Carabidae and Tenebrionidae diversity in the Great Basin Province of California

The high desert regions of eastern California within the Great Basin are vast areas of shrub-dominated habitat heavily impacted by invasive exotic grasses and forbs. Trapping efforts within these areas provided distributional information about various surface-active arthropod taxa. Two groups with high species diversity and abundance encountered at our sites were the coleopteran families Carabidae and Tenebrionidae. Here, we report trapping of 45 species of carabids and 46 species of tenebrionids, along with mitochondrial cytochrome c oxidase subunit 1 (COI) sequence data for 65 of these 92 species. These results build upon existing distributional information regarding these families in California and further refine our knowledge of the biodiversity of the understudied Great Basin provinces.

Do mites eat and run? A systematic review of feeding and dispersal strategies

Dispersal is an important process affecting the survival of organisms and the structure and dynamics of communities and ecosystems in space and time. It is a multiphase phenomenon influenced by many internal and external factors. Dispersal syndromes can be complicated, but they are vital to our knowledge of the biology of any organism. We analysed dispersal ability in mites (Acariformes and Parasitiformes), a highly diverse group of wingless arthropods, taking into consideration various modes of dispersal, feeding strategies, body size and the number of articles published for each species. Based on 174 articles summarized for this study, it appears that mites are opportunistic when it comes to dispersal, regardless of their feeding habits, and are often able to adopt several different strategies as needs arise. Moreover, we find a significant positive relationship between the amount of research effort that was put into studying a given species and the number of modes of dispersal that were described. The most salient conclusion to be drawn from this positive correlation is that additional studies are needed, especially on a broader set of mite taxa, until the aforementioned correlation is no longer demonstrably significant.

A New Aculodes Species (Prostigmata: Eriophyidae) Described from an Invasive Weed by Morphological, Morphometric and DNA Barcode Analyses

A new species of eriophyoid mite, Aculodes marcelli sp. nov., was discovered on cheatgrass, Anisantha tectorum (L.) Nevski (syn. Bromus tectorum L.), an annual grass that is native to Eurasia and Northern Africa. This grass was introduced to North America near the end of the 19th century and now is widespread and associated with the observed increases in the size, frequency, and intensity of wildfires in western N. America. In this paper, A. marcelli sp. nov., is morphologically described and illustrated. Compared with other Aculodes spp., it differs based on morphology and the sequence of the mitochondrial cytochrome oxidase gene, subunit I (MT-CO1). Results of morphometric analysis showed clear differentiation between A. marcelli sp. nov., and the most similar congener, A. altamurgiensis from Taeniatherum caput-medusae. Analysis of MT-CO1 sequence divergence revealed significant levels of genetic variation (17.7%) and supported the results from the morphometric analysis; therefore, it is determined that they are two different species. Aculodes marcelli sp. nov., is a new candidate agent for classical biological control of A. tectorum.

Phylogenetic Position of a New Trisetacus Mite Species (Nalepellidae) Destroying Seeds of North American Junipers and New Hypotheses on Basal Divergence of Eriophyoidea

Simple Summary

Eriophyoid mites are microscopic herbivores associated with higher plants. Some of them are serious pests due to their ability to vector viruses and cause other damage to host plants. Mites of the genus Trisetacus are widespread parasites of conifers. They usually live in buds, cones, and rarely within needles of Pinaceae (pine family) and Cupressaceae (cypress family). We discovered a new species, Trisetacus indelisn. sp., severely damaging seeds of three North American junipers in the western USA. This species possesses two morphologically different forms of females and has two deletion mutations in the gene cytochrome oxidase subunit I (Cox1). Such mutations are rare in eriophyoids and were previously detected only in two pestiferous species from palms and hazelnut. Our molecular-phylogenetic analyses determine the closest known relatives of the new species and suggest that Old and New World Trisetacus independently transitioned to living in seeds of junipers. Additionally we show that reconstruction of the phylogeny of Eriophyoidea based on one gene, Cox1, produces a poorly-resolved but biologically consistent tree topology to hypothesize the evolution of Eriophyoidea. Overall, our study improves our understanding of the diversity of conifer-inhabiting mites and indicates further needs in investigating the phylogeny of Eriophyoidea.

