Kathy L. Flanders

Insect resistance in potatoes: sources, evolutionary relationships, morphological and chemical defenses, and ecogeographical associations.

SummaryThe past 25 years, 1686 potato accessions, representing 100 species in the genus Solanum L., subgenus Potatoe, section Petota, were evaluated for field resistance to one or more of the following insect pests: green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); Colorado potato beetle, Leptinotarsa decemlineata (Say); potato flea beetle, Epitrix cucumeris (Harris); and potato leafhopper, Empoasca fabae (Harris). Accessions highly resistant to green peach aphid were identified within 36 species, to potato aphid within 24 species, to Colorado potato beetle within 10 species, to potato flea beetle within 25 species, and to potato leafhopper within 39 species. Resistance levels were characteristic within Solanum species. Insect resistance appears to be a primitive trait in wild potatoes. Susceptibility was most common in the primitive and cultivated Tuberosa. Insect resistance was also characteristic of the most advanced species. The glycoalkaloid tomatine was associated with field resistance to Colorado potato beetle and potato leafhopper. Other glycoalkaloids were not associated with field resistance at the species level. Dense hairs were associated with resistance to green peach aphid, potato flea beetle, and potato leafhopper. Glandular trichomes were associated with field resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Significant correlations between insect score and altitude of original collection were observed in six of thirteen species. Species from hot and arid areas were associated with resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Species from cool or moist areas tended to be resistant to potato aphid.

Eavesdropping on Insects Hidden in Soil and Interior Structures of Plants

Abstract Accelerometer, electret microphone, and piezoelectric disk acoustic systems were evaluated for their potential to detect hidden insect infestations in soil and interior structures of plants. Coleopteran grubs (the scarabaeids Phyllophaga spp. and Cyclocephala spp.) and the curculionids Diaprepes abbreviatus (L.) and Otiorhynchus sulcatus (F.) weighing 50–300 mg were detected easily in the laboratory and in the field except under extremely windy or noisy conditions. Cephus cinctus Norton (Hymenoptera: Cephidae) larvae weighing 1–12 mg could be detected in small pots of wheat in the laboratory by taking moderate precautions to eliminate background noise. Insect sounds could be distinguished from background noises by differences in frequency and temporal patterns, but insects of similarly sized species could not be distinguished easily from each other. Insect activity was highly variable among individuals and species, although D. abbreviatus grubs tended to be more active than those of O. sulcatus. Tests were done to compare acoustically predicted infestations with the contents of soil samples taken at recording sites. Under laboratory or ideal field conditions, active insects within ≈30 cm were identified with nearly 100% reliability. In field tests under adverse conditions, the reliability decreased to ≈75%. These results indicate that acoustic systems with vibration sensors have considerable potential as activity monitors in the laboratory and as field tools for rapid, nondestructive scouting and mapping of soil insect populations.

Trapping Phyllophaga spp. (Coleoptera: Scarabaeidae: Melolonthinae) in the United States and Canada using sex attractants.

Abstract The sex pheromone of the scarab beetle, Phyllophaga anxia, is a blend of the methyl esters of two amino acids, L-valine and L-isoleucine. A field trapping study was conducted, deploying different blends of the two compounds at 59 locations in the United States and Canada. More than 57,000 males of 61 Phyllophaga species (Coleoptera: Scarabaeidae: Melolonthinae) were captured and identified. Three major findings included: (1) widespread use of the two compounds [of the 147Phyllophaga (sensu stricto) species found in the United States and Canada, males of nearly 40% were captured]; (2) in most species intraspecific male response to the pheromone blends was stable between years and over geography; and (3) an unusual pheromone polymorphism was described from P. anxia. Populations at some locations were captured with L-valine methyl ester alone, whereas populations at other locations were captured with L-isoleucine methyl ester alone. At additional locations, the L-valine methyl ester-responding populations and the L-isoleucine methyl ester-responding populations were both present, producing a bimodal capture curve. In southeastern Massachusetts and in Rhode Island, in the United States, P. anxia males were captured with blends of L-valine methyl ester and L-isoleucine methyl ester. Resumen La feromona sexual del escarabajo, Phyllophaga anxia, es una mezcla de los ésteres metílicos de dos aminoácidos, L-valina y L-isoleucina. Se condujo un estudio de campo usando diferentes mezclas de los dos componentes en 59 sitios de Estados Unidos y Canada. Más de 57,000 machos de 61 especies dePhyllophaga fueron capturados e identificados. Tres de los resultados más importantes incluyen: (1) el extenso uso de los dos componentes [de las 147 especies de Phyllophaga (sensu stricto), en Estados Unidos y Canada, fueron capturados machos de cerca del 40% de ellas.]; (2) para la mayoría de las especies, la respuesta intraespecífica de los machos a las combinaciones de los dos aminoácidos fue consistente entre años diferentes, y en todos los sitios geográficos; y (3) un inusual polymorfismo de la feromona fue descrito para P. anxia. Poblaciones de algunos sitios fueron atrapados sólo con valina, mientras que poblaciones de otros sitios fueron atrapados sólo con isoleucina. También se encontraron sitios donde las poblaciones responden a ambos componentes, valina e isoleucina, produciendo una curva de captura bimodal. En el sureste del estado de Massachusetts y en Rhode Island, en Estados Unidos, machos de P. anxia fueron atrapados en trampas con mezclas de valina e isoleucina.

