The effect of seston on mortality of Simulium vittatum (Diptera: Simuliidae) from insecticidal proteins produced by Bacillus thuringiensis subsp. israelensis.
Water was collected from a site on the Susquehanna River in eastern Pennsylvania, where less-than-optimal black fly larval mortality had been occasionally observed after treatment with Bacillus thuringiensis subsp. israelensis de Barjac insecticidal crystalline proteins (Bti  ICPs). A series of experiments was conducted with Simulium vittatum Zetterstedt larvae to determine the water related factors responsible for the impaired response to Bti ICPs (Vectobac 12S, strain AM 65-52). Seston in the water impaired the effectiveness of the ICPs, whereas  the dissolved substances had no impact on larval mortality. Individual components of the seston then were exposed to the larvae followed by exposure to Bti ICPs. Exposure of larvae to selected minerals and nutritive organic material before ICP exposure resulted in no significant decrease  in mortality. Exposure of larvae to silicon dioxide, cellulose, viable diatoms, and purified diatom frustules before Bti ICP exposure resulted in significant reductions in mortality. Exposure of larvae to purified diatom frustules from Cyclotella meneghiniana Kützing resulted in  the most severe impairment of mortality after Bti ICP exposure. It is postulated that frustule-induced impairment of feeding behavior is responsible for the impairment of larval mortality.
The University of Georgia, Department of Entomology, Athens, GA 30602, USA. jpiburg@gmail.com
Joseph P
JP
Iburg
Elmer W
EW
Gray
Roger D
RD
Wyatt
Julia E
JE
Cox
Robert A
RA
Fusco
Raymond
R
Noblet
D000818:Animals; D001413:Bacillus thuringiensis / Q000502:physiology*; D001426:Bacterial Proteins / Q000633:toxicity*; D017377:Diatoms / Q000737:chemistry; D007306:Insecticides / Q000633:toxicity*; D007814:Larva / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology; D008903:Minerals / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry; D010414:Pennsylvania; D010572:Pest Control, Biological; D010933:Plankton / Q000737:chemistry; D012843:Simuliidae / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology*
D001426:Bacterial Proteins; D007306:Insecticides; D008903:Minerals; D009930:Organic Chemicals