Sean M. Prager

Culex quinquefasciatus larval microbiomes vary with instar and exposure to common wastewater contaminants.

Like many insects, mosquitoes, rely on endosymbionts to grow and develop. These can be acquired from the environment. We used next generation 454 pyrosequencing to discern the whole-body microbiome of the mosquito species Culex quinquefasciatus in various larval stadia and following exposure to common pharmaceutical and personal care products (PPCPs) found in wastewater. PPCP treatments included environmentally-relevant concentrations; 1) a combination of common antibiotics, 2) a combination of mammalian hormones, 3) a mixture of the antibiotic and hormone treatments plus acetaminophen and caffeine and, 4) an untreated control. Within control groups, the predominant families of bacterial symbionts change with each larval instar despite consistent diets and rearing conditions. This trend was also seen in hormone treatments but not in the antibiotic or the mixture treatments. Richness and evenness were reduced in both antibiotic and mixture treatments, suggesting that antibiotics remove certain bacteria or inhibit them from increasing to proportions seen in the control treatment. Interestingly, the mixture treatments had greater richness and evenness compared to antibiotic alone treatments, possibly due to the other contaminants facilitating growth of different bacteria. These findings illuminate the complexity of the microbiome of C. quinquefasciatus and may have implications for more effective control strategies.

Pharmaceuticals and personal care products alter the holobiome and development of a medically important mosquito

The increasing demand for fresh water has forced many countries to use reclaimed wastewater for agricultural purposes. This water contains pharmaceuticals and personal care products (PPCPs) that remain biologically active following passage through wastewater treatment plants. Run-off from farms and contaminated water from treatment facilities exposes aquatic ecosystems to PPCPs. This study examined the effects of PPCPs on a lower trophic organism. Culex quinquefasciatus larvae were reared in water contaminated with environmentally relevant concentrations of common PPCPs. Acetaminophen alone and a mixture of contaminants were found to increase developmental time of larvae. Susceptibility to Bti increased in larvae exposed to antibiotics, acetaminophen, or a mixture of PPCPs. Antibiotics, hormones, and the mixture altered the mosquito bacterial microbiome. Overall, the results indicate that at environmentally relevant concentrations, PPCPs in reclaimed water can have biologically important effects on an ecologically and medically important lower trophic level insect.

A sequential binomial sampling plan for potato psyllid (Hemiptera: Triozidae) on bell pepper (Capsicum annum)

BACKGROUND Potato psyllids (Bactericera cockerelli Sulc) are a pest on solanaceous crop plants, including bell peppers. Potato psyllids vector Candidatus Liberibacter psyllaurous, but bell peppers (Capsicum annum L.) do not exhibit symptoms from infection. Potato psyllids show variation in spatial patterns and host choice with cultivar and plant species. Consequently, a study of spatial distribution and sampling plan specific to bell peppers is necessary for management of this insect pest, as those developed for other crops are unlikely to transfer among crops. RESULTS Potato psyllids were evenly distributed on both sides of leaves but prefer the top two-thirds of pepper plants. Within fields, psyllids demonstrated an aggregated spatial distribution, but the edge effect observed in other crop plants was absent. Eggs and nymphs had similar spatial distributions that differed from adults. A series of nymph-based sampling plans were examined. Sampling plans based on an infestation of less than 41% of plants infested (5 nymphs plant(-1)) were statistically unacceptable, while little difference was found between the 41% infestation plan and 56% (20 nymphs plant(-1)) infestation plan. At 41%, an average of 11 and maximum of 49 samples would be necessary to make a treatment decision. CONCLUSION The binomial sequential sampling plan presented here offers an important yet simple tool for managing potato psyllids in bell pepper.

The efficacy of Beauveria bassiana, jasmonic acid and chlorantraniliprole on larval populations of Helicoverpa armigera in chickpea crop ecosystems.