Biological Control of Alfalfa Weevil in North America

Alfalfa weevil, Hypera postica (Gyllenhall) (Coleoptera: Curculionidae), is of Eurasian origin. This destructive pest of alfalfa (lucerne) was accidentally established in North America on three separate occasions. These introductions are commonly identified in the literature as biological strains: western alfalfa weevil, Egyptian alfalfa weevil (=Hypera brunneipennis Boheman), and eastern alfalfa weevil. Alfalfa weevil has been the target of classical biological control almost since its discovery in North America more than 90 years ago. These efforts have resulted in establishment of at least nine exotic parasitoids and egg predators: Bathyplectes curculionis (Thomson), B. anurus (Thomson) and B. stenostigma (Thomson) (Hymenoptera: Ichneumonidae); Microctonus aethiopoides Loan and M. colesi Drea (Hymenoptera: Braconidae), the latter of undetermined origin; Oomyzus incertus (Ratzenberg) (Hymenoptera: Eulophidae); Dibrachoides dynastes (Forester) and Peridesmia discus (Walker) (Hymenoptera: Pteromalidae); and Anaphes luna (Girault) (Hymenoptera: Mymaridae). A fungal pathogen, Zoophthora phytonomi Arthur (Phycomycetes: Entomophthoraceae), of undetermined origin, is becoming an increasingly important alfalfa weevil mortality factor. Most major USA alfalfa production areas now benefit from a complex of alfalfa weevil biological control agents. Collectively, these agents have effected substantial reduction in the economic importance of alfalfa weevil across the northern USA However, biological agents provide only partial control of alfalfa weevil, and importance of their contribution differs considerably with production area. Still, the benefits achieved, especially from reduced need for insecticides in alfalfa production, mark this as one of the great success stories of classical biological control in North America.

Virulence in Hessian fly (Diptera: Cecidomyiidae) field collections from the southeastern United States to 21 resistance genes in wheat.

ABSTRACT Genetic resistance in wheat, Triticum aestivum L., is the most efficacious method for control of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). However, because of the appearance of new genotypes (biotypes) in response to deployment of resistance, field collections of Hessian fly need to be evaluated on a regular basis to provide breeders and producers information on the efficacy of resistance (R) genes with respect to the genotype composition of Hessian fly in regional areas. We report here on the efficacy of 21 R genes in wheat to field collections of Hessian fly from the southeastern United States. Results documented that of the 21 R genes evaluated only five would provide effective protection of wheat from Hessian fly in the southeastern United States. These genes were H12, H18, H24, H25, and H26. Although not all of the 33 identified R genes were evaluated in the current study, these results indicate that identified genetic resistance to protect wheat from Hessian attack in the southeastern United States is a limited resource. Historically, R genes for Hessian fly resistance in wheat have been deployed as single gene releases. Although this strategy has been successful in the past, we recommend that in the future deployment of combinations of highly effective previously undeployed genes, such as H24 and H26, be considered. Our study also highlights the need to identify new and effective sources of resistance in wheat to Hessian fly if genetic resistance is to continue as a viable option for protection of wheat in the southeastern United States.

Using Haplotypes to Monitor the Migration of Fall Armyworm (Lepidoptera: Noctuidae) Corn-Strain Populations from Texas and Florida

Abstract Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.

