Kevin M. O’Neill

Effects of livestock grazing on rangeland grasshopper (Orthoptera: Acrididae) abundance

Livestock may impact habitat quality for grasshoppers by reducing food availability and by altering microclimate and potential oviposition sites. A 5-year study was conducted to create consistent grazing impacts on replicated plots and measure their effects on plant cover, microclimate, and grasshopper abundance. Cattle were used to produce two levels of grazing intensity that were compared to ungrazed controls. Differences in plant cover were greatest immediately after grazing each summer, grasshopper microhabitats tending to be shadier, cooler, less windy, and more humid in the ungrazed plots. The grasshopper assemblage included five of the worst pest grasshopper species in North America: Ageneotettix deorum, Aulocara elliotti, Melanoplus sanguinipes, M. packardii, and Camnula pellucida. Most species had greater abundance on ungrazed pastures, particularly during the 4–6 weeks after grazing each year. However, A. elliotti was often more abundant in heavily grazed areas early in the year when early instars were present and in late summer when adults were predominant. There was no strong evidence that the effect of grazing on grasshopper abundance increased over the 5-year study. At this time, all changes in grasshopper numbers cannot be directly attributed to particular habitat characteristics that changed after grazing, but the results suggest that grazing management could be used to reduce pest grasshopper densities.

Impact of livestock grazing on abundance of Miridae and Reduviidae (Hemiptera) in crested wheatgrass pastures.

Abstract Miridae of the genera Labops and Irbisia, collectively referred to as “black grass bugs,” can cause significant damage to wheatgrasses (Poaceae) of several genera on western North American rangeland. Another mirid in the same area, Capsus cinctus (Kolenati), causes damage to bluegrass (Poa spp.). Previous studies suggest that grazing management may reduce mirid populations on rangeland by eliminating preferred oviposition sites and reducing accumulations of litter that provide diurnal refuges for nymphs. We tested the hypothesis that grazing reduces mirid populations, along with those of Reduviidae, during a controlled grazing experiment. Densities of mirids and reduviids declined with increasing intensity of grazing, even though grazing occurred after the peak of mirid abundance each year. This suggests that declines in hemipteran densities resulted from grazing that occurred during previous years, perhaps because the most heavily grazed plots had the least plant litter. The results further confirm that grazing has the potential to control black grass bug populations, although the benefits could be potentially offset by negative impacts on beneficial insects such as reduviids.

Pollen load composition and size in the leafcutting bee Megachile rotundata (Hymenoptera: Megachilidae)

We examined how the species composition and volumes of pollen loads of Megachile rotundata varied seasonally and among females of different body sizes. Alfalfa and mustards (Brassicaceae) made up, on average, 88–95% of the pollen load volumes in each of three seasonal samples; in total, the 300 females sampled carried ten different pollen types. Because of variation in pollen grain size among plant species, estimates of the contribution of different species to pollen loads, based on pollen counts only, differed from those adjusted for pollen grain size. The overall size of pollen loads, as well as the contribution of alfalfa declined seasonally, while that for mustards (with smaller individual grain sizes) increased. The type of pollen carried by females did not vary with body size, but we found a significant relationship between female size and the size of the largest loads. Surprisingly, females of intermediate size carried the largest pollen loads, whether measured by counts or volume.

Sublethal effect of brood parasitism on the grass‐carrying wasp Isodontia mexicana

Abstract 1. The nests of solitary, nest‐provisioning wasps (Sphecidae and Crabronidae) are commonly attacked by brood parasites, including flies of the families Phoridae and Sarcophagidae. Larvae of the flies commonly kill the wasp offspring directly or starve it by consuming prey provided by the adult female wasps.

Seasonal trends in the condition of nesting females of a solitary bee: wing wear, lipid content, and oocyte size

During the nesting season, adult females of the solitary bee Megachile rotundata (F.) face considerable physical and energy demands that could include increasing wear and tear on their bodies and decreasing lipid reserves. Consequently, their reproductive performance may be affected not only by extrinsic factors (e.g., weather and floral resource availability), but intrinsic changes in their own bodies. Because of the potential fitness effects of seasonal changes in body condition, our objectives were to determine how wing wear, lipid reserves, and oocyte sizes vary during nesting seasons, beginning when females emerge as adults. As nesting progressed, females in two populations experienced a steady increase in wing wear, which is known to reduce foraging efficiency and increase risk of mortality in other bees. Soon after emergence, females exhibited sharp declines in lipid content which remained low for the remainder of the season. Newly-emerged females ingested pollen, an activity known to be correlated with the initiation of egg maturation in this species. Additionally, the early summer drop in lipid stores was correlated with an increase in the size of the oocytes carried. However, by ∼6 weeks after emergence, oocytes began to decrease in length and volume, perhaps due to nutrient deficiencies related to loss of stored lipids. Our results suggest management of M. rotundata should include rearing bees at temperatures that maximize stored lipid reserves in adults and timing bee release so that significant pollen resources are available for both adults and offspring.

Oocyte size, egg index, and body lipid content in relation to body size in the solitary bee Megachile rotundata.

