2018 Highlights of Mosquito and Vector Biology and Control in Latin America

The American Mosquito Control Association (AMCA) is dedicated to the study and control of mosquitoes and other arthropod vectors, promoting cooperation and interaction among professionals and students both in the USA and internationally. To encourage more active participation among international members, a Spanish-language symposium was first held at the AMCA Annual Meeting in 1991 and at all subsequent meetings thereafter. To facilitate understanding despite the language barrier, all presentations are simultaneously translated into English, and most slides are in English. In addition to providing a forum for scientists whose first language is Spanish, the session promotes interaction with mosquito control industry representatives; professional colleagues in the USA who are involved in mosquito vector control, training, and university research; and with local, state, and federal government officials.

Vector biology topics addressed in the symposia included larval habitats, insecticide resistance, new Aedes mosquito traps, blood meal analysis and fitness outcomes, fitness of Aedes aegypti (L.), mating behavior of Anopheles albimanus (Wiedemann), vertical transmission of dengue, and transstadial composition of midgut microbiota. Management techniques discussed included sterile insect technique (SIT) with radiation, SIT Wolbachia, thermal fogging, ultra-low volume insecticide applications, indoor residual spraying, Bacillus thuringiensis israelensis de Barjac (Bti) and Spinosad larval treatments. Additionally, presentations regarding the species composition and diversity of phlebotomine sand flies were given. Vector insect species included Ae. aegypti, Ae. albopictus (Skuse), Anopheles albimanus, An. darlingi Root, An. nuneztovari Galbaldon, Culex nigripalpus (Theobald), Cx. quinequefasciatus Say, and collections of phlebotomine sand fly species. Pathogens discussed included dengue, chikungunya, Zika, Plasmodium species, and Leishmania. Summaries of 25 of the previous 27 symposia have been published (Clark and Suarez 1991, 1992, 1993; Clark 1995, 1996; Clark and Rangel 1997, 1998, 1999; Clark et al. 2000; Clark and Quiroz-Martinez 2001, 2002, 2004, 2005; Clark and Rubio-Palis 2006, 2007, 2008, 2009, 2010, 2011, 2012; Clark and Fernandez-Salas 2013, 2014; Cohnstaedt et al. 2015, 2016, 2017).

Understanding Aedes aegypti behavior will provide insight into the design of entomological surveillance devices. The objective of this work was to design and build a trap for the elimination and control of Ae. aegypti. Various mosquito trap characteristics, such as color, color contrasts, and size, were tested for attraction. Culex quinquefasciatus, Cx. nigripalpus, and Ae. aegypti were collected significantly more when devices had a large entry (KW = 22.26, P = 0.0002) and contrast red/black (KW = 64; P < 0.0001), whereas trap size was not significant (KW = 3.46; P = 0.8394). The optimized trap collected 10% more mosquitoes when installed in the field.

The implementation of new strategies for dengue, chikungunya, and Zika virus vector management requires the release of high mosquito densities capable of competing successfully against wild mosquito populations. For this reason, the efficient and sustainable mass rearing of transgenic, sterilized, and/or Wolbachia-infected Aedes aegypti is a determining factor to diminish the occurrence of arboviral outbreaks in an area-wide intervention program where this mosquito is the main vector. In this study, a laboratory experiment was carried out to compare fecundity, fertility, and adult emergence of 85 Ae. aegypti parental females fed with dog, chicken, human, rabbit, or mouse blood through an artificial membrane system. The number of eggs laid, percent egg hatch, and number of adults emerged by sex were statistically analyzed among the 5 groups of parental females. The results revealed that the fertility of females fed on human blood (53.9 eggs/female) was significantly lower compared to other hosts (94.4–102.9 eggs/female), without differences between percent egg hatch by groups (82.2–94.2%). Averages of females and males were similar between all experimental groups. However, females fed with human blood produced significantly fewer adults (23.2 females, 21.1 males) than the dog-blood group (44.9 females, 47.4 males). In conclusion, dog blood significantly increases the reproductive capacity of Ae. aegypti females under insectary conditions and, therefore, can be considered as an alternative blood source for massive mosquito rearing.

