Studies were conducted to determine if individual American, German, or Oriental cockroaches could acquire a naladixic acid-resistant strain of Salmonella typhimurium from an infected food source and then infect noncontaminated colony members, food, and water. Cockroaches, food, and water were sampled after 24, 48, 72, and 96 h and assayed for S. typhimurium. Cockroaches, food, and water samples were positive for S. typhimurium at each 24-h sampling period. American and Oriental cockroaches were contaminated twice as often as German cockroaches. In a second study, the incidence of S. typhimurium cross-contamination between 1 or 5 infected cockroaches and 10 noninfected cockroaches was followed over 4 d. The highest frequency of cross-contamination occurred within 24 h and declined thereafter. Water sites were heavily contaminated throughout the 4-d test period. In a third study, the potential for contamination of table eggs via S. typhimurium-infected cockroaches was evaluated. Whole egg rinses of eggs exposed for 24 h to infected cockroaches contained a minimum of 75 S. typhimurium cells per egg. In a final study, American cockroaches captured from a commercial poultry feed mill and hatchery were assayed for salmonellae using an ELISA method. Five of 45 feed mill and eight of 45 hatchery cockroach samples were confirmed positive for salmonellae. These findings clearly suggest that cockroaches are capable of acquiring and infecting other cockroaches and objects, therefore implicating them as potential vectors of foodborne pathogens in poultry production and processing facilities.
Summary1. A possible adaptive benefit of coprophagy was investigated in nymphs of the German cockroach Blattella germanica (L.).2. Newly ecdysed first instars, given no source of food other than conspecific faeces, survived significantly longer than first instars deprived of faeces. The faeces of adult males and females may be of different quality, however, because nymphs given female faeces were more likely to moult into the second stadium than nymphs given male faeces.3. In contrast to first instars, second instars provided adult faeces survived only slightly longer than starved counterparts. Faecal feeding is therefore stage‐specific, as is the benefit derived from it.4. The relationship between the nutrient composition of faeces and the survival of nymphs was also examined. First instars fed the faeces of adults that had been maintained on a high (50%) protein diet, died more slowly than first instars fed the faeces of adults that had been maintained on medium (22.5%) and low (5%) protein diets. Chemical analysis of faeces showed that the concentration of protein in adult faeces increased with the level of protein in the diet. Moreover, food choice assays showed that first instars, unlike adults, ingested more of the high‐protein diets.5. These data support the idea that coprophagy is a stage‐specific adaptive behaviour that permits first instars to moult into the second stadium with minimal foraging.
Foraging cockroaches ingest insecticide baits, translocate them, and can cause mortality in untreated cockroaches that contact the foragers or ingest their excretions. Translocation of eight ingested baits by adult male Blattella germanica (L.) was examined in relation to the type of the active ingredient, formulation, and foraging area. Ingested boric acid, chlorpyrifos, fipronil, and hydramethylnon that were excreted by adults in small dishes killed 100% of first instars within 10 d and >50% of second instars within 14 d. Residues from these ingested baits were also highly effective on nymphs in larger arenas and killed 16-100% of the adults. However, when the baits and dead cockroaches were removed from the large arenas and replaced with new cockroaches, only residues of the slow-acting hydramethylnon killed most of the nymphs and adults, whereas residues of fast acting insecticides (chlorpyrifos and fipronil) killed fewer nymphs and adults. Excretions from cockroaches that ingested abamectin baits failed to cause significant mortality in cockroaches that contacted the residues. These results suggest that hydramethylnon is highly effective in these assays because cockroaches that feed on the bait have ample time to return to their shelter and defecate insecticide-laden feces. The relatively high concentration of hydramethylnon in the bait (2.15%) and its apparent stability in the digestive tract and feces probably contribute to the efficacy of hydramethylnon. To control for differences among baits in inert ingredients and the amount of active ingredient, we compared 1% chlorpyrifos with 1% hydramethylnon in identical baits. Again, hydramethylnon residues provided greater secondary kill, but the results highlighted the importance of the inert ingredients. We conclude that, in the absence of cannibalism and necrophagy, translocation of baits and secondary kill are most effective with slow acting insecticides in palatable baits that can traverse the digestive tract and be deposited within and around the cockroach aggregation.
A novel experimental design that selectively excluded feeding of adults or nymphs on insecticidal baits was used to distinguish mortality caused by ingestion of bait from mortality caused by horizontal transfer of insecticide by foraging to non foraging cockroaches. In large cage laboratory assays and in apartments, exposure of Blattella germanica (L.) to an insecticidal bait containing hydramethylnon resulted in high mortality in adult females and 1st instars. However, exclusion of adult females from feeding on the bait resulted in a significant decline in mortality among nymphs, suggesting that neonate mortality was caused primarily by adult-mediated horizontal toxicant transfer through feces. A reciprocal experiment provided support for this hypothesis: Adult females with access to bait transferred insecticide to neonates that were prevented from feeding on bait, resulting in high mortality in both groups. Conversely, mortality among 2nd instars was high and significantly less dependent on adult foraging, suggesting a shift to active foraging (i.e., direct ingestion of bait) during the 2nd stadium. We conclude that horizontal toxicant transfer is a key factor in suppression of cockroach pest populations. Small nymphs, especially 1st instars, which forage infrequently and are therefore least vulnerable to direct contact with insecticides, are most susceptible to this type of insecticide translocation. Horizontal toxicant transfer should be optimized to deliver insecticides and pathogens to nonforaging stages of B. germanica.
Baits offer several advantages over other insecticide formulations in the control of populations of the German cockroach, Blattella germanica (L.). However, they may fail to target certain life stages that feed only sparingly. Recently we have demonstrated that 1st instars are signiÞcantly more vulnerable to insecticidal baits when adults are present. By preventing adults or nymphs from eating bait we now conclude that adults translocate insecticide bait to the shelter, thus facilitating a horizontal transfer of the insecticide to nymphs. By tracking bait movement with a tracer dye, we show that nymphs take up adult-delivered bait via coprophagy. An alternative hypothesis, that adults delivered novel food odors to nymphs thereby stimulating them to forage and eat bait, was experimentally rejected. Analysis of time-lapse video records showed that 1st instars foraged sparingly compared with 2nd instars and adults, indicating that direct ingestion of a remotely placed bait accounted for little, if any, mortality in 1st instars. The magnitude of coprophagy in 1st instars was related to the proximity of the food to their aggregation site; nymphs ate signiÞcantly more adult feces when food was far from the shelter. We conclude that aggregating 1st instars are relatively sedentary, and that they depend on conspeciÞc foragers to deliver widely dispersed food. Innovative baiting strategies should therefore maximize forager-mediated translocation and delivery of slowacting bait insecticides to inaccessible cockroach aggregations.
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