Custo adaptativo e resistência à alta temperatura de Lipaphis pseudobrassicae (Davis, 1914) (Hemiptera: Aphididae) resistente ao parasitoide Diaeretiella rapae (McIntosh, 1855) (Hymenoptera: Braconidae, Aphidiinae)

Abstract

Secondary endosymbionts have been pointed out as causing aphids’ resistance to parasitoids and increased heat tolerance. However, symbionts can be eliminated by high temperatures, so that resistant insects become susceptible to parasitoids. Resistance to parasitoid can generate adaptive costs, such as reduced fecundity and longevity. The objectives of this study were to assess the adaptive cost for aphid Lipaphis pseudobrassicae (Davis) resistant to parasitoid Diaeretiella rapae (McIntosh) at optimum temperature for aphid development, observe if resistance increases heat tolerance and analyze if resistance diminishes after high temperature shock. Four groups obtained from three clones (C1, C2 and C3) of L. pseudobrassicae were formed in laboratory. One of the clones produced two groups, one with resistant individuals (C1R) and the other with individuals susceptible (C1S) to D. rapae. The other two groups were composed of parasitoid-resistant clones (C2R and C3R). For each group, six Petri dishes (5cm), each containing twenty first-instar nymphs, were maintained at optimum temperature for insect development (22ºC), and six plates were submitted to high temperature shock (37ºC) for one hour. After this period, insects were maintained at 22ºC in Petri dishes (5cm) with a cabbage leaf disk over an agar layer. Aiming to verify if resistance was maintained after thermal shock, 24 nymphs from each third generation group were parasitized after thermal shock. No difference was observed in survival or fecundity of resistant and susceptible clones at optimum temperature for development of L. pseudobrassicae. Resistant clones showed longer generation time (T). However, net reproductive rate (Ro), longevity and reproductive period of resistant L. pseudobrassicae were higher than those of susceptible individuals, even when comparing resistant and susceptible individuals from the same clone. No difference in the intrinsic rate of increase (rm) was observed between resistant and susceptible individuals. Survival of immatures and fecundity of all clones were reduced by thermal shock. Regardless of thermal shock, there was no parasitism in resistant clones; meanwhile, parasitism in susceptible clones was 100% without thermal shock and 95.2% after heat shock. Biological aspects and parameters in the Fertility Life Table of L. pseudobrassicae under ideal conditions for its development or after thermal shock did not show any costs or adaptive advantages to aphids resistant to D. rapae. Resistance to parasitoid was maintained even after exposure of aphids at high temperature.