Effects of heavy metal toxicity on immunological response in the tobacco hornworm, Manduca Sexta
Nodule formation is one of the main cellular mechanisms insects utilize in response to infection. The nodulation reaction accounts for clearing nearly 90% of the bacterial cells from circulation. Furthermore, the nodulation assay is a useful tool for developing an understanding of how insects immune response to challenge. Little is known of environmental effects such as heavy metal toxicity on insect immunity. This study was designed to investigate a variety of heavy metals influence on the cellular immune response of the tobacco homworm, Manduca sexta, to bacterial challenge. The proposed study is a quantitative style. The first of several trials investigated the tolerance of the homworm to the heavy metal toxicity. Selected heavy metals were dissolved in the insect's artificial diet which was prepared in the laboratory. Data was collected on insect body mass and length, diet consumption and the amount of frass produced. After a sub-lethal level of heavy metal concentration in the diet was determined, the next step was to observe the effects of the heavy metal toxicity in combination with challenge. This portion of the study was performed when the insects reached the fifth instar in their larval development. The insects were then injected with a standard does of bacterium, Serratia marcescens and allowed to incubate for several hours. After incubation, the nodulation assay was performed. The results of this study suggest that some heavy metals may enhance insect cellular immune response to challenge while other heavy metals may impede cellular immune response to challenge.