The effect of spermine on Tetranychus urticae-Cucumis sativus interaction.

BACKGROUND: Two spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) is one of the most important plant pests in the world. Due to increased resistance of mites to acaricides, it is necessary to use other methods such as inducing resistance in plants by natural compounds for pests' management. Polyamins such as spermine are effective in increasing plant resistance to biotic and abiotic stressors. In this research, the effect of spermine treatments in cucumber plants on life table parameters of T. urticae was investigated. Also, top-down effect of spermine and T. urticae on cucumber biochemical parameters was measured. In the experiments, 1, 2 and 3 mM spermine concentrations were used. RESULTS: Amongst the spermine treatments, those mites that fed on cucumbers which received 1 mM spermine showed the shortest protonymphal period and higher ovipositon period, fecundity, gross and net reproductive rates and life expectancy compare to control. Treatment with 2 mM spermine lead to the longest teleochrysalis period and shortest range of age-stage-specific fecundity period. In addition, 2 mM spermine lowered intrinsic and finite rate of population increase in T. urticae. The longest larval period of T. urticae was observed in 3 mM spermine. Feeding of T. urticae from cucumber plants increased hydrogen peroxide (H2O2), malondialdehyde (MDA) content, electrolyte leakage (EL) level and ascorbate peroxidase (APX) activity but inhibited catalase (CAT) activity in this plant. Infested cucumber plants treated with 2 mM spermine showed lower H2O2 and MDA content and highest activity of APX and CAT on day 1 and 3 compare to the others. The 3 mM spermine increased H2O2 content in infested plants during the whole experiment as well as non-infested plants in day 5 and 9 only. This treatment induced the highest MDA content and lowest catalase activity on day1, 3 and 5 of experiment in infested plants. CONCLUSION: This study showed that 2 mM spermine was the only effective concentration that reduce cucumber sensitivity to T. urticae. The trend of changes in biochemical parameters, especially H2O2, in 3 mM spermine was abnormal, and this concentration could be considered toxic.

Age stage, two-sex life table of Habrobracon hebetor (Braconidae) on Spodoptera exigua (Noctuidae) reared on different sugar beet genotypes.

The present study was carried out to unveil interactive relevance among consecutive and alternate members of a tritrophic system comprised of sugar beet genotypes, beet armyworm, Spodoptera exigua (Hübner), and its parasitoid, Habrobracon hebetor (Say) using demographic parameters. To do so, H. hebetor was reared on S. exigua fed on 10 sugar beet genotypes, including SB26; SB27; SB29; SB33; SB34; (7112*SB36)*Sh-1-HSF-5; FC220; FC301; SBSI006; and HM 1339RZ in a growth chamber at 25 ± 1 °C, 60 ± 5% RH, and 16:8 (L: D) h photoperiod. The data was analyzed based on the age-stage, two-sex life table theory. Our results revealed high variation in duration of different life stages of H. hebetor on S. exigua reared on different sugar beet genotypes examined. The shortest (10.605 days) and longest (13.721 days) pre-adult period of H. hebetor was on S. exigua reared on SB26 and SB34, respectively. The longest (17.2 days) and shortest adult longevity (7.5 days) was on S. exigua reared on SB26 and SB27, respectively. The highest values of the intrinsic rate of increase (r) (0.209 day-1) and finite rate of increase (λ) (1.233 day-1) were observed on S. exigua reared on SB34 and their lowest values (0.159 and 1.172 day-1, respectively) were recorded on SB27. Resistant and susceptible genotypes to S. exigua, FC301 and (7112*SB36)*Sh-1-HSF-5, respectively, were only genotypes on which H. hebetor had greater and approximately equal r compared with S. exigua. This finding indicates high capability of H. hebetor to be successfully employed against S. exigua on sugar beet genotypes which are extremely different in resistance to this pest.

Screening of Potential Sources of Resistance to Spodoptera exigua (Lepidoptera: Noctuidae) in 24 Sugar Beet Genotypes.

Spodoptera exigua (Hübner) is one of the polyphagous pests destroying crops such as sugar beet worldwide. The aim of this experiment was to evaluate the resistance of 24 sugar beet genotypes to S. exigua. In this study, nine sugar beet cultivars (Dorotea, Tous, Persia, Silenta, Jaam, HM1339RZ, Jolgeh, Ekbatan, and SBSI006), three hybrids ((7112*SB36)*Sh-1-HSF-5, (7112*SB36)*Sh-1-HSF-15, and (7112*SB36)*Sh-1-HSF-16), four lines (FC201, FC301, FC220, and FC221), and eight populations (SB26, SB27, SB28, SB29, SB30, SB33, SB34, and SB35) were assessed. The experiments were performed under laboratory conditions at 25 ± 1 °C, 60 ± 5% RH, and a photoperiod of 16:8 (L:D) h using age-stage, two-sex life table procedure. The larval period ranged from 17.09 d on FC301 to 14.47 d on SB30. The total fecundity (F) was highest on (7112*SB36)*Sh-1-HSF-5 (905.13 eggs) and lowest on FC301 (312.46 eggs). (7112*SB36)*Sh-1-HSF-5 and FC220 with 318.02 and 26.76 eggs per individual had the highest and lowest net reproductive rates (R0), respectively. The highest values of the intrinsic rate of increase (r) and finite rate of increase (λ) were on (7112*SB36)*Sh-1-HSF-5 (r: 0.187 d - 1, λ: 1.205 d - 1) and the lowest were on FC301 (r: 0.104 d - 1, λ: 1.11 d - 1). SB26 (r: 0.185 d - 1, λ: 1.203 d - 1) and FC220 (r: 0.114 d - 1, λ: 1.12 d - 1) had no significant difference with (7112*SB36)*Sh-1-HSF-5 and FC301, respectively. The comparison of demographic parameters of S. exigua on 24 sugar beet genotypes suggested that FC220 and FC301 were the most resistant and (7112*SB36)*Sh-1-HSF-5 and SB26 were the most susceptible genotypes to this pest.