Life tables of the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on tomato in the middle Jordan Valley

Field experiments were conducted to construct life tables for Bemisia tabaci Genn. on growing tomato during fall and spring growing seasons (Sep 20, 1995 - May 30, 1996). During this period, the effect of mortality factors, mainly weather conditions and others, and parasitism, on the population growth of B. tabaci was determined under plastic house simulated conditions (in a cage made of wood and covered with plastic) and in the open field. Assessment of both mortality factors was carried out by following the development of B. tabaci population on 6 tomato plants (6 replicates) and 12 tomato plants (12 replicates) in each generation, for the open field and the cage, respectively. In addition, Eretmocerus mundus Mercct was introduced at the rate of 1:12 (1 female parasitoid : 20 second and third nimphal instars of whitefly), to assess the efficacy of the parasitoid as a biocontrol mean. Results indicated that B. tabaci can produce 7 generations under plastic-house-simulated conditions, and 6 generations under open field. In both cases, 3 generations were produced during the fall growing season, whereas the other generations were produced during the spring growing season. The duration of the 1st, 2nd, 3rd, 4th, 5th, 6th and 7th generations in the cage was 24,32, 79,30, 28, 22 and 19 days, respectively. However, the generation duration in the open field was 29,39, 40,33 and 27 days for the 1st, 2nd, 4th, 5th, and 6th generation, respectively. The duration of the 3th generation could not be determined in the open field because the tested tomato plants collapsed due to adverse weather conditions. Furthermore, the whitefly populations were regulated by two mortality factors: weather conditions and others, and parasitisms. Weather conditions and others were the most detrimental mortality factor causing death in whitefly individuals ranging from 35.2% to 77.3%. Parasitism by E. mundus ranked second as it killed 6.6 to 15.8%. Life tables analysis using stepwise linear regression revealed that the 3rd nymphal instar was the most vulnerable among all whitefly developmental stages. Its mortality percentage ranged from 18.0 - 41.0% in the cage and from 21.0 - 48.0% in the open field in all successive generations. The introduction of the parasitoid E. mundus, at the rate of 1:20 did not control B. tabaci eff1ciently. Only 8.8 to 21.8% of whiteflies were parasitized. Intervention by man to control B. tabaci infesting tomato plants during the two growing seasons was discussed in view of the above mentioncd results and possible control measures were recommended