No abstract

The performance of herbivores, natural enemies and their interactions may be affected directly or indirectly by host plant traits, e.g. the physical plant characteristics may influence the search pattern and the functional response of predators. We studied the functional response of adult females of the predatory mite Neoseiulus cucumeris to first instar larvae of Thrips tabaci on three host plants (sweet pepper, eggplant and cucumber). The 24-h leaf disc experiments conducted at 25 ± 1°C, 60 ± 10% relative humidity and 16 : 8 h (light : dark) showed that N. cucumeris exhibited a type II functional response on all host plants. The following search rates and handling times were estimated from fitting the data to the disc equation 0.043/h and 1.798 h (cucumber); 0.048/h and 1.030 h (sweet pepper) and 0.0441/h and 2.294 h (eggplant) giving an estimated maximum predation of 13.35, 23.31 and 10.46 larvae per day respectively. The data from sweet pepper could also be described by the random predator equation (a¢: 0.051/h; T h : 0.472 h). The host plant species interacted significantly with prey density on the functional response of N. cucumeris with the relative differences in the number of thrips eaten on each host plant increasing with density. It is suggested that it is mainly the difference in trichome density between the three host plants that is responsible for the observed differences in the functional response of N. cucumeris. These results emphasize the importance of the host plant characteristics on the performance of natural enemies and for optimizing their use in biological control of pests.

Lady beetles are among the most successful predators of aphids in different environments. The functional responses of different life stages of Hippodamia variegata (Goeze) towards cotton aphids were examined in two different set-ups, a two-dimensional Petri dish set-up with detached leaves and a three-dimensional set-up with whole plants. In addition, the functional responses in two-dimensional set-ups towards cotton aphids and the pea aphids were compared. H. variegata exhibited a functional type II response to both cotton aphids and pea aphids irrespective of life stage and spatial scale of the set-up. Females and fourth instars generally had higher search rates than third instars whereas handling times were consistently lower for the fourth instar stage compared with the preceding juvenile stage and with females. The spatial dimensions did not have any significant influence on the functional responses towards cotton aphids, except for third instars which in the three-dimensional set-up reduced their search rate and increased their handling time. Fourth instars reacted in the same way to both Aphis gossypii and Acyrthosiphon pisum whereas the functional response parameters for third instars and females were significantly different on the two prey species. Our study, a part of this first-step evaluation of H. variegata as a biocontrol agent against A. gossypii and A. pisum under field condition, suggest that the voracity of all tested stages of H. variegata towards both aphid species hold good promises for a use of especially fourth instars and females in inundative biocontrol.

The tomato leaf miner Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a devastating pest of tomato plants originating from South America. In this study, the effect of three tomato cultivars on the life , and mean generation times (T) on the three cultivars were 30.09 AE 0.29, 30.22 AE 0.27 and 31.12 AE 0.65 days, respectively. The egg incubation period, pre-adult duration and fecundity on these tomato cultivars was also calculated. The results showed no significant differences between r, R 0 , and T on the three tested tomato cultivars. These findings can be useful for developing an integrated pest management strategy against this noxious pest.