Time, concentration and temperature relationships for phosphine activity in tests on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera: Pyralidae)

Abstract

The activity of phosphine against diapausing larvae of Ephestia elutella was shown to depend on several different interactions of duration of exposure, temperature and gas concentration. Using the model proposed by Knight, (C-C,) x ( t -to) = k , a constant for mortality, the minimum effective concentration C, was raised and the minimum effective exposure to extended as temperatures were increased. The effect of temperature on these thresholds was reduced at higher mortality levels. A range of concentration levels, influenced by temperature, elicited an increase in tolerape at the LD,, level over that evident at higher or lower concentrations. These concentration ranges were 0.9-2.1 mg litre-' at 25"C, 0-7-2.3 mg litre-' at 20°C and 0-1-1.5 mg litre-' at 15°C.A mathematical model was fitted to relate concentration and time thresholds, mortality and temperature. At the LD,, level, values for to ranged from 2.5 h at 15°C to 5.0 h at 25°C. C, values increased from about 0.6 to 7.0 pg litre-' over this temperature range. At the LD,, level, to values ranged from 21 to 28 h and C, values from 11 to 19pg litre-'. Phosphine appeared most effective at each temperature at concentrations from about 40 to 6@-100 pg litre-'.

The potential efficiency of irrigation management and propargyl bromide in controlling three soil pests: Tylenchulus semipenetrans, Fusarium oxysporum and Echinochloa crus‐galli

“…Statistical analysis indicated that C 0 was not significantly different from zero for all but two regressions (two formulations on the fungi). A minimal threshold value of zero ( C 0 ) was also obtained for methyl bromide and for different pests 25. A large b value indicates a steeper slope, ie a small change in concentration has a large effect on pest control.…”

Concentration–Time Exposure Index for Modeling Soil Fumigation under Various Management Scenarios

“…Model simulation using CTEI as a numeric variable can be used as an effective alternative to help make management decisions for soil fumigation by drip irrigation. The model prediction can be improved by inclusion of temperature effects on efficacy (Bell, 1992; Xue et al, 2000) in calculating CTEI. The modeling approach using CTEI is limited by the availability of threshold CT values for pest–pesticide combinations.…”

Predicting mortality of phosphine‐resistant adults of Sitophilus oryzae (L) (Coleoptera: Curculionidae) in relation to changing phosphine concentration

“…Although useful, eqn (1) must be used with caution because the value of n may vary for a number of reasons. Within the same life stage the value of n may vary depending on fumigation temperature and the concentration range 2. Different values of n have been reported for adults of susceptible and resistant strains of the same species 3, 4.…”

“…The toxicity of phosphine to grain insects has long been known to be influenced by both concentration and exposure period, and some researchers have sought to quantify these effects 1–6. In these published studies, insects were exposed to constant concentrations only.…”