Escape Behaviour of Dalbulus maidis (DeLong and Wolcott): Subsidies for Insecticide Application and Field Sampling

Dalbulus maidis (Hemiptera: Cicadellidae) is the primary pest of corn crops in Brazil due to its high efficiency in transmitting pathogens associated with the corn stunt disease complex, including maize bushy stunt phytoplasma (MBSP) and corn stunt spiroplasma (CSS), as well as maize rayado fino virus (MRFV) and maize striate mosaic virus (MSMV). However, many aspects of the behaviour and bioecology of this insect vector are still poorly understood. Accordingly, we investigated the escape behaviour of D. maidis at three different times of the day (6:00 a.m., 1:30 and 6:00 p.m.) under controlled conditions. This behaviour was compared between sexes and among populations of healthy leafhoppers and those carrying bacteria that cause corn stunt diseases (phytoplasma and spiroplasma). The studies were conducted in November/2022 (first crop season conditions) and April/2023 (second crop season conditions). Groups of 100 leafhoppers (50 males and 50 females), healthy or infected with phytoplasma or spiroplasma, were placed in cages containing maize plants. Following the application of mechanical disturbances, the number of individuals that left the maize plants was recorded. Temperature positively influenced the escape behaviour of D. maidis. Moreover, a higher proportion of leafhoppers abandoned maize plants under conditions that simulated the first crop season (27.3%) than the second crop season (14.3%). This propensity was consistently higher during the hottest period of the day (1:30 p.m.). Meanwhile, infected leafhoppers were less active than healthy leafhoppers under the second crop season conditions and lower average temperatures. No differences were observed in escape behaviour between the sexes. The behaviour of D. maidis observed in this study supports the recommendation of applying insecticides during the cooler hours of the day, which may enhance their effectiveness against this insect vector. Similarly, field sampling involving direct insect counts on maize plants is also recommended under these same conditions.