters of Taylor’s power law. Additionally, two methods were used to calculate optimal sample sizes for use in future pest sampling. In one approach, Taylor’s power law parameters were used to compute optimal sample sizes needed to estimate populations at two fixed-precision levels, 10 or 20%. In another method, the minimum number of samples required to collect at least one insect in 95% of samples was calculated. Results based on Taylor’s power law parameters suggest that prohibitively large sample sizes would be required for even 20% precision, whereas the other method required substantially fewer samples and may thus be of more practical value in a pest monitoring program. All insect populations varied between aggregated and random distributions over the season, but A. vaccinii eggs and larvae were more often aggregated than G. packardii. Analysis of within-field distribution of fruitworm populations showed that A. vaccinii eggs were significantly more abundant in blueberries closer to woods when populations were at their peak. The distribution of eggs suggests that adjacent wooded habitats, which often contain wild hosts of this insect, may provide a source for individuals that colonize commercial fields.

Over a period of 3 yr we collected 19 samples (1 kg each) of recently harvested beans (Phaseolus vulgaris L.) from eight small-scale farms in Restrepo, Valle de Cauca, Colombia. Initial infestation by Acanthoscelides obtectus (Say) was low, but frequent. At harvest, 90% of the bean samples were infested by the weevil. The average level of infestation was 16 weevils per 1,000 beans, with a maximum of 55 weevils. Infested beans usually carried multiple larvae with a maximum of 13 larvae per bean. Emergence data indicate that oviposition by A. obtectus in the field is confined to a very short period before harvest. This relatively narrow time window can be exploited for proper timing of control measures. Only one species of parasitoid, Horismenus ashmeadii (Dalla Torre) (Hymenoptera: Eulophidae), was recorded, emerging from 21% of the samples. Samples with parasitoids had an average of five parasitoids per 1,000 beans, with a maximum of 12 parasitoids. This represented a parasitization level of 18%. During the 16 wk of storage, two weevil generations emerged, which caused visible damage in 0.5 and 34% of the beans (average of 14%). Although H. ashmeadii was successful in attacking the first generation of A. obtectus in the field, it failed to attack or develop under storage conditions. This indivates H. ashmeadii cannot serve as a postharvest control agent.

Effective management of adult northern and western corn rootworms, Diabrotica barberi Smith & Lawrence and D. virgifera virgifera LeConte, respectively, requires knowledge of their emergence pattern so that scouting and adult insecticide applications can be accurately timed. The objective of this study was to develop and validate species- and sex-specific models that reliably predicted adult corn rootworm emergence in Iowa. Prediction began from a biofix defined as the date of first beetle emergence in a field. The models were fit with a 3-parameter Weibull function using emergence data collected in 57 Iowa cornfields over 5 yr. Models were validated with emergence data collected in 21 additional fields from a separate year. A single Pherocon CRW Trap per field was as effective as 13 emergence cages per field at detecting the biofix. Air temperature degree-days accumulated from the emergence cage biofix explained 85% of the variability in total corn rootworm emergence over 5 yr. This model explained 89% and 83% of the variability in total beetle emergence observed in the validation year from the emergence cage and Pherocon CRW Trap biofixes, respectively. These models do not eliminate scouting for adult corn rootworms but should improve the scouting efficiency by allowing growers to focus scouting to key periods, such as peak beetle emergence, when populations should be at their maximum abundance in the field.

Body size of polyphagous parasitoids of agromyzid leafminers directly depends on that of their hosts. The possible influence of plant host on parasitoid body size was studied for the pea leafminer, Liriomyza huidobrensis Blanchard, and three of its most abundant solitary parasitoids: Phaedrotoma scabriventris (Nixon) (Braconidae), Halticoptera helioponi De Santis (Pteromalidae), and Chrysocharis flacilla (Walker) (Eulophidae) on 12 plant species. The relationship between host and parasitoid sizes was also examined to determine whether parasitoids use a consistent proportion of the host or whether different host plants allow varying degrees of resource exploitation. Significant differences were found in L. huidobrensis wing length, as well as in body and wing length of all parasitoid species studied, depending on the plant where the leafmining larvae had fed. Female parasitoid and host sizes were highly correlated. Despite leafminers attaining large body size, the host exploitation rate was consistently lower on Beta vulgaris cycla L., suggesting that plant aspects other than those determining leafminer size could be impairing host suitability on this plant. Within the range of plant hosts considered, Vicia faba L. would be the most adequate for rearing L. huidobrensis and the three parasitoid species studied, providing large individuals and an efficient biomass exploitation.