BACKGROUND A robust integrated pest management (IPM) programme is needed to reduce the use of insecticides in controlling Helicoverpa armigera. Therefore, a 2 year field study was conducted to evaluate the use of alternative control measures (biochemical use) for H. armigera relative to exclusively using chemical insecticides. The entomopathogenic fungus Beauveria bassiana, jasmonic acid and the insecticide chlorantraniliprole were each applied twice during the chickpea growing season. RESULTS All three applied materials (either alone or combined) significantly (P ≤ 0.05) reduced the larval population of H. armigera and pod infestation. Effects increased with time, and the maximum difference was observed 7 days after the second application in each year. The lowest numbers of larvae per plant and pod infestation were in the B. bassiana 3.21 × 106 + chlorantraniliprole treatment in both 2009/2010 and 2010/2011 year. The reduction in the larval population and pod infestation increased chickpea yield and the highest yield in both seasons, and the maximum yield was obtained in the B. bassiana 3.21 × 106 + chlorantraniliprole treatment. The populations of natural enemies were highest in the jasmonic acid treatment. CONCLUSION The results suggest that B. bassiana, jasmonic acid and chlorantraniliprole may be useful components for the H. armigera IPM strategy.

The Complete Mitochondrial Genome Sequence of Bactericera cockerelli and Comparison with Three Other Psylloidea Species.

Potato psyllid (Bactericera cockerelli) is an important pest of potato, tomato and pepper. Not only could a toxin secreted by nymphs results in serious phytotoxemia in some host plants, but also over the past few years B. cockerelli was shown to transmit “Candidatus Liberibacter solanacearum”, the putative bacterial pathogen of potato zebra chip (ZC) disease, to potato and tomato. ZC has caused devastating losses to potato production in the western U.S., Mexico, and elsewhere. New knowledge of the genetic diversity of the B. cockerelli is needed to develop improved strategies to manage pest populations. Mitochondrial genome (mitogenome) sequencing provides important knowledge about insect evolution and diversity in and among populations. This report provides the first complete B. cockerelli mitogenome sequence as determined by next generation sequencing technology (Illumina MiSeq). The circular B. cockerelli mitogenome had a size of 15,220 bp with 13 protein-coding gene (PCGs), 2 ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs), and a non-coding region of 975 bp. The overall gene order of the B. cockerelli mitogenome is identical to three other published Psylloidea mitogenomes: one species from the Triozidae, Paratrioza sinica; and two species from the Psyllidae, Cacopsylla coccinea and Pachypsylla venusta. This suggests all of these species share a common ancestral mitogenome. However, sequence analyses revealed differences between and among the insect families, in particular a unique region that can be folded into three stem-loop secondary structures present only within the B. cockerelli mitogenome. A phylogenetic tree based on the 13 PCGs matched an existing taxonomy scheme that was based on morphological characteristics. The available complete mitogenome sequence makes it accessible to all genes for future population diversity evaluation of B. cockerelli.

Indirect Effects of One Plant Pathogen on the Transmission of a Second Pathogen and the Behavior of its Potato Psyllid Vector

ABSTRACT Plant pathogens can influence the behavior and performance of insect herbivores. Studies of these associations typically focus on tripartite interactions between a plant host, a plant pathogen, and its insect vector. An unrelated herbivore or pathogen might influence such interactions. This study used a model system consisting of Tobacco mosaic virus (TMV), the psyllid Bactericera cockerelli Sulc, and tomatoes to investigate multipartite interactions among a pathogen, a nonvector, and a plant host, and determine whether shifts in host physiology were behind potential interactions. Additionally, the ability of TMV to affect the success of another pathogen, ‘Candidatus Liberibacter solanacearum,’ which is transmitted by the psyllid, was studied. In choice trials, psyllids preferred nearly fourfold noninfected plants to TMV-infected plants. No-choice bioassays demonstrated that there was no difference in psyllid development between TMV-infected and control plants; oviposition was twice as high on control plants. Following inoculation by psyllids, ‘Candidatus Liberibacter solanacearum’ titers were lower in TMVinfected plants than control plants. TMV-infected plants had lower levels of amino acids and sugars but little differences in phenolics and terpenoids, relative to control plants. Possibly, these changes in sugars are associated with a reduction in psyllid attractiveness in TMV-infected tomatoes resulting in decreased infection of ‘Candidatus Liberibacter solanacearum.’

