Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Proceedings
Publication Acceptance Date: 5/22/1997
Publication Date: N/A
Interpretive Summary: Citrus Tristeza Virus (CTV) is one of the most destructive diseases of citrus worldwide. The virus is transmitted by aphid. Until recently in the US, the main vector has been the melon aphid. The most efficient vector of CTV is the brown citrus aphid, which was recently introduced into Florida in November 1995. This study contains data from over 160 research plots located in Florida, California, Spain, Costa Rica, Dominican Republic, and Trinidad to study the different effects that these two aphids have on CTV increase and spread. This information will be used in the U.S. to help regulatory agencies and growers to better understand and prepare for increased economic losses due to CTV. It was found that CTV increases 3-4 times faster in the presence of the brown citrus aphid. It was also found that CTV infected trees tend to be in aggregates or groups in a grove when the brown citrus aphid is present whereas, CTV infected trees were much more widespread when only the melon aphid was present. Such basic information on the study of aphid dynamics and their effect on CTV increase and spread will be used in future studies to help develop control strategies to lessen the effect of the brown citrus aphid on CTV associated losses.
Technical Abstract: Data from Florida, Spain, Taiwan, Costa Rica, the Dominican Republic, and California were used to develop models for increase and spread of CTV. In locations where the melon aphid, Aphis gossypii, was the predominant CTV vector, CTV progressed from low (approximately five percent) to high (approximately 95 per cent) levels in eight to fifteen years. In contrast, when the brown citrus aphid, Toxoptera citricida, was predominant, this same increase often occurred in only two to four years. Where the melon aphid was the predominant vector, new infections were diffuse and not closely associated with existing infected trees but rather with trees several tree spaces distant. Where both species coexisted, but the brown citrus aphid was the dominant species, spread to trees immediately adjacent to existing infections was common, resulting in aggregations of CTV-infected trees, although longer distance spread also occurred. CTV infections were generally diffuse or quite aggregated where the melon aphid or the brown citrus aphid was the predominant species, respectively. Thus, aphid species greatly influenced the rate and patterns of CTV epidemics and their presence or absence was important to predict how CTV will increase and spread over time.