Christopher J. Vitek

Understanding population dynamics and genetics can be critical to understanding distribution, spread, and vectorial capacity of disease vectors. One well-studied disease vector, Aedes aegypti, has been the focus of research due to the wide range of diseases it vectors and the high transmission capabilities. We examined the genetic diversity of A. aegypti utilizing a large number of individual samples from a small geographic range, as opposed to previous studies that focus on a large range and small collection. Using the COI locus, we examined 107 mosquitoes from South Texas, with multiple haplotypes identified. We observed that the samples from South Texas have a unique distribution of haplotypes relative to several invasive global locations from North America, Central America, South America, and Asia. Population measurements suggest a recent population expansion in South Texas, with multiple rare alleles identified. Our intensive sampling strategy using a small geographic scale revealed high levels of diversity not found in non-East African countries and unique haplotypes. We hypothesize that expanding sampling size when studying genetic diversity could help inform movement of mosquitoes. In addition, increased haplotype diversity may be correlated with increased insecticide resistance and differing vector competence.

El pulgón de sorgo (PS; Melanaphis sorghi Theobald) es una nueva plaga invasora en sorgo, reportada por primera vez en los Estados Unidos en 2013. Desde entonces el uso de agentes químicos y plaguicidas en sorgo ha aumentado, causando diferencias a nivel de las poblaciones del PS, y apuntando al posible surgimiento de nuevos biotipos. La mayoría de las investigaciones con el PS se han enfocado en las comparaciones entre el daño causado al sorgo, caña de azúcar, y otras plantas huéspedes, lo cual puede no haber detectado las diferencias que pudieran existir entre las poblaciones del PS en sorgo. Para discernir estos biotipos, recolectamos tres poblaciones del PS -con sorgo como planta huésped- en tres diferentes sitios en el Valle del Río Grande al sur de Texas, Estados Unidos. Examinamos las posibles variaciones en sus características de vida, su comportamiento alimenticio usando electrical penetration graphs (gráficas de penetración eléctricas, GPE), y defensas de las plantas huésped (sorgo-sudangrass) después de la infección del PS. Nuestros resultados sobre las características de vida mostraron diferencias significativas en la tasa de reproducción entre las tres poblaciones del PS examinadas. Sin embargo, no hubo diferencias significativas en el comportamiento alimenticio del PS usando GPE. También encontramos que la cantidad de cera epicuticular del sorgo-sudangrass varió significativamente con la infección del PS, mientras que la cantidad de polifenol oxidasa no varió. En conclusión demostramos que las diferencias a nivel de las poblaciones del PS se traducen en variaciones de características específicas en la interacción plantainsecto, pero una investigación más extensa se requiere para entender completamente la presencia de biotipos del PS.

Mexican fruit fly (Anastrepha ludens (Loew)) (Diptera: Tephritidae) represents a major threat to fruit production in the Western Hemisphere. Sterile insect technique is used to suppress and eradicate wild populations. Success of this control method necessitates weekly production of hundreds of millions of flies, their sterilization by irradiation, and their aerial release. Diet needed to produce large fly numbers are conducive to the spread of bacteria. Pathogenic bacteria were isolated from 3 rearing facilities and from multiple sources: eggs, larvae, pupae and spent diet, and were found to include some isolates identified to the genus Providencia (Enterobacteriales: Morganellaceae). We identified 41 Providencia isolates and tested their pathogenicity to A. ludens. Based on 16s rRNA sequences, 3 groups were clustered into several species of Providencia with varying capacities to affect the Mexican fruit fly production. Isolates putatively identified as P. alcalifaciens/P. rustigianii were all pathogenic causing larval and pupal yield reduction of 46–64% and 37–57%, respectively. Among them, Providencia isolate 3006 was the most pathogenic reducing larval and pupae yield by 73 and 81%, respectively. Isolates identified as P. sneebia were not pathogenic. The final cluster, P. rettgeri/P. vermicola, were variable in pathogenicity with 3 isolates yielding like the control and the rest causing larval and pupal yield reduction of 26–53% and 23–51%, respectively. Isolates putatively identified as P. alcalifaciens/P. rustigianii were more virulent than P. rettgeri/P. vermicola. Accurate identification of species is needed to diagnose and monitor pathogenic versus nonpathogenic Providencia strains.

Insect species are subjected to disparate selection pressure due to various biotic and abiotic stresses. Management practices including the heavy use of chemical insecticides and introduction of insect-resistant plant cultivars have been found to accelerate these processes. Clearly, natural selection coupled with human intervention have led to insect adaptations that alter phenotypes and genetic structure over time, producing distinct individuals with specialized traits, within the populations, commonly defined as biotypes. Biotypes are commonly found to have better fitness in the new environment and, in the case of aphids, the most commonly studied system for biotypes, have the ability to successfully infest previously resistant host plants and new species of host plants. Although a large number of studies have explored biotypes, the concept for defining biotypes varies among scientists, as we lack a consistency in estimating biotype behavior and their variation within and between biotypes. The concept of biotypes is even more complicated in aphid species (Aphidoidea), as they undergo parthenogenetic reproduction, making it difficult to understand the source of variation or quantify gene flow. In this review, we aim to illuminate the concept of biotype and how it has been used in the study of aphids. We intend to further elaborate and document the existence of aphid biotypes using sugarcane aphid (Melanaphis sacchari) as a model to understand their differences, level of variation, evolution, and significance in pest management.

