Laboratory Evaluation of Indigenous and Commercial Entomopathogenic Nematodes against Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae).

The red palm weevil (RPW) is a significant threat to date palms. Conventional pest control has been ineffective. This study aims to evaluate entomopathogenic nematodes (EPNs) indigenous to Saudi Arabia and commercial against RPW. We used 33 soil samples collected from four areas of Saudi Arabia. The indigenous EPNs were isolated and cultured using an insect baiting method to obtain infective juveniles. Pathogenicity bioassays were conducted against different stages of RPW, including eggs, larvae, and adults. The bioassay was performed using all the isolates at 1 × 106 IJ/mL. Distilled water was used as a control. The results revealed that only 9.09% of soil samples contained positive EPNs. Through DNA sequencing analysis, the positive samples were identified as indigenous isolates belonging to Heterorhabditis indica and Steinernema carpocapsae EPN species. In pathogenicity tests, 90% mortality of RPW eggs was observed after five days. Similar mortality trends were seen in RPW larvae and adults, with 90% mortality recorded after ten days for all the EPN treatments. Mortality increased with the duration of post-EPN inoculation exposure. The 1 × 106 IJ/mL concentrations of EPN effectively killed various stages of RPW in the laboratory. More research is needed to test EPNs against RPW in the field.

Acoustic Comparisons of Red Palm Weevil (Rhynchophorus ferrugineus) Mortality in Naturally Infested Date Palms after Injection with Entomopathogenic Fungi or Nematodes, Aluminum Phosphide Fumigation, or Insecticidal Spray Treatments.

Red palm weevil (RPW) management is important to the economic success of date palm agriculture. Monitoring with acoustic sensors was conducted in naturally infested trees in date palm orchards for six months after treatments with entomopathogenic fungi (Beauveria bassiana and Metarhizium anisopliae), entomopathogenic nematodes (Steinernema carpocapsae), aluminum phosphide, emamectin benzoate, or fipronil to evaluate their efficacy in an integrated pest management treatment vs. a distilled water injection. Reductions in the mean rates of RPW sound impulse bursts over time after treatment were used as indicators of RPW mortality. Entomopathogenic fungi and nematodes, aluminum phosphide, and emamectin benzoate were the most effective treatments, reducing RPW impulse burst rates within 2-3-months to levels indicating absence of infestation. However, when applied as a spray, fipronil had only a minor effect. The results indicate that treatments utilizing entomopathogenic fungi or nematodes can beneficially manage RPW in palm orchards and can help to limit treatments that may induce insecticide resistance or cause human and environmental harm. Furthermore, the use of an acoustic sensor can be beneficial in monitoring the activities of insect borers inside the tree trunk.

Field Evaluation of Promising Indigenous Entomopathogenic Fungal Isolates against Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae).

The rate of the sounds (i.e., substrate vibrations) produced by the movement and feeding activity of red palm weevil (RPW) pest infestations in a date palm tree was monitored over time after trees were separately treated with injection of entomopathogenic fungal isolates, Beauveria bassiana and Metarhizium anisopliae, or water treatment as the control. The activity sensing device included an accelerometer, an amplifier, a digital recorder, and a signal transmitter that fed the data to a computer that excluded background noise and compared the rates of bursts of movement and feeding sound impulses among treated trees and controls. Observations were made daily for two months. The rates of bursts were representative of the feeding activity of RPW. The unique spectral pattern of sound pulses was typical of the RPW larval feeding activity in the date palm. The microphone confirmed that the same unique tone was produced in each burst. Two months after fungal injection, the RPW sound signal declined, while the RPW sound signal increased in the control date palms (water injection). The mean rates of bursts produced by RPW decreased to zero after the trees were injected with B. bassiana or M. anisopliae compared with the increased rates over time in the control treatment plants.

Genes involved in sex pheromone biosynthesis of Ephestia cautella, an important food storage pest, are determined by transcriptome sequencing.

BACKGROUND: Insects use pheromones, chemical signals that underlie all animal behaviors, for communication and for attracting mates. Synthetic pheromones are widely used in pest control strategies because they are environmentally safe. The production of insect pheromones in transgenic plants, which could be more economical and effective in producing isomerically pure compounds, has recently been successfully demonstrated. This research requires information regarding the pheromone biosynthetic pathways and the characterization of pheromone biosynthetic enzymes (PBEs). We used Illumina sequencing to characterize the pheromone gland (PG) transcriptome of the Pyralid moth, Ephestia cautella, a destructive storage pest, to reveal putative candidate genes involved in pheromone biosynthesis, release, transport and degradation. RESULTS: We isolated the E. cautella pheromone compound as (Z,E)-9,12-tetradecadienyl acetate, and the major pheromone precursors 16:acyl, 14:acyl, E14-16:acyl, E12-14:acyl and Z9,E12-14:acyl. Based on the abundance of precursors, two possible pheromone biosynthetic pathways are proposed. Both pathways initiate from C16:acyl-CoA, with one involving ∆14 and ∆9 desaturation to generate Z9,E12-14:acyl, and the other involving the chain shortening of C16:acyl-CoA to C14:acyl-CoA, followed by ∆12 and ∆9 desaturation to generate Z9,E12-14:acyl-CoA. Then, a final reduction and acetylation generates Z9,E12-14:OAc. Illumina sequencing yielded 83,792 transcripts, and we obtained a PG transcriptome of ~49.5 Mb. A total of 191 PBE transcripts, which included pheromone biosynthesis activating neuropeptides, fatty acid transport proteins, acetyl-CoA carboxylases, fatty acid synthases, desaturases, ß-oxidation enzymes, fatty acyl-CoA reductases (FARs) and fatty acetyltransferases (FATs), were selected from the dataset. A comparison of the E. cautella transcriptome data with three other Lepidoptera PG datasets revealed that 45% of the sequences were shared. Phylogenetic trees were constructed for desaturases, FARs and FATs, and transcripts that clustered with the ∆14, ∆12 and ∆9 desaturases, PG-specific FARs and potential candidate FATs, respectively, were identified. Transcripts encoding putative pheromone degrading enzymes, and candidate pheromone carrier and receptor proteins expressed in the E. cautella PG, were also identified. CONCLUSIONS: Our study provides important background information on the enzymes involved in pheromone biosynthesis. This information will be useful for the in vitro production of E. cautella sex pheromones and may provide potential targets for disrupting the pheromone-based communication system of E. cautella to prevent infestations.