A measure of the specific impact for herbivore–plant interactions was used to test whether 7 insect species differ in the severity of their effects on young cruciferous plants. Specific impact was estimated as a biomass conversion ratio (reduction in plant biomass per unit gain in insect biomass) based on dry weights. The armyworm Mamestra configurata (Walker) had a specific impact of 4–5 on both canola, Brassica napus L., and mustard, Sinapis alba L., in the laboratory, and a similar specific impact of 3.4 was estimated for a natural field population. Two herbivore densities showed little if any difference in the specific impact for M. configurata on canola, nor for the flea beetle Phyllotreta striolata (F.), which had impacts of 81 and 96 at the 2 densities tested. The flea beetle Phyllotreta cruciferae (Goeze) had a specific impact of 148 on canola, not significantly different from that of its relative, P. striolata, which feeds in a similar way. The specific impact of the beetle Entomoscelis americana Brown was 3.5, similar to that of M. configurata, and both species had lower specific impacts than another folivore, Plutella xylostella (L.), with an impact of 12. The specific impacts of 2 aphids, Lipaphis erysimi (Kaltenbach) and Myzus persicae (Sulzer), were similar with values of 12 and 16, respectively. Although different herbivores showed substantial differences in their impacts on canola, no consistent pattern of difference was found between herbivores belonging to the leaf-chewing and sap-feeding guilds, nor were there consistent differences between generalist and specialist herbivores.

The solitary bee Osmia lignaria Say has been developed as an orchard pollinator in the western United States. Immatures develop through the spring and summer. By late summer, bees become adults and remain in this stage inside their cocoons throughout the winter. In this study, we reared O. lignaria at various temperature regimes in the laboratory and outdoors. Developmental rates increased with temperature: bees reared at 18°C took >120 d to complete development, whereas bees reared at 29°C took half that long. Bees reared outdoors under fluctuating ambient conditions took ≈95 d. At 18°C, some bees were unable to complete prepupal dormancy. Different developmental stages responded differently to the various temperature regimes. Fluctuating temperatures averaging 22°C significantly shortened the dormant prepupal stage, and, as a result, bees developed faster than at the equivalent constant temperatures. Bees that developed faster (29°C and fluctuating temperatures) could be wintered as early as August and incubated for emergence in March, 1 mo ahead of bees exposed to natural conditions. These results can be applied to field populations for pollination of early-blooming crops such as almonds, Prunus amygdalus Batsch.

The attraction of female oriental fruit flies, Bactrocera dorsalis (Hendel), to protein and host fruit odors was examined in field-cage and field experiments. In field-cage experiments, we examined how the physiological state of laboratory-cultured female oriental fruit flies affected their responses to protein (Nu-Lure) and fruit (orange) odors. Both mated and unmated, protein-fed females (10–12 d old) were more attracted to fruit odors than to protein odors, whereas mated, protein-deprived females (10–12 d old) and unmated, protein-fed females (2–3 d old) were equally attracted to fruit and protein odors. The combination of fruit and protein odors was less attractive to protein-fed females than fruit odors alone. Field tests were conducted to compare capture rates of wild oriental fruit flies in traps baited with commercially available protein baits, Nu-Lure, Trécé A.M. Supercharger, and BioLure, and in traps baited with either fruit (orange) or Nu-Lure in a commercial guava orchard. Spheres baited with either Supercharger or BioLure captured more female oriental fruit flies than unbaited spheres when the lures were hung above spheres. Traps baited with Nu-Lure were more effective for capturing females than traps baited with orange puree in field tests.

Stand conditions associated with outbreak populations of the roundheaded pine beetle, Dendroctonus adjunctus Blandford, in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests were studied in the Pinaleno Mountains, AZ, and the Pine Valley Mountains, UT. Classification tree models to estimate the probability of infestation based on stand attributes were built for both study areas using growth rate and ponderosa pine basal area information. Cross-validation estimates of correct classification were 0.60 for the Pinaleno Mountains and 0.58 and 0.78 for the Pine Valley Mountains. Regression tree and linear regression models to estimate amount of mortality caused by the beetles were also built for both sites using growth rate, ponderosa pine basal area, and trees per hectare information. The occurrence and mortality levels caused by the roundheaded pine beetle are positively related at both the stand and tree scale with reduced growth rates caused by high stocking densities.

