Robert J. O'Neil

Potential Winter Hosts of Soybean Aphid

Abstract Species and cultivars of the genus Rhamnus and related genera in the Rhamnaceae were tested for their suitability as overwintering hosts of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). The tests were carried out in outdoor cages during the fall through spring of 2002–2003 and 2003–2004. Response of the aphid to the hosts varied from successful overwintering on three Rhamnus hosts to complete rejection of all species in other genera. Fall migrants (gynoparae), egg layers (oviparae), males and eggs were found on the exotic Rhamnus cathartica (L.), and native Rhamnus alnifolia L’Héritier and Rhamnus lanceolata Pursh. In the spring eggs hatched, colonies developed and spring migrants were produced on these hosts. Other Rhamnus spp. were accepted by fall migrants and some level of colony development occurred, but no overwintering eggs were deposited on them. The phenology of the production of the various morphs, egg deposition, and egg hatch are documented on the suitable hosts. The implications of our findings on soybean aphid ecology and management are discussed.

Tests of Suitability of Overwintering Hosts of Aphis glycines: Identification of a New Host Association with Rhamnus alnifolia L’Héritier

Abstract Eleven species from the family Rhamnaceae, including both species exotic and native to North America, were tested for their acceptability to the fall migrants of the soybean aphid, Aphis glycines Matsumura. Two species, Rhamnus cathartica L. and Rhamnus alnifolia L’Héritier were accepted and had overwintering eggs deposited on them. Eggs survived the winter, and colonies developed on both hosts in the spring. R. alnifolia is a new overwintering host for the soybean aphid.

Applications of sugar solutions to maize, and the impact of natural enemies on fall armyworm

Abstract Natural enemy abundance and impact on fall armyworm, Spodoptera frugiperda (J. E. Smith), populations were compared in sugar-treated and water-treated maize fields in Honduras. Counts of natural enemy abundance were made immediately after and also 1 week following sugar applications. Higher numbers of natural enemies were found in sugar-treated maize than in maize treated with water alone. The most abundant species were Solenopsis geminata (F.) (Hymenoptera; Formicidae), Lespesia archippivora (Riley) (Diptera; Tachinidae) and Doru taeniatum (Dorhn) (Dermaptera; Forficulidae). Of these species, S. geminata and L. archippivora showed consistently higher numbers in sugar-treated maize than in water-trated maize. Coccinellids were also consistently concentrated in sugar-treated maize, although they were not as abundant as either S. geminata and L. archippivora . In sugartreated maize, average leaf area damaged by fall armyworm was reduced by 35% and average fall armyworm infestation rates were 18% lo...

Soybean Plant Stage and Population Growth of Soybean Aphid

Abstract The soybean aphid, Aphis glycines Matsumura, is a newly invasive species of aphid in North America. Previous studies disagree as to whether soybean, Glycine max (L.) Merr., plant stage has an impact on aphid intrinsic rate of increase. Therefore, the growth rate of soybean aphids on soybean plants of different stages was examined at two different scales in the field. A planting date experiment was used to measure the population growth of soybean aphids on plants of different stages. Clip-cages were used to measure life history characteristics of individual aphids on plants of different stages. No differences were found in the population growth or dynamics of soybean aphids in the planting date experiment. The life history characteristics of individual aphids also showed no significant difference when feeding on different growth stages of soybean plants. The impact of these findings on soybean aphid management is discussed and the possible reasons why the results differ from previous estimates of the aphid growth–plant stage relationship are considered.

Symposium: Insect Behavioral Ecology--'86: Adaptations of Arthropod Predators to Agricultural Systems

Agricultural systems are habitat islands that are colonized by generalist arthropod predators. How predators find prey and apportion captured prey energy into competing physiologic demands are central adaptations that provide for the subsistence of predator populations. We have found that predators in soybeans maintain a low, consistent rate of predation, and compensate for changes in leaf area, the searching universe of predators in soybeans. Predators maintain survivorship but not reproductive effort at low prey inputs suggesting physiologic trade-offs at low prey densities. We find a major discrepancy between functional response theory and our field results, and suggest an alternative framework for study of predation under field-realistic conditions.

Spatial Distribution of Aphis glycines (Hemiptera: Aphididae): A Summary of the Suction Trap Network

ABSTRACT The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an economically important pest of soybean, Glycine max (L.) Merrill, in the United States. Phenological information of A. glycines is limited; specifically, little is known about factors guiding migrating aphids and potential impacts of long distance flights on local population dynamics. Increasing our understanding of A. glycines population dynamics may improve predictions of A. glycines outbreaks and improve management efforts. In 2005 a suction trap network was established in seven Midwest states to monitor the occurrence of alates. By 2006, this network expanded to 10 states and consisted of 42 traps. The goal of the STN was to monitor movement of A. glycines from their overwintering host Rhamnus spp. to soybean in spring, movement among soybean fields during summer, and emigration from soybean to Rhamnus in fall. The objective of this study was to infer movement patterns of A. glycines on a regional scale based on trap captures, and determine the suitability of certain statistical methods for future analyses. Overall, alates were not commonly collected in suction traps until June. The most alates were collected during a 3-wk period in the summer (late July to mid-August), followed by the fall, with a peak capture period during the last 2 wk of September. Alate captures were positively correlated with latitude, a pattern consistent with the distribution of Rhamnus in the United States, suggesting that more southern regions are infested by immigrants from the north.

