Influence of temperature and humidity on insecticidal effect of three diatomaceous earth formulations against larger grain borer (Coleoptera: Bostrychidae).

Laboratory experiments were carried out to evaluated three diatomaceous earth (DE) formulations--Protect-It, PyriSec (at dose rates 500, 1000, and 1500 ppm), and DEA-P (at dose rates 75, 150, and 500 ppm)--against the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), adults in stored maize, Zea mays L., at three temperatures (20, 25, and 30 degrees C) and two relative humidity (RH) levels (55 and 75%). At these conditions, the capability of progeny production in the treated substrate also was assessed. Adult survival was high, at all doses of Protect-It and PyriSec. Progeny production was also high. In contrast with the other two DEs, DEA-P was highly effective and caused complete mortality to the exposed P. truncatus adults, even at the lowest dose rate (75 ppm). In addition, progeny production was completely suppressed. Generally, Protect-it and PyriSec were more effective at 20 degrees C than at 30 degrees C. In contrast, the efficacy of DEA-P was continuously high in all temperatures and relative humidities examined.