Females of solitary, nest-provisioning bees have relatively low fecundity, but produce large eggs as part of their overall strategy of investing substantially in each offspring. In intraspecific comparisons of several species of solitary, nest-provisioning bees and wasps, the size of the mature eggs produced increases with female body size. We further examined oocyte size–body size correlations in the solitary bee Megachile rotundata (F.), an important crop pollinator. We hypothesized that larger females carry larger basal oocytes (i.e., those next in line to be oviposited) but that body size–oocyte size correlations would be absent soon after emergence, before their first eggs fully matured. Because egg production is likely affected by the quantity of stored lipids carried over from the bees’ immature stages, we also tested the hypothesis that female body size is correlated with the body lipid content at adult emergence, the time during which oocyte growth accelerates. We found significant correlations of body size with oocyte size variables chosen to reflect: (1) the magnitude of the investment in the next egg to be laid (i.e., the length and volume of the basal oocyte) and (2) the longer term potential to produce mature oocytes (i.e., the summed lengths and volumes of the three largest oocytes in each female). Positive correlations existed throughout the nesting season, even during the first week following adult emergence. The ability to produce and carry larger oocytes may be linked to larger females starting the nesting season with greater lipid stores (which we document here) or to greater space within the abdomen of larger females. Compared to other species of solitary bees, M. rotundata appears to have (1) smaller oocytes than solitary nest-provisioning bees in general, (2) comparable oocyte sizes relative to congeners, and (3) larger oocytes than related brood parasitic megachilids.

Bumble Bees (Hymenoptera: Apidae) of Montana

Abstract Montana supports a diverse assemblage of bumble bees (Bombus Latreille) due to its size, landscape diversity, and location at the junction of known geographic ranges of North American species. We compiled the first inventory of Bombus species in Montana, using records from 25 natural history collections and labs engaged in bee research, collected over the past 125 years, as well as specimens collected specifically for this project during the summer of 2015. Over 12,000 records are included, with 28 species of Bombus now confirmed in the state. Based on information from nearby regions, four additional species are predicted to occur in Montana. Of the 28 species, Bombus bimaculatus Cresson and Bombus borealis Kirby are new state records. The presence of B. borealis was previously predicted, but the presence of B. bimaculatus in Montana represents a substantial extension of its previously reported range. Four additional “eastern” bumble bee species are recorded from the state, and three species pairs thought to replace one another from the eastern to western United States are now known to be sympatric in Montana. Additionally, our data are consistent with reported declines in populations of Bombus occidentalis Greene and Bombus suckleyi Greene, highlighting a need for targeted surveys of these two species in Montana.

Brood Parasitism of the Resin Bee Megachile campanulae (Robertson) by Coelioxys modesta Smith (Hymenoptera: Megachilidae)

ABSTRACT:  In North America, brood parasitic bees of the genus Coelioxys attack nests of solitary nest-provisioning bees of the genus Megachile. Using trap-nests in central New York State, we found Coelioxys modesta (Smith) in 49% of 72 nests and 27% of 313 cells provisioned by Megachile campanulae (Robertson). Because we had a nearly complete record of the species and sex of individuals developing in nest cells, we were able to use logistic regression to test several hypotheses concerning the risk of brood parasitism, the spatial distribution of infested cells, and the sex and size of C. modesta at different cell positions. The probabilities that a nest was infested or contained multiple C. modesta were higher in nests of larger diameter and in those had been active for longer durations. Cells of the host and cells infested with C. modesta tended to cluster with those of conspecifics within nests, an observation consistent with the hypothesis that individual female C. modesta remain at or frequently revisit individual host nests in which they have already oviposited. One nest contained a string of six consecutive cells attacked by C. modesta. As is typical of cavity-nesting Megachile, M. campanulae female offspring tended to predominate in inner cells of nests. Because the risk of attack by C. modesta was unrelated to cell position, however, M. campanulae offspring sex ratio did not differ between infested and uninfested nests. Brood parasites within inner nest cells were more likely to be Females. Males in inner cells tended to be above average in body size, probably as a result of inner cells containing larger pollen masses. A review of studies of Coelioxys brood parasitism of Megachile revealed that the percent of M. campanulae nests infested in our study is one of the highest published values.

Acute Toxicity of Permethrin, Deltamethrin, and Etofenprox to the Alfalfa Leafcutting Bee

Abstract Current regulatory requirements for insecticide toxicity to nontarget insects focus on the honey bee, Apis mellifera (L.; Hymenoptera: Apidae), but this species cannot represent all insect pollinator species in terms of response to insecticides.Therefore, we characterized the toxicity of pyrethroid insecticides used for adult mosquito management (permethrin, deltamethrin, and etofenprox) on a nontarget insect, the adult alfalfa leafcutting bee, Megachile rotundata (F.; Hymenoptera: Megachilidae) in two separate studies. In the first study, the doses causing 50 and 90% mortality (LD50 and LD90, respectively) were used as endpoints and 2-d-old adult females were exposed to eight concentrations ranging from 0.0075 to 0.076 μg/bee for permethrin and etofenprox, and 0.0013–0.0075 μg/ bee for deltamethrin. For the second study, respiration rates of female M. rotundata were also recorded for 2 h after bees were dosed at the LD50 values to give an indication of stress response. Results indicated a relatively similar LD50 for permethrin and etofenprox, 0.057 and 0.051 μg/bee, respectively, and a more toxic response, 0.0016 μg/ bee for deltamethrin. Comparatively, female A. mellifera workers have a LD50 value of 0.024 μg/bee for permethrin and 0.015 μg/bee for etofenprox indicating that female M. rotundata are less susceptible to topical doses of these insecticides, except for deltamethrin, where both A. mellifera and M. rotundata have an identical LD50 of 0.0016 μg/ bee. Respiration rates comparing each active ingredient to control groups, as well as rates between each active ingredient, were statistically different (P < 0.0001).The addition of these results to existing information on A. mellifera may provide more insights on how other economically beneficial and nontarget bees respond to pyrethroids.