Dense populations of extracellular bacteria were detected in midgut crypts of the southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae). Examination by epifluorescent and transmission electron microscopy revealed that the bacteria covered the luminal surface of the crypts and filled the entire lumen. Attempts to culture the extracellular endosymbionts in various media failed. Sequencing and phylogenetic analyses of 16S rRNA gene clones obtained from insects of five Florida populations showed high nucleotide homology to either betaproteobacterial Burkholderia spp. (243 clones from five populations) or gammaproteobacterial Pseudomonas spp. (58 clones from one population). Using Burkholderia‐specific primers, bacteria were detected in the egg, nymph, and adult stages. Fluorescent in situ hybridization with genus‐specific oligonucleotide probes confirmed the localization of Burkholderia in the crypts. Quantitative real‐time PCR showed that antibiotic treatments of nymphs significantly reduced the amount of Burkholderia 16S rRNA gene copies in chinch bugs sampled 11 days after the treatment. Furthermore, these treatments resulted in retarded development and high mortality of B. insularis, indicating a beneficial impact of Burkholderia on its host.
Electrical penetration graph (EPG) monitoring has been used extensively to elucidate mechanisms of resistance in plants to insect herbivores with piercing-sucking mouthparts. Characterization of waveforms produced by insects during stylet probing is essential to the application of this technology. In the studies described herein, a four-channel Backus and Bennett AC-DC monitor was used to characterize EPG waveforms produced by adults of two economically important chinch bug species: southern chinch bug, Blissus insuhris Barber, feeding on St. Augustinegrass, and western chinch bug, Blissus occiduus Barber, feeding on buffalograss. This is only the third time a heteropteran species has been recorded by using EPG; it is also the first recording of adult heteropterans, and the first of Blissidae. Probing of chinch bugs was recorded with either AC or DC applied voltage, no applied voltage, or voltage switched between AC and DC mid-recording, at input impedances ranging from 106 to 1010 Ω, plus 1013 Ω, to develop a waveform library. Waveforms exhibited by western and southern chinch bugs were similar, and both showed long periods of putative pathway and ingestion phases (typical of salivary sheath feeders) interspersed with shorter phases, termed transitional J wave and interruption. The J wave is suspected to be an Χ wave, that is, in EPG parlance, a stereotypical transition waveform that marks contact with a preferred ingestion tissue. The flexibility of using multiple input impedances with the AC-DC monitor was valuable for determining the electrical origin (resistance vs. electromotive force components) of the chinch bug waveforms. It was concluded that an input impedance of 107 Ω, with either DC or AC applied voltage, is optimal to detect all resistanceand electromotive force-component waveforms produced during chinch bug probing. Knowledge of electrical origins suggested hypothesized biological meanings of the waveforms, before time-intensive future correlation experiments by using histology, microscopy, and other techniques.
Over 400,000 ha of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, are managed as a turfgrass in the southern United States, and the southern chinch bug, Blissus insularis Barber, is its most important insect pest. New sources of host plant resistance to southern chinch bugs became necessary due to the development of virulent populations of chinch bugs which were able to feed on the only acceptable resistant cultivar, Floratam. Initial testing evaluated 14 lines for chinch bug resistance using insects collected from five locations from Palm Beach Co., FL. Host plant resistance was determined by mortality of adult chinch bugs held on a turfgrass for 14 d. A second study was conducted with five lines from the first test with southern chinch bugs collected from nine locations throughout Florida. Tests showed a high level of southern chinch bug resistance in NUF 76, NUF 216 and FX-10. Leaf blades of NUF-76 are significantly shorter and narrower than other tested St. Augustinegrass lines when evaluated 2 wks after mowing. NUF-76 is unique because for the first time, resistance to the southern chinch bug has been identified within a diploid line of St. Augustinegrass. Prior to this, southern chinch bug resistance was only associated with polyploid lines which generally have large leaves and reduced or no seed set due to sterility problems. This discovery will allow chinch bug resistance to be more easily bred into other St. Augustinegrass lines.
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