Background: Oyster mushroom, Pleurotus spp. are considered healthy foods with high nutritional value. This mushroom is exposed to many pests, including Megaselia halterata infestation, which causes it to lose its quantity and quality. The current study was conducted to evaluate the efficacy of Avermectin from Streptomyces avermitilis in controlling M. halterata. 
 
Methods: Avermectin was partially purified from S. avermitilis and its quantity and quality were determined using HPLC. Standard conditions were calibrated for maximum productivity and its effectiveness against M. halterata was tested in the mushroom growing room. 
 
Result: The results showed that the insect was identified as M. halterata through molecular diagnosis based on nucleotide sequence analysis of the gene cytochrome oxidase C subunit 1 and it was registered on the NCBI website under the name M. halterata voucher Amna-1 (accession number PP320397.1). Results of the partially purified avermectin from S. avermitilis strain Amna-4 analyzed by HPLC showed a retention time of 12.5 minutes, close to the standard avermectin retention time of 12.4 minutes. The optimal conditions for avermectin production from S. avermitilis were identified, with the highest concentration recorded at 342.59 mg/L in SCM (Starch Casein Medium) supplemented with 5% carboxymethyl cellulose and 5% isoleucine at a pH of 7.5, incubated at 30oC for 14 days. When evaluating the efficiency of the partially purified avermectin in infecting P. pulmonarius with M. halterata, the results showed no insect infestation comparable to the commercial insecticide Proclaim and the uninfected control treatment. The biological efficiency was recorded as 101.27, 99.72 and 98.86% for the partially purified avermectin, Proclaim and the healthy uninfected control, respectively. The results also demonstrated a clear effect on the fruit bodies&rsquo; protein content in the M. halterata treatment only, where it decreased to 18.51%, while no significant differences were observed among the partially purified avermectin, Proclaim&yuml;&thorn; and the uninfected control treatments, which reached 35.21, 34.78 and 34.59%, respectively. 
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Extraction, Purification of Avermectin from the Iraqi Streptomyces avermitilis Strain Amna-4 and Evaluation of its Efficacy in Killing Megaselia halterata Parasitizing the Edible Mushroom Pleurotus pulmonarius