Abstract

Eriophyoid mites of the genus Trisetacus Keifer are widespread parasites of conifers. A new oligophagous species, T. indelis n. sp., was discovered severely damaging seeds of North American junipers (Juniperus osteosperma, J. occidentalis, and J. californica) in the western USA. It has two codon deletions in the mitochondrial gene Cox1 rarely detected in Eriophyoidea and includes distinct morphological dimorphism of females. A phylogenetic analysis based on amino acid alignment of translated Cox1 sequences using a large set of out-groups (a) determined that two North American congeners, T. batonrougei and T. neoquadrisetus, were the closest known relatives of T. indelis n. sp., and (b) indicated that Old and New World seed-inhabiting Trisetacus from junipers do not form a distinct clade, suggesting a possible independent transition to living in seeds of junipers in America and Eurasia by Trisetacus spp. Our analysis produced a new topology consistent with a scenario assuming gradual reduction of prodorsal shield setation in Eriophyoidea and an ancient switch from gymnosperms to other hosts. Additionally, our analysis did not support monophyly of Trisetacus; recovered a new host-specific, moderately supported clade comprising Trisetacus and Nalepellinae (Nalepella + Setoptus) associated with Pinaceae; and questioned the monophyly of Trisetacus associated with Cupressaceae.

Taxonomic Description of Stenodiplosis tectori n. sp. (Diptera: Cecidomyiidae), a Seed Parasite of Cheatgrass, Anisantha tectorum, Based on Morphological and Mitochondrial DNA Data

Cheatgrass is an annual grass species from Eurasia that has become invasive in much of western North America. It has been implicated in recent increases in the frequency, size, and intensity of wildfires, contributing to severe economic, environmental, and social destruction. In order to reduce this damage, the USDA-ARS established a classical biological control program against cheatgrass. In 2018 and 2019, adult gall midges were collected emerging from cheatgrass seed heads collected at several sites in Bulgaria and Greece; this is the first gall midge ever recorded from cheatgrass. Morphological comparisons with related midge species recorded from other plant hosts revealed that this midge from cheatgrass is a new species, described here as Stenodiplosis tectori n. sp. This status was supported by sequence comparisons of a barcode region of the gene encoding the mitochondrial cytochrome c subunit I (CO1) protein in Stenodiplosis tectori n. sp. and three congeners. The present study is the first to report MT-CO1 data in the genus Stenodiplosis. The ingroup Stenodiplosis tectori n. sp. collected in the Balkans grouped in one phylogenetic supported clade, with an average K2P-distance from its closest related congener, S. sorghicola, of 7.73% (SD = 1.10). The findings indicated relatively high year-to-year within-population diversity. Implications for this gall midge's utility as a biological control agent of cheatgrass are discussed.

A Preliminary Assessment of Amblyseius andersoni (Chant) as a Potential Biocontrol Agent against Phytophagous Mites Occurring on Coniferous Plants

Development, survival and reproduction of Ambyseius andersoni (Chant), a predatory mite widely distributed in Europe, were assessed on different food items. These included two key pests of ornamental coniferous plants, i.e., Oligonychus ununguis (Jacobi) and Pentamerismus taxi (Haller) and pollen of Pinus sylvestris L. The rationale behind these experiments was to provide a preliminary assessment of the potential of A. andersoni as a biocontrol agent of the above phytophagous arthropods and evaluate pine pollen as an alternative food source for the predator. Under laboratory conditions (23 ± 0.5 °C, 70 ± 10% RH and 16L:8D) A. andersoni was able to feed, develop and reproduce on all tested diets. The shortest development time (egg to female) was obtained when the predator fed on P. taxi (mean = 5.12 d) and the longest was on pine pollen (mean = 6.55 d). The r_m value was significantly higher on both tested prey (0.166 on P. taxi and 0.160 on O. ununguis) than on pollen (0.139). Thus, we do not recommend pine pollen for mass rearing of A. andersoni; however, we conclude that pollen may provide sufficient sustenance for the predator population under field conditions when prey are absent. The potential of A. andersoni as a biocontrol agent of O. ununguis and P. taxi is discussed.

