THE IMPACT OF A SINGLE TREATMENT WITH THE CHITIN SYN THESIS INHIBITOR LUFENURON ON GERMAN COCKROACH BLATTELLA GERMANICA (L.) (DICTYOPTERA: BLATTELLIDAE) POPULATIONS

Abstract:
The present investigation demonstrates the effect of a single treatment with a chitin synthesis inhibitor (lufenuron) on small, medium and large nymphs as well as adults of the German cockroach, Blattella germanica (L.). The trial was conducted as a long-term field study in three mass food producing kitchens. The spraying was carried out by the use of a compressed-air sprayer at a rate of approximately 1 litre/200 mg a.i./25 m in a 0.3-0.5 m band. The changes in population size, age structure, etc. were monitored with sticky traps. Within the first 4 to 6 weeks after the treatment, the cockroach populations were reduced by more than 95% in two localities. Approximately 4 months after the treatment, the number of adults began to rise again in one of the localities. The age structure was followed in all three localities treated. It was done by calculating the nymph-to-adult ratio and relating it to the similar value obtained before the treatment. In one locality the population was so heavily affected by the treatment that the age structure could only be followed for a short period, and in one of the other two localities immigration from an adjacent building affected the results. In the last locality, the age structure could be followed in detail throughout the trial period. In the first 4 to 6 weeks after the treatment the nymph-to-adult ratio decreased to 0.15 compared to a value of 0.63 before the treatment. After this initial period it increased to 0.96. This indicates that the initial high proportion of adults in the population was followed by a high proportion of nymphs. Then for a couple of months the nymph-to-adult ratio could not be calculated, due to the low number of specimens, but when it was possible to calculate the nymph-to-adult ratio again, it was still high indicating an over-representation of nymphs. Four months after the treatment, the nymph-to-adult ratio declined rapidly indicating a synchronized moult into adults. It is shown that adult cockroaches living in mass food producing kitchens in Denmark only live for 30 to 40 days. This is quite a short time compared to similar data obtained in laboratories. The consequences of such a short lifetime are that a female only has the possibility to produce one ootheca in her lifetime. It is also demonstrated that nymphs need 2½ months to develop into adults in such a domestic environment.