4,4’-dichlorodiphenyltrichloroethane (DDT) has been re-recommended by the World Health Organization for malaria mosquito control in Africa. Previous DDT use has resulted in predisposition of resistance, and with continued use resistance will increase further in terms of level and extent. Drosophila melanogaster is a model dipteran that has many available genetic tools, has been widely used for elucidating insecticide resistance mechanisms, and is related to malaria mosquitoes allowing for extrapolation. The 91-R strain of D. melanogaster is highly resistant to DDT (>1500-fold); however, there is no mechanistic scheme that accounts for this level of resistance. Recently, reduced penetration, increased detoxification, and direct excretion have been identified as resistance mechanisms in the 91-R strain. Their interactions, however, remain unclear. Use of Gal4/UAS-RNAi transgenic lines of D. melanogaster allowed for the targeted knockdown of genes putatively involved in DDT resistance and has identified the role of several cuticular proteins (Cyp4g1 and Lcp1), cytochrome P450 monooxygenases (Cyp6g1 and Cyp12d1), and ATP binding cassette transporters (mdr50, mdr65, and mrp1) in increased sensitivity to DDT. These findings have been further validated in 91-R flies using a nanoparticle-enhanced RNAi strategy, directly implication these genes in DDT resistance in 91-R flies.

The body and head lice (Pediculus humanus humanus and Pediculus humanus capitis, respectively) are hematophagous ectoparasites of humans and only the body louse between two is known to transmit three bacterial diseases through its feces. The proliferation profiles of Bartonella quintana, the causative agent of trench fever, inside the louse body and its excretion patterns were investigated in the two louse subspecies following oral challenge with B. quintana-infected blood meal. The initial density of B. quintana was sustained inside head lice without any noticeable proliferation for the entire period after infection. In contrast, B. quintana proliferated rapidly inside body lice and the maximum density reached at 10 days post-infection. The numbers of bacteria detected in feces from infected lice were almost the same and steadily decreased over time in both body and head lice. Nevertheless, the viability of the bacteria, as determined by fluorescence, was significantly higher in body louse feces, especially at 1 day post-infection and this tendency lasted for 11 days. These findings suggest that excretion of feces containing more viable B. quintana that is proliferated inside body lice following ingestion of infected blood meal is responsible for the higher vector competence of body lice.