Mr. Pest Control
Do insect growth regulators [IGRs] work on all insects? What about brown recluse spiders?
Yes, insect growth regulators, which are mostly juvenile hormone analogues (JHAs), should work on all insects, but the results depend on the target pest’s life cycle length and type of metamorphosis. Since JHAs are only effective during the molt from juvenile to adult, they work best on insects with quick life cycles. For example, American cockroaches may develop into adults over a year after hatching. If JHAs are present during the last molt into adulthood, they should work as expected. However, they are not going to have as quick an impact as they do with German cockroaches, which develop into adults two to three months after hatching. Since cockroaches have incomplete metamorphosis, what results is a sterile adult. In insects with complete metamorphosis, like stored product beetles and moths, JHAs block pupation into adults.
Spiders are a different story because they are not insects. Juvenile hormone does not play the same role in spiders as it does in insects. I cannot find a consensus as to what effect, if any, JHAs have on spiders. Also, spiders are not usually listed as target pests on IGR product labels.
Is it true that spiders recycle their webs? Is spraying webs and leaving them in place an effective control method?
It is true that SOME spiders recycle, or ingest, their webs. Web recycling is most common in the araneid orb-weaving spiders. This spider family spins the flat, circular webs most people are familiar with on a vertical plane. Yes, applying a pesticide to webs may help manage THESE spiders. However, a customer may not interpret leaving webs behind as effective spider management.
Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. The answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and/or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.