Variation in pollinator visitation among garden cultivars of marigold, portulaca, and bidens.

Due to declines in pollinator populations, many people are now interested in learning about which annual flowers they can plant in their garden to better support pollinators. However, reports of experimental evaluation of cultivars of annual flowers for attraction to pollinators are scarce. We sampled pollinators visiting six cultivars of marigold (Tagetes erecta and T. patula), ten cultivars of bidens (Bidens ferulifolia and B. aurea), and eight cultivars of portulaca (Portulaca oleracea and P. grandiflora) for two years to compare pollinator visitation rates among cultivars within each flower type. Pollinators collected on flowers in research plots were categorized into four groups, honey bees (Apis mellifera), common eastern bumble bees (Bombus impatiens), wild bees, and syrphids, to show the proportion of different pollinator visitors to each cultivar. Pollinator visitation rates varied significantly among cultivars of marigold, bidens, and portulaca, with some cultivars having as much as 10-fold the visitation rate of other cultivars of the same flower type. In the second year we also evaluated nectar production and nectar quality of the most and least visited cultivars of portulaca and bidens. Our results show that pollinators have a strong preference for cultivars that produce the most nectar or nectar with the highest sugar content. This research will better inform entomologists, growers, educators, and plant breeders, about which cultivars of marigold, portulaca, and bidens are visited the most by pollinators, and how to accurately determine this at the cultivar level.

Gradual Decline of Japanese Beetle (Coleoptera: Scarabaeidae) Populations in Michigan Follows Establishment of Ovavesicula popilliae (Microsporidia).

The purpose of this research was to document the incidence of Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), infection by the microsporidian pathogen, Ovavesicula popilliae Andreadis & Hanula (Microsporida: Pleistophoridae) while monitoring Japanese beetle populations at nine golf courses in Michigan from 1999 to 2018. We also compared the current distribution of the pathogen in Michigan to the known distribution in 1999. Beetles were sampled a total of seven different years, in three time periods: 1999-2000, 2005-2007, and 2015-2018. At these nine golf courses, O. popilliae infection rates of adults increased from 0.39% in 2000 to 29.5% in 2018, while Japanese beetle adult populations declined 73.2%, and Japanese beetle larval density declined 78.6% (from 1999 to 2018). In previous research, larval infection rates averaged at least twice the infection rates of adults, because all infections originate in the larval stage, and at least 75% of infected larvae die before pupation. This means that an adult infection rate of 29.5%, combined with previously observed 50% reductions in egg production by infected females, are consistent with the observed population declines. The current distribution of O. popilliae in southern Michigan was determined by sampling Japanese beetle larvae and adults at 38 sites in 2017 and 2018. Ovavesicula popilliae was found at 21 of 38 sites and in 16 of 21 counties, compared with two sites in one of 16 counties when it was first detected in Michigan in 1999 and 2000.

Geographic distribution of Ovavesicula popilliae in the United States and sensitivity of visual diagnosis compared with qPCR detection.

The Japanese beetle (Popillia japonica) is one of the most destructive invasive pests in North America, causing significant economic impact to many fruit crops, turfgrass and the nursery industry. A microsporidian pathogen of Japanese beetle, Ovavesicula popilliae, discovered in 1985, proliferates in the Malpighian tubules of larvae and adults, disrupting waste-removal, mineral filtering, and fluid balance in heavily infected individuals. Most infected larvae do not survive from fall to spring, and egg production by infected females is reduced by 50%. Ovavesicula popilliae is promising as a classical biological control agent for Japanese beetle, but outside of surveys completed in Connecticut and Michigan little is known about its geographic distribution in North America. The objective of this research is to obtain a better understanding of the distribution of O. popilliae in North America. Japanese beetles were collected at 59 locations in a total of 19 different states in the USA for pathogen analysis. Overall, the proportion of Japanese beetle adults infected by O. popilliae was much greater in Michigan, Ohio, Tennessee and four states in the northeastern USA compared with sites located west of the Mississippi River (18.6 ± 13.3% and 0.6 ± 1.2%, respectively). Nucleotide sequences of the gene encoding a small subunit of nuclear ribosomal RNA (ssrDNA), obtained from GenBank for O. popilliae was used to develop a highly specific qPCR test for O. popilliae DNA. A subsample of 110 individual Japanese beetles were visually diagnosed first, then analyzed via qPCR. Visual diagnosis and qPCR detection agreed for 80.9% of the beetles tested. The qPCR assay is more sensitive than visual diagnosis (56 visually positive, 73 qPCR positive), is highly specific for O. popilliae, and will be useful for detecting the pathogen in large batches of beetles, or in beetle frass.

Survival of Japanese beetle, Popillia japonica Newman, larvae in field plots when infected with a microsporidian pathogen, Ovavesicula popilliae.

Japanese beetle, Popillia japonica Newman, is an important invasive pest that causes significant damage to golf courses, blueberries, raspberries, hops and many other crops and ornamentals in the eastern United States. This study was conducted to determine the survival of Ovavesicula popilliae-infected larvae compared with uninfected larvae from October to May. Larvae were collected from two sites, one where O. popilliae was active and one where it had not yet been detected. Larvae were placed into plastic sleeve-pots containing 15 cm-diameter cores of turfgrass with roots and soil intact. Larvae collected from both locations were put into sleeve-pots at both locations to account for soil and site factors. Results of this experiment in both years confirm that Japanese beetle larvae infected with O. popilliae do not survive well from October to May. We estimate that at an epizootic location where the pathogen has been active for several years, at least 76.5% of the Japanese beetle larvae infected in October do not survive until May. When the observed amount of population reduction (27-29%) due to natural pathogen infection of larvae in our field plots is combined with a 50% reduction in eggs produced by infected females as previously reported, annual population declines due to O. popilliae would average 40% (assuming a typical adult female infection rate of 25%). This rate of population reduction is consistent with previous reports of Japanese beetle population decline over a period of several years at O. popilliae epizootic sites.

