Acaricide susceptibility of Oligonychus coffeae Nietner (Acari: Tetranychidae) with corresponding changes in detoxifying enzyme levels from tea plantations of sub-Himalayan Terai, India

Oligonychus coffeae Nietner is cosmopolitan in its distribution and is an important pest of a number of economically important tropical and sub-tropical crops including tea. It is the most damaging acarine pest of tea crops in the sub-Himalayan Terai region of India which is mostly controlled chemically in the conventionally managed tea plantations of the region. Objectives of the present study were to i) investigate the tolerance level of O. coffeae collected from bio-organically managed plantations (BMP) (with no synthetic acaricide application) and conventionally managed plantations (CMP) (with periodic application of synthetic acaricide) to the acaricides, ’ethion’ and ’fenpropathrin’, ii) Quantify the detoxifying enzymes, general esterases (GE) of phase I and glutathione S-transferases (GST) of phase II, in O. coffeae as these are deemed important in acquiring pesticide tolerance, iii) Establish the relation of GE and GST activity levels with acaricide tolerance levels in populations of O. coffeae. The study revealed that i) BMP populations of O. coffeae were susceptible to both of the acaricides whereas CMP populations were tolerant. CMP populations of the pest showed low to medium tolerance to the organophosphate acaricide ’ethion’ whereas tolerance to the synthetic pyrethroid, ’fenpropathrin’ was high; ii) Corresponding GE and GST levels were significantly higher in CMP populations compared to that of BMP population. Electrophoretic analysis of GE isozymes of CMP and BMP populations further corroborated the quantitative study; iii) activity of the detoxifying enzymes, GE and GST were positively correlated with the tolerance level of O. coffeae populations indicating involvement of these enzymes in the development of acaricide tolerance.

Host plant-based variation in fitness traits and major detoxifying enzymes activity in Scirtothrips dorsalis (Thysanoptera: Thripidae), an emerging sucking pest of tea

Scirtothrips dorsalisHood is a polyphagous species and an important sucking pest of tea (Camellia sinensis) (Theaceae). The fitness traits ofS. dorsalison two alternative host plants:Capsicum annuumL. (chilli) (Solanaceae) andRicinus communis(castor oil plant) (Euphorbiaceae) and onC. sinensisand corresponding levels of defence enzymes was studied. The study revealed thatC. sinensisis the more suitable host ofS. dorsalisbased on faster development (13.6 days) compared to the alternative hosts,C. annuum(15.5 days) andR. communis(16.7 days), a higher fecundity (C. sinensis: 11.4 eggs;C. annuum: 9.7 eggs;R. communis: 8.6 eggs), and superior egg hatchability (C. sinensis, 92.6%;C. annuum: 82.5%; andR. communis: 74.6%). The host-based variation in the fitness traits ofS. dorsaliscorroborated in light of differential activity of three major detoxifying enzymes, such as the general esterases (GEs), glutathioneS-transferases (GSTs), and cytochrome P450 mediated monooxygenases (CYPs). Densitometric analysis of GEs showed five esterase isozymes (EST I–V) with retardation factor (Rf) values of 0.17, 0.22, 0.27, 0.35 and 0.52, respectively. The pixel density, and accordingly the profile height, varied in different host-specificS. dorsalis. A significant variation of the quantity of these enzymes was also apparent in the insect when reared on the three hosts. A 2.4 and 2.7, 1.6 and 2.0, and 2.0 and 2.3-fold higher GEs, GSTs and CYPs activity on the two non-tea hosts possibly signify a predisposition of the species for higher tolerance to insecticides, enabling the pest to switch to tea where synthetic insecticides are routinely used.

DETOXICATIVE ENZYME ACTIVITIES IN FIVE SPECIES OF FIELD-COLLECTED MELANOPLINE GRASSHOPPERS (ORTHOPTERA: ACRIDIDAE)

Detoxicative enzyme systems, such as the cytochrome P450 monooxygenases, gluthione S-transferases, and general esterases, have been widely studied in holometabolous insects (e.g. Lepidoptera, Diptera, and Coleoptera). These, and other enzyme systems, play important roles in insecticide resistance, but are also important in insect–host plant relationships, because host range can partially depend on the ability of an insect to cope with putatively toxic allelochemicals in an otherwise suitable host plant (e.g. Lindroth 1989). In some cases, differences in the relative activities of these enzymes between closely related insect taxa can have significant biological consequences (Siegfried and Mullin 1989).

Development of protein polymorphisms in redwing blackbirds

Breeding populations of the redwing blackbird, Agelaius phoeniceus, were studied to compare protein differences during development. Proteins which represented a minimum of ten loci were studied in egg white, embryonic, nestling and adult tissue. In starch-gel electrophoresis at several conditions of pH only ovoglobulin, ovotransferrin and general esterases were polymorphic. Tissue specificity was observed in other isozymes. These data suggest that developmental sequences of proteins may be considered an adaptative response of the organism.