Three German cockroach strains were used. The Johnson Wax strain (JWax-S) has been maintained in the laboratory for >80 yr without insecticide exposure and was used as a standard susceptible strain. Two field strains were collected from multifamily housing sites in Danville, IL (D-IL strain), and Indianapolis, IN (I-IN strain), during December 2014 and March 2015. Full human subjects research approval was granted by the Purdue University Institutional Review Board (Protocol number 1411015460R001). The field strains were collected from multiple apartments across each site and pooled to establish laboratory “meta” populations. These populations were maintained without insecticide selection pressure. Colonies were reared in Ziploc plastic containers (44.3 by 30 by17 cm3/15.14 liter; S.C. Johnson Inc., Racine WI, USA) with screened lids and held in a controlled-environmental chamber at 26 ± 1 °C and a photoperiod of 12:12 (L:D) h. Cardboard for shelter, rodent diet (number 8604; Harlan Teklad, Madison, WI), and water were provided ad libitum to the rearing boxes. Bioassay experiments were done with 1–2-wk-old adult males. To obtain enough adult males of appropriate age for experiments, rearing containers were established with gravid adult females and mixed-age nymphs. Adult male cockroaches were separated out of these containers at the beginning of every week and aged for an additional week before using in insecticide bioassays. All bioassays with field strains were performed after three to four generations (within 12 mo after collection).
Technical grade gel bait and spray product AIs used in vial bioassays were purchased from ChemService (West Chester, PA), Fisher Scientific (Pittsburgh, PA), or Sigma-Aldrich (St. Louis, MO). These AIs included indoxacarb (99.1% purity), abamectin (98.3%), boric acid (99.9%), beta-cyfluthrin (99.5%), bifenthrin (99%), lambda-cyhalothrin (99.5%), fipronil (98.3%), dinotefuran (98.4%), imidacloprid (99.4%), acetamiprid (99.5%), clothianidin (99.5%), thiamethoxam (99.5%), chlorfenapyr (99.1%), and hydramethylnon (99.5%). These AIs were selected because they are currently registered for use in cockroach control products. Three cockroach gel baits, InVict Gold (imidacloprid 2.15%; Rockwell Lab Ltd, Kansas City, MO), Maxforce Professional Insect Control (hydramethylnon 2.15%; Bayer, Research Triangle Park, NC), and Magnetic (boric acid 33.3%; Nisus Co., Rockford, TN) were purchased from Univar (Indianapolis, IN) for follow-up testing in no-choice feeding bioassays.
Technical grade gel bait and spray product AIs used in vial bioassays were purchased from ChemService (West Chester, PA), Fisher Scientific (Pittsburgh, PA), or Sigma-Aldrich (St. Louis, MO). These AIs included indoxacarb (99.1% purity), abamectin (98.3%), boric acid (99.9%), beta-cyfluthrin (99.5%), bifenthrin (99%), lambda-cyhalothrin (99.5%), fipronil (98.3%), dinotefuran (98.4%), imidacloprid (99.4%), acetamiprid (99.5%), clothianidin (99.5%), thiamethoxam (99.5%), chlorfenapyr (99.1%), and hydramethylnon (99.5%). These AIs were selected because they are currently registered for use in cockroach control products. Three cockroach gel baits, InVict Gold (imidacloprid 2.15%; Rockwell Lab Ltd, Kansas City, MO), Maxforce Professional Insect Control (hydramethylnon 2.15%; Bayer, Research Triangle Park, NC), and Magnetic (boric acid 33.3%; Nisus Co., Rockford, TN) were purchased from Univar (Indianapolis, IN) for follow-up testing in no-choice feeding bioassays.