T. A. Royer

Virulence Analysis of Hessian Fly Populations From Texas, Oklahoma, and Kansas

ABSTRACT In recent years, the number of wheat, Triticum aestivum L., fields heavily infested by Hessian fly, Mayetiola destructor (Say), has increased in the Great Plains of the United States. Historically, resistance genes in wheat have been the most efficient means of controlling this insect pest. To determine which resistance genes are still effective in this area, virulence of six Hessian fly populations from Texas, Oklahoma, and Kansas was determined, using the resistance genes H3, H4, H5, H6, H7H8, H9, H10, H11, H12, H13, H16, H17, H18, H21, H22, H23, H24, H25, H26, H31, and Hdic. Five of the tested genes, H13, H21, H25, H26, and Hdic, conferred high levels of resistance (>80% of plants scored resistant) to all tested populations. Resistance levels for other genes varied depending on which Hessian fly population they were tested against. Biotype composition analysis of insects collected directly from wheat fields in Grayson County, TX, revealed that the proportion of individuals within this population virulent to the major resistance genes was highly variable (89% for H6, 58% for H9, 28% for H5, 22% for H26, 15% for H3, 9% for H18, 4% for H21, and 0% for H13). Results also revealed that the percentages of biotypes virulent to specific resistance genes in a given population are highly correlated (r2 = 0.97) with the percentages of susceptible plants in a virulence test. This suggests that virulence assays, which require less time and effort, can be used to approximate biotype composition.

Functional Responses of an Introduced Parasitoid and an Indigenous Parasitoid on Greenbug at Four Temperatures

Abstract Functional responses and superparasitism by the indigenous parasitoid wasp Lysiphlebus testaceipes Cresson (Hymenoptera: Aphidiidae) and the introduced parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) on the greenbug, Schizaphis graminum Rondani (Homoptera: Aphididae), were measured at four temperatures (14, 18, 22, and 26°C) during a 24-h period (12:12 L:D). At each temperature, 5–75 greenbugs were exposed to individual wasp mating pairs for 24 h. At all experimental temperatures, functional responses for both wasps most closely fit the type III model. Instantaneous attack rates (a) for A. colemani were not significantly different among experimental temperatures. However, for L. testaceipes, the estimate for a at 14°C was significantly lower than estimates at 22 and 26°C when data were fit to a type II functional response model. When data were fit to a type III functional response model for L. testaceipes, the estimate for a at 14°C was significantly lower than estimates at 18, 22, and 26°C. Superparasitism for both wasps was often less than expected if superparasitism were a random occurrence, suggesting that these parasitoids may be able to sense when the host has been previously parasitized. A. colemani achieved higher parasitism rates than L. testaceipes at lower temperatures. This observations suggests that A. colemani may be an effective addition to the parasitoid guild for biological control of the greenbug during cooler periods in the Southern Great Plains.

Development and Validation of a Binomial Sequential Sampling Plan for the Greenbug (Homoptera: Aphididae) Infesting Winter Wheat in the Southern Plains

Abstract From 1997 to 1999, Schizaphis graminum (Rondani), intensity (number per tiller) was estimated on 115 occasions from hard red winter wheat fields located throughout the major wheat growing regions of Oklahoma. A total of 32 and 83 fields was sampled during the fall and spring, respectively. The parameters of linear regressions relating the mean number of greenbugs per tiller (m) and the proportion of infested tillers (PT) differed significantly between fall and spring infestations. The PT - m linear model provided a good fit for data on S. graminum for fall and spring infestations at tally thresholds of 0, 1, 2, and 3. A tally threshold (T) represents the number of greenbugs present on a tiller before the tiller is classified as infested by >T greenbugs. A regression model with a tally threshold of 2 was the most precise for classifying S. graminum populations during fall growth of winter wheat because it explained a greater amount of the variation in the PT - m relationship (97%) than models with other tally thresholds. A separate spring model with a tally threshold of 1 was the most precise for classifying S. graminum populations during spring growth of winter wheat. Sequential sampling stop lines based on sequential probability ratio tests were calculated for economic thresholds of 3 or 6 greenbugs per tiller for fall infestations and 6 or 9 greenbugs per tiller for spring infestations. With the newly developed parameters, the average sample number required to classify greenbug populations near economic thresholds (as above or below the economic threshold) varied from 69 to 207. We expect that the sampling plans for greenbugs in winter wheat developed during this study will be efficient and useful tools for consultants and producers in the southern plains.

