Abstract The ages of parasitoid females and their hosts can have substantial effects on parasitism and parasitoid efficacy. This relationship has been investigated over the last few decades and found to vary among species. To our knowledge, it was virtually unknown for Trichogramma pretiosum wasps that parasitize Anticarsia gemmatalis eggs. Therefore, the influence of parasitoid and host age on the parasitism of T. pretiosum on eggs of A. gemmatalis was here evaluated in three independent bioassays. Neither the number of parasitized eggs nor that of emerged parasitoids differed between T. pretiosum females of different age. The number of parasitoids per egg and the sex ratio were higher for 5-day-old females. Regarding host age, the number of parasitized eggs was highest for A. gemmatalis eggs aged 24 h (9.60), followed by eggs aged 48 h (1.00), while no parasitism was observed for eggs aged 72 h. The number of parasitoids per egg and sex ratio were not influenced by host age. Preference was significantly higher for host eggs aged 24 h (79.67%), followed by eggs aged 48 h (16.99%) and 72 h (3.33%). Accordingly to these results, the key challenge for a successful T. pretiosum release to control A. gemmatalis in the field is to synchronize the presence of up to 5-day-old adults with the most susceptible phase of the host eggs (1 day).

Este trabalho foi desenvolvido com o objetivo de caracterizar o comportamento ingestivo de vacas da raça Jersey durante duas épocas do ano (estações fria e quente) e aos 30, 60 e 90 dias pós-parto. Os tempos diários gastos com ingestão, ruminação e descanso foram estimados a partir de observações visuais realizadas por um único observador bem treinado. Os registros das atividades comportamentais foram realizados a intervalos de 10 minutos, durante 24 horas por dia, cinco dias por período, totalizando 30 dias de observações. Os animais foram observados individualmente. Os tempos médios de ingestão e ruminação foram maiores na estação quente, comparados à estação fria e aos 30 dias pós-parto comparados aos 90 dias pós-parto, e associados com os efeitos positivos de temperatura, fotoperíodo e teor de fibra da silagem. O peso vivo decresceu até 30 dias pós-parto, apresentando recuperação aos 90 dias pós-parto. A produção de leite apresentou interação significativa entre época e período, com menor produção de leite aos 60 dias pós-parto em relação aos 30 e 90 dias pós-parto, principalmente na estação quente, fato parcialmente atribuído às mudanças na composição química da silagem. Concluiu-se que as vacas leiteiras modificaram seu comportamento ingestivo para se adaptarem às mudanças nutricionais, ambientais (efeito de época) e anatômicas e fisiológicas (efeito do número de dias após o parto).

This trial aimed to characterize the ingestive behavior of Jersey dairy cows during cool and warm seasons, and at 30, 60 and 90 days post-partum. Daily time spent eating, ruminating and idling was estimated through visual observations recorded by a well trained observer. Records were made intermittently, using 10 minutes interval during 24 hours, five days per period, totalizing 30 days of observations. Ingestive behavior was recorded for each individual animal. Daily eating and rumination times were larger at warm season compared to the cool one and at 30 days post-partum compared to 90 days post-partum, being associated with positive effects of temperature, photoperiod and fiber content of silage. Live weight decreased from parturition until 30 days post-partum and recovered by 90 days post-partum. Milk production showed a significant interaction effect among season and period, presenting smaller values at 60 than at 30 or 90 days post-partum, specially at warm season, what might be partially related to changes in the silage chemical composition. It is concluded that dairy cows changed ingestive behavior to adapt themselves to different nutritional, environmental (season effect) and anatomical, physiological conditions (effect of number of days after parturition)