Aims: To determine the ability of the southern green stink bug (SGSB) (Nezara viridula L.) to transmit Pantoea agglomerans into cotton (Gossypium hirsutum) bolls. Methods and Results: An SGSB laboratory colony was kept on fresh green beans. A P. agglomerans variant resistant to rifampicin (Rif) (strain Sc 1-R) was used as the opportunistic cotton pathogen. Adult insects were individually provided green beans that were sterilized and then soaked in either sterile water or in a suspension of strain Sc 1-R. Insects were individually caged with an unopened greenhouse-grown cotton boll. After 2 days, live SGSB were collected, surfaced sterilized, ground, serially diluted, and then plated on nonselective media and media amended with Rif. Exterior and interior evidence of feeding on bolls was recorded 2 weeks after exposure to insects. Seed and lint tissue were harvested, ground, serially diluted, and then plated on media with and without Rif. Bacteria were recovered on nonselective media from all insects, and from seed and lint with signs of insect feeding at concentrations ranging from 10 2 to 10 9 CFU g )1 tissue. The Sc 1-R strain was isolated only from insects exposed to the marked strain and from seed and lint of respective bolls showing signs of insect feeding. Evidence of insect feeding on the exterior wall of the carpel was not always apparent (47%), whereas feeding was always observed (100%) on the interior wall in association with bacterial infections of seed and lint. Conclusions: Nezara viridula readily ingested the opportunistic P. agglomerans strain Sc 1-R and transmitted it into unopened cotton bolls. Infections by the transmitted Sc 1-R strain caused rotting of the entire locule that masked internal carpel wounds incurred by insect feeding. Bacteria were recovered from penetration points by insects not exposed to the pathogen, but locule damage was limited to the area surrounding the feeding site (c. 3 mm).Significance and Impact of the Study: This is the first study that demonstrates the ability of SGSB to acquire and transmit plant pathogenic bacteria into cotton bolls.
Southern green stink bugs, Nezara viridula (L.) (Hemiptera: Pentatomidae), and related species are significant pests of cotton, Gossypium hirsutum L. (Malvaceae), in the USA Cotton Belt. Using their stylets, adults introduce pathogens of cotton into cotton bolls, and preliminary data indicate nymphs can also ingest these pathogens. However, data are lacking regarding stylet penetration potential of N. viridula nymphs, and records of stylet penetration by adults are typically determined after damage has occurred. In this study, rostral segments of all developmental stages of N. viridula were measured to estimate potential stylet penetration depth using a novel mathematical model. Overall mean stylet penetration estimates for all stages ranged from 135.3 μm for first instars to 2 389.3 μm for adult females. Potential stylet penetration significantly increased as the insect progressed through nymphal stages. Penetration was also significantly affected by insect posture while feeding. Overall minimum and maximum observed lengths of rostrum ranged from 835.3 μm (first instars) to 7 088.2 μm (adult females), and mean rostral lengths were significantly different between all stages. This report establishes conservative baselines of potential stylet penetration depths by all nymphal stages and both adult sexes of N. viridula. Additionally, the model presented here can be used to estimate potential stylet penetration for other Hemiptera and closely related insects with similar modes of feeding. In conjunction with crop phenology data, accurate estimates of potential stylet penetration will allow more proactive approaches to pest management in a wide range of high‐value cash crops affected worldwide by N. viridula.
Recently, we showed that the southern green stink bug (SGSB), Nezara viridula (L.), can transmit Pantoea agglomerans (Ewing and Fife), an opportunistic bacterium, into green cotton bolls resulting in plant disease. Here, we hypothesized that our established model could be used to determine if the SGSB was a general, non-discriminate vector by using two other opportunistic bacterial pathogens of bolls (Pantoea ananatis [Serano] and Klebsiella pneumoniae [Schroeter]) and the known fungal pathogen Nematospora coryli (Peglion). Variants of P. ananatis (strain Pa-1R) and K. pneumoniae (strain Kp 5-1R) selected for rifampicin (Rif) resistance were used as bacterial opportunists. N. coryli was detected only from laboratory-reared SGSB directly exposed to the fungus. Both Pa-1R and Kp 5-1R were recovered from SGSB previously provided a contaminated food source (2 days), sterile food (5 days), and then harvested after being caged on bolls (2 days) at levels reaching 10(3) and 10(4) colony forming units (cfus) per insect, respectively. However, bolls caged with insects infected with Pa-1R or Kp 5-1R and with evidence of feeding did not become diseased nor were either opportunists detected from boll tissues. Insects infected with N. coryli transmitted the pathogen, which resulted in diseased bolls and fungi concentrations reached 10(6) cfus/g locule tissue at 2 weeks following the caging period. Notably, each of the three pathogens independently caused boll disease when mechanically inoculated using a needle puncture. Generally, these results suggest that cotton pathogen acquisition by the SGSB was not sufficient to determine whether the insects were disease vectors of the opportunists.
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