There is a crucial need for innovative and effective means to control mosquitoes, such as the sterile insect technique (SIT). Sterile insect technique involves mass-rearing of the target species, sterilization, and continuous release of sterile male insects into the target population. Sterilization by irradiation remains the most practical way to sterilize mosquitoes. The objective of this study was to determine the dose–sterility curves for Aedes aegypti and Ae. albopictus. The mosquito strain used was the genetically diverse strain from Chiapas, Mexico. Pupae were exposed to gamma rays generated by a cobalt 60 source (dry storage irradiator, Gamma Beam GB-127, Nordion) with a dose rate of 1.8 Gy/min. Pupae of Ae. aegypti were exposed to 6 doses: 0 (control), 15, 30, 50, 70, and 90 Gy, whereas pupae of Ae. albopictus were exposed to 0, 15, 25, 35, 40, and 50 Gy. After irradiation, groups of 20 pupae were caged with non-irradiated pupae of the same strain. Five days postemergence a blood meal was provided. Engorged females were isolated and allowed to oviposit for 3 days. Radiation treatments did not significantly affect survival of adults and pupae, adult emergence, or flight ability of either species. Fecundity and fertility in both species were negatively correlated with dose. Eggs of females that mated with Ae. aegypti–irradiated males were totally infertile at 70–90 Gy. Irradiated females of this species were completely infertile following a dose of 30 Gy. Irradiated males of Ae. albopictus were almost totally infertile at a dose of 50 Gy, whereas females were infertile following doses of 35–50 Gy. Future studies will focus on the efficacy of SIT as a vector-control strategy in small villages in southern Mexico.

Dengue fever is a vector-borne viral disease of major public health importance. Globally, the disease shows an increasing trend in the number of cases and frequency of epidemics. This behavior could be favored by the vertical transmission of the virus in the mosquito vector. Virus surveillance in mosquitoes would provide relevant entomological information to develop more timely strategies. The main objective of this study was to analyze the epidemiological importance of vertical transmission of dengue virus in Aedes aegypti during the largest dengue epidemic in Medellín, Colombia. During this study, mosquitoes were collected in houses near ovitraps during surveillance of entomological indices that were carried out in Medellín during March–December 2016. The mosquito specimens were identified, pooled, and then analyzed for virus detection by reverse transcriptase–polymerase chain reaction. A total of 2,897 adult mosquitoes were collected, the majority of which corresponded to Ae. aegypti with a few Ae. albopictus. Of the 827 pools, 162 were positive for dengue virus, and 27 of these corresponded exclusively to male Ae. aegypti mosquitoes. Multiple infection with 2 dengue virus serotypes was detected in some individual mosquitoes, and it was observed that the largest number of infected males occurred before the period of maximum transmission of dengue. Presence of male Ae. aegypti mosquitoes naturally infected suggests that vertical transmission is an event of epidemiological relevance. Therefore, larval control during epidemics would make a substantial contribution in mitigating the impact of the disease.

Aedes aegypti is the main vector of dengue, chikungunya, and Zika viruses in Latin America. In Mexico, pyrethroid insecticides have been commonly used for more than a decade. Although insecticides are the most important element in vector control, their use has led to the development of different resistance mechanisms in target populations. Insecticide resistance has been associated with a fitness cost, a process that can be considered a consequence of trade-offs between the allocation of energy underlying insecticide resistance mechanisms and insect fitness. In this study, we evaluated several fitness parameters in 2 populations of Ae. aegypti from Yucatan, Mexico, with the forward selection with deltamethrin. We analyzed the activity of detoxifying enzymes, energy performance (lipid, glycogen, and trehalose), and life parameters. The higher the fitness cost in resistant individuals, the longer it takes for them to spread in the population, which is 1 important factor in the design of successful management programs.

During the present study, the effectiveness of a thermal fog Aqua K-Othrine (deltamethrin 2%) formulation was evaluated against Aedes aegypti, a vector of dengue, chikungunya, and Zika viruses. The study site was located in El Manzano, a rural locality 20 km away from Tapachula with endemic transmission of the arboviruses. Fifteen adult female Ae. aegypti, laboratory strain Tapachula, 1–3 days old, fed with 10% glucose solution, were placed in individual cages. Later, each of 4 mosquito cages were placed in typical indoor resting shelters such as living room, dining room, bedroom, kitchen, and bathroom of each household. Then, 4 liters of a formulation mixture (80.0 ml Aqua K-Othrine plus 3.9 ml water) was applied with a Swingfog® thermo-fog machine (Swingtec, Germany). A flow rate of 342 ml/min dispensing a dose of 0.4 mg AI/m³ was calculated.

