Studies were conducted in the laboratory to determine the photosensitive stage to diapause induction in Euschistus heros (Fabr.). Two photoperiods (10L: 14D and 14L: 10D) were used, maintaining the temperature at 25 ± 1ºC and the relative humidity at 65 ± 5%. Distinct developmental stages were submitted to the following photoperiodic combinations: T1 = 10L: 14D (egg-adult); T2 = 14L:10D (egg), and 10L:14D (1st instar-adult); T3 = 14L:10D (egg-1st instar), and 10L: 14D (2nd instar-adult); T4 = 14L: 10D (egg-2nd instar), and 10L: 14D (3rd instar-adult); T5 = 14L: 10D (egg-3rd instar), and 10L: 14D (4th instar-adult); T6 = 14L: 10D (egg-4th instar), and 10L: 14D (5th instar-adult). Under short photophase from egg to adult (T1), the incubation period was longer (6.1 days) than that observed for bugs in the other treatments (5.3 to 5.6 days). The developmental time was longer (35.5 days) for insects reared under short photophase from egg to adult (T1), 1st instar to adult (T2), 2nd instar to adult (T3) or 3rd instar to adult (T4), than that presented by insects maintained under short photophase starting on the 4th (T5) or 5th instar (T6) (32.0 days). Nymph mortality was greater (56.7%) under T1 than under the other treatments (26.7 to 45.0 %). Insects submitted to short photophase from egg to adult (T1), and long photoperiod from egg to 2nd instar (T2-T4), showed 84.8% to 100.0% of individuals in diapause. Diapause did not occur in bugs exposed to short photophase only after the 4th or 5th instar. These results showed that E. heros photosensitivity occurs during the first stages of development, and that from the 3rd instar on, photosensitivity increased.
Insecta; Neotropical brown stink bug; diapause; photosensitivity; soybean