When standing and fallen grand firs, Abies grandis (Douglas ex D. Don) Lindley, were co-attacked by fir engravers, Scolytus ventralis LeConte, and Pityokteines elegans (Swaine), 5.8% of galleries of the latter species were initiated from galleries of the former. Larval S. ventralis avoided contact with both con- and heterospecific galleries, whereas P. elegans adult and larval galleries freely crossed those of S. ventralis. There were strong and weak negative relationships for gallery establishment and emergence, respectively, between the 2 species, but numerous instances in which both species co-inhabited the same resource. Unlike many scolytids, the 2 species did not partition the host according to the diameter of the bole. The results indicate a moderate level of competitive interaction between the 2 species in which P. elegans would either colonize an area of bark before S. ventralis, which would then not initiate attack, or in which both species would co-attack a host, but S. ventralis would avoid phloem colonized by P. elegans.

Animals can reduce the risk of being preyed upon by foraging less in the presence of predators. Animals often face a diverse group of predators that vary in their effectiveness at preying upon the animal, and thus pose different potential risks. In laboratory microcosms, we investigated the ability of the spotted cucumber beetle, Diabrotica undecimpunctata howardi (Barber), a polyphagous herbivore, to accurately recognize dangerous predators versus taxonomically related predators that posed no true risk, and to adjust the intensity of their antipredator behavior accordingly. Spotted cucumber beetles reduced their feeding, and reduced damage to host plants, in the presence of the large wolf spider Hogna helluo (Hentz), which previous experiments identified as the most dangerous predator we examined. Beetles did not significantly alter their feeding rate in the presence of 3 other less-dangerous predators. Laboratory mesocosm studies verified that, indeed, Hogna was the most effective at capturing D. u. howardi in a structurally complex environment more similar to that in the field. Spotted cucumber beetles responded to Hogna, whereas several similar-sized but less-dangerous predators were ignored, suggesting that D. u. howardi may have been able to recognize Hogna specifically. Our results suggest that reduced feeding by herbivores as a strategy to reduce predation risk can allow predators to improve biological control even when actual predation does not occur.

The cottonwood leaf beetle, Chrysomela scripta F., is a major defoliating pest of Populus in North America. We determined the relationship between larval population densities and defoliation levels in central Iowa, and related that to potential biomass loss. During the 1995 and 1996 growing seasons, egg mass surveys were performed: in 1995 for generation 2 and in 1996 for all 3 generations. Open and caged Populus trees were infested with different populations of freshly eclosed larvae on actively growing terminals. The 1996 observations from the open and caged trees in the 2nd generation and from the caged trees in generations 1 and 3 are consistent with those of the open and caged trees of the 1995 2nd generation. The results from the open trees during the 1st and 3rd generations in 1996 are much different from those of the 2nd generation in either year. The probability of reaching damage levels that cause biomass loss is greatest for the 2nd generation. Egg mass density may be useful in predicting damage levels. Damage rating is an accurate estimator of foliage loss.

We examined the effect of shoot size distribution within plants and different stage of host plant development on the pattern of attack of Andricus sp. on gambel oak, Quercus gambelli Nuttall. The gall-inducing wasp preferred large diameter shoots to small ones in 2 populations of host plant. Attack on larger shoots was significantly nonrandom and occurred even though these shoots were relatively scarce in the shoot population. Large shoots accounted for only 5.51 and 12.72% of the total shoots in an urban and forest site, respectively. The percentage of attack on shoots in the largest shoot diameter class was 10.53 and 48.74% in the urban and forest site, respectively. Gall density decreased with maturity of the host plant and was 3 times higher on juvenile plants compared with mature plants. The distribution of attack in relation to plant age was not related to changes in shoot size with the age of the plants. Gambel oak may become resistant to gall formation with increasing age. Survival was 33.72% higher on large shoots (83.72%) compared with small shoots (50.00%). Larval survival did not change with plant age among host plants. The pattern of attack in relation to shoot size suggests that Andricus sp. prefer to oviposit on large shoots in which larval performance was highest. Andricus sp. might show a flexible oviposition preference hierarchy for shoot lengths. Females attacked the longest shoots available rather than showing a fixed preference for specific shoot lengths.

