Abstract
We challenged Locusta migratoria (Meyen) grasshoppers with simultaneous doses of both the insecticide chlorantraniliprole and the fungal pathogen, Metarhizium anisopliae. Our results showed synergistic and antagonistic effects on host mortality and enzyme activities. To elucidate the biochemical mechanisms that underlie detoxification and pathogen-immune responses in insects, we monitored the activities of 10 enzymes. After administration of insecticide and fungus, activities of glutathione-S-transferase (GST), general esterases (ESTs) and phenol oxidase (PO) decreased in the insect during the initial time period, whereas those of aryl acylamidase (AA) and chitinase (CHI) increased during the initial period and that of acetylcholinesterase (AChE) increased during a later time period. Activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) decreased at a later time period post treatment. Interestingly, treatment with chlorantraniliprole and M. anisopliae relieved the convulsions that normally accompany M. anisopliae infection. We speculate that locust mortality increased as a result of synergism via a mechanism related to Ca2+ disruption in the host. Our study illuminates the biochemical mechanisms involved in insect immunity to xenobiotics and pathogens as well as the mechanisms by which these factors disrupt host homeostasis and induce death. We expect this knowledge to lead to more effective pest control.
Highlights
Controlling insect pests, which continue to be agricultural, medical, and economic threats worldwide, requires constant human innovation[1]
L. migratoria was treated with M. anisopliae alone for 3 d before introducing wheat sprouts treated with chlorantraniliprole in Treatment 4, the resulting co-toxicity coefficient was 127 (Table 2)
Treatments 1, 2, and 4 revealed synergistic interactions with co-toxicity coefficients of 1646, 1619, and 127, respectively. These high co-toxicity coefficients, which were accompanied by insect mortalities >97% for some treatments, illustrate the effectiveness of this dual-attack method of insect pest control
Summary
Controlling insect pests, which continue to be agricultural, medical, and economic threats worldwide, requires constant human innovation[1]. Multi-function oxidases (MFO), glutathione-S-transferase (GST) and general esterases (ESTs) are most commonly involved in defence processes in insects[22] Because of their abundance, genetic diversity, broad substrate specificity and catalytic versatility, MFO, such as those involved in the P450 pathways in insects, are responsible for detoxification of natural and synthetic xenobiotics[23]. It is well known that both insecticide poisoning and fungal infections alter enzyme activities in insects[18,21,42,43,45], few studies have explored the complex enzymatic consequences of simultaneous insecticide and pathogenic assaults in insects[46], and no detailed investigations have been reported concerning the synergistic effect of M. anisopliae and insecticides on enzyme activities in insects
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