Mapping of Soil Insect Infestations Sampled by Excavation and Acoustic Methods

Abstract Geostatistical analysis was used to map traditionally and acoustically sampled populations of soil invertebrates at two different times in a hayfield at Grove Hill, AL, and once in an Auburn, AL, hayfield. The distributions of nearly all the soil invertebrates and their sounds were nonrandom in all three mapping studies. The maps constructed by excavation and acoustic sampling methods were compared by correlating the estimated (kriged) soil invertebrate counts with the estimated (kriged) counts of sounds per minute (pulse rate). Acoustic and traditional estimates were positively correlated in the Auburn study. Kriged estimates for green June beetle grub counts overlapped significantly with kriged estimates of sound pulse rate (R2 = 0.47). Overlap with sound pulse rates increased slightly when other soil organisms were counted along with green June beetle grubs: estimates of sound pulse rates were significantly correlated with counts of all white grubs (R2 = 0.50), all white grubs with earthworms (R2 = 0.52), all white grubs with earthworms and earwigs (R2 = 0.59), and total invertebrates (R2 = 0.59). The correlation between acoustic and traditional estimates was not significant at Grove Hill in either year, possibly because of a lack of experience in signal analysis or because the soil invertebrates may not have generated enough sounds to be detected above the background noise levels. These results suggest that acoustic technology is a promising tool for detecting insect pests in soil, but that further study and additional analysis are needed to improve interpretation of acoustic data obtained in the field.

Geographic distribution of insect resistance in potatoes

Potato germplasm accessions representing 92 Solanum species and associated with known coordinates of latitude, longitude, and elevation were rated for resistance to one or more of the following potato insect pests: green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); Colorado potato beetle, Leptinotarsa decemlineata (Say); potato flea beetle, Epitrix cucumeris (Harris); and potato leafhopper, Empoasca fabae (Harris), in Minnesota field trials (1966–1986). Chi-square tests were used to determine if the proportion of resistant accessions differed from expected among altitude classes, small geographic quadrants (4° latitude by 4° longitude), and larger geographic regions (Mexico-USA, Colombia-Ecuador, Peru, Bolivia, and Argentina). Resistant potatoes were not evenly distributed throughout North and South America. Fourteen quadrants were identified that had greater or fewer resistant accessions than expected. The Mexico-USA potatoes as a group had more resistance than expected to all insects except Colorado potato beetle. Potatoes from Colombia and Ecuador were less resistant than expected to all but green peach aphid. Potatoes from Peru were more resistant than expected to green peach aphid. Potatoes from Bolivia were less resistant than expected to potato aphid, but more resistant than expected to Colorado potato beetle, potato flea beetle, and potato leafhopper. Potatoes from Argentina were more resistant than expected to Colorado potato beetle and green peach aphid, but less resistant than expected to potato aphid and potato leafhopper. Potatoes from North America and collected at or below 2,500 m were more resistant than expected to green peach aphid, Colorado potato beetle and potato flea beetle. Potatoes from South America and elevations greater than 3,000 m were more resistant than expected to green peach aphid and potato aphid and those collected at or below 3,000 m were more resistant than expected to Colorado potato beetle, potato flea beetle and potato leafhopper.

Acoustic Indicators for Mapping Infestation Probabilities of Soil Invertebrates

Abstract Acoustic and traditional excavation methods were used in consecutive summers to conduct two geospatial surveys of distributions of white grubs and other soil invertebrates in two forage fields. Indicator variables were constructed from listener- and computer-based assessments of sounds detected at each recording site and then applied in geostatistical analysis, contingency analysis, and spatial analysis of distance indices (SADIE) of soil invertebrate distributions. Significant relationships were identified between the acoustic indicators and the counts of sound-producing soil invertebrates in a majority of the geostatistical and contingency analyses. Significant clusterings and overall spatial associations were identified also in most of the SADIE analyses. In addition, significant local spatial associations were identified between acoustic indicators and counts of sound-producing soil invertebrates that could be of potential value in selection of specific sites as targets for treatment or for untreated reserves in integrated pest management programs. An example is presented of the relative efficiency of acoustic surveys for targeting of white grub treatments.

Oviposition Site and Food Preference of the Green June Beetle (Coleoptera: Scarabaeidae)

Abstract Relative preferences of green June beetle, Cotinis nitida (L.), adults and grubs for different organic fertilizers were determined in field and laboratory choice experiments. Six organic fertilizer treatments (low rate of broiler litter, high rate of broiler litter, cow manure, hay, Milorganite, or no fertilizer [the control]) were applied to sandy-loam soil and exposed to adults in 2.7 by 3.7 by 2.4-m screen cages. More eggs and larvae were found in pots treated with broiler litter (43%), cow manure (23%), and hay (30%) than in pots treated with Milorganite (4%) or no fertilizer (0%). Orientation preferences of third-instar grubs were tested in Y-tube and satellite olfactometers. Of the five treatments (broiler litter, cow manure, hay, Milorganite, and a blank control), preference was greatest for broiler litter and cow manure, but all organic fertilizer treatments were generally preferred over the blank control. These experiments suggest that use of organic fertilizers may result in higher densities of green June beetle grubs both by attracting the ovipositing females, and by acting as a food attractant for the mobile larvae.