Galerucella calmariensis L. has been widely released in North America to control Lythrum salicaria L., an invasive Eurasian wetland perennial. Previous studies suggest that generalist predators such as Coleomegilla maculata (DeGeer) may affect establishment and spread of G. calmariensis. The objectives of this study were to determine the preferred feeding sites of neonate G. calmariensis, to quantify neonate survivorship on L. salicaria leaves and shoot tips, to assess the relationship between larval density and residence time in shoot tips, and to determine if larval density influences survivorship of larvae on L. salicaria in the presence/absence of predators. Neonate G. calmariensis exhibited a significant propensity to ascend L. salicaria stems and conceal themselves inside shoot tips, where 77% were located after 1 h. Neonate survival in the presence of C. maculata was higher in shoot tips (70%) than on leaves (7.1%). At low densities (one to two larvae per shoot tip), G. calmariensis fed inside shoot tips for a prolonged period of time with only 25–30% exiting the shoot tip by 126 h. At higher densities, larvae left shoot tips more rapidly with 50% (seven larvae per shoot tip) and 80% (16 larvae per shoot tip) exiting by 126 h. The number of larvae that fed externally on foliage, i.e., were exposed to potential predation, similarly increased with increasing larval density. In the presence of adult C. maculata, G. calmariensis survival was inversely density dependent. At low larval densities, larvae remained concealed in shoot tips longer and were protected from predation. However, at high densities, larvae left shoot tips resulting in greater mortality by predators. This study indicates that density-dependent predation of G. calmariensis may occur as sheltered feeding sites within shoot tips become a limiting resource. This would occur under high G. calmariensis density and require the concurrent presence of effective predators. Further studies are necessary to determine if these conditions occur in nature and are of sufficient magnitude to alter G. calmariensis establishment or spread as a biological control agent of L. salicaria.

We surveyed 154 sites in north-central Argentina and sampled 2,528 fire ant colonies for the presence and intracolonial prevalence of the microsporidium, Vairimorpha invictae Jouvenaz & Ellis, in the red imported fire ant, Solenopsis invicta Buren. The concentrations of meiospores and binucleate spores were quantified in workers and sexuals; and the occurrence and intracolonial prevalence of dual infections with Thelohania solenopsae Knell, Allen & Hazard were studied. To study the effect of V. invictae in infected colonies of S. invicta, we compared the proportion of infected living workers to the proportion of infected dead workers, and compared the survival of uninfected and infected workers. V. invictae occurred at 13% of the sites and 2.3% of the colonies. At times, the disease reached epizootic levels in certain areas. We found vegetative stages in 4.8–52.3% of eggs, larvae, pupae, and queens, meiospores in 4–56.3% of pupae and mature stages, and binucleate spores in 9.5–63% of all life stages, except eggs. Evidence for transovarial transmission is provided. The percentage of sexual males infected was significantly higher than that of sexual females (44.9 versus 15.9%, respectively). Dual infections (V. invictae T. solenopsae) occurred in 0.24% of the colonies. V. invictae was present in 9.3% of living workers and in 56.7% of dead workers. Mortality rates of workers from Vairimorpha-infected colonies were higher than those of workers from uninfected colonies. Survival times of infected workers were 18.8–31.7% less than those of uninfected workers. The studies reported here contribute to the evaluation of V. invictae for use as a classical biological control agent against the red imported fire ant in the United States.