Predator-prey relationships are a driving force when examining community ecology. One question in predator-prey interactions is how a predator may respond to novel prey phenotypes, a form of frequency dependent prey selection. A predator may selectively target or avoid the novel prey, a behavior referred to as anti-apostatic or apostatic selection respectively. We examined apostatic prey selection by observing feeding behavior in two species of assassin bugs (Hemiptera: Reduviidae), the white-spotted assassin bug (Platymeris biguttatus) and the red-spotted assassin bug (Platymeris rhadamanthus) which were fed unmodified and modified (novel) phenotypes of Turkistan cockroaches, Blatta lateralis (Blattodea: Blattidae). The two species of assassin bugs represent either generalist (P. biguttatus) or specific feeders (P. rhadamanthus). We hypothesized that the generalist feeder would engage in anti-apostatic feeding while the specific feeder would engage in apostatic feeding. Our results indicated that there was no difference in feeding behavior between the two species, however an overall trend of apostatic feeding was observed in response to two of the four novel prey phenotypes. Factors beyond prey phenotype may also be influencing feeding choice in these insects. While the two predator species did not exhibit different feeding behaviors, the observation of apostatic feeding in this genus suggest an overall trend of utilizing specific prey images in feeding.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), vectors ‘Candidatus Liberibacter spp.’, the causative agent of Citrus Greening Disease (CGD) or Huanglongbing (HLB). Managing populations of psyllids in the Lower Rio Grande Valley (LRGV), TX, United States is imperative given a continuous increase in HLB-positive trees. A component of integrated pest management (IPM) program is the use of strains of entomopathogenic fungi for the biological control of D. citri. In an attempt to find endemic strains of entomopathogenic fungi that grow favorably under LRGV environmental conditions and naturally infect D. citri, psyllids were collected from local residential areas, surface sterilized, and plated on a semi-selective agar medium. Collection of over 9,300 samples from 278 sites throughout the LRGV led to the positive identification of two Beauveria bassiana (Balsamo-Crivellii) Vuillemin (Hypocreales: Cordycipitaceae) isolates, ACP18001 and ACP18002. Chi-square analysis of primary and secondary acquisition bioassays revealed that both field isolated strains outperformed Cordyceps (Isaria) fumosorosea (Wize) (Hypocreales: Cordycipitaceae) Apopka97 under both primary (direct spray) and secondary acquisition (adult exposure to sprayed foliage) bioassays with ACP18002 marginally outperforming ACP18001 under secondary acquisition. Slopes of the dose response regression lines for the three fungi were not significantly different. In addition, the thermal profiles for vegetative growth of each isolate indicated that the field isolates grew at higher rates than the standard at higher temperatures. The new isolates may prove to be good candidates for the management of D. citri populations in the LRGV.

From 2016 to 2018, Hidalgo County observed the emergence of Zika virus (ZIKV) infections along with sporadic cases of Dengue virus (DENV) and West Nile virus (WNV). Due to the emergence of ZIKV and the historical presence of other mosquito-borne illnesses, Hidalgo County obtained funding to enhance mosquito surveillance and educate residents on arboviruses and travel risks. During this time period, Hidalgo County mosquito surveillance efforts increased by 1.275%. This increase resulted in >8000 mosquitoes collected, and 28 mosquito species identified. Aedes aegypti, Ae albopictus and Culex quinquefasciatus made up approximately two-thirds of the mosquitoes collected in 2018 (4122/6171). Spatiotemporal shifts in vector species composition were observed as the collection period progressed. Significantly, temperature variations (p < 0.05) accounted for associated variations in vector abundance, whereas all other climate variables were not significant.

Aedes aegypti and Aedes albopictus (Diptera: Culicidae) are vectors for several arboviruses, including dengue, Zika virus and chikungunya virus. The primary method of controlling these diseases is controlling the vector population, often with insecticides. Insecticide resistance may impact the success of these efforts. We tested the effect of variable temperature exposures on susceptibility to insecticides by exposing adult A.aegypti and A. albopictus to different temperatures and tested their susceptibility to insecticides. We hypothesized that adults maintained at high temperatures would show increased susceptibility to insecticides relative to lower temperatures. Colony mosquitoes were hatched, reared to adulthood and then maintained in three temperature regimes that reflect average seasonal temperatures in the Rio Grande Valley, TX. Susceptibility to permethrin and deltamethrin was assessed using the CDC bottle bioassay method. Overall Aedes albopictus had higher susceptibility to all insecticides than Aedes aegypti. Mosquitoes kept at different temperatures exhibited differential susceptibility to insecticides. Low temperature exposed mosquitoes had decreased susceptibility while high temperature conditions resulted in increased mortality. Our results suggest public health officials must consider temperature effects when controlling mosquitoes with insecticides.

Mosquito-borne viruses are the cause of significant morbidity and mortality worldwide, especially in low- and middle-income countries. Assessing risk for viral transmission often involves characterization of the vector competence of vector–virus pairings. The most common determination of vector competence uses discreet, terminal time points, which cannot be used to investigate variation in transmission aspects, such as biting behavior, over time. Here, we present a novel method to longitudinally measure individual biting behavior and Zika virus (ZIKV) transmission. Individual mosquitoes were exposed to ZIKV, and from 9 to 24 days post-exposure, individuals were each offered a 180 μL bloodmeal every other day. Biting behavior was observed and characterized as either active probing, feeding, or no bite. The bloodmeal was then collected, spun down, serum collected, and tested for ZIKV RNA via qRT-PCR to determine individuals’ vector competence over time. This included whether transmission to the bloodmeal was successful and the titer of expectorated virus. Additionally, serum was inoculated onto Vero cells in order to determine infectiousness of positive recovered sera. Results demonstrate heterogeneity in not only biting patterns but expectorated viral titers among individual mosquitoes over time. These findings demonstrate that the act of transmission is a complex process governed by mosquito behavior and mosquito–virus interaction, and herein we offer a method to investigate this phenomenon.