Effects of photoperiod on the development and growth of Podisus nigrispinus, a predator of cotton leafworm

Abstract

The effects of photoperiod on nymphal development, growth and adult size in Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) were studied. Predators were collected in cotton fields in Patos (7°S, 37°W), Paraiba State, Brazil. A randomized block experimental design was used, with treatments consisting of photoperiods of 10L:14D, 11L:13D, 12L:12D, 13L:11D, 14L:10D, 15L:9D and 16L:8D (LD, in h), at a constant temperature of 28 ± 1°C and relative air humidity of 70 ± 10%. Treatments were distributed in four replications, with each experimental unit composed of 40 nymphs. The development period for each instar of P. nigrispinus varied according to the photoperiod exposure. Regardless of the photophase (PhP), the 5th instar nymphs exhibited the longest development period, except for the 15-h PhP, in which the development period of 2nd instar nymphs (4.13 days) was as long as that of the 5th instar nymphs (4.23 days). In the 1st, 3rd and 5th instars of P. nigrispinus, the development period was inversely proportional to the increase in light period in which the nymphs developed, for the PhP intervals of 10–14 h, 12–14 h, and 12–15 h, respectively. Predators exposed to a 14-h PhP developed a wider pronotum than those exposed to extreme PhP’s (of 10 h, 11 h and 16 h). Conditions from 14 h to 15 h of light resulted in higher daily growth rates in P. nigrispinus than those obtained with the other PhP’s tested. P. nigrispinus females exhibited faster daily growth rates than did males.