The incorporation of an insect growth regulator (IGR), such as NyGuard (pyriproxyfen), can be a very important part of a successful German cockroach (Blattella germanica) control strategy.
IGRs are Often Used in Combination With Insecticides
IGRs prevent immature cockroaches from reaching their full “pest potential” by interfering with the nymphs’ molting process and reproductive development. Because IGRs do not directly kill the cockroaches, they are often coupled with an insecticide.
The insecticide will kill most of the German cockroach adults and nymphs. The nymphs not killed by the insecticide will be affected by the IGR, either dying in the process of molting or rendered unable to reproduce due to induced deformations as adults.
Those who are not familiar with the effects of pyriproxyfen on German cockroach development may be concerned that a German cockroach infestation remains unaffected by treatment if immature cockroaches continue to be caught in post-treatment monitoring sticky-traps.
Nymphal German cockroaches that have been exposed to pyriproxyfen will often exhibit specific developmental traits dependent on the insect’s life stage at the time of exposure.
IGR Effects on Nymphal German Cockroaches
The pictures below show the effects of pyriproxyfen on nymphal German cockroaches, signifying that the IGR is, in fact, affecting the pest population.
These German cockroaches are 8 weeks old. They were exposed to pyriproxyfen as 1st instars. They appear as small, round, very dark (melanistic) early instar nymphs. Many of these cockroaches will not survive the molting process as they continue to age and will not make it to the nymphoid stage.
These German cockroach nymphoids are 18 weeks old. They were exposed to pyriproxyfen as 1st instars. Notice the twisted wing pads of the larger female and the darker color of the male. Due to deformities of their genitalia, these cockroaches will not successfully mate.
These German cockroaches are 16 weeks old. They were exposed to pyripoxyfen as 3rd instars. Because they were more developed at the time of exposure, they developed further than the nymphoids in Figure 2. Notice the extreme deformation of the wings in both the female and the male. These external deformities can be indicative of internal deformities that negatively affect reproductive success.