Abstract

-newline"> Neoseiulus californicus is a relatively aggressive predator and like several other phytoseiid species also prone to attack and kill its larvae. The level of aggressiveness, measured as latency to attack, could be an appropriate indicator of the nutritional value of or preference for a given prey. This study aimed at determining the aggressiveness of this predator against Tetranychus urticae (TSSM) and conspecific larvae as affected by starvation. Even-aged eggs of N. californicus were obtained by placing gravid females on detached bean leaves. Every 24 h, newly laid eggs were collected. Eggs to be used as prospective predators were transferred to experimental cages each consisting of a circular cavity of 20mm diameter and 6mm height with a fine gauze at the bottom and closed on the upper side by a microscope slide. Eggs to be used as prospective prey were transferred to a leaf arena without T. urticae. After another 24 h, newly hatched larvae were collected and used as conspecific prey in experiments. Immature stages of the predator were reared on pollen. For the experiment, <1 day old adult females were assigned to two groups. The first group was starved in cages for 24h before the start of the experiment (starved), whereas the second group was fed on pollen until the experiment started (satiated). Each group was then subdivided to 3 treatments: a) 5 mobile immatures of TSSM as prey (no choice), b) 3 conspecific larvae as prey (no choice) and c) both TSSM and conspecific larvae (choice). The experimental cages were monitored in 30 min intervals for 8 h or until the first prey was successfully attacked (i.e. killed and sucked out). 10 to 14 replicates were carried out for each experimental treatment. All starved N. californicus females and 90% of fed females attacked conspecific larvae in the no-choice test within the 8h experimental period. Starved predators attacked TSSM after 30 ± 0 (SE) min whereas satiated predators attacked TSSM only after 68± 8 (SE) min. Similarly, latency to attack on conspecific larvae was shorter in starved than satiated predators (54 ± 7 versus 216± 35 min.). In choice tests, starved predators attacked rapidly TSSM within 33±2.8 min but satiated ones attacked TSSM only after 140±33 min. Latency to attack TSSM of starved predators did not differ between the choice and no-choice test (33±2.8 min versus 30±0 min. respectively, P = 0.22). In contrast, satiated female predators attacked the first prey (TSSM) more than two times earlier (68± 8 min) in the no-choice test than in the choice test (140±33 min) (P = 0.02).