Oscilações térmicas sobre o parasitoide de ovos Telenomus podisi (Ashmead) (Hymenoptera: Scelionidae)

Abstract

Inadequate weather conditions can adversely affect the performance and even the survival of most insects. Temperature is one of the major factors that interferes with the success of biological pest control agents. The parasitoid of Telenomus podisi (Ashmead) (Hymenoptera: Scelionidae) has been widely used for the control of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae). Release of the parasitoid in soybean crops under conditions of inadequate temperatures may result in the failure of the control of this phytophagous bug, compromising the final productivity of the crop. The objective of this work was to evaluate the effect of thermal oscillations on the T. podisi parasitoid. The biological parameters of the parasitoid were evaluated in two experiments. For this, females of the parasitoid with up to 24 hoursof age and previously fed with honey were individualized in glass tubes. In the first experiment the parasitoids were submitted to oscillations of temperatures above and below 25ºC, being the minimum studied temperature of 17°C and the maximum of 41°C, with oscillations of 2ºC every hour, totaling 13 treatments with 20 repetitions each . In the second experiment, new females of the parasitoid were individualized in glass tubes and subjected to thermal shocks, in which the parasitoids were transferred from the initial temperature of 25°C directly to the extreme temperature, with shocks of 2°C, until reaching the temperature maximum of 41°C. After exposure to temperature fluctuations and thermal shock, the survival of the T. podisi females was evaluated, and afterwards, each female received ten viable eggs from E. heros. After 24 hours, these eggs were individualized in glass tubes and kept in a B.O.D 25 ± 1 C conditioned room, 60% ± 10% relative humidity and 12 hours photophase until the emergence of the parasitoids, aiming to evaluate the percentage of eggs parasites, emergency and sexual reason. Females, after parasitism, were also kept in an air-conditioned room, to later evaluate longevity. Exposure of the T. podisi parasitoid at temperatures above 33 ° C in temperature and temperature shock experiments caused a decrease in survival, longevity, parasitism, emergence and sexual ratio, temperatures below 21°C under the oscillation condition also caused reduction in parasitism, emergence and sex ratio, but in these conditions of oscillation and thermal shock, temperatures above 33°C and below 21°C drastically affect progeny emergence. While the temperature of 41°C was lethal to the parasitoids in the two experiments. The biological characteristics of the T. podisi parasitoid when subjected to temperature oscillations and thermal shock between 21°C to 33°C do not suffer interference, that is, in this wide temperature range this parasitoid can develop and parasite without compromising its characteristics and its efficiency in the control of the E. heros stink bug.