Gabor Neumann

Horseweed (Conyza canadensis) seed collected in the planetary boundary layer

Abstract Horseweed is a winter or summer annual plant, native to North America and distributed worldwide in temperate climates. This plant is considered an important agricultural weed because it can reduce agricultural yields by 90% at high densities and becomes problematic under low-tillage agriculture. Seed production is robust with an estimated 200,000 seeds produced per plant, and seed dispersal is wind-assisted. The confirmation of glyphosate-resistant horseweed in Delaware in 2001 and the rapid spread of the resistant biotype, currently covering more than 44,000 ha, has necessitated a change in the discussion about weed dispersal. Large radio-controlled airplanes were used to sample the lower atmosphere for the presence of horseweed seeds during a 3-d period in early September 2005 in southern Delaware. The collection of multiple seeds at heights ranging from 41 to 140 m above ground level strongly suggests that horseweed seeds are entering the Planetary Boundary Layer (PBL) of the atmosphere, where long-ranged transport of aerial biota frequently occurs. With wind speeds in the PBL frequently exceeding 20 m s−1, seed dispersal can easily exceed 500 km in a single dispersal event. Nomenclature: Horseweed, Conyza canadensis (L.) Cronq.

Multiple-Species Natural Enemy Approach for Biological Control of Alfalfa Snout Beetle (Coleoptera: Curculionidae) Using Entomopathogenic Nematodes

Abstract Multiple-species natural enemy approach for the biological control of the alfalfa snout beetle, Otiorhynchus ligustici (L.) (Coleoptera: Curculionidae), was compared with using single-species of natural enemies in the alfalfa ecosystem by using entomopathogenic nematodes with different dispersal and foraging behaviors. Steinernema carpocapsae NY001 (ambush nematode), Heterorhabditis bacteriophora Oswego (cruiser nematode), and Steinernema feltiae Valko (intermediate nematode) were applied in single-species, two-species combinations, and one three-species combination treatments at 2.5 × 109 infective juveniles per hectare. All nematode species persisted for a full year (357 d). S. carpocapsae NY001 protected the plants from root-feeding damage better than H. bacteriophora Oswego but allowed for higher larval survival than all other nematode treatments. S. feltiae Valko protected the plants better than H. bacteriophora Oswego and controlled alfalfa snout beetle larvae better than S. carpocapsae NY001. H. bacteriophora Oswego allowed for similar root damage compared with control plots but reduced larval populations better than S. carpocapsae NY001. The combination of S. carpocapsae NY001 and H. bacteriophora Oswego provided significantly better protection for the plants than the control (unlike H. bacteriophora Oswego alone) and reduced host larva survival more than S. carpocapsae NY001 alone. The combination S. feltiae Valko and H. bacteriophora Oswego could not be statistically separated from the performance of S. feltiae Valko applied alone.

Molecular Markers Discriminate Closely Related Species Encarsia diaspidicola and Encarsia berlesei (Hymenoptera: Aphelinidae): Biocontrol Candidate Agents for White Peach Scale in Hawaii

ABSTRACT We genetically characterized Encarsia diapsidicola Silvestri and Encarsia berlesei Howard (Hymenoptera: Aphelinidae) by two molecular methods: phylogenetic analysis of the cytochrome oxidase subunit I gene (COI) and intersimple sequence repeat-polymerase chain reaction (ISSR-PCR) DNA fingerprinting. These two closely related endoparasitoids are candidate biological control agents for the white peach scale, Pseudaulacaspis pentagona Targioni-Tozetti (Hemiptera: Diaspididae), in Hawaii. We developed species-specific COI molecular markers that discriminated the two species, and we tested the utility of the E. diaspidicola-specific COI marker to detect parasitism of white peach scale. The COI sequence data uncovered 46-bp differences between the two Encarsia spp. The level of COI genetic divergence between the two species was 9.7%, and the two clustered into their own clade on a parismonious phylogram. ISSR-PCR readily discriminated the two Encarsia spp. because each was observed with fixed species-specific banding patterns. The COI molecular markers were specific for each species because cross-reactivity was not observed with nontarget species. The E. diaspidicola-specific COI markers were successful at detecting parasitism of white peach scale by E. diaspidicola by 24 h. Both molecular marker types successfully discriminated the two Encarsia spp., whereas the COI markers will be useful as tools to assess levels of parasitism in the field and to study competitive interactions between parasitoids.

Interspecific Interactions Among Three Entomopathogenic Nematodes, Steinernema carpocapsae Weiser, S. feltiae Filipjev, and Heterorhabditis bacteriophora Poinar, with Different Foraging Strategies for Hosts in Multipiece Sand Columns

Abstract Multipiece sand columns were used to study the dispersal and interspecific interactions at different depths among three nematode species with different foraging strategies. Steinernema carpocapsae Weiser, strain ‘NY001’, an ambusher nematode, Heterorhabditis bacteriophora Poinar, strain ‘Oswego’, a cruiser nematode, and S. feltiae Filipjev, strain ‘Valko’, an intermediate nematode were applied to multipiece sand columns in single-, two-, and three-species combinations 7 d before host introduction. The effect of interspecific interactions on nematode performance was estimated by comparing the percent host infected by a nematode species at specified depths when applied alone to the performance of the same nematode species when applied in combination with other nematode species. All three nematodes were capable of infecting some proportion of hosts down to the 32.5-cm depth when applied singly. In nematode combinations, interspecific competition occurred, but negative impacts of competition on nematode performance were not observed at all depths. S. carpocapsae ‘NY001’ was only affected negatively in the surface layer when combined in the three-species combination but not in the two-species combinations. S. feltiae ‘Valko’ was positively affected by the presence of S. carpocapsae ‘NY001’ at 26- and 32.5-cm depths in the two-species combination. In the presence of S. carpocapsae ‘NY001’ and S. carpocapsae ‘NY001’ + S. feltiae ‘Valko’, the performance of H. bacteriophora ‘Oswego’ was positively affected at 32.5-cm depth. The results suggest spatial niche separation of nematodes with different foraging and dispersal strategies that may contribute to coexistence in the field.