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Emerald ash borer, Agrilus planipennis Fairmaire, an Asian wood-boring beetle, has devastated ash (Fraxinus spp.) trees in North American forests and landscapes since its discovery there in 2002. In this study, we collected living larvae from EAB-resistant Manchurian ash (Fraxinus mandschurica), and susceptible white (Fraxinus americana) and green (Fraxinus pennsylvanica) ash hosts, and quantified the activity and production of selected detoxification, digestive, and antioxidant enzymes. We hypothesized that differences in larval physiology could be used to infer resistance mechanisms of ash. We found no differences in cytochrome P450, glutathione-S-transferase, carboxylesterase, sulfotransferase, and tryptic BApNAase activities between larvae feeding on different hosts. Despite this, Manchurian ash-fed larvae produced a single isozyme of low electrophoretic mobility that was not produced in white or green ash-fed larvae. Additionally, larvae feeding on white and green ash produced two serine protease isozymes of high electrophoretic mobility that were not observed in Manchurian ash-fed larvae. We also found lower activity of β-glucosidase and higher activities of monoamine oxidase, ortho-quinone reductase, catalase, superoxide dismutase, and glutathione reductase in Manchurian ash-fed larvae compared to larvae that had fed on susceptible ash. A single isozyme was detected for both catalase and superoxide dismutase in all larval groups. The activities of the quinone-protective and antioxidant enzymes are consistent with the resistance phenotype of the host species, with the highest activities measured in larvae feeding on resistant Manchurian ash. We conclude that larvae feeding on Manchurian ash could be under quinone and oxidative stress, suggesting these may be potential mechanisms of resistance of Manchurian ash to EAB larvae, and that quinone-protective and antioxidant enzymes are important counter-adaptations of larvae for dealing with these resistance mechanisms., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Phytophagous insects frequently encounter reactive oxygen species (ROS) from exogenous and endogenous sources. To overcome the effect of ROS, insects have evolved a suite of antioxidant defense genes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). The emerald ash borer (Agrilus planipennis Fairmaire), an exotic invasive insect pest from Asia has killed millions of ash trees and continues to invade North America at a rapid pace. From an on-going expressed sequence tag (EST) project of A. planipennis larval tissues, we identified ESTs coding for a Cu-Zn SOD (ApSOD1), a CAT (ApCAT1) and a GPX (ApGPX1). A multiple sequence alignment of the derived A. planipennis sequences revealed high homology with other insect sequences at the amino acid level. Phylogenetic analysis of ApSOD1 grouped it with Cu-Zn SODs of other insect taxa. Quantitative real time PCR (qRT-PCR) analysis in different larval tissues (midgut, fat body, Malpighian tubule and cuticle) revealed high mRNA levels of ApCAT1 in the midgut. Interestingly, high mRNA levels for both ApSOD1 and ApGPX1 were observed in the Malpighian tubules. Assay of mRNA levels in developmental stages (larva, prepupa and adults) by qRT-PCR indicated high transcript levels of ApCAT1 and ApGPX1 in larval and prepupal stages with a decline in adults. On the other hand, the transcript levels of ApSOD1 were observed to be constitutive in all the developmental stages assayed. Results obtained reflect a plausible role of these A. planipennis antioxidant genes in quenching ROS from both diet (ash allelochemicals) as well as endogenous sources. These studies further help in understanding the adaptation/invasiveness of A. planipennis., (Copyright © 2011 Elsevier Ltd. All rights reserved.)