Antimicrobial Nectar Inhibits a Florally Transmitted Pathogen of a Wild Cucurbita Pepo (Cucurbitaceae) (pdf)
Authors: Miruna A. Sasu, Kelly L. Wall, and Andrew G. Stephenson, Department of Biology, Center for Chemical Ecology, and Center for Infectious Disease Dynamics, The Pennsylvania State University, PA
Journal: American Journal of Botany, 97(6): 1025-1030 (2010)
Premise of the study: Floral nectars of many species contain antimicrobial chemicals, but their function in nectar is subject to debate. Previously, we have shown that Erwinia tracheiphila, the causative agent of bacterial wilt disease in cucurbits, can be transmitted via the floral nectaries.
Methods: We used a disk diffusion assay (DDA) to determine the antimicrobial effects of nectar from a wild gourd on lawns of Escherichia coli and Erwinia tracheiphila. We also used E. tracheiphila to inoculate flowers of wild gourd plants, with and without nectar.
Key results: The DDA showed that paper disks saturated with 10 μL of nectar inhibited the growth of E. coli on a larger area of the lawn than 40% glucose but a smaller area than 5% ampicillin for 12 h. On lawns of E. tracheiphila, nectar inhibited growth on a larger area than glucose for 24 h and there were no significant differences between ampicillin and nectar for 12 h. A significantly larger proportion of the plants inoculated via flowers without nectar contracted wilt disease than plants with nectar.
Conclusions: These findings indicate that nectar reduces transmission of E. tracheiphila via the nectaries and reveal the potential for florally transmitted pathogens to influence the evolution of floral traits.
Landscape diveristy influences ladybeetle abundance (pdf)
Authors: M. M. Gardiner, D. A. Landis, C. Gratton, N. Schmidt, M. O'Neal, E. Mueller, J. Chacon, G. E. Heimpel and C. D. DiFonzo
Journal: Diversity and Distributions, 15, 554:564 (2009)
Aim: Coccinellid beetles are important predators that contribute to pest suppression in agricultural landscapes. Since the introduction of the exotic coccinellids Coccinella septempunctata L. and Harmonia axyridis Pallas into the USA, several studies have reported a decline of native Coccinellidae in agroecosystems. We aimed to investigate the influence of landscape composition on native and exotic coccinellid abundance within soybean fields.
Location: Iowa, Michigan, Minnesota and Wisconsin.
Methods: As part of a 2-year study (2005-06) on the biological control of the soybean aphid, Aphis glycines Matsumura, we examined coccinellid communities in 33 soybean fields using yellow sticky card traps. Landscape heterogeneity and composition were measured at multiple spatial scales ranging 1-3.5 km from focal soybean fields where coccinellid sampling took place.
Results: Exotic species made up 90% of the total coccinellid community in Michigan soybean fields followed by Wisconsin (84%), Minnesota (66%) and Iowa (57%). Harmonia axyridis was the dominant exotic coccinellid in all states comprising 45-62% of the total coccinellid community, followed by C. septempunctata (13-30%). Two additional exotic species, Hippodamia variegate (Goeze) and Propylea quatuordecimpunctata (L.) were also found in the region. Overall, the most abundant native coccinellid was Hippodamia convergens Guerin- Meneville; however, its abundance varied across the region, comprising 0% (Michigan) to 28% (Iowa) of the total coccinellid community. Landscape structure significantly influenced the composition of coccinellid communities in soybean agroecosystems. We found that native coccinellids were most abundant in low-diversity landscapes with an abundance of grassland habitat while exotic coccinellids were associated with the abundance of forested habitats.
Main conclusion: We propose that grassland dominated landscapes with low structural diversity and low amounts of forested habitat may be resistant to exotic coccinellid build-up, particularly H. axyridis and therefore represent landscapescale refuges for native coccinellid biodiversity.