Traces of Imidacloprid Induce Hormesis as a Stimulatory Conditioned Response of Sweetpotato Whitefly (Hemiptera: Aleyrodidae).

Our purpose is to determine whether extremely low concentrations of imidacloprid (2-8 ppb) typically found in field soil 1-3 yr after a crop is grown using seed with a standard imidacloprid seed-coating could impact the fitness of whiteflies, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae). Results of our experiments indicate that imidacloprid-resistant whitefly larvae feeding on cotton seedlings growing in soil with 8.0 ppb imidacloprid are conditioned so that when the same individuals feed on plants treated with imidacloprid as adults their fitness, measured as fecundity, increases 30-70% compared with individuals that were not primed as larvae. This conditioning hormesis stimulates resistant whiteflies more than susceptible whiteflies, which may contribute to the selection of resistant populations.

Protection of individual ash trees from emerald ash borer (Coleoptera: Buprestidae) with basal soil applications of imidacloprid.

We conducted field trials at five different locations over a period of 6 yr to investigate the efficacy of imidacloprid applied each spring as a basal soil drench for protection against emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Canopy thinning and emerald ash borer larval density were used to evaluate efficacy for 3-4 yr at each location while treatments continued. Test sites included small urban trees (5-15 cm diameter at breast height [dbh]), medium to large (15-65 cm dbh) trees at golf courses, and medium to large street trees. Annual basal drenches with imidacloprid gave complete protection of small ash trees for three years. At three sites where the size of trees ranged from 23 to 37 cm dbh, we successfully protected all ash trees beginning the test with <60% canopy thinning. Regression analysis of data from two sites reveals that tree size explains 46% of the variation in efficacy of imidacloprid drenches. The smallest trees (<30 cm dbh) remained in excellent condition for 3 yr, whereas most of the largest trees (>38 cm dbh) declined to a weakened state and undesirable appearance. The five-fold increase in trunk and branch surface area of ash trees as the tree dbh doubles may account for reduced efficacy on larger trees, and suggests a need to increase treatment rates for larger trees.

Native Vaccinium spp. and Gaylussacia spp. infested by Rhagoletis mendax (Diptera: Tephritidae) in the Great Lakes Region: a potential source of inoculum for infestation of cultivated blueberries.

In this study, we addressed the question of whether or not native stands of blueberry (Vaccinium spp.) and/or huckleberry (Gaylussacia spp.) support populations of blueberry maggot, Rhagoletis mendax Curran, in the Great Lakes region. Infestation of commercial blueberries by the blueberry maggot, R. mendax, is a serious problem in many areas where blueberries are grown. In the past 10-20 yr, commercial bighbush blueberry, Vaccinium corymbosum L., production has expanded into places such as southern Ontario and southern Quebec where blueberry maggot had not previously been reported. In the mid-1990s, isolated infestations of commercial highbush blueberry were reported in southern Ontario. Because R. mendax was not considered endemic to that area, it was widely assumed that the pests had come into the fields via movement from exotic localities. Here we present an alternative hypothesis, that the blueberry maggots infesting newly established highbush plantations are derived from native blueberries growing in the vicinity. To test this hypothesis, in 1997-1999, we sampled potential native hosts for R. mendax (Vaccinium spp. and Gaylussacia spp.) from 31 localities in the Great Lakes region, primarily in Michigan and Ontario. R. mendax was reared from fruits of native hosts collected at four sites in Michigan and one site each in Ontario, Indiana, and Ohio. V. corymbosum was the predominant host infested, with infestation of this host observed at five of the seven sites. However, two huckleberry species [Gaylussacia baccata (Wangenheim) K. Koch, and Gaylussacia dumosa (Andersson) Torrey & Gray] had the highest rates of infestation that we observed (25.4 and 17.6%, respectively). These data represent the first published reports of R. mendax infesting native host plants in the Great Lakes region, and support the hypothesis that infestations observed in commercial fields may have originated from infested native host plants.

Influence of Irrigation and Heterorhabditis bacteriophora on Plant-parasitic Nematodes in Turf.

Daily irrigated, 80% pan replacement, and nonirrigated field plots of Kentucky bluegrass (Poa pratensis L.) were inoculated with a mixture of Steinernema carpocapsae (All strain) and Heterorhabditis bacteriophora (HP-88 strain) in 1988. In 1989, daily irrigated and nonirrigated plots were inoculated with HP-88 alone. The turf and associated soil contained populations of Tylenchorhynchus dubius, T. nudus, Pratylenchus penetrans, Paratylenchus projectus, and Criconemella rustica. In irrigated plots in 1988, population densities of Tylenchorhynchus spp. were lower in plots inoculated with HP-88 plus All compared with that in control plots. The same effect was absent under nonirrigated conditions. In 1989, population densities of Pratylenchus penetrans associated with inoculated turf were lower than those recovered from noninoculated turf in irrigated but not under nonirrigated conditions. Population densities of plant-parasitic nematodes were generally higher in the irrigated compared with the nonirrigated environment.