The biology and thermal requirements of the fennel aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae)

The relationship between the insect development rate and temperature was established very early and represents an important ecological variable for modeling the population dynamics of insects. The accurate determination of thermal constant values and the lower and upper developmental thresholds of Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) on fennel (Foeniculum vulgare Miller (Apiales: Apiaceae)) crops would obviously benefit the effective application of control measures. This paper is a study of the biology and thermal requirements of H. foeniculi. Winged insects were collected from fennel crops at the Embrapa Algodao in Campina Grande, Paraiba. Nymphs (age <= 24 h) produced by winged insects were subjected to constant temperatures of 15, 20, 25, 28, 30 or 33 degrees C, a photophase of 12 h and a relative humidity of 70 +/- 10%. The results of the study showed that at temperatures between 15 and 30 degrees C, H. foeniculi nymphs were able to develop normally. The four instars were found at all temperatures tested. However, temperatures of 3 and 33 degrees C were lethal to the nymphs. The nymph stage development time varied from 5 (30 degrees C) to 19 (15 degrees C) days. The influence of temperature on the development time is dependent on the instar. The base temperature (Tb) and the thermal constant (K) for the nymph stage were estimated at 11.2 degrees C and 107.5 degree-days, respectively. The shortest nymph development stage was observed at 30 degrees C, and the highest nymph viability (85.0%) was observed at 28 degrees C. This information can be used for developing phenological models based on the temperature and development rate relationships so that outbreaks of H. foeniculi in the fennel crop can be predicted, therefore improving the application of control programs targeting this fennel pest.