Brian G. Rector

Identification of molecular markers linked to quantitative trait loci for soybean resistance to corn earworm

Abstract One hundred and thirty nine restriction fragment length polymorphisms (RFLPs) were used to construct a soybean (Glycine max L. Merr.) genetic linkage map and to identify quantitative trait loci (QTLs) associated with resistance to corn earworm (Helicoverpa zea Boddie) in a population of 103 F2-derived lines from a cross of ‘Cobb’ (susceptible) and PI229358 (resistant). The genetic linkage map consisted of 128 markers which converged onto 30 linkage groups covering approximately 1325 cM. There were 11 unlinked markers. The F2-derived lines and the two parents were grown in the field under a plastic mesh cage near Athens, Ga., in 1995. The plants were artificially infested with corn earworm and evaluated for the amount of defoliation. Using interval-mapping analysis for linked markers and single-factor analysis of variance (ANOVA), markers were tested for an association with resistance. One major and two minor QTLs for resistance were identified in this population. The PI229358 allele contributed insect resistance at all three QTLs. The major QTL is linked to the RFLP marker A584 on linkage group (LG) ‘M’ of the USDA/Iowa State University public soybean genetic map. It accounts for 37% of the total variation for resistance in this cross. The minor QTLs are linked to the RFLP markers R249 (LG ‘H’) and Bng047 (LG ‘D1’). These markers explain 16% and 10% of variation, respectively. The heritability (h2) for resistance was estimated as 64% in this population.

Proteomic analysis of novel Cry1Ac binding proteins in Helicoverpa armigera (Hübner).

Aminopeptidase N (APN) and cadherin-like proteins have been previously identified as Cry1Ac-binding proteins in Helicoverpa armigera (Hübner). In this study, a proteomic approach was used to identify novel Cry1Ac-binding proteins in H. armigera. Brush border membrane vesicles (BBMV) of H. armigera were extracted and separated by two-dimensional gel electrophoresis (2-DE). Cry1Ac-binding proteins were detected using antisera against Cry1Ac. Peptide mass fingerprinting (PMF) was used to identify Cry1Ac-binding proteins. In total, four proteins were identified as candidate Cry1Ac-binding proteins in H. armigera: vacuolar ATP synthase (V-ATPase) subunit B, actin, heat shock cognate protein (HSCP), and a novel protein.

Quantitative trait loci for maysin synthesis in maize (Zea mays L.) lines selected for high silk maysin content

Maysin is a naturally occurring C-glycosyl flavone found in maize (Zea mays L.) silk tissue that confers resistance to corn earworm (Helicoverpa zea, Boddie). Recently, two new maize populations were derived for high silk maysin. The two populations were named the exotic populations of maize (EPM) and the southern inbreds of maize (SIM). Quantitative trait locus (QTL) analysis was employed to determine which loci were responsible for elevated maysin levels in inbred lines derived from the EPM and SIM populations. The candidate genes consistent with QTL position included the p (pericarp color), c2 (colorless2), whp1 (white pollen1) and in1 (intensifier1) loci. The role of these loci in controlling high maysin levels in silks was tested by expression analysis and use of the loci as genetic markers onto the QTL populations. These studies support p, c2 and whp1, but not in1, as loci controlling maysin. Through this study, we determined that the p locus regulates whp1 transcription and that increased maysin in these inbred lines was primarily due to alleles at both structural and regulatory loci promoting increased flux through the flavone pathway by increasing chalcone synthase activity.

