The potential impact of heat mortality as part of thermal cotton defoliation was evaluated among late-season insect pests in New Mexico. Prior research comparing thermal to chemical defoliation showed that chemically defoliated plants had increasing aphid populations for the first six days post application. Thermally treated plants had none. In the current study, field mortality of cotton aphids, Aphis gossypii, and adult and immature silverleaf whiteflies, Bemisia argentifolii, was determined at harvest. Immediately following movement of the defoliation machine through the field, leaves from the upper and lower canopy were removed, placed in Petri dishes, and taken to the laboratory to measure the mortality of aphids and adult whiteflies. The same was done for control treatments which were chemical and no defoliation. Leaves were then placed in an incubator maintained at 25C to determine mortality of developing immature whiteflies.

To determine the levels of heat produced in the thermal defoliation process in the field, a series of randomly-selected plants was fitted with twenty ultra fine thermocouple wires recorded by a data logger (Agilent 34970A). Temperatures were evaluated in both the upper and lower canopy at various locations including open and closed bolls, leaf surfaces, and soil surface. Each junction was repeatedly scanned while the defoliation machine passed over, measuring the extent and duration of temperature rise at those locations on the plant.

Based on average temperatures attained on plants in the field, insect mortality was evaluated in the laboratory. Leaves with known levels of aphid and whitefly adults and immatures were subjected to heat for a period equivalent to that of the defoliation machine. The insects were then maintained in an incubator until all immatures emerged to determine mortality.