Abstract
The Southern chinch bug, Blissus insularis, possesses specialized midgut crypts that harbor dense populations of the exocellular symbiont Burkholderia. Oral administration of antibiotics suppressed the gut symbionts in B. insularis and negatively impacted insect host fitness, as reflected by retarded development, smaller body size, and higher susceptibility to an insecticide, bifenthrin. Considering that the antibiotics probably had non-lethal but toxic effects on host fitness, attempts were conducted to reduce gut symbionts using bacteriophage treatment. Soil-lytic phages active against the cultures of specific Burkholderia ribotypes were successfully isolated using a soil enrichment protocol. Characterization of the BiBurk16MC_R phage determined its specificity to the Bi16MC_R_vitro ribotype and placed it within the family Podoviridae. Oral administration of phages to fifth-instar B. insularis, inoculated with Bi16MC_R_vitro as neonates had no deleterious effects on host fitness. However, the ingested phages failed to impact the crypt-associated Burkholderia. The observed inactivity of the phage was likely due to the blockage of the connection between the anterior and posterior midgut regions. These findings suggest that the initial colonization by Burkholderia programs the ontogeny of the midgut, providing a sheltered residence protected from microbial antagonists.
Highlights
Many insect species in the order Hemiptera live on nutritionally deficient food sources that lack essential amino acids, water soluble vitamins (B-vitamins), and/or lipids [1,2]
Augustinegrass had fewer Burkholderia 16S rRNA gene copies in the midgut crypts, exhibited lower survivorship and slower development than insects fed antibiotic-free grass. These findings suggested that gut-symbiotic Burkholderia assisted in the fitness of B. insularis [11]
During the 10-day exposure to food supplemented with a rotation of antibiotics, fifth instars of
Summary
Many insect species in the order Hemiptera live on nutritionally deficient food sources (i.e., plant phloem, xylem, seed, or vertebrate blood) that lack essential amino acids, water soluble vitamins (B-vitamins), and/or lipids [1,2]. Studies that used antibiotic treatment (ingestion or injection) and/or egg surface sterilization suppressed or eliminated gut symbionts, resulting in increased mortality rates, slower growth, reduced body size, and/or abnormal pale body coloration of their respective host insects [9,10,11,12]. These bacteria are believed to provide a nutritional role, promote overall fitness (i.e., growth, body size, longevity, fecundity), and/or affect other phenotypic characters (i.e., body coloration) of their hosts [10,13,14]. Gut-symbiotic bacteria have been reported to protect hosts against pathogens [15], parasites [16], and/or xenobiotics [17]
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