Abstract
CO2 has been registered as an alternative fumigant in several countries for the control of stored product pests. Under a given set of conditions, the success of a fumigation depends on controlling the most tolerant stages of pests. Furthermore, compared with lethal durations for fixed concentrations or lethal concentrations for fixed durations, concentration-time products (Cnt) are more applicable in pest control practices. Therefore, this study was designed to reevaluate the concentration and exposure duration combinations that will reliably cause high mortality of Liposcelis entomophila (Enderlein) (Psocoptera: Liposcelididae) and to clarify the effects of sublethal dosages of CO2 on population growth of L. entomophila in view of practical application of CO2 for psocid control. Newly-laid eggs were most tolerant to CO2 modified atmospheres (MAs) followed by 5-d-old eggs, female adults, 2nd-instar nymphs and male adults. Lethal time for female adults and newly-laid eggs in CO2 MAs all decreased with increasing CO2 concentrations. Exposure to 100% CO2 for 9 h was adequate to kill almost all L. entomophila stages except eggs. The response of eggs and female adults of L. entomophila to hypercarbia (13-94% CO2) did not differ from the simple Cnt relationship, Ct = k, which means that both dosage variables are equally significant. The fertility of females and males was both negatively affected by CO2 MAs and delay in the pre-adult developmental period was positively correlated with increasing CO2 exposure durations, which explains the effectiveness of hermetic storage in pest control. In consideration of low airtightness of bulk grain storehouses and inevitable loss of CO2, paired treatments with CO2 are recommended in control practices of this pest and the interval between the first and second CO2 treatment should be more than 10 d.
