Evaluation of two free-living, and one entomopathogenic nematode species (Rhabditida) for controlling Bactrocera zonata (Diptera: Tephritidae) in Iraq.

Abstract

Fruit flies (Diptera: Tephritidae) are among the most serious agricultural pests globally, causing significant economic losses in fruit production and posing major quarantine concerns for many countries. Bactrocera zonata, one of the most harmful species in the family Tephritidae, has recently established in Iraq. Entomopathogenic nematodes (EPNs) and potential EPNs can be used as vital tools in integrated pest management (IPM) programs for both organic and conventional production systems. In our study, three species - two native and free-living, and the other, a native EPN - were isolated from various orchards in Iraq. Their pathogenicity was evaluated in laboratory and greenhouse experiments against the soil-dwelling third-instar larvae of B. zonata. In laboratory bioassays, mortality rates varied from 70-98% for Oscheius myriophilus, 12-58% for Acrobeloides saeedi, and 14-56% for Heterorhabditis bacteriophora 12 days post-treatment. The mean lethal concentration (LC₅₀) values, measured by infective juveniles (IJs)/larva, were 7.08 for O. myriophilus, 104.49 for A. saeedi, and 97.74 for H. bacteriophora in data set 1. They were 13.50, 86.04, and 86.67 IJs/larva, respectively, in data set 2. These values were determined for third-instar larvae in laboratory tests conducted 12 days post-treatment at 25°C and 60% relative humidity (RH). Under greenhouse conditions, applications of O. myriophilus, H. bacteriophora, and A. saeedi resulted in 50.00-91.75% mortality in fruit tests at a concentration of 250 IJs/larva, and 33.58-67.82% mortality in soil tests against B. zonata, at a concentration of 1,000 IJs/larva 19 days after treatment. Our results suggest that two presently studied free-living native nematodes are potential EPNs, and together with native isolate of Heterorhabditis bacteriophora, could be integrated into pest management programs against B. zonata in Iraqi orchards.