Grass Pollen Affects Survival and Development of Larval Anopheles arabiensis (Diptera: Culicidae)

Abstract

Nutrients in breeding sites are critical for the survival and development of malaria mosquitoes, having a direct impact on vectorial capacity. Yet, there is a limited understanding about the natural larval diet and its impact on the individual fitness of mosquitoes. Recent studies have shown that gravid Anopheles arabiensis Patton (Diptera: Culicidae) are attracted by and oviposit in grass-associated habitats. The pollen provided by these grasses is a potential source of nutrients for the larvae. Here, we assess the effect of Typha latifolia L. (Poales: Typhaceae), Echinochloa pyramidalis Lamarck, Pennisetum setaceum Forsskål, and Zea mays L. pollen on larval survival and rate of development in An. arabiensis under laboratory conditions. In addition, we characterize the carbon to nitrogen ratio and the size of pollen grains as a measure of diet quality. Carbon-rich pollen with a small grain size (T. latifolia and P. setaceum; 9.7 ± 0.3 × 103 and 5.5 ± 0.2 × 104 µm3, respectively) resulted in enhanced rates of development of An. arabiensis. In contrast, the larva fed on the nitrogen-rich control diet (TetraMin) was slower to develop, but demonstrated the highest larval survival. Larvae fed on carbon-rich and large-grained Z. mays pollen (4.1 ± 0.2 × 105 µm3) survived at similar levels as those fed on the control diet and also took a longer time to develop compared with larvae fed on the other pollens. While males and females did not appear to develop differently on the different pollen diets, males consistently emerged faster than their female counterparts. These results are discussed in relation to integrated vector management.

Keywords: Carbon to nitrogen ratio; malaria; mosquito; nutrient; pollen grain.

Fig. 1.

Size (A) and carbon to nitrogen (C:N) ratios (B) of Typha latifolia, Echinochloa pyramidalis, Pennisetum setaceum, and Zea mays pollen are described in box plots (whiskers ± maximum and minimum values). The C:N ratio of the TetraMin control is also shown. Means with different letter designations are significantly different from one another (analysis of variance with Tukey’s HSD post hoc analysis; P < 0.05).

Fig. 2.

The survival to adulthood of Anopheles arabiensis, presented as number of mosquitoes emerged (A), and the probable life expectancy of the larvae in response to Echinochloa pyramidalis, Pennisetum setaceum, Typha latifolia, and Zea mays pollen alone (B), and pollen-supplemented TetraMin fish food (C) diets. Control diets include the effective dose for 50% survival (ED₅₀) and 2× ED₅₀ TetraMin fish food (0.75 mg and 1.5 mg, respectively). The error bars represent the standard error of the mean (A) and whiskers represent the upper and lower limits of variation (B and C). Means with different letter designations are significantly different from one another (analysis of variance with Tukey’s HSD post hoc analysis; P < 0.05) (A).

Fig. 3.

The probability of pupation of female (A and B) and male (C and D) mosquitoes over time in response to Echinochloa pyramidalis, Pennisetum setaceum, Typha latifolia, and Zea mays pollen alone (A and C) and pollen-supplemented TetraMin fish food (B and D) diets. Control diets include the effective dose for 50% survival (ED₅₀) and 2× ED₅₀ TetraMin fish food (0.75 mg and 1.5 mg, respectively). The whiskers represent the upper and lower limits of variation.

Fig. 4.

The probability of adult emergence of female (A and B) and male (C and D) mosquitoes over time in response to Echinochloa pyramidalis, Pennisetum setaceum, Typha latifolia, and Zea mays pollen alone (A and C) and pollen-supplemented TetraMin fish food (B and D) diets. Control diets include the effective dose for 50% survival (ED₅₀) and 2× ED₅₀ TetraMin fish food (0.75 mg and 1.5 mg, respectively). The whiskers represent the upper and lower limits of variation.