Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2005
Publication Date: N/A
Interpretive Summary: A bacterium, Serratia marcescens, causes Cucurbit Yellow Vine Disease and is transmitted by the squash bug. The goal of this work was to describe, in part, how the bacterium is acquired by squash bug and transmitted to healthy plants. Ultimately this knowledge would be useful in determining the specific relationship between S. marcescens and squash bug. Three generally accepted types of relationships among insect vectors and plant pathogens have been described. These include noncirculative (nonpersistent and semipersistent transmission) circulative, and propagative relationships and are based, in part, upon the pathogen retention site in the vector (foregut or hemocoel), minimum latent period, retention time, retention after molting, and ability to multiply within the vector. The fact that some squash bugs transmitted S. marcescens to cubes or plants within 24-48 hr indicates that if there is a latent period it is moderately short. These insects were also capable of intermittent transmission for at least 21 days, indicating a long retention time. Transmissibility of nonpersistently- or semipersistently-transmitted viruses is lost after 24 or 48 hrs, respectively, so the long S.marcescens retention time would suggest that this bacterium is not transmitted in a non- or semipersistent manner. This is consistent with fact that no non- or semipersistently-transmitted bacteria have been described. The information reported in this paper not only confirms that squash bug transmits S. marcescens, the causal agent of Cucurbit Yellow Vine Disease, but also provides important basic information relevant to insect transmission in general and to development of management strategies for the disease.
Technical Abstract: Symptoms of cucurbit yellow vine disease (CYVD) in squash, pumpkin, watermelon, and cantaloupe include chlorosis, rapid wilting, and death. The causal agent of CYVD, Serratia marcescens, is transmitted by the squash bug, Anasa tristis. In this study, we characterized basic parameters of S. marcescens transmission by A. tristis. A. tristis adults of both sexes acquired by feeding on bacteria-infiltrated cubes of squash fruit. A few bugs transmitted S. marcescens to a fresh, unilfiltrated cube within 24 hr, but most transmissions occurred between 2 and 8 days post-acquisition. The squash bugs retained S. marcescens and were able to transmit the bacterium at least as long as 21 days post-acquisition, the duration of the experiments. When a pumpkin plant, rather than a squash cube, was the target, transmission occurred between 11 and 21 days post-acquisition. S. marcescens was detected inconsistently in the hemolymph of bacteria-fed insects; its presence there did not correlate with ability to transmit. Eggs laid by female A. tristis that had transmitted bacteria tested negative for S. marcescens by specific PCR, suggesting that this bacterium is not vertically transmitted.