Insect parasitoids have to disperse to locate host habitat and host, and individuals of small species, such as egg parasitoids, are expected to be very sensitive to climatic conditions during dispersal. The effect of 16 environmental variables on the spatio-temporal pattern of dispersion of Trichogramma evanescens Westwood, originating from Egypt, and Trichogramma pretiosum Riley, originating from Quebec, was quantified. In T. evanescens, the accumulation of solar radiation at temperatures >15°C had a significant effect on its dispersion. When >15,000 kJ/m² were accumulated, more parasitism was observed in a larger area. When wind blew above 15 km/h for >4 h in a day, dispersion also decreased significantly. In T. pretiosum, accumulated solar radiation had no significant effect, whereas it took 8 h of wind >15 km/h to significantly reduce dispersion. T. evanescens, a warm climate species, thus appears to be more sensitive to temperature. Its relatively higher sensitivity to wind condition may indicate that this species is adapted to aggregated or rare hosts, which require more flight control for location.

We investigated the life history and populations characteristics of the Carolina mantid,. Stagmomantis carolina (Johannson), in central Arkansas. Unlike several studies on other mantid species found in the United States, this species was found at very low densities in the field as measured by adult abundance and ootheca density. We found that mortality was high during the egg stage because of developmental failure or egg parasitism. In replicated field plots, mortality and emigration was high during the 1st and 2nd stadia, resulting in very low numbers of in-plot survivors (<1%) by the 3rd stadium of development. Synchronous versus asynchronous hatching had statistically significant effects on emigration and in-plot mortality but a nonsignificant effect on in-plot survival, although the trend was for increased survival in asynchronous plots. Although arthropod abundance tended to be lower in mantid plots, S. carolina had no significant effects on total arthropod abundance, total arthropod biomass, or the abundance and biomass of any arthropod order. Laboratory experiments indicated that this species has slower development during the egg stage and slower development during the nymph stages compared with related mantid species. This slow growth may in part explain the high mortality rate and therefore explain the low density of S. carolina found in this population. However, this growth strategy seems necessary for survival because it allows for proper timing of oviposition for a univoltine life cycle in central Arkansas. Comparative studies of this species in other portions of its range would be interesting in determining the generalities of our findings.

Moving actively nesting populations of the orchard pollinator Osmia cornuta (Latreille) from a pollinated crop to one beginning to bloom could increase both the number of flowers pollinated and the number of bee progeny produced. This study investigates the possibility of moving actively nesting O. cornuta populations, and evaluates the effects of moving distance and nest site artificial visual landmarks on orientation and establishment of moved females. Nesting shelters with known numbers of nesting females were nocturnally relocated for distances ranging from 0 to 240 km, and the numbers of nesting females were counted after each move. Nearly all females continued to nest at shelters that were moved short (0–3 m) distances. Moves of intermediate distances (135–235 m) resulted in considerable (30–76%) bee loss (dispersal), and many females flew back to the original nesting site. At long distances (3–240 km), dispersal was higher (63–78%) and no bees were seen hovering at the original site. Moving distance was correlated positively with dispersal and with orientation (zigzagging) flights made by females when they first exited their nests after the moves. The addition or removal of supplementary visual landmarks (2 by 1.5-m banner with colored patterns) at the nesting shelter did not affect dispersal rates. Bees appeared to respond to supplementary landmarks but used other signals as primary orientation cues. An additional experiment showed that O. cornuta populations can be removed and stored at low temperature for up to 4 d (e.g., to avoid pesticide treatments) and then reinstalled at their nesting site, without affecting female orientation or nesting.