Temperature-dependent development and survival of an invasive genotype of wheat curl mite, Aceria tosichella

Quantifying basic biological data, such as the effects of variable temperatures on development and survival, is crucial to predicting and monitoring population growth rates of pest species, many of which are highly invasive. One of the most globally important pests of cereals is the eriophyoid wheat curl mite (WCM), Aceria tosichella, which is the primary vector of several plant viruses. The aim of this study was to evaluate temperature-dependent development and survival of WCM at a wide range of constant temperatures in the laboratory (17-33 °C). The development time of each stage depended significantly on temperature and it was negatively correlated with temperature increase. At high temperatures (27-33 °C), individuals had shorter developmental times, with the shortest (6 days) at 33 °C, whereas at the lowest tested temperatures (17-19 °C), developmental time was almost 3× longer. Moreover, temperature had a clear effect on survival: the higher the temperature, the lower the survival rate. These data provide information promoting more efficient and effective manipulation of WCM laboratory colonies, and further our understanding of the ramifications of temperature change on WCM physiology and implications for the growth and spread of this globally invasive pest.

A comprehensive and cost-effective approach for investigating passive dispersal in minute invertebrates with case studies of phytophagous eriophyid mites

Dispersal is a fundamental biological process that operates at different temporal and spatial scales with consequences for individual fitness, population dynamics, population genetics, and species distributions. Studying this process is particularly challenging when the focus is on microscopic organisms that disperse passively, whilst controlling neither the transience nor the settlement phase of their movement. In this work we propose a comprehensive approach for studying passive dispersal of microscopic invertebrates and demonstrate it using wind and phoretic vectors. The protocol includes the construction of versatile, modifiable dispersal tunnels as well as a theoretical framework quantifying the movement of species via wind or vectors, and a hierarchical Bayesian approach appropriate to the structure of the dispersal data. The tunnels were used to investigate the three stages of dispersal (viz., departure, transience, and settlement) of two species of minute, phytophagous eriophyid mites Aceria tosichella and Abacarus hystrix. The proposed devices are inexpensive and easy to construct from readily sourced materials. Possible modifications enable studies of a wide range of mite species and facilitate manipulation of dispersal factors, thus opening a new important area of ecological study for many heretofore understudied species.

The Interface Between Wheat and the Wheat Curl Mite, Aceria tosichella, the Primary Vector of Globally Important Viral Diseases

Wheat production and sustainability are steadily threatened by pests and pathogens in both wealthy and developing countries. This review is focused on the wheat curl mite (WCM), Aceria tosichella, and its relationship with wheat. WCM is a major pest of wheat and other cereals and a vector of at least four damaging plant viruses (Wheat streak mosaic virus, High plains wheat mosaic virus, Brome streak mosaic virus, and Triticum mosaic virus). The WCM-virus pathosystem causes considerable yield losses worldwide and its severity increases significantly when mixed-virus infections occur. Chemical control strategies are largely ineffective because WCM occupies secluded niches on the plant, e.g., leaf sheaths or curled leaves in the whorl. The challenge of effectively managing this pest-virus complex is exacerbated by the existence of divergent WCM lineages that differ in host-colonization and virus-transmission abilities. We highlight research progress in mite ecology and virus epidemiology that affect management and development of cereal cultivars with WCM- and virus-resistance genes. We also address the challenge of avoiding both agronomically deleterious side effects and selection for field populations of WCM that can overcome these resistance genes. This report integrates the current state of knowledge of WCM-virus-plant interactions and addresses knowledge gaps regarding the mechanisms driving WCM infestation, viral epidemics, and plant responses. We discuss the potential application of molecular methods (e.g., transcriptomics, epigenetics, and whole-genome sequencing) to understand the chemical and cellular interface between the wheat plant and WCM-virus complexes.

Population growth rate of dry bulb mite, Aceria tulipae (Acariformes: Eriophyidae), on agriculturally important plants and implications for its taxonomic status

Dry bulb mite (DBM), Aceria tulipae, is an economically important mite with a worldwide distribution and a broad host range. As a generalist, it is the most important eriophyoid mite attacking bulbous plants such as garlic, onion and tulip. To date, DBM has been recorded on host plants belonging to the families Liliaceae, Amaryllidaceae, Melanthiaceae and Asparagaceae. However, a precise understanding of DBM host range is lacking as it is largely based on casual records of mites on plants, some of which may include accidental hosts. Moreover, the possible existence of cryptic species has not been considered. In this study the hypothesis that DBM may be a complex of distinct genetic lineages or cryptic species was tested by comparing the common barcode sequence marker mtDNA COI of specimens from several populations originating from the Netherlands and Poland. The population growth rate of DBM on seven agriculturally important plant species and on various parts of the garlic plant was also experimentally assessed in the laboratory. The results did not support the first hypothesis, and indicated that DBM populations originating from Poland and the Netherlands shared essentially the same genome. In addition, they indicated that DBM reached the highest population growth rate on leek and also displayed high growth rates on garlic, chive and red onion, whereas white onion and wheat were not colonized by the mites. Answering the question of whether DBM is a single polyphagous species rather than a complex of cryptic lineages is of particular importance since the misidentification of pests may lead to ineffective control strategies. Moreover, improved knowledge of DBM host range is essential for assessing risk to crops.

