The Response of Susceptible and Pyrethroid-Resistant Blattella germanica (Dyctioptera: Blattellidae) to Shelter-Associated Cues

Abstract

In this work, it was studied the role of faeces in the location and permanence in a shelter in susceptible and pyrethroid-resistant individuals of Blattella germanica (Linnaeus 1767). Additionally, the effect of different concentrations of palmiticacid on the modulation of these behaviours was tested. A shelter constituted by a square cardboard structure was offered tosusceptible as well as to resistant specimens. The shelter bases were treated with faecal extracts obtained from susceptibleor resistant cockroaches, or with solutions of palmitic acid. The behaviour of susceptible as well as resistant specimens wasanalysed using infrared videography software. Susceptible’s faecal extract attracted both specimens since the time spent bycockroaches to locate the treated shelters was lower, whereas the faecal extract from resistant insects did not elicit any effecton both strains. Faecal extracts showed an arrestant effect on both strains, suggested by the time spent inside the shelter thatwas significantly higher in their presence. On the other hand, treatment with palmitic acid produced an attractant or a repel-lent effect depending on the concentration and strain. The tested lower concentration was attractant to susceptible insects, butdid not produce any effect on resistant ones. In addition, the higher concentrations did not produce any effect on susceptibleindividuals, but resulted repellent for resistant ones. Palmitic acid did not produce an arrestant effect on the strains as therewas not an increase in time spent inside the shelter in the presence of this substance. An increase in the number of visits tothe shelter and to the periphery was also observed in shelters treated with the faecal extract and with the lower concentrationof palmitic acid. These results show that compounds of the susceptible faeces were attractant to cockroaches of both strains,while faecal extracts from resistant insects were not. Moreover, a dual effect of palmitic acid was observed, being attractantat low concentrations and repellent as concentration increased. Additionally, a difference in the concentration threshold atwhich the effect of this substance changes was observed between strains.