Role of symbiotic bacteria in the growth and development of the Sunn pest, Eurygaster integriceps.

The Sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), is the most important pest of wheat and barley in wide areas of the world. Different aspects of the insect's life history have been studied, but to date nothing is known about their microbial symbionts. Here, the contribution of symbiotic bacteria to the fitness of the bug was investigated by combining two different approaches to manipulate the host's microbial community: the supplementation of antibiotics into the insects' diet and egg surface sterilization. First, bacteria cultured from gut homogenates were subjected to antibiotic screening tests using 20 different antibiotics. Norfloxacin was the most effective antibiotic, with the greatest inhibition zone among all antibiotics tested. Feeding norfloxacin to adult E. integriceps individuals significantly impaired growth and development of the offspring in a dose-dependent manner, i.e., higher antibiotic doses increased the negative effects on nymphal growth and development. Total developmental time from first nymphal instars to adult emergence in control animals was 30.1 days, but when adults had been offered diets with 10, 20, and 30 µg antibiotic per mg diet, the offspring's developmental time was prolonged to 32.8, 34.0, and 34.8 days, respectively. In the highest two doses of norfloxacin, all of the nymphs died before reaching the fifth nymphal instar. Similar results as for the antibiotic treatment were obtained when egg surface sterilization was used to manipulate the microbial community of E. integriceps. These results indicate that bacterial symbionts play a crucial role in the successful development of the host.

Effect of host plants on developmental time and life table parameters of Amphitetranychus viennensis (Acari: Tetranychidae).

The effect of host plant species including black cherry (Prunus serotina cv. Irani), cherry (Prunus avium cv. siahe Mashhad) and apple (Malus domestica cv. shafi Abadi) was studied on biological parameters of Amphitetranychus viennensis (Zacher) in the laboratory at 25 +/- 1 degrees C, 70 +/- 10% RH and 16L: 8D photoperiod. Duration of each life stage, longevity, reproduction rate, the intrinsic rate of natural increase (rm), net reproductive rate (R0), mean generation time (T), doubling time (DT), and finite rate of increase (lambda) of the hawthorn spider mite on the three host plants were calculated. Differences in fertility life table parameters of the spider mite among host plants were analyzed using pseudo-values, which were produced by jackknife re-sampling. The results indicated that black cherry might be the most suitable plant for hawthorn spider mite due to the shorter developmental period (10.6 days), longer adult longevity (25.5 days), higher reproduction (65.6 eggs), and intrinsic rate of natural increase (0.194 females/female/day). Cherry was the least suitable host plant. To determine the effect of host shifts, the mite was transferred from black cherry onto cherry and apple. In the first generation after shifting to apple, the developmental period, reproduction and life table parameters were negatively influenced. However, population growth parameters in the first generation on cherry were actually better than after three generations on this new host. This underscores the relevance of the mites' recent breeding history for life table studies.