Landscape diversity enhances biological control of an introduced crop pest in the north-central USA (pdf)
Authors: M. M. Gardiner,D. A . Landis, C. Gratton, C. D. Difonzo, M. O'Neal, J. M. Chacon, M. T. Wayo, N. P. Schmidt, E. E. Mueller, and G. E. Heimpel
Journal: Ecological Applications, 19(1), 143:154 (2009)
Abstract: Arthropod predators and parasitoids provide valuable ecosystem services in agricultural crops by suppressing populations of insect herbivores. Many natural enemies are influenced by non-crop habitat surrounding agricultural fields, and understanding if, and at what scales, land use patterns influence natural enemies is essential to predicting how landscape alters biological control services. Here we focus on biological control of soybean aphid, Aphis glycines Matumura, a specialist crop pest recently introduced to the north-central United States. We measured the amount of biological control service supplied to soybean in 26 replicate fields across Michigan, Wisconsin, Iowa, and Minnesota across two years (2005- 2006). We measured the impact of natural enemies by experimentally excluding or allowing access to soybean aphid infested plants and comparing aphid population growth over 14 days.
We also monitored aphid and natural enemy populations at large in each field. Predators, principally coccinellid beetles, dominated the natural enemy community of soybean in both years. In the absence of aphid predators, A. glycines increased significantly, with 5.3-fold higher aphid populations on plants in exclusion cages vs. the open field after 14 days. We calculated a biological control services index (BSI) based on relative suppression of aphid populations and related it to landscape diversity and composition at multiple spatial scales surrounding each site. We found that BSI values increased with landscape diversity, measured as Simpson's D. Landscapes dominated by corn and soybean fields provided less biocontrol service to soybean compared with landscapes with an abundance of crop and non-crop habitats. The abundance of Coccinellidae was related to landscape composition, with beetles being more abundant in landscapes with an abundance of forest and grassland compared with landscapes dominated by agricultural crops. Landscape diversity and composition at a scale of 1.5 km surrounding the focal field explained the greatest proportion of the variation in BSI and Coccinellidae abundance. This study indicates that natural enemies provide a regionally important ecosystem service by suppressing a key soybean pest, reducing the need for insecticide applications. Furthermore, it suggests that management to maintain or enhance landscape diversity has the potential to stabilize or increase biocontrol services.
An Inexpensive Immunomarking Technique for Studying Movement Patterns of Naturally Occurring Insect Populations (pdf)
Authors: Vincent P. Jones, James R. Hagler, Jay F. Brunner, Callie C. Baker and Tawnee D. Wilburn
Journal: Environmental Entomology, 35(4): 827-836 (2006)
Abstract: An immunomarking system useful for determining insect movement patterns was developed that allows the marking of naturally occurring populations of insects within large areas with inexpensive and readily available proteins that can be applied using standard spray equipment. Enzyme-linked immunosorbent assay (ELISA) protocols were developed to detect chicken egg albumin (as egg whites), bovine casein (as cows' milk), and soy protein (as soy milk) at levels ≤30 ppb. Field applications showed that all of the proteins were stable and detectable at high levels on apple leaves at least 19 d after application. When adult pear psylla (Cacopsylla pyricola Foerster, Homoptera: Psyllidae) walked across apple leaves with _eld-aged residues of the marker proteins plus either Sylgard 309, EDTA, or both, they acquired the mark over the 19-d test period an average of 78.9, 19.4, and 2.1% of the time for egg whites, milk, and soy milk, respectively. Two _eld applications of the three markers were applied to an apple orchard during the first generation flight of codling moth (Cydia pomonella L., Lepidoptera: Tortricidae).Wefound that 46.5% of moths captured within a 2.8-ha area (including 1.6-ha surrounding the treated areas) tested positive for at least one of the three proteins. The marker systems developed cost between $0.12 and $0.26liter versus older immunomarkers (using purified vertebrate IgG) that cost roughly $500/liter.
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