How fresh is that frass

Many insects inhabit concealed locations, such as within timber, but leave outward signs of their presence, such as frass. Deposits of fresh frass on the outside of infested material would indicate a high probability of live insects being present within. A method for estimating the age of frass could therefore be useful for assessing treatment efficacy. For example, the success of termite eradication could be monitored by regularly checking for the presence of fresh frass near old colonies. Similarly, the presence of fresh frass in borer holes in fumigated timber would raise concerns that the fumigation had been ineffective. This study examined whether the age of frass could be estimated from levels of esterase enzyme activity in frass of four species; the termites Stolotermes inopinus and Kalotermes brouni, and the weevils Sitona lepidus and Listronotus bonariensis. With the termites, active esterases were found in 1-day-old frass, but not in 1-month-old frass, indicating clear potential for development of a test. With the weevils, esterase activity occurred both in 1-day-old frass and in 1-month-old frass, so development of a method for these species requires a faster degrading enzyme.