Methods in Anopheles Research - MR4

Chapter 1 : Insectary Operation1.4 Maintaining Stock PurityPage 1 of 21.4 Maintaining Stock PurityMR4 StaffIntroductionAny lab that cultures more than one stock must prevent contamination. Stock identity is determinedultimately by genetic composition; therefore, stocks that are contaminated are of little value, especially iftheir only known distinguishing characteristic was origin location. Physical isolation in different rooms isoften used to prevent contamination but this has limits as the number of stocks increases. Therefore,keeping stocks pure ultimately depends on conscientious methodical attention to detail when makinglabels, transferring pupae and adults, putting egg dishes into cages, etc. Moreover, if your strains are notphenotypically defined, it may be impossible to determine that they are contaminated later.Diligent exercise of precautionary methodology is the only way you will prevent contamination. This canbe augmented by using phenotypically marked stocks when possible. Recessive markers are the bestchoice since contamination is more readily detected. The best advice is to stay conscious, careful andfollow routines designed to avoid contamination.Ways to avoid contamination:There is no substitute to consistent attention to detail, but the following are some ways stocks canbecome contaminated with suggestions for avoiding them.Use carefully decontaminated materialsCause: Pupae and larvae easily get stuck in devices and are very difficult to see at a glance. Whenswitching to another stock, it is easy to not notice the contaminant and transfer from strain to strain(Figures 1.4.1 and 1.4.2).To prevent: visually examine tools and rinse in hot water between handling each stock. If you keep only acouple of stocks, separate, clearly marked tools should be kept for each. Use white and transparentcontainers when possible and white countertops.Figure 1.4.1. Hand held pupa pickers with asingle pupae stuck in the apparatus, shownby arrows.Figure 1.4.2. Larval strainer with a singlelarva stuck in the apparatus, shown witharrow.Cause: Eggs in water can easily spill or splash onto the lid of a pan or cup (Figure 1.4.3). Reusing thesame lid or cup for another stock without decontamination can lead to egg transfer.To prevent: use fresh lids and cups that are decontaminated by desiccation, washing, and/or autoclaving,and consistently return the same lid to each container.