Is body size important? Seasonal changes in morphology in two grass-feeding Abacarus mites

Overwintering strategies in herbivorous mites (Acariformes: Eriophyoidea) are poorly understood. A study of two Abacarus spp. was conducted to compare body size parameters of adult females in different seasons. Mites of Abacarus n. sp. (under description) and A. lolli were sampled from Bromopsis inermis and Lolium perenne, respectively, in April, September and December of 2001 in Poznań, Poland; 21 morphological traits were measured for each specimen. A principal component analysis revealed significant differences in body size parameters between collection dates, with larger females collected in December in both species. Larger body size in winter is consistent with the hypothesis that mites of these species, for which deutogyny has not been observed, undergo physiological changes such as accumulation of nutritional reserves, that enable them to withstand adverse environmental conditions. Larger body size has also been shown in other invertebrates to reduce heat loss in cold conditions. Filling gaps in the current knowledge of eriophyoid overwintering strategies, whether in the presence or absence of deutogyny, will contribute to both basic and applied future studies of this important arthropod group.

Spatial and Host-Related Variation in Prevalence and Population Density of Wheat Curl Mite (Aceria tosichella) Cryptic Genotypes in Agricultural Landscapes

The wheat curl mite (WCM), Aceria tosichella Keifer, is a major pest of cereals worldwide that also comprises a complex of at least 16 genetic lineages with divergent physiological traits, including host associations and specificity. The goal of this study was to test the extent to which host-plant species and landscape spatial variation influence WCM presence and population density across the entire area of Poland (>311,000 km2). Three important findings arose from the results of the study. (1) The majority of WCM lineages analyzed exhibited variation in patterns of prevalence and/or population density on both spatial and host-associated scales. (2) Areas of occurrence and local abundance were delineated for specific WCM lineages and it was determined that the most pestiferous lineages are much less widespread than was expected, suggesting relatively recent introductions into Poland and the potential for further spread. (3) The 16 WCM lineages under study assorted within four discrete host assemblages, within which similar host preferences and host infestation patterns were detected. Of these four groups, one consists of lineages associated with cereals. In addition to improving basic ecological knowledge of a widespread arthropod herbivore, the results of this research identify high-risk areas for the presence of the most pestiferous WCM lineages in the study area (viz. the entirety of Poland). They also provide insight into the evolution of pest species of domesticated crops and facilitate testing of fundamental hypotheses about the ecological factors that shape this pest community.

Change in abundance of three phytophagous mite species (Acari: Eriophyidae, Tetranychidae) on quackgrass in the presence of choke disease

Phytophagous mites and endophytic fungi may interact when sharing a host plant, potentially influencing one another's growth or population dynamics; however, interactions between them are poorly known and remain largely unexplored. In this study, quantitative associations between three species of phytophagous mites and the endophytic fungus Epichloë bromicola Leuchtm. & Schardl (Clavicipitaceae, Ascomycotina) on quackgrass, Elymus repens (L.) Gould are reported. The mites' abundance was assessed on field-collected grass shoots that were either exhibiting choke disease symptoms or without the fungus. Overall, the abundance of Tetranychus urticae and Aculodes mckenziei was significantly lower on quackgrass plants infected by E. bromicola compared to plants without the fungus. Conversely, populations of Abacarus hystrix were significantly larger on plants colonised by the fungus than on uninfected plants. Thus, the presence of this endophytic fungus may have divergent effects on different phytophagous mite species although the basis of these effects is not yet known.

