Biological control of economically important insect pests of crop plants has a long history (Clausen 1956) during which releases of insect parasites have played a dominant role. The method has been particularly used in attempts to control such alfalfa insect pests as the alfalfa weevil,Hypera postica(Gyllenhal) (Brunson and Coles 1968), the Egyptian alfalfa weevil,H. brunneipennisBoheman (Clancy 1969), and the spotted alfalfa aphid,Therioaphis maculata(Buckton) (Van den Bosch et al. 1959). However, in all such work, the parasites were released in relatively small numbers, and control was not anticipated until after a sufficient period of natural buildup. Thus when Knipling (1966) suggested inundation of insect populations by mass production and sustained release of parasites and predators as a means of suppressing insect populations, Ridgway and Jones (1969) attempted to control the bollworm,Heliothis zea(Boddie), and the tobacco budworm,H. virescens(F.), on cotton by making inundative releases of eggs of a lacewing,Chrysopa carneaStephens. Knipling and McGuire (1968) indicated the importance of the plant-growth factor on limiting the efficiency ofTrichogramma. Fye and Larson (1969) made preliminary evaluations ofT. minutumRiley as a released regulator of lepidopteran pests of cotton, and Surber (1970)3subsequently pointed out that these releases ofTrichogrammasp. on cotton were apparently ineffective, because the 10,000 wasps/ week that were released could not completely search the area of the host plant which had increased 7.6–fold in 8 weeks. The increase in leaf area may therefore be an important consideration in use of inundative releases of insects for immediate control of harmful insect populations. Also, this increase is important in determining optimum rates of insecticides to insure maximum control of the target insect while minimizing costs, effect on nontarget species, residues, and environmental pollution. We therefore investigated the possibility of producing accurate estimates of the daily increase in the area of alfalfa leaves in relation to temperature in southern Arizona.