The fast-growing Central American tree Leucaena leucocephala (Lam.) de Wit (Leguminosae: Mimosoidaeae) has been widely planted in the tropics since the 1970s for agro-forestry, reforestation, and fodder. Since the mid-1980s the tree has suffered serious damage throughout its exotic range from the psyllid Heteropsylla cubana Crawford, which is also native to Central America. This article summarizes field studies on the tree and the psyllid conducted at 2 sites in north Thailand: a cool highland and a warm valley site. In the highlands, mean psyllid densities per shoot were slightly higher, defoliation was greater, and dry matter production losses due to the psyllid were >3 times higher than those at the valley site (62.5 and 18.3% losses, respectively). Using field data, the lower thermal thresholds for tree growth and psyllid development were 11.2 and 9.6°C, respectively. Psyllid abundance was negatively correlated to temperature. When maximum temperatures exceeded 36°C, psyllid abundance fell dramatically, mortality increased, and body size decreased. These data suggest that the tree and the psyllid are climatically mismatched. H. cubana prefers new shoots, and population cycles were related to tree growth cycles. Finally, populations of the introduced parasitoid Psyllaephagus yaseeni Noyes (Hymenoptera: Encyrtidae), native coccinellids, and spiders showed little correlation to the psyllid population’s intrinsic rate of increase. Percentages of parasitism by P. yaseeni were low (mean = 1.2–1.9%, maximum = 6.0%) and no evidence of density dependent regulation was found.

Naive female Diachasmimorpha longicaudata (Ashmead), a solitary endoparasitoid of tephritid fruit flies, exhibited positive responses toward volatiles of host fruits in olfactometer and wind tunnel bioassays. Although no significant preference for one of the test fruits, mango, Mangifera indica L., or grapefruit, Citrus paradisi Macfaden, was observed, the number of flights in the wind tunnel was higher in the presence of mangos. In the olfactometer trials, parasitoids preferred fly infested over noninfested grapefruits, and infested over noninfested mangos. Reproductive performance bioassays were conducted using Anastrepha ludens (Loew) larvae (Diptera: Tephritidae) reared in grapefruit, orange, mango, or artificial diet, and Anastrepha obliqua (Macquart) larvae reared in mango as parasitoid hosts. Parasitoid performance was compared for 2 Anastrepha species and 3 fruit species. Significant effects of fruit fly species and of the diet of fruit fly larvae on longevity, size, and progeny production of D. longicaudata were observed. Anastrepha ludens reared in grapefruit was the best host in terms of offspring longevity, size, and number of female progeny, but parasitoids that developed in A. ludens reared in mango had higher overall fecundity. Anastrepha ludens reared in mango was a better host than A. obliqua in the same fruit. No correlation between parasitoid size and demographic parameters was found. The results of this laboratory study showed that host preference and offspring performance are partially related.

Fall flaming of harvested peppermint, Mentha piperita L., fields for disease control immediately decreased levels of the predatory phytoseiid mite Neoseiulus fallacis (Garman) by 84–98%, while suppressing the spider mite pest Tetranychus urticae Koch to a lesser extent. By the following spring, more T. urticae were found in flamed fields than unflamed fields and in many cases the pest reached outbreak densities (>5 per leaf) and required use of miticides for control. After harvest on unflamed mint, more N. fallacis were found on prostrate plants near the humid soil surface than on erect plants, whereas spider mites were near equal on prostrate and erect plants. The 1st erect plant type was 15–25 cm tall without leaves on the lower 7.5 cm. The 2nd was 2.5–7.5 cm tall with at least 3 sets of leaves and the prostate plants extended to only 1.3 cm above the soil surface. The net effect of this temporal–spatial asynchrony between predators and prey was to uncouple the system, temporarily. This uncoupling for a short time (physiologically) seemed to stabilize interactions by keeping the predators from overexploiting spider mite populations in the fall and spring. Tests of selective flaming in small field plots showed that predaceous mites dispersed 7–8 m from unflamed plots to recolonize flamed plots before spider mites reached outbreak conditions. Allowing small, unflamed refuges to exist where predaceous mites can survive may reduce negative impact of flaming on control of spider mites at whole field levels.