Overall, hot mist penetration of Aqua K-Othrine caused a 24-h mortality of 100% in all the indoor areas of the dwellings: living room, dining room, bedroom, kitchen, and bathroom. Our results showed that Aqua K-Othrine (deltamethrin 2%) may be highly effective when used as a thermal fogging treatment. Therefore, thermal application of Aqua K-Othrine may be considered as a valuable choice for treating indoor housing and interiors to manage Ae. aegypti in tropical rural locations of Mexico.

Prevention of dengue, chikungunya, and Zika virus transmission is based mainly on the control of Aedes aegypti through the application of ultra-low volume insecticides. In the present study, linear and obstacle tests were performed to evaluate the effectiveness of Lethal Mist® 44 EW adulticide (40% malathion). A dose of 112 g AI/ha, with a flow rate of 416 ml/min and a droplet size of 23.5 μm, was used. A formulation of a water-based mixture was prepared with 260 ml of LETHAL MIST 44EW plus 740 ml water. Linear and obstacle tests were conducted in Tapachula, Chiapas in the southeast region of Mexico. Environmental conditions recorded during the obstacle tests were ambient temperature of 28.3°C, relative humidity (RH) 70.7%, and wind speed of 4.2 km/h. Twenty 2-day-old female mosquitoes were placed in cages and distributed in the bedrooms, kitchens, and backyards of each household. For linear tests, 20 mosquitoes per cage were placed every 10 m in a 100-m transect. Environmental conditions recorded include temperature of 28.86°C, RH 70.3%, and wind speed of 4.18 km/h. The average 24-h mortality of Ae. aegypti exposed to Lethal Mist® 44 EW in the linear tests ranged from 90.8 to 96.7%, whereas in the obstacle tests the mortality in the bedrooms was 95.4%, followed by 93.75% in the kitchen, and 91.8% in the backyard. Our results support the effectiveness of Lethal Mist® 44 EW (malathion 40%) to control Ae. aegypti during outbreaks of dengue, chikungunya, and Zika in endemic localities in Mexico.

In the present study, adulticide efficacy of Actellic® 300 CS (AI: pirimiphos-methyl, 28.16%) and Actellic® Vectors/Actellic® 50 CE (AI: pirimiphos-methyl, 49%) was determined as residual and spatial spraying against 2–3-day-old Aedes aegypti, Tapachula strain, and the F1 progeny. Actellic 300CS formulation was applied with the use of a manual compression spraying pump (Hudson X-Pert) at a dose of 1 g AI. The residual effect was measured for 120 days. The controls were untreated surfaces. Every 15 days, 15 female Ae. aegypti mosquitoes were exposed to 4 World Health Organization cones per sprayed surface to check for mortality. Actellic Vectores Actellic 50 CE was applied by 2 ultra-low volume techniques: one for the evaluation of effectiveness of space spraying for the space-spraying ULV tests, and the other for the obstacle tests. In the former case, 15 2–3-day-old female Ae. aegypti mosquitoes were placed inside cages every 10 m in a 100-m linear transect, whereas in the latter, mosquitoes in cages were placed in bedroom, kitchen, and backyard houses. The insecticide formulations were applied with an ultra-low volume space mist generator London Fog®; 18–20 with18 HP compressor, dispensing a dose of 200 g AI/ha, and a droplet size of 20 microns. The average 24-h mortality of Ae. aegypti in the linear and obstacle tests was 95 and 91.8%, respectively. On the other hand, the residual effectiveness on the wood surface was 91.67% followed by ceramics with 90%, brick with 88.33%, and cement 85%. Our results support the effectiveness of Actellic 300CS and Actellic 50CE as a promising Ae. aegypti management tools during outbreaks of dengue, chikungunya, and Zika viruses in Mexico.