A Binomial Sequential Sampling Plan for Bactericera cockerelli (Hemiptera: Triozidae) in Solanum lycopersicum (Solanales: Solanacea)

ABSTRACT The tomato—potato psyllid Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) is a pest of many solanaceous plants, including tomato (Solanum lycopersicum L.) and potato (Solanum tuberosum L.). In tomato, feeding by nymphs is associated with “psyllid yellows.” B. cockerelli also vectors “Candidatus Liberibacter psyllaurous,” an infectious bacterium that causes “vein greening” disease. Decisions about management action are much more effective when guided by robust sampling. However, there are few previous studies of potato psyllid spatial distribution in tomato fields, and no published sequential sampling plans for the pest in tomato. We studied B. cockerelli in various tomato fields in California and used these data to generate a sequential sampling plan. We found that juvenile B. cockerelli in tomato fields exhibit an edge effect, an aggregated distribution, and individuals are primarily located on the bottom of leaves. Psyllids were concentrated in the upper segments of plants, but this changed over time. Finally, we present three binominal sequential sampling plans for managing tomato psyllids in tomato fields. These plans differed from both those for bell pepper (Capsicum annum L.) and potato, indicating that B. cockerelli needs to be sampled using crop-specific sampling plans.

De Novo Genome Sequence of "Candidatus Liberibacter solanacearum" from a Single Potato Psyllid in California.

ABSTRACT The draft genome sequence of “Candidatus Liberibacter solanacearum” strain RSTM from a potato psyllid (Bactericera cockerelli) in California is reported here. The RSTM strain has a genome size of 1,286,787 bp, a G+C content of 35.1%, 1,211 predicted open reading frames (ORFs), and 43 RNA genes.

Psyllids: Biology, Ecology, and Management

Abstract The tomato psyllid ( Bactericera cockerelli ) (Sulc) (Hemiptera: Triozidae) is a pest on solanaceous vegetable crops. The psyllid was recognized as an occasional pest in western North America nearly a century ago. Historically, the psyllid was associated with psyllid yellows, a disease of unknown origin associated with feeding by nymphs. In the last decade, tomato psyllids have been identified as the vector of Candidatus Liberibacter solanacearum (Cls) a bacterial pathogen that causes zebra chip disease in potato and vein greening disease in tomatoes. Vein greening results in a variety of symptoms that can include reduced fruit set and death in extreme cases. The discovery of Cls has led to an increasing body of research on the management and biology of tomato psyllids. It is now recognized that there are at least three haplotypes of the psyllid associated with various geographic regions. Management of the psyllid is complicated both by the various haplotypes and by the presence or absence of Cls. There is currently only one sampling plan for management of tomato psyllids on tomatoes. That plan is designed for use in California with the western psyllid haplotype, and it does not account for Cls. Presently, there are no varieties of tomato resistant to the psyllid or Cls. Management of potato psyllid is currently based on multiple calendar-based applications of insecticides. Less focus has been placed on management in tomatoes versus potatoes, but there is a small list of materials that are effective in controlling the insect. Resistance is already developing in some regions for certain materials. The tomato psyllid has numerous natural enemies which have been identified in California. Unfortunately, most of the identified enemies are generalists and there are none that are effective for biological control when Cls is present. Further research will be required to refine management techniques for these increasingly important pests.

Examining the Potential Role of Foliar Chemistry in Imparting Potato Germplasm Tolerance to Potato Psyllid, Green Peach Aphid, and Zebra Chip Disease

Abstract Long-term, sustainable management of zebra chip disease of potato, caused by ‘Candidatus Liberibacter solanacearum’ (Lso) and vectored by potato psyllids (Bactericera cockerelli Sulc [Hemiptera: Triozidae]), requires development of cultivars resistant or tolerant to infection or capable of reducing spread or both. We examined the influence that five experimental breeding clones of potato had on potato psyllids and their ability to vector Lso.The ability of these potato clones to resist aphids (green peach aphids, Myzus persicae Sulzer [Hemiptera: Aphididae]) also was examined. Due to the importance of host chemistry on plant–insect interactions, levels of primary metabolites of amino acids and sugars, as well as secondary metabolites including polyphenolics, terpenoids, and alkaloids were compared between breeding clones and a commercial cultivar. Findings for compound levels then were associated with observed changes in host susceptibility to psyllids or aphids. Psyllids oviposited less on three breeding clones than Atlantic, but no significant effects of breeding clones on psyllid feeding or choice were observed. Aphid reproduction was reduced on two clones relative to Atlantic. A05379-211 had greater sugar levels and postpsyllid amino acid levels than Atlantic.Total alkaloid and phenolic levels were greater in all breeding clones than Atlantic.Total terpenoid levels were greater in PALB03016-3 and PALB03016-6 than Atlantic, which might explain, in part, the observed resistance to psyllid oviposition and aphid reproduction. Overall, these results suggest that increased levels of certain metabolites in breeding clones could affect psyllid and aphid reproduction.