Developmental Response of Three Geographic Isolates of Lysiphlebus testaceipes (Hymenoptera: Aphididae) to Temperature

Abstract Using greenbugs, Schizaphis graminum (Rondani), as a host, the number of days required for development, survival, and sex ratio (female:male) were studied at five constant temperatures (10, 14, 18, 22, and 26°C) for colonies of Lysiphlebus testaceipes (Cresson) collected in south Texas, central Oklahoma, and central Nebraska. Developmental rate and lower development threshold were described by a linear function and compared among wasp colonies. The temperature thresholds for development from egg to adult for the Nebraska, Oklahoma, and Texas wasp colonies were estimated to be 5.64, 6.61, and 6.42°C, respectively; corresponding degree-day requirements for development were 181.2, 169.5, and 188.0 DD, respectively. No differences in developmental rate or lower development threshold estimates were observed among the wasp colonies. However, adult survival at 10°C was greater in the Nebraska colony, suggesting that there may be variation in the ability of L. testaceipes populations to tolerate and survive cold temperatures.

Sugarcane Aphid (Hemiptera: Aphididae): A New Pest on Sorghum in North America

In 2013, the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), a new invasive pest of sorghum species in North America, was confirmed on sorghum in 4 states and 38 counties in the United States. In 2015, the aphid was reported on sorghum in 17 states and over 400 counties as well as all sorghum-producing regions in Mexico. Ability to overwinter on living annual and perennial hosts in southern sorghum-producing areas and wind-aided movement of alate aphids appear to be the main factors in its impressive geographic spread in North America. Morphological characteristics of the sugarcane aphid include dark tarsi, cornicles, and antennae, allowing easy differentiation from other aphids on the crop. Sugarcane aphid damages sorghum by removing sap and covering plants with honeydew, causing general plant decline and yield loss. Honeydew and sooty mold can disrupt harvesting. The aphid’s high reproductive rate on susceptible sorghum hybrids has resulted in reports of yield loss ranging from 10% to greater than 50%. In response, a combination of research-based data and field observations has supported development of state extension identification, scouting, and treatment guides that aid in initiating insecticide applications to prevent yield losses. Highly efficacious insecticides have been identified and when complemented by weekly scouting and use of thresholds, economic loss by sugarcane aphid can be minimized. Some commercial sorghum hybrids are partially resistant to the aphid, and plant breeders have identified other lines with sugarcane aphid resistance. A very diverse community of predators and parasitoids of sugarcane aphid has been identified, and their value to limit sugarcane aphid population growth is under investigation.

Airborne Multi-Spectral Remote Sensing of Russian Wheat Aphid1 Injury to Wheat

Abstract The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a severe pest of wheat in the High Plains region of the United States. Remote sensing may be an effective way to detect RWA infestations in fields for pest management decision-making purposes. We evaluated an airborne multi-spectral remote sensing system for its ability to differentiate varying levels of injury caused by RWA infestation in winter wheat fields. Two fields located in southeastern Colorado were studied in spring 2004 and two fields located in far western Oklahoma were studied in spring 2005. The proportion of wheat stems damaged by RWA in each field was measured in 20 to 24 3×3-m plots with varying levels of RWA infestation. Prior to sampling plots, multi-spectral imagery was obtained using an SSTCRIS® multi-spectral imaging system mounted NADIR in a Cessna 172 aircraft. The multi-spectral data were compared with the intensity of RWA damage to wheat plants within the plots. Correlations between vegetation indices calculated from the multi-spectral data with the proportion of RWA damaged wheat tillers per plot were negative for all vegetation indices. Regressions of vegetation indices versus the proportion of RWA damaged wheat tillers per plot were usually significant and had negative slopes. However, slopes and intercepts of regressions differed significantly among fields. Any one or a combination of differences in time of day, atmospheric conditions, edaphic factors (e.g. soil type and soil moisture), wheat variety, and possibly other factors could have caused the differences observed in regressions.

