Larval food quantity affects development time, survival and adult biological traits that influence the vectorial capacity of Anopheles darlingi under laboratory conditions

Abstract

Background: The incidence of malaria in the Amazon is seasonal and mosquito vectorial capacity parameters, including abundance and longevity, depend on quantitative and qualitative aspects of the larval diet. Anopheles darlingi is a major malaria vector in the Amazon, representing >95% of total Anopheles population present in the Porto Velho region. Despite its importance in the transmission of the Plasmodium parasite, knowledge of the larval biology and ecology is limited. Studies regarding aspects of adult population ecology are more common than studies on larval ecology. However, in order develop effective control strategies and laboratory breeding conditions for this species, more data on the factors affecting vector biology is needed. The aim of the present study is to assess the effects of larval food quantity on the vectorial capacity of An. darling under laboratory conditions.

Methods: Anopheles darlingi was maintained at 28°C, 80% humidity and exposed to a daily photoperiod of 12 h. Larvae were divided into three experimental groups that were fed either a low, medium, or high food supply (based on the food amounts consumed by other species of culicids). Each experiment was replicated for six times. A cohort of adults were also exposed to each type of diet and assessed for several biological characteristics (e.g. longevity, bite frequency and survivorship), which were used to estimate the vectorial capacity of each experimental group.

Results: The group supplied with higher food amounts observed a reduction in development time while larval survival increased. In addition to enhanced longevity, increasing larval food quantity was positively correlated with increasing frequency of bites, longer blood meal duration and wing length, resulting in greater vectorial capacity. However, females had greater longevity than males despite having smaller wings.

Conclusions: Overall, several larval and adult biological traits were significantly affected by larval food availability. Greater larval food supply led to enhance larval and production and larger mosquitoes with longer longevity and higher biting frequency. Thus, larval food availability can alter important biological traits that influence the vectorial capacity of An. darlingi.

Figure 1

Survival and average instar duration of Anopheles darlingi larvae fed with increasing food amounts. L1, L2, L3 and L4 indicate the first, second, third and fourth larval instars, respectively and L5 indicates the pupal stage. See Table 1 for food amount supplied to each instar.

Figure 2

Daily proportion of biting Anopheles darlingi emerged from larvae fed with increasing food amounts. One Way Repeated measures ANOVA. NS: indicates no significant differences (P>0.05). See Table1 for food amount supplied to each instar.

Figure 3

Adult longevity (A) and wing length of male and female (B) Anopheles darlingi emerged from larvae fed with increasing food amounts. Anova on ranks (Kruskal-Wallis) and Dunn's method (comparisons); n=38 (Low) and n=80 (Medium and High); Different letters indicate significant differences (P<0.05). See Table 1 for food amount supplied to each instar.