Temporal analysis of cotton boll symptoms resulting from southern green stink bug (Nezara viridula L.) feeding and transmission of a bacterial pathogen

Authors: Medrano, Enrique; Esquivel, Jesus; NICHOLS, ROBERT - COTTON INC; Bell, Alois - Al

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2008
Publication Date: 2/28/2009
Citation: Medrano, E.G., Esquivel, J.F., Nichols, R.L., Bell, A.A. 2009. Temporal analysis of cotton boll symptoms resulting from southern green stink bug (Nezara viridula L.) feeding and transmission of a bacterial pathogen. Journal of Economic Entomology. 102:36-42.

Interpretive Summary: An emerging disease and significant cause of cotton yield losses that was first reported in South Carolina has since afflicted fields located along the southeastern cotton belt. Characteristics of this disease include an apparently normal green boll that contains dead seeds and discolored fiber. Therefore, affected fields appear healthy until infected bolls crack open, only then revealing the dark, matted lint instead of fluffy fiber. Previously, we determined that the disease is caused by bacteria and identified a Pantoea agglomerans strain as an agent capable of producing the same symptoms and that the pathogen is transmitted by a prominent cotton pest called the southern green stink bug. In this report, we describe the progression of infection based on boll age at the point of infection and the symptoms observed one, two and three weeks following the introduction of the P. agglomerans germ by stink bugs. We found that bolls at one or two weeks after the flowering stage are susceptible to the spread of the disease; whereas at three weeks past flowering, boll infections are minimal and contained to the point of insect introduction of the disease agent. Collectively, these results may assist in informing the growers when pesticide applications are no longer necessary despite insect infestation, and thus provide a savings in both insecticides and costs associated with applications.

Technical Abstract: The southern green stink bug (SGSB)(Nezara viridula L.) is a significant pest of cotton and is becoming an increasing challenge due to the decrease in use of broad spectrum insecticides on the crop. The SGSB can vector an opportunistic Pantoea agglomerans strain (designated Sc 1-R) into cotton bolls resulting in infection. The appearance of stink bug damage varies and pest managers can not readily identify its source. This research reports a systematic depiction of green, immature boll responses at various stages of maturity (one, two, and three week post-anthesis [WPA]) to stink bug injury and to infection by the vectored cotton pathogen by demonstrating the progression of effects one, two, and three weeks after exposure (WAE). When lab-reared adult SGSB not harboring Sc 1-R deposited bacteria into greenhouse-grown bolls at one, two, or three WPA during feeding/probing, bacteria reached concentrations of 10**9, 10**9, and 10**3 colony forming units (CFU)/g tissue, respectively, at three WAE, yet caused minimal seed and lint damage regardless of the age of the bolls that were penetrated. Bolls at a maturity of one or 2 WPA showed similar susceptibility when exposed to stink bugs that vectored Sc 1-R. After a week of infection, seeds were salmon-pink in color with normal white lint and up to 10**4 CFU/g tissue when Sc 1-R was detected. Necrosis of the entire inoculated locule(s) with a maximum Sc 1-R concentration detected at 10**8 CFU/g tissue occurred in samples harvested two or three WAE. Conversely, seed and lint deterioration due to the transmitted opportunist into bolls exposed three WPA was confined to the puncture site. In summary, after a week of development, bolls were tolerant to SGSB feeding/probing damage and to non-pathogenic bacteria, but were severely damaged when the opportunistic pathogen Sc 1-R was transmitted. At three WPA the fruit was immune to the spread of the pathogen with infections confined to the puncture site.