Bacillus cereus French & French increased the mortality of 3rd-instar gypsy moths, Lymantria dispar (L.), caused by Bacillus thuringiensis subsp. kurstaki Berliner. B. cereus did not cause mortality of L. dispar when applied alone. The activity of various B. cereus strains was correlated positively with their accumulation of zwittermicin A, an aminopolyol antibiotic, in culture. When a constant dose of B. thuringiensis subsp. kurstaki and increasing concentrations of purified zwittermicin A were applied to artificial diet, mortality of larvae was directly proportional to the dose of zwittermicin A. Zwittermicin A by itself caused no mortality at the concentrations tested. Addition of zwittermicin A to a culture of a mutant strain of B. cereus that does not accumulate zwittermicin A restored synergistic activity. These results indicate synergy between B. thuringiensis subsp. kurstaki and zwittermicin A. The potential for enhancing efficacy of B. thuringiensis and delaying development of insect resistance are discussed.

The activity of the nuclear polyhedrosis virus (NPV) of the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), against the beet armyworm, Spodoptera exigua (Hübner), was greatest when the virus was fed to larvae on foliage of tomato, Lycopersicon esculentum Mill., least on cotton, Gossypium hirsutum (L.), and intermediate on collard, Brassica oleracea L. Activity of AfMNPV against the corn earworm, Helicoverpa zea (Boddie), was greatest on corn, Zea mays L., least on cotton, and intermediate on bean, Phaseolus vulgaris L. Survival time (days between the start of the test and death) of larvae that were killed by virus was usually lower on treatments on which rates of mortality were higher, but these differences were usually small (≤1 d). Effects of host plants on viral activity were not related closely to their effects on larval feeding rates. Effects of host plants on viral activity were also not specific to AfMNPV; cotton and collard affected AfMNPV and the homologous NPV of the beet armyworm to similar degrees. Similar results were found for AfMNPV and the homologous NPV of the corn earworm on cotton and bean. Levels of control provided by these viruses may thus be higher on tomato or corn than on cotton, and intermediate on collard or bean.

We studied ant predation on eggs and larvae of the black cutworm, Agrotis ipsilon (Hufnagel), and on eggs of the Japanese beetle, Popillia japonica Newman, on golf courses and lawns in central Kentucky. Lasius neoniger Emery accounted for >99% of the ant mounds on golf putting greens and collars. Although often regarded as a nuisance pest, L. neoniger preyed heavily upon A. ipsilon eggs on turfgrass cores implanted into putting greens, collars, fairways, and roughs. Predation on eggs was lower in fairways than in roughs, and in plots where ant populations were reduced by insecticides. When 1,600 individual 1st-instar cutworms were placed near L. neoniger nests on putting greens, 62% were attacked and killed upon their 1st encounter with the ants. Third- and 4th-instar cutworms generally fended off attacks by L. neoniger and Formica pallidifulva nitiventris Emery, but were invariably killed during encounters with Formica schaufussi Mayr and Formica subsericea Say, larger ants that are common in lawns and golf roughs. Predation on implanted Japanese beetle eggs also tended to be greater in roughs than in fairways, and fewer grubs were found in areas of golf roughs where ants were abundant than where ants had been controlled. This study suggests that predation by indigenous ants provides an important buffer against pest outbreaks on lawns and golf courses.

The entomopathogenic fungi Metarhizium anisopliae (Metschnikoff) Sorokin and Beauveria bassiana (Balsamo) Vuillemin and the bethylid parasitoid Prorops nasuta Waterston are natural enemies of the coffee berry borer, Hypothenemus hampei (Ferrari), and are considered valuable biocontrol agents in the coffee-growing regions of Central and South America. Laboratory evaluations were made on the impact of three isolates of each fungus on adult P. nasuta. These isolates were selected because of their high virulence toward H. hampei in previous studies. B. bassiana isolate Bb25 and M. anisopliae isolate Ma4 caused the lowest infection levels in P. nasuta with LC₅₀ values of 8.31 × 10⁶ and 4.08 × 10⁶ spores per milliliter, respectively, by direct inoculation. Spore suspensions of each of these isolates were applied to coffee berry borer infested coffee berries. P. nasuta adult females were allowed to search and parasitize hosts within the treated berries. Despite the high virulence of these fungi to P. nasuta, neither pathogen significantly affected the predatory or parasitic capacity of P. nasuta, indicating that these isolates may be compatible with the action of the parasitoid under field conditions provided that pathogen applications and parasitoid liberations are timed not to coincide.