Effects of age and environmental conditions on cockroach gel bait performance

Cockroach baits are one of the most effective tools used for German cockroach (Blattella germanica L.) control. This is due in part to the number of cockroach baits on the market with various matrix compositions and active ingredients, aiding in the control of insecticide-resistant cockroach populations through bait rotation. However, it remains unclear how cockroach gel baits perform over time and under different environmental conditions. Therefore, we aged six cockroach gel baits for varying times (24 h, 1 mo, 3 mo, and 6 mo) and at three relative humidities (15%, 40%, and 80%), and tested their performance (consumption and efficacy) against fresh baits. German cockroaches consumed various quantities of bait depending upon both bait product and age, with significant declines in aged bait consumption compared to fresh bait consumption for most products tested. However, all baits aged over 24 h caused greater than 93% mortality in all B. germanica (L.) populations. Low relative humidity (15%) did not significantly affect bait consumption or efficacy compared to standard relative humidity (40%), but high humidity (80%) resulted in excessive mold growth (Mucoraceae) in all trials, preventing testing of aged baits at high humidity. Our findings show that cockroach gel baits remain palatable and effective up to 6 mo after application at 40% and 15% relative humidity in laboratory conditions. This suggests that even though consumption declines in comparison to fresh baits, aged baits may play a role in cockroach control for an extended time after application.