Host plant suitability of Rhamnaceae for soybean aphid (Homoptera: Aphididae)

Abstract We tested host plant suitability of 10 taxa in the Rhamnaceae for successful preoverwintering development of soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae). In the laboratory, we offered each gynopara and ovipara a single member of each putative host plant and measured survivorship and fecundity. Rhamnus cathartica L. and Rhamnus alnifolia L’Héritier were confirmed as suitable host plants, and eight other taxa were confirmed as unsuitable. This study supports results from a companion study in which soybean aphids were offered multiple members of the Rhamnaceae in field cages. Of the two suitable host plants, R. cathartica supported greater longevity and oviposition rates in oviparae. The importance of R. cathartica as an overwintering host to soybean aphid ecology and management is discussed.

Indiana Soybean System Model (ISSM): I. Crop model evaluation

Abstract A soybean crop model, SOYGRO version 5.41, satisfactorily simulates soybean growth, development and yield under Indiana conditions, following the calibration of varietal coefficients and the use of water retention values to approximate soil water limits. Century 84 (MG II) and Williams 82 (MG III) soybeans were grown at two locations during 1985–1989 to provide crop growth and yield data for model calibration and validation. Model predictions tracked the observed trends in soybean yield over the years, and the patterns of crop growth and development through the season. Predicted values of yields, leaf area index and other crop growth indicators were mostly within one standard error (SE) of observed means in 1988 (severe drought) and 1989. Simulation experiments showed that yield potential at Bedford (southern Indiana) was higher than at Throckmorton (central Indiana) for all planting dates (10 and 25 May and 5 June). Century 84 has a slight yield advantage over Williams 82 for 10 May planting. If 1988 drought is excluded, this yield advantages is stochastically dominant. For late planting (5 June), the reverse is true (Williams 82 yielded more). There was no difference for 25 May planting. Using Duncans multiple range test groupings, a set of typical weather years were obtained. This grouping, based on crop yield potential, will be useful in simulation analysis for pest management strategy evaluation.

Potential of Suction Traps As a Monitoring Tool for Aphis glycines (Hemiptera: Aphididae) in Soybean Fields

ABSTRACT The current study evaluated the potential of using counts of winged adults captured in suction traps to forecast the local abundance of soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in soybean, Glycine max (L.) Merr., fields. The abundance of aphids was evaluated weekly by sampling plants in four to 11 soybean fields and recording the number of aphids in suction traps between 2006 and 2008 in four counties in Indiana and Illinois. Fields in each county were located within 10 km of their respective suction trap, which allowed us to evaluate the relation between aphid abundance on soybean plants and in suction traps at the county level. Migrant soybean aphids caught in suction traps exhibited distinct seasonal trends each year: in 2006, trapped migrants consisted predominantly of individuals dispersing from soybean to buckthorn (Rhamnus sp.); in 2007, in contrast, the majority of trapped migrants were apparently individuals dispersing among soybean fields. The cumulative number of aphids captured in suction traps was positively related to aphid densities on soybean plants. However, the utility of suction traps as a monitoring tool may be limited by the variation in temporal patterns observed in suction traps and on soybean plants each year, and the spatial variation in aphid abundance among soybean fields within a county.

Voracity and prey preference of insidious flower bug (hemiptera: anthocoridae) for immature stages of soybean aphid (hemiptera: aphididae) and soybean thrips (thysanoptera: thripidae).

Abstract The generalist predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid, Aphis glycines Matsumura. Soybean thrips, Neohydatothrips variabilis (Beach), serve as an important prey resource for O. insidiosus in soybeans, sustaining the predator’s population before the arrival of the soybean aphid. Although generalist predators can forage on a broad range of prey, they may show distinct preferences for particular prey, attacking prey at levels disproportionate to their relative numbers. To assess the preference of O. insidiosus for soybean aphid and soybean thrips, attack rates of nymphal and adult O. insidiosus were measured in the laboratory. For both adults and nymphs, the number of prey attacked increased as more prey were provided. For nymphs, the total number of prey attacked increased as the predator matured. In general, the number of prey attacked by adult predators was relatively constant as the predator aged. Both O. insidiosus nymphs and adults displayed a preference for soybean thrips, by disproportionately attacking soybean thrips over soybean aphid regardless of the relative densities of the two prey. We discuss implications of this preference on O. insidiosus life history characteristics and the potential impact on O. insidiosus–prey dynamics in the field.