Gamma irradiation on canola seeds affects herbivore-plant and host-parasitoid interactions.

As an agricultural modernization, gamma irradiation is an important method for enhancing crop yield and quality. Nevertheless, its use can alter other plant traits such as nutrition and resistance to different biotic/abiotic stresses that consequently affect plant-insect interactions. A tritrophic system was utilized based on two canola mutant lines produced through gamma irradiation (RGS 8-1 and Talaye 8-3). Plutella xylostella (L.), as a worldwide pest of Brassicaceae and Cotesia vestalis (Holiday) as a key biocontrol agent of P. xylostella were examined for the potential indirect effects of canola seed irradiation on the experimental insects' performance when acting on the respective mutant lines. This study showed that physical mutation did not affect plant nitrogen and herbivore-damaged total phenolics; however, phenolic compounds showed greater concentration in damaged leaves than undamaged leaves of both mutant and control plants. The relative growth rate and pupal weight of P. xylostella reared on RGS 8-1 were significantly higher than those reared on the control RGS. There was no significant difference by performance parameters of the parasitoid, C. vestalis, including total pre-oviposition period, adult longevity, adult fresh body weight of males and females, pupal weight, forewing area, and total longevity of both sexes on tested canola cultivars in comparison with their mutant lines. Life table parameters of C. vestalis on mutant lines of both cultivars, RGS and Talaye, were not significantly different from their control treatments. Comprehensive studies should be conducted to find out the mechanisms under which gamma rays affect plant-insect interactions.

Thermal effect on the biology and life tables of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae).

The life history and life table of Bemisia tabaci Gennadius on cucumber was studied under laboratory conditions at 20, 25 and 30 degrees C. The overall developmental time varied from 34.8 days at 20 degrees C to 14.1 days at 30 degrees C. Immature mortality decreased from 45.8 to 17.3% with increasing temperature. The threshold temperatures of egg, 1st, 2nd, 3rd and 4th nymphal stage and a generation were 14.72, 14.36, 10.18, 11.40, 14.36 and 13.07 degrees C whereas the degree-day requirement at each stage was 64.44, 42.39, 49.19, 33.19, 35.46 and 229.52 DD, respectively. Female longevity ranged from 16.8-34.1 days. Mean total fecundity ranged from 150-263 eggs/female. Mean daily fecundity ranged from 4.2-12.7 eggs/female, increasing with increasing temperature. Values for r(m) varied from 0.066 to 0.191 being least at 20 degrees C and greatest at 30 degrees C. Generation times decreased from 43 to 19 days with increasing temperature. The results indicate that B. tabaci is well adapted to high temperatures and may extend its distribution if mean world temperatures increase as a result of global warming.