Methods in Anopheles Research - MR4

Chapter 2 : Anopheles Laboratory Biology and Culture2.3 Modifying Fecundity, Longevity and Size v2Page 1 of 62.3 Modifying Fecundity, Longevity and SizePaul Howell and Liz WilkinsIntroductionMaintaining proper nutrition throughout larval development will have positive effects for the entirety of amosquito’s life. Optimization of nutrition, photoperiod, competition, and temperature will result in healthierlarvae and a more productive colony. If any of these is suboptimal, smaller and generally less vigorousmosquitoes will result. Large size has been often associated with increased fecundity and longevity inmany different species (Blackmore and Lord 2000, Briegel 1990, and Takken et al. 1998). Here wepresent some general information to assist in establishing rearing protocols for anopheline mosquitoes.Larval Diet and NutritionIncreased fecundity and longevity result partly from reserves accumulated during immature stages.Several factors can reduce these reserves and result in poor quality adults. Some studies indicate thatdiets high in protein are superior in producing larger, more fecund mosquitoes. Increases in egg clutchsize have been positively associated with high protein diets (Akoh et al. 1992, Lang 1978). Conversely,sub-optimal diets resulted in the production of smaller adults which were less likely to seek out a bloodmeal (Klowden et al. 1988). A high protein diet also reduced immature development times inToxorhynchites splendens (Amalraj et al. 2005). Therefore the quality of the diet can have significanteffects on colony production and growth.Not only is the quality of diet fed to larvae important, but the quantity is also significant. Reisen et al.(1984) illustrated the relationship between the concentration of food and larval development to pupation.Overfeeding larvae will often lead to high larval mortality (Reisen 1975). However, the surviving larvae willdevelop rapidly and result in large adults (Lillie and Nakasone 1982; Reisen et al. 1984). Conversely,underfed larvae will result in the production of smaller adults. In Cx. pipiens fatigans, underfeeding leadsto a reduction in the number of ovarian follicles (Ikeshoji 1965; Arrivillaga and Barrera 2004). Therefore,measured amounts of a larval diet should be supplied to ensure optimal growth and fecundity.Dietary Restriction (DR) has been studied for its effect on longevity extensively in flies and mice. Thoughthe results are not completely in agreement, the general conclusions are compatible. By and large, inanimals and insects, one of the most successful ways to extend longevity is through DR (Burger andPromislow 2004). For many species of animals, restricting diets yields animals that are leaner and haveincreased longevity (Hopkin 2003). These same animals, however, are typically less fertile and becomeinfected or sick more easily. DR animals are much slower than their better-fed counterparts (Hopkin2003). DR-affected animals live longer but show signs of age much more quickly (Hopkin 2003; Burgerand Promislow 2004). Longevity benefits are easily reversed with the introduction of any stressors to theenvironment as the DR animals are extraordinarily susceptible, especially to infection and sickness. Inthose cases, the better nourished animals will have the greater longevity (Hopkin 2003). A balanced dietat the beginning of life has the greatest benefit on overall lifetime longevity (Rasnitsyn and Yasyukevich1988; McCay et al. 1989).In flies, DR increased the life span of all females including fertile or sterile flies. Dietary manipulationgenerally has a greater and longer effect on females than males, though in a few studies, the opposite istrue (Burger and Promislow 2004).Alternately, it has also been reported that in some animals, the quality of the diet is the more importantfactor in increased growth and longevity than the amount (McCay et al. 1989). Most generally, in the wild,reproduction and speed are the most important elements for survival, and both are severely hindered byDR (Hopkin 2003). So, for a wild animal or insect, the best bet for reproduction and evasion of predatorsis to be big and fat (Hopkin 2003)!