The World Health Organization (WHO) recently recommended indoor residual spraying (IRS) as part of a vector control strategy to combat Aedes-borne diseases, including dengue, chikungunya, and Zika. Manual-compression sprayers have been used in malaria prevention and control programs worldwide since the 1950s and are a standard for IRS application. However, there are technological advances that should be considered to improve IRS application (e.g., control flow valves, rechargeable-battery–operated equipment, reduced drift nozzles, etc.), particularly if interventions are performed in urban areas to control Ae. aegypti. We performed a comparative evaluation of potential IRS equipment following procedures and specifications outlined by the WHO. We evaluated the following spray equipment: manual compression sprayers (Hudson X-pert, Goizper Vector Control Super), motorized sprayers (Honda WJR 2525, Kawashima AK35GX), and rechargeable-battery sprayers (Solo 416, Birchmeier REC 15ABZ, Hudson NeverPump). Flow (the most important parameter) of the Hudson was stabilized at 550 ml/min by the use of a control flow valve (CFV). Goizper has integrated CFV and produced a similar flow as the Hudson. All motorized sprayers required CFVs to keep a constant flow, but their weight, high noise pollution when used indoors, and high engine temperature made them highly unpleasant for the technician. Battery-powered equipment provided constant flow with CFV as well as negligible noise. We identify alternatives to the Hudson X-pert equipment (Goizper and the 3 electric pumps) with technical and operational improvements for performing indoor residual spraying in urban areas.

Ultra-low volume (ULV) aerial applications and their measurement have been a topic of debate since their inception. As technology moves forward and ULV applications are well-established spraying techniques in the USA, there is a greater need for sharing the details and knowledge with our neighboring countries. Latin America and Brazil have been fighting mosquito-borne diseases, mainly malaria, dengue, and yellow fever since their local mosquito control services were established. However, over the last decade, a series of “new” mosquito-borne diseases have emerged, including chikungunya and Zika, increasing the pressure for local mosquito abatement authorities to deploy techniques that they have not used before and at the same time balance their budget to decrease the ever-looming threat of upcoming mosquito-borne diseases such as Mayaro virus (MV). Aerial ULV is a technique that can be paired with applications such as ground ULV and both ground and aerial larvicide use to help in the reduction of the transmitting vector population. This presentation illustrates the improvements and challenges that entailed the conception and technologies required for the development of effective aerial ULV treatments done in Mexico over the last decade.

Malaria is one of the most important mosquito-borne diseases worldwide. In Colombia, 83,295 cases of malaria were reported in 2016. Anopheles albimanus is one the primary vectors of malaria in Colombia, and containment of the disease there is currently focused on the use of insecticides and bed nets. However, because of changes in mosquito behavior and an increase in insecticide resistance, it is necessary to develop new methods of control that exploit the biological traits of An. albimanus, potentially allowing for more specific targeting of this disease vector. Reproduction is one of the main mosquito biological traits related to vectorial capacity. However, little is known about An. albimanus behavior (s) during courtship and mating. Our goal is to better understand mating biology and behavior of An. albimanus in order to develop and/or improve tools implemented in vector control. To gain insight into An. albimanus copulation behavior, we are using methods such as artificial vision and acoustic source separation techniques to dissect the basics of mating in this species under laboratory conditions, examining copulation position, copulation duration, swarming behavior, and mating acoustics. We find that mating pairs copulate primarily in a tail-to-tail position, characteristic of other Anopheles species. Successful copulation lasts between 4 and 10 s. Finally, we are characterizing acoustic signals produced by individuals, males and females, during flight. We previously described that the fundamental frequency of An. albimanus females is around 376 (±30.4) Hz and around 547 (±61.2) Hz in males. However, we do not observe changes in fundamental frequency to be associated with the size of the individuals. Taken together, these results contribute to our knowledge of An. albimanus mating behavior and will potentially aid in future vector control efforts.