The ability of entomopathogenic nematodes to reduce abundance of subterranean root weevils was evaluated in three small fruit crops of Washington State. In cranberry, the entomopathogenic nematodes Steinernema carpocapsae (Weiser) and S. glaseri Steiner applied at 30 IJ (infective juveniles) per square centimeter reduced abundance of black vine weevil, Otiorhynchus sulcatus (F.), by 96 or 100% respectively compared with the untreated control. According to a waxmoth [Galleria mellonella (L.)] bait bioassay, S. carpocapsae persisted at higher levels than S. glaseri (0.48 versus 0.04% infested waxmoth per applied infective juvenile at 30 d after treatment) and for a longer interval (at least 60 d after treatment), but neither species dispersed beyond the treatment plots. At one of two strawberry sites, S. carpocapsae and Heterorhabditis marelatus Liu OH10 significantly reduced the abundance of black vine weevil (all stages) and pupal strawberry root weevil, O. ovatus (L.), compared with the untreated control. The same treatments were applied at the other site, but only pupal black vine weevils were significantly affected. Neither S. carpocapsae nor H. bacteriophora Poinar significantly reduced the abundance of black vine weevil in two trials conducted in red raspberry. Entomopathogenic nematodes were recovered from larval waxmoth Galleria mellonella baits placed on soil from the red raspberry sites 6 wk after treatment. Efficacy of entomopathogenic nematodes in all trials was likely most limited by cool soil temperatures that are typical to Pacific Northwest small fruit crops during spring when root weevils are in late larval and pupal stages, but soil structure and crop characteristics, particularly dense strawberry foliage and large crowns, were also important.

The abundance of nontarget Lepidoptera on the shrub Ribes cereum Douglas was monitored from 1997 to 2000 in an Interior Douglas-fir forest in British Columbia to assess potential side effects of an operational program to control the western spruce budworm, Choristoneura occidentalis Freeman. The treatment was a single application of Bacillus thuringiensis subsp. kurstaki (Btk) (Foray 48B) at the rate of 30 BIU/ha in 2.4 liter/ha. The guild of leaf-feeding Lepidoptera on R. cereum was dominated by Gelechia ribesella Chambers, and Euhyponomeutoides gracilariella Busck, which made up 24 and 62% of the guild, respectively. The remaining 14% of the guild comprised numerous sparsely distributed species (at least 45 different species based on morphotypes). Total larval abundance was significantly lower on plants that were sprayed with Btk than on plants that were covered to exclude Btk. Covering the plants was a novel approach that enabled us to replicate the treatment within a single spray area. G. ribesella and E. gracilariella were significantly reduced by Btk, but a modest reduction of ‘sparsely distributed species’ was not significant. Both G. ribesella and E. gracilariella appeared to make a full recovery within 2 yr of the Btk spray, but as a group the abundance of the sparsely distributed species was lowest in the year 2000 in both the Btk sprayed area and an untreated comparison area. This suggests a general decline independent of the treatment. Microscopic examination of cadavers of the two major nontarget species showed the presence of Btk in some of the larvae reared from the treated plot, but Btk was absent in larvae from the reference plot.

We examined plant use versus plant availability by a leafhopper guild from a Chihuahuan Desert plant community. Some native woody plants species of the Chihuahua Desert behave as weeds (e.g., Gutierrezia spp.) and could be subjects of augmentative biological control. As a first step, we wanted to know how the leafhopper guild used the woody plant community in the Chihuahua Desert to identify possible candidates to be studied. At least 37 leafhopper species were sampled on 13 woody and perennial plant species. Individual plants were sampled with sticky-traps on nine dates from June 1997 to July 1998. Leafhopper counts and plant availability were used to determine if leafhoppers used plants in proportion to their availability. Analysis of the 13 most abundant leafhopper species indicated differential use of at least one or more plant species in proportion to plant occurrence. Approximately 40% of all possible plant-insect pairs (169 pairs, 13 plants, and 13 insects) demonstrated under-utilization of plants (less than expected) by the leafhoppers. Nearly 50% of the pairs demonstrated plant use in proportion to their availability (random utilization), and in only 10% of pairs, leafhoppers used plants more often than expected. In our study site, 66.7% of the leafhopper species exhibited preference for one or two plant species, whereas the remaining 33.3% exhibited no preference for any studied plant. Our plant utilization results reaffirm published available host plant records for the leafhoppers analyzed. Qualitative temporal patterns in plant utilization were not detected. Specialist species exhibited different host uses in response to increasing leafhopper abundance. At seasonal peak abundance, specialist leafhoppers showed two different strategies: leafhoppers increased their preference toward their preferred host plants, and leafhoppers decreased their preference toward their preferred plants. The possible use of this methodology for augmentative biological control is discussed.