Divergent Host Acceptance Behavior Suggests Host Specialization in Populations of the Polyphagous Mite Abacarus hystrix (Acari: Prostigmata: Eriophyidae)

Abstract For phytophagous arthropods, host acceptance behavior is a key character responsible for host plant specialization. The grain rust mite, Abacarus hystrix (Nalepa), is an obligately phytophagous, polyphagous eriophyid mite recorded from at least 70 grass species. In this study, the hypothesis that two host populations of this mite (one collected from quackgrass and the other from ryegrass) are highly host-specific was tested using behavioral data. For this purpose, female behavior when exposed to familiar and novel host plants was observed in no-choice cross experiments. Altogether, 13 variables were used to describe mite behavior. Data were subjected to principal component analysis, and host acceptance behavior was subsequently tested with generalized estimating equations (GEE). Distinct variation in female behavior between familiar and novel hosts was observed. Females from neither population accepted novel hosts. This was recorded as significant differences in the occupation of and overall activity on particular plant parts. On their familiar host, females were not active and showed little tendency to move. On novel hosts females were more active and mobile, spending more time walking, running, and climbing on the whole plant surface and showing a tendency to disperse. Other differences in behavior between studied populations were also observed. Thus, the results suggest that mites of these two studied populations (1) differ in their behaviors during plant exploitation and (2) can quickly distinguish between their familiar host and an unfamiliar host used by a conspecific. These findings support the hypothesis of narrow host specialization of ryegrass and quackgrass populations of this highly polyphagous species.

Cryptic speciation in the Acari: a function of species lifestyles or our ability to separate species?

There are approximately 55,000 described Acari species, accounting for almost half of all known Arachnida species, but total estimated Acari diversity is reckoned to be far greater. One important source of currently hidden Acari diversity is cryptic speciation, which poses challenges to taxonomists documenting biodiversity assessment as well as to researchers in medicine and agriculture. In this review, we revisit the subject of biodiversity in the Acari and investigate what is currently known about cryptic species within this group. Based on a thorough literature search, we show that the probability of occurrence of cryptic species is mainly related to the number of attempts made to detect them. The use of, both, DNA tools and bioassays significantly increased the probability of cryptic species detection. We did not confirm the generally-accepted idea that species lifestyle (i.e. free-living vs. symbiotic) affects the number of cryptic species. To increase detection of cryptic lineages and to understand the processes leading to cryptic speciation in Acari, integrative approaches including multivariate morphometrics, molecular tools, crossing, ecological assays, intensive sampling, and experimental evolution are recommended. We conclude that there is a demonstrable need for future investigations focusing on potentially hidden mite and tick species and addressing evolutionary mechanisms behind cryptic speciation within Acari.

Within-day variation in continuous hive weight data as a measure of honey bee colony activity*