The insect microbiota plays an important role in the growth, metabolism, and protection to pathogens. The mosquito microbiota is influenced by factors such as feeding source, female-to-egg, and larva-to-adult transitions; however, there is still lack of knowledge on the impact of each of these factors on the mosquito bacterial community composition. Various reports have revealed an important role of bacteria of the Anopheles midgut in reducing the Plasmodium parasite. The identification of native bacteria is relevant in the search for biocontrol candidates for malaria control. Therefore, in this study the gut bacteria of larvae, field-captured, and emerged An. albimanus from Colombia were characterized to elucidate the influence of the environment and transstadial transition on the bacterial community composition. Bacterial identification was performed by culture-dependent methods and 16S rDNA gene sequencing by Sanger and Illumina-Mi seq. A greater bacterial richness of field-collected mosquitoes was detected with Bacillus spp. predominating, whereas Acinetobacter spp. and Enterobacter spp. prevailed on the emerging mosquitoes. Additionally, a decrease in the number of taxa on the larva-to-adult transition was evident. The results indicate a strong influence of the environment on the bacterial community composition of adult mosquitoes and bacterial colonization after the larva-to-adult transition

The aquatic systems in the state of Nuevo Leon have been threatened by the incorporation of external agents causing contamination increases over time, creating ideal sites for the development of mosquito species of the genus Culex, vectors of diseases such as West Nile and lymphatic filariasis, being a risk factor for the public's health. The aim of this study was to evaluate the efficacy of a local formulation of Bacillus thuringiensis israelensis (Bti) and Spinosad formulation in larval habitats of Culex spp. in the Pesqueria river in Santa Rosa, Apodaca, Mexico. Three ponds were selected, the first for Bti (C1), the second for Spinosad (C2), and the last one as control (C). A pretreatment sampling was performed on April 19, 2017. The next day, the formulation of Bti (3.55 g/m²) and Spinosad (1 tablet/200 liter) was applied. The postapplication samples were taken at 24, 48, and 72 h, keeping 7 repetitions of each treatment. The samples were transported to the laboratory and identified through the use of taxonomic keys to carry out the statistical analysis with ANOVA. The results showed that there was a significant difference between the treatments of Bti and Spinosad. The efficacy of the Bti and Spinosad formulations in Culex larval habitats was evaluated by observing a 100% decrease in the mosquito population at 72 h postapplication of Spinosad larvicide, whereas Bti did not show a good result in the controlling the mosquito populations in this trial.

Fifty species of sand flies have been registered in Mexico, of which Bichromomyia olmeca is a known vector of cutaneous leishmaniasis (CL), and 7 other species are suspected of being involved in the transmission of leishmaniasis. This study was performed in a tropical forest named Guadalupe Miramar (GM) with fragmented vegetation of tropical forest at 432-m altitude, and mixed patches of tropical and pine–oak forest of San Antonio Buena Vista (SABV) at 1,380-m altitude. This border region between Mexico and Guatemala is a zone of CL transmission. To compare phlebotomine diversity among vegetation types, samples were taken with the use of miniature CDC light traps (mod. 512) at 50, 100, 250, and 500 m from the edge of each habitat at each site based on 4 transects from July 2009 to June 2010. In total, 3,989 sand flies were collected belonging to 10 genera and 23 species. Overall, 97.2% of phlebotomines were collected in GM comprising 23 species, compared with 7 species at SABV. The most prevalent species collected in GM was Psychodopygus panamensis (25.9%), followed by Lutzomyia hartmanni (5.7%), and Psathyromyia carpenteri (5.3%). In contrast, in SABV the most abundant species was Lu. cruciata (80.2%), followed by Ps. shannoni (5.4%) and Pintomyia ovallesi (4.5%). Five of these species have been implicated in the transmission of leishmaniasis. Species diversity and equity was highest in GM (Shannon's H' = 2.31, E = 0.7) and lowest in SABV (H' = 0.84, E = 0.4). Significant differences were observed in species diversity between coffee plantations and perturbed vegetation (P < 0.05), and at different distances (P < 0.05) at GM, but not at the SABV (P < 0.05). Differences in the abundance and diversity of phlebotomines are likely caused by climatic factors, habitat type, and human perturbation.

Financial support for the 28th Annual Symposium was provided by Clarke Mosquito Control. Funds from this sponsor provided support for the Annual Meeting of the Latin American Student Competition. The continuing support by the AMCA for this symposium is also acknowledged. Enthusiasm and interest for this symposium among Spanish- and non-Spanish-speaking participants continues to be high and it will continue to be a part of the future annual meetings.