Effects of temperature on the immature development and emergence of five species of Trichogramma

Five constant temperatures between 14 and 30A degrees C were used to evaluate their effect on the development time and adult emergence of five Trichogramma species found parasitizing eggs of the velvetbean caterpillar Anticarsia gemmatalis Hubner (Lepidoptera: Noctuidae) on soybeans in subtropical Southern Brazil. Host eggs were parasitized at 20A degrees C and then transferred to the study temperatures to follow development and emergence of parasitoids. All five species were able to develop and emerge within the range of temperatures evaluated, and the effect of temperature on development rates could be described by linear regression. Trichogramma acacioi Brun, Moraes & Soares and T. rojasi Nagaraja & Nagarkatti were the most cold-tolerant species, with lower threshold temperatures of 8.1 +/- A 0.16A degrees C and 9.2 +/- A 0.16A degrees C, respectively. Trichogramma atopovirilia Oatman & Platner was the least cold-adapted species, with a lower threshold of 10.2 +/- A 0.13A degrees C. Degree-day accumulation ranged from 153.8 DD for T. atopovirilia to 190.7 DD for T. acacioi. Adult emergence was higher than 90% for T. atopovirilia and T. pretiosum at all temperatures, whereas T. lasallei Pinto emergence dropped to 71.3% at 14A degrees C and to 58.3% at 26A degrees C, both significantly lower than the emergence of T. pretiosum and T. atopovirilia. Significantly less T. acacioi adults emerged at 30A degrees C than either T. pretiosum or T. atopovirilia. The sex-ratio was not affected within the range of temperatures studied, and varied from 0.65 to 0.88 (female/(male + female)). Differences among Trichogramma spp. densities in the field can be attributed to slower development rates and/or reduced emergence of adults, both at low and high temperatures.