Thermal effects on the biological parameters of the predatory mirid Pilophorus gallicus (Hemiptera: Miridae)

Abstract

Pilophorus gallicus Remane (Hemiptera: Miridae) is a predatory mirid reported in deciduous trees in the western Mediterranean area. This work aimed to determine the biological and demographic parameters for this species at different temperatures (15, 20, 25 and 30°C). Egg hatching times shortened from 57.8 days at 15°C to 9.2 days at 30°C, and nymphal development times declined from 62.8 days at 15°C to 11.1 days at 30°C. The hatching and nymphal survival rates were low at 15 and 30°C. The lower thermal thresholds for the egg and nymphal development were 12.4 and 12.0°C, respectively. These high thermal thresholds could be a safety mechanism to avoid the emergence of nymphs in the unfavorable winter period. Female weight increased between 15 and 25°C and decreased at 30°C. The fecundity increased from 70.2 eggs per female at 15°C to 212.4 eggs per female at 25°C, and decreased to 88.5 eggs per female at 30°C. Fertility ranged from 9.4% at 15°C to 40.9% at 25°C, being 24.9% at 30°C. The intrinsic rate of natural increase (rm) rose from 0.001 to 0.081 between 15 and 25°C and decreased to 0.05 at 30°C. In summary, this species performs poorly at low temperatures and has a relative tolerance of high temperatures (30°C); its performance was best at 25°C. Knowledge of the variation in the biological parameters with temperature may be very useful for the understanding of its ecology and population dynamics.

When natural enemies go to sleep: diapause induction and termination in the pear psyllid predator Pilophorus gallicus (Hemiptera: Miridae)

“…24,54,[87][88][89] However, the emergence of nymphs from 70 days of exposure onwards suggests that some overwintering eggs of P. gallicus probably complete diapause before the arrival of spring, but remain in post-diapause quiescence until the thermal requirements are satisfied. 37 Another interesting aspect found in the present work is that the longer the diapausing eggs were exposed to low temperature the shorter their hatching time once they were transferred to standard conditions (25 ∘ C, 16L:8D). This means that the synchronization of nymph emergence in spring will largely depend on the temperature diapausing eggs are exposed to during winter.…”

“…Curiously, temperature was found to have a significant effect on non‐diapausing eggs , the percentage of hatched eggs being significantly lower at 18 °C than at 23 °C. However, this is more likely related to higher mortality of eggs at low temperatures than to an influence of temperature on the type of egg laid.…”

“…Therefore, the characterization of the status of the eggs was established on the basis of their hatching when exposed to standard conditions. According to previous essays performed with P. gallicus populations from southeast Spain, eggs that had not hatched at two to three times the development time at standard conditions (11.9 ± 0.1 days at 25 ± 1 °C, 16L:8D, 60 ± 10% RH) were considered either as inviable or diapausing. To identify the diapausing eggs and distinguish them from inviable ones, it was necessary to know the requirements for the termination of the diapause.…”

“… Temperatures lower than 18 °C (i.e. 15 °C) are known to substantially reduce the development and oviposition rates . The photoperiods were chosen based on the extreme values registered annually at the latitude where the insects were collected (http://siam.imida.es/).…”

“…15 ∘ C) are known to substantially reduce the development and oviposition rates. 37 The photoperiods were chosen based on the extreme values registered annually at the latitude where the insects were collected (http://siam.imida.es/). The numbers of eggs hatched and nymphs emerged per female were registered.…”