Hourly weight data, from 4 honey bee hives placed on balances linked to dataloggers, were divided into two independent parts: (1) daily running average and (2) detrended weights, obtained by subtracting the running average from raw data. Weekly changes in running average weights, WCRAW, were correlated with food store changes but not adult or brood weights. Detrended weights showed daily fluctuation due to water and foraging bee movement and were modeled using sine curves, which fit all weekly subsets. Adult and brood populations, measured independently, were expressed as colony consumption rates via published per capita rates, and those consumption rates were correlated with sine amplitudes. Amplitudes were more sensitive to hive activity than WCRAW and unlike WCRAW detected high activity when foraging success was masked by high consumption Estimating food store changes with WCRAW and colony consumption with amplitudes reveals hive growth and activity without disturbing bees.ZusammenfassungWir analysierten hier wie stündlich aufgenommene Gewichtsdaten Hinweise auf dynamische Veränderungen in Honigbienenvölkern liefern können. Das Wiegen von Völkern ist zwar eine schnelle und eingriffsfreie Massnahme, andererseits aber muss in regelmässigen Abständen und mit ausreichender Präzision gewogen werden, wenn man zuverlässige Informationen über Stockaktivität und Volksdynamik erhalten will. In dieser Studie wurden Bienenvölker in 2005 und im Frühjar 2006 in zweiwöchigen Abständen inspiziert. Die einzelnen Waben wurden gewogen und das Gewicht der verdeckelten Brut, der erwachsenen Bienen und der eingelagerten Futtervorräte wurden bestimmt. Die Völker waren auf elektronischen Waagen aufgestellt und mit Dataloggern verbunden. Stündlich registrierten Gewichtsdaten wurden aufgeteilt in einen Mittelwert über 25 Stunden hinweg, als Langzeitmittel, und einen trendfreien Gewichtswert, als Kurzzeitinformation. Letzterer gibt die Abweichung der Rohdaten für die jeweilige Stunde von dem laufenden Mittelwert für die entsprechende Stunde an. Laufende Mittelwerte wurden auch benutzt, um die Wöchentliche Änderung im Laufenden Mittel (WCRAW, übersetzt WÄLM) zu berechnen, indem Wochenmittel von dem der jeweils folgenden Woche subtrahiert wurden. Die WCRAW-Daten wurden mit denen der Inspektionsdaten von 2005 für Gewichte der verdeckelten Brut und der adulten Bienen, sowie der Futtervorräte verglichen, und diese Vergleichsergebnisse wurden gegen die der in 2006 vorgenommenen Inspektionen verglichen. An die trendfreien Gewichtsdaten wurde eine Sinuskurve angepasst und die Parameter dieser Kurvenanpassungen wurden für WCRAW-ähnliche Analysen benutzt, ausser dass hier die Daten über die Brut- und Adultpopulationen in Verbrauchsraten umgerechnet worden waren.Die WCRAW-Daten zeigten eine gute Korrelation mit den täglichen Veränderungen im Gewicht der Futtervorräte (Tab. I), aber nicht mit den Gewichtswerten für die Brut und für adulte Bienen. Die trendfreien Daten zeigten klare aber variable Tagesverlaufsmuster. Sinuskurven konnten an alle trendfreien Daten angepasst werden und diese wiesen stets eine Periodik zwischen 22 und 26 Stunden auf. Die Futtergewichtsdaten und die geschätzten Werte der Verbrauchsraten wurden für 2005 und 2006 mit den jeweiligen täglichen Amplituden der Sinuskurven und den WCRAW-Schätzwerten verglichen (Abb. 6 und 7). Die Amplituden und die Gewichte der meisten Komponenten zeigten eine signifikante Beziehung (Tab. I). Insbesonders die Beziehung zwischen den Verbrauchsraten für die Brut und adulte Bienen war signifikant mit der jeweiligen Amplitude korreliert (Abb. 8) und kann damit wichtige Informationen über den Volkszustand geben. Die Kombination der Wägungen mit der kontinuierlichen Datalogger-Information wurde hier benutzt, um Rückschlüsse über die Sammelaktivität, Wasserbewegungen, Schwarmvorgänge, Ruhezustände, sowie über Veränderungen in Futtervorräten und Futterverbrauch zu treffen. Diese Methode ist damit in der Lage, sowohl die Notwendigkeit invasiver Inspektionen zu reduzieren, als auch die Information aus solchen Inspektionen umfassender auszuwerten.

Identification of Multiple Ear-Colonizing Insect and Disease Resistance in CIMMYT Maize Inbred Lines with Varying Levels of Silk Maysin

Abstract Ninety four corn inbred lines selected from International Center for the Improvement of Maize and Wheat (CIMMYT) in Mexico were evaluated for levels of silk maysin in 2001 and 2002. Damage by major ear-feeding insects [i.e., corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae); maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae); brown stink bug, Euschistus servus (Say); southern green stink bugs, Nezara viridula (L.) (Heteroptera: Pentatomidae)], and common smut [Ustilago maydis DC (Corda)] infection on these inbred lines were evaluated in 2005 and 2006 under subtropical conditions at Tifton, GA. Ten inbred lines possessing good agronomic traits were also resistant to the corn earworm. The correlation between ear-feeding insect damage or smut infection and three phenotypic traits (silk maysin level, husk extension, and husk tightness of corn ears) was also examined. Corn earworm and stink bug damage was negatively correlated to husk extension, but not to either silk maysin levels or husk tightness. In combination with the best agronomic trait ratings that show the least corn earworm and stink bug damage, lowest smut infection rate, and good insect-resistant phenotypic traits (i.e., high maysin and good husk coverage and husk tightness), 10 best inbred lines (CML90, CML92, CML94, CML99, CML104, CML108, CML114, CML128, CML137, and CML373) were identified from the 94 lines examined. These selected inbred lines will be used for further examination of their resistance mechanisms and development of new corn germplasm that confers multiple ear-colonizing pest resistance.

