Exploring Bruchus rufimanus Egg Substage Dynamics at Different Constant Temperatures

The broad bean weevil Bruchus rufimanus is a major pest of faba bean in Europe, where infestations are responsible for increasing economic losses. Despite its importance for both predictive modelling and biological control strategies based on oophagous parasitoids, the thermal biology of egg development remains poorly understood. This study aimed to address this gap by collecting pods bearing eggs and incubating them under 11 constant temperatures ranging from 12°C to 40°C. Egg development through four morphological substages was monitored daily. Data were organised as stage-frequency matrices and life-tables' parameters were estimated through an optimisation problem that reconstructed the distributions of stage-specific development times. Early substages (S1-S2) were generally longer at lower temperatures, whereas differences among substages became minimal within the optimal thermal range of 20°C-35°C. At 40°C, development ceased at stage S3, preventing egg hatching. The proposed method provided reliable estimates of development time distributions and showed consistent thermal responses across substages. These findings provide the first quantitative baseline for the egg development of B. rufimanus and offer valuable parameters for physiologically based models. Moreover, they supply essential information for synchronising parasitoid releases with susceptible egg stages, thereby supporting the development of sustainable integrated pest management strategies.