Biological Parameters of Two-Spotted Spider Mite, Tetranychus urticae, on Two Plants with Insect Hormone-Like Compounds

Plants produce some compounds for defense against phytophagous insects and mites that may disrupt their endocrine system. Plant phytoecdysteroids and juvenoids are of these compounds that has been isolated and identified from some species. The main function of ecdysteriod is to stimulate development from one molting cycle to the next and compounds like that has been identified in Spinacea oleracea L.. The main function of JH in insect ontogenesis is to inhibit morphogenetic process and compounds like that has been identified in Calendula officinalis L.. The two-spotted spider mite, Tetranychus urticae Koch, is a polyphagous pest worldwide on a variety of host plants which has become resistant to pesticides. Since insect hormone-like compounds in plants, act selectively and are safe for environment they can compete with common pesticides.

A study was carried out to investigate the effect of above mentioned plants on biological parameters of T. urticae in the University of Maragheh. The life table parameters of T. urticae were studied on leaf discs under laboratory conditions (RH 65±5%, 25±1ºC and 16:8 h L:D) with 50 replicates. The raw data were analyzed based on age stage two-sex life table theory with TWO SEX-MS Chart software.

The intrinsic rate of increase (r) were 0.2188 and -0.0199 day-1, the finite rate of increase (λ) were 1.244 and 0.0980 day-1, the net reproductive rate (R0) were 21.52 and 0.74 (eggs/individual), the mean generation time (T) were 14 and 16.75 days, and the gross reproduction rate (GRR) were 48.37 and 5.7 (eggs/individual) on Spinacea oleracea and Calendula officinalis, respectively.

The results showed that Calendula officinalis affect T. urticae negatively and only 10% of the mite population can mature on this host. Spinacea oleracea had no inhibitory effect on the biology of T. urticae and the performance of this mite on this host was like its performance on its main hosts. Calendula officinalis has juvenoid compounds that have negative effects on biology of T. urticae. So these compounds can be used in the management of T. urtcae.