Determination of predator feeding preference on immature stages of Anopheles mosquitos

Abstract

Malaria is a serious threat to the social and economic advancement of this country and it is among the top ranking tropical diseases under consideration by the World Health Organization (WHO). Vector control is considered as an important component in malaria control initiatives. Currently, there has been emphasis on integrated pest control management due to insecticide resistance and environmental contamination by chemical insecticides. This has resulted to increased interest in alternative approaches such as exploitation of predators and pathogens of medically important arthropods. Predation pressure on mosquito larvae is a key mechanism for regulation of mosquito populations. Understanding the interrelationships of predators and their final impact on mosquito larvae, will provide information on the types of predation pressure present.

This research focused on predation level of anopheline larvae by five most common aquatic predators collected from four semi-permanent habitats in Jaribuni area of Kilifi district. The five predators evaluated for their feeding preference were Dytiscids, Notonectids, Hydrometrids, Veliids and Gerrids. An evaluation was done on one and two-predator treatments to determine their trophic level at 6 and 24 hours and a comparison done between one and two-predator treatments to determine whether there was any synergistic or antagonistic effects. Anopheline larvae and pupae were collected by the dipping technique while predators were collected by the use of aquatic net.

Predation levels of one and two-predator treatments were determined by computing the mean number of the surviving larvae and pupae at 24 hours using a Mann-Whitney U test for independence. The paired t-test (SPSS 11.0) was used to determine the mortality of test predators by comparing the paired mortality events for predators that died in onepredator treatments with those which died in the two-predator treatments.

In one-predator treatment Notonectids consumed the highest number of anopheline larvae in all instars tested (P<0.05). In the two-predator treatments, when Notonectids were added to any of the other four predators the results were additive, meaning that more larvae were consumed. However, consumption was highest when Notonectids were added to Dytiscids (P<0.05, Mean Change= -18.4)). For the evaluation of intraguild predation, Notonectids and the Dytiscids beetles had antagonistic interactions, with more Dytiscids dying in the presence of Notonectids than when alone (P=0.007). The number of Notonectids that died alone did not increase when Dytiscids were added (P=0.684). Notonectids were the most predominant and prevalent potential predators that showed strong feeding preference for the mosquito larvae and pupae and can therefore be exploited as invertebrate predators against anopheline larvae and pupae.