Lauren L. Pinault

Recent collection data indicate that at least four potential malaria vectors occupy more widespread distributions within the Andean highlands than in the past. Since habitat elimination is an important aspect of malaria control, it is vital to characterize larval habitats for Anopheles species within both lowland and highland sites. To that end, 276 sites within Ecuador were surveyed between 2008 and 2010. Characteristics of Anopheles-present sites for four species were compared to Anopheles-absent sites within the same geographical range and also to Anopheles-absent sites within a highland range representing potential future habitats. Thermochron iButtons(©) were used to describe the daily temperature variation within a subset of potential habitats. Anopheles albimanus (W.) was positively associated with permanent habitats, sand substrates, floating algae (cyanobacterial mats), and warmer temperatures in both comparisons. Anopheles pseudopunctipennis (T.) was associated with floating algae (cyanobacterial mats), warmer temperatures, and higher water clarity in both comparisons. Anopheles punctimacula (D.&K.) was negatively associated with floating algae and positively associated with dissolved oxygen in both comparisons. Anopheles oswaldoi s.l. (P.) was not significantly associated with any parameters more often than expected given larval-absent sites. The results indicate that minimum water temperatures might limit the upper altitudinal distribution of An. albimanus (18.7° C) and An. pseudopunctipennis (16.0° C).

A recent epidemic of malaria in the highlands of Bolivia and establishment of multiple Anopheles species mosquitoes in the highlands of Ecuador highlights the reemergence of malaria in the Andes Mountains in South America. Because malaria was endemic to many highland valleys at the beginning of the 20th century, this review outlines the 20th century history of malaria in the highlands of Ecuador, and focuses on its incidence (e.g., geographic distribution) and elimination from the northern highland valleys of Pichincha and Imbabura and the role of the Guayaquil to Quito railway in creating highland larval habitat and inadvertently promoting transportation of the vector and parasite. Involvement of control organizations in combating malaria in Ecuador is also outlined in a historical context.

Larval habitat for three highland Anopheles species: Anopheles albimanus Wiedemann, Anopheles pseudopunctipennis Theobald, and Anopheles punctimacula Dyar and Knab was related to human land uses, rivers, roads, and remotely sensed land cover classifications in the western Ecuadorian Andes. Of the five commonly observed human land uses, cattle pasture (n = 30) provided potentially suitable habitat for A. punctimacula and A. albimanus in less than 14% of sites, and was related in a principal components analysis (PCA) to the presence of macrophyte vegetation, greater surface area, clarity, and algae cover. Empty lots (n = 30) were related in the PCA to incident sunlight and provided potential habitat for A. pseudopunctipennis and A. albimanus in less than 14% of sites. The other land uses surveyed (banana, sugarcane, and mixed tree plantations; n = 28, 21, 25, respectively) provided very little standing water that could potentially be used for larval habitat. River edges and eddies (n = 41) were associated with greater clarity, depth, temperature, and algae cover, which provide potentially suitable habitat for A. albimanus in 58% of sites and A. pseudopunctipennis in 29% of sites. Road-associated water bodies (n = 38) provided potential habitat for A. punctimacula in 44% of sites and A. albimanus in 26% of sites surveyed. Species collection localities were compared to land cover classifications using Geographic Information Systems software. All three mosquito species were associated more often with the category “closed/open broadleaved evergreen and/or semi-deciduous forests” than expected (P ≤ 0.01 in all cases), given such a habitat’s abundance. This study provides evidence that specific human land uses create habitat for potential malaria vectors in highland regions of the Andes.

Several recent climate change reviews have stressed the possibility of some malaria vectors occupying regions of higher altitudes than previously recorded. Indeed, highland malaria has been observed in several African nations, possibly attributable to changes in land use, vector control and local climate. This study attempts to expand the current knowledge of the distribution of common Anopheles species in Ecuador, with particular attention to highland regions (> 500 m) of the Andes.

To control malaria effectively, it is essential to understand the current knowledge, beliefs, concerns, land management practices, and mosquito bite protection methods in use by citizens. This study presents a comparative, quantitative, interview-based study of land owners and/or managers () in the Ecuadorian lowlands (presently considered malarious) () and highlands (potentially malarious in the future) (). Although respondents had a strong understanding of where the disease occurs in their own country and of the basic relationship among standing water, mosquitoes, and malaria, about half of respondents in potential risk areas denied the current possibility of malaria infection on their own property. As well, about half of respondents with potential anopheline larval habitat did not report its presence, likely due to a highly specific definition of suitable mosquito habitat. Most respondents who are considered at risk of malaria currently use at least one type of mosquito bite prevention, most commonly bed nets.

In two recent studies it was reported that feeding on foliage of multiple age classes can improve insect fitness, but it was not determined whether the increase in fitness was due to larvae obtaining a more balanced diet (the balanced-diet hypothesis) or to a difference in the nutritional requirements between young and old larvae (the ontogenetic hypothesis). To test these two hypotheses, we examined the foraging behaviour and performance of young (second or third to fourth instar) and old (third or fourth to fifth instar) larvae of the pale-winged gray moth, Iridopsis ephyraria (Walker) (Lepidoptera: Geometridae), on different-aged foliage of eastern hemlock, Tsuga canadensis (L.) Carrière (Pinaceae), during an outbreak in southwestern Nova Scotia. Defoliation attributed to I. ephyraria was highest on current-year foliage and gradually declined with foliage age. Young larvae were only observed feeding on current-year shoots but old larvae fed on foliage of all ages. When forced to feed on foliage of specific ages in manipulative field studies, survival rates of young and old larvae were highest on current-year and old (≥1 year old) foliage, respectively. However, both young and old larvae had higher survival rates when provided with access to foliage of all age classes than when they were forced to feed on only young or old foliage. Thus, this study supports both the balanced-diet and ontogenetic hypotheses.