Thermal Niches of Two Invasive Genotypes of the Wheat Curl Mite Aceria tosichella: Congruence between Physiological and Geographical Distribution Data

The wheat curl mite (WCM), Aceria tosichella Keifer, is a major pest of cereals worldwide. It is also a complex of well-defined genetic lineages with divergent physiological traits, which has not been accounted for in applied contexts. The aims of the study were to model the thermal niches of the two most pestiferous WCM lineages, designated MT-1 and MT-8, and to assess the extent to which temperature determines the distribution of these lineages. WCM population dynamics were modeled based on thermal niche data from March to November on the area of Poland (>311,000 km²). The most suitable regions for population development were predicted and compared to empirical field abundance data. Congruence between modeled parameters and field data for mite presence were observed for both WCM lineages although congruence between modeled thermal suitability and mite field abundance was observed only for MT-8. Thermal niche data for MT-1 and MT-8 provide biological insights and aid monitoring and management of WCM and the plant viruses it vectors. The presented models accurately estimate distributions of WCM and can be incorporated into management strategies for both current and predicted climate scenarios.

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.

Biology of Leipothrix dipsacivagus (Acari: Eriophyidae), a candidate for biological control of invasive teasels (Dipsacus spp.)

The present study describes key aspects of the biology of Leipothrix dipsacivagus, an eriophyid mite that is under study as a biological control candidate of Dipsacus fullonum and D. laciniatus (Dipsacaceae). Preliminary host-specificity tests have shown that it can develop and reproduce only on Dipsacus spp. (teasels). Studies were conducted in a laboratory at 26 ± 2(o)C with 16 h of light per day. Mites for the stock colony were collected from D. laciniatus in Klokotnitsa, Bulgaria and reared on rosettes of D. laciniatus in the laboratory. Unfertilized L. dipsacivagus females reared in isolation from the juvenile stage produced male offspring only, while progeny of fertilized females were of both sexes, suggesting arrhenotokous parthenogenesis with haplodiploid sex determination. Experiments were designed to compare male progeny from fertilized females to males from unfertilized females and to compare males and females from fertilized females. Male progeny of virgin mothers had significantly longer durations of active immature stages and total egg-to-adult period than male progeny of fertilized females. Female progeny had significantly longer durations of egg incubation, active immature stages and egg-to-adult period than male progeny from fertilized mothers. Adult longevity was significantly greater in females than in males. Fertilized females produced significantly more eggs per day and overall than virgin females. The results of this study suggest that fertilization status of L. dipsacivagus females can affect both their own fecundity and the development of their male progeny.

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.

A sterile-female technique proposed for control of Striga hermonthica and other intractable weeds: advantages, shortcomings and risk management

Weeds have posed intractable challenges to farmers since the dawn of agriculture. This article describes in detail a proposed control strategy based on the introduction of genes conferring female sterility into the genome of an intractable target weed. Spread of these genes through target populations via pollen would be facilitated by their incorporation within active transposable elements. Advantages (e.g. self-dissemination, self-proliferation, target specificity) and shortcomings (e.g. high cost, long project incubation period, limited range of possible targets) of this strategy are discussed in depth, as are assessment and management of its attendant biological and ecological risks, such as the risk of introduced genes spreading to non-target species. The parasitic weed Striga hermonthica (Del.) Benth. is examined as a potential target.

Identification of multiple ear-colonizing insect and disease resistance in CIMMYT maize inbred lines with varying levels of silk maysin

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.

Divergent host acceptance behavior suggests host specialization in populations of the polyphagous mite Abacarus hystrix (Acari: Prostigmata: Eriophyidae)

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.

Divergent host acceptance behavior suggests host specialization in populations of the polyphagous mite Abacarus hystrix (Acari: Prostigmata: Eriophyidae)

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.

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.

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.

Effect of husk characters on resistance to corn earworm (Lepidoptera: Noctuidae) in high-maysin maize populations

Two maize (Zea mays L.) breeding populations with very high concentrations of maysin, a silk-expressed flavone glycoside, were tested for their ability to resist ear damage by the corn earworm, Helicoverpa zea Boddie, under field conditions. Tests were conducted in 2000 and 2001 at multiple locations in Georgia. The high maysin populations, EPM6 and SIM6, as well as resistant and susceptible checks, were scored for silk-maysin content, H. zea damage, and husk characters. In 2000, there was a negative correlation between husk tightness and earworm damage at three of five locations, while there was no significant correlation between damage and maysin content at any location. In 2001, EPM6 and SIM6 had approximately ten times the maysin content of the low-maysin control genotypes; nevertheless, earworm damage to EPM6 and SIM6 was either greater than or not significantly different from the low-maysin genotypes at all locations. The resistant control genotype, Zapalote Chico, had significantly less earworm damage than EPM6 and SIM6 for both years at all locations. The results of this study highlight the importance of identifying and quantifying husk and ear traits that are essential to H. zea resistance in maize.