Species Composition and Seasonal Occurrence of Phyllophaga (Coleoptera: Scarabaeidae) Infesting Intensely Managed Bermudagrass in Oklahoma

Abstract Larvae of Phyllophaga spp. (Coleoptera: Scarabaeidae) are important turfgrass pests in many regions of the United States. However, not all of the species associated with turfgrass are known, including species most likely to be of economic concern in Oklahoma turfgrasses, especially Bermuda grass. This study documented the species composition and seasonal occurrence of Phyllophaga associated with high maintenance Bermuda grass turf in Oklahoma over a 2-yr period. In 2005 and 2006, adult Phyllophaga spp. were collected with blacklight traps from selected golf courses throughout Oklahoma. Phyllophaga larvae were obtained from Bermuda grass stands at selected sod production facilities adjacent to or near the light traps. We collected 20 species of Phyllophaga beetles in light traps, and nine species of Phyllophaga larvae from turfgrass. Peak flight periods for most species occurred in May and June, but some were captured as early as mid-April and others as late as September. The cytochrome c oxidase I (COI) gene from adults and larvae was amplified using polymerase chain reaction, sequenced, and then used to compare larval DNA against DNA from identified adults. These results confirmed the validity of using COI sequences to identify species of some Phyllophaga larvae. The identifications will aid in optimizing the timing of insecticide applications against Phyllophaga white grubs as discussed.

Molecular Markers for Species Identification of Hessian Fly Males Caught on Sticky Pheromone Traps

ABSTRACT Pheromone traps have been widely used to monitor insect population activity. However, sticky pheromone traps for the Hessian fly (Mayetiola destructor), one of the most destructive pests of wheat, have been used only in recent years. Hessian fly male adults are small and fragile, and preserving specimens during sorting of sticky pheromone traps is a challenge when intact specimens are often required to visually distinguish them from related insects such as fungus gnats. In this study, we have established a quick and reliable method based on polymerase chain reaction markers to correctly distinguish Hessian fly males from other closely related insects. Two Hessian fly-specific markers were established, one based on the trypsin gene MDP-10 and the other based on a gene encoding the salivary gland protein SSGP31-5. Both markers provided >98% identification success of 110 Hessian fly samples prepared from single insects. The method should provide a useful tool to allow for identification of Hessian fly individuals on sticky pheromone traps or in other situations when Hessian fly eggs, larvae, pupae, and adults are difficult to distinguish from other insects.

Survival and growth of foodborne pathogens in pesticide solutions routinely used in leafy green vegetables and tomato production

BACKGROUND The consumption of fresh produce has increased tremendously in the past few years as have outbreaks of foodborne illnesses associated with these commodities. Pesticides routinely used in crop production could influence the outcomes of foodborne pathogen contamination of fresh produce. Experiments were performed to determine the effects of pesticides on the survival and growth characteristics of Escherichia coli O157:H7 and Salmonella spp. Eight commercial fungicides and insecticides commonly used for disease and insect pest control on leafy green vegetables and tomatoes were evaluated. RESULTS Among the pesticides tested, copper hydroxide, acetamiprid, cypermethrin and permethrin were found to be significantly (P < 0.05) inhibitory to pathogens while no effect was observed for chlorothalonil, flonicamid and methoxyfenozide. At the highest concentration tested (2.66%), azoxystrobin had a significant (P < 0.05) stimulatory effect on the growth of E. coli O157:H7 after 24 h incubation. The results indicated that some pesticides can stimulate the growth of human pathogens if contaminated water is used in their preparation, whereas others were likely to inhibit or reduce pathogen populations. CONCLUSION This information is helpful in mitigating the risk of microbial contamination in fresh produce, which is critical to public health and safety.

Transformations of Count Data for Tests of Interaction in Factorial and Split-Plot Experiments

In applied entomological experiments, when the response is a count-type variable, certain transformation remedies such as the square root, logarithm (log), or rank transformation are often used to normalize data before analysis of variance. In this study, we examine the usefulness of these transformations by reanalyzing field-collected data from a split-plot experiment and by performing a more comprehensive simulation study of factorial and split-plot experiments. For field-collected data, significant interactions were dependent upon the type of transformation. For the simulation study, Poisson distributed errors were used for a 2 by 2 factorial arrangement, in both randomized complete block and split-plot settings. Various sizes of main effects were induced, and type I error rates and powers of the tests for interaction were examined for the raw response values, log-, square root-, and rank-transformed responses. The aligned rank transformation also was investigated because it has been shown to perform well in testing interactions in factorial arrangements. We found that for testing interactions, the untransformed response and the aligned rank response performed best (preserved nominal type I error rates), whereas the other transformations had inflated error rates when main effects were present. No evaluations of the tests for main effects or simple effects have been conducted. Potentially these transformations will still be necessary when performing these tests.