Effect of Maysin on Wild-Type, Deltamethrin-Resistant, and Bt-Resistant Helicoverpa armigera (Lepidoptera: Noctuidae)

Larvae of the Old World corn earworm, Helicoverpa armigera (Hübner), were fed diets containing lyophilized silks from maize genotypes expressing varying levels of maysin, a flavone glycoside known to be toxic to the New World corn earworm, Helicoverpa zea Boddie. Three different H. armigera colonies were tested: a wild-type colony (96-S), a colony selected for resistance to deltamethrin (Del-R), and a colony selected for resistance to the Cry1Ac protoxin of Bacillus thuringiensis (Bt-R). A colony of H. zea was also tested as a control. High-maysin silk diets significantly slowed the growth and arrested the development of larvae from all H. armigera colonies compared with low-maysin silk diets, maysin-lacking silk diets, and no-silk control diets. The effects on the H. armigera and H. zea colonies were similar across maysin levels, although H. zea is a larger insect than H. armigera and this overall size difference was observed. Among the H. armigera colonies, maysin effects were generally similar, although 7-d-old Del-R larvae were significantly smaller than 7-d-old Bt-R and 96-S larvae for one no-silk control and two maysin-containing silk treatments. The toxic effect of maysin on the Bt-R and Del-R colonies suggests that physiological mechanisms of H. armigera resistance to Cry1Ac and deltamethrin do not confer cross-resistance to maysin.

DNA Fingerprinting to Improve Data Collection Efficiency and Yield in an Open-Field Host-Specificity Test of a Weed Biological Control Candidate

Abstract An open-field test was conducted in southern France to assess the host-specificity of Ceratapion basicorne (Illiger), a candidate for biological control of yellow starthistle. Test plants were infested by naturally occurring populations of C. basicorne but were also exposed to sympatric herbivore species, including other Ceratapion spp. Insects from the test plants were collected directly into tubes of ethanol and were subsequently identified to species according to DNA sequence similarity with morphologically identified reference specimens. This integrated, morphological and molecular identification method was used in an effort to maximize the amount of data gained in the field bioassay and to minimize the number of taxonomist–hours necessary to complete the study. The results obtained showed that the French C. basicorne population only attacked yellow starthistle and cornflower, another known host of C. basicorne. Molecular phylogenetic analysis of the insects collected from all other nonhost plants rejected the possibility that any were C. basicorne. Nomenclature: Cornflower, Centaurea cyanus L. CENCY; yellow starthistle, Centaurea solstitialis L. CENSO; Ceratapion basicorne (Illiger)

Morphological injury of cut-leaf teasel, Dipsacus laciniatus L. (Dipsacaceae) induced by the eriophyid mite Leipothrix dipsacivagus Petanovic et Rector (Acari: Eriophyoidea)

Abstract The eriophyid mite Leipothrix dipsacivagus Petanovic et Rector provokes severe malformations to its host plant, cut-leaf teasel (Dipsacus laciniatus L.), in the field. These injuries were examined at the morpho-anatomical level in infested plants collected in the field and experimentally infested plants kept under controlled laboratory conditions. A number of symptoms were observed including reduced growth, internode shortening, leaf rolling and wrinkling, and shrunken inflorescences. After severe attack, the leaves of bolted plants became chlorotic with necrotic spots and started to wilt. Young rosettes died. Morphometric analysis revealed significant differences between infested and healthy field-collected bolting plants. Infested plants were significantly shorter than healthy plants, with smaller leaves and flower heads. Striking injuries were also observed on young leaves of experimentally infested plants. It is expected that further investigations will elucidate the full extent of the damage to aboveground parts of D. laciniatus due to infestation by L. dipsacivagus.