Extracts from the bark of Fagara heitzii (Aubr. et Pel.) (Rutaceae) tree are toxic to two weevils and the American cockroach

Abstract

The bark of the Fagara heitzii tree in the west‐central African Republic of Congo (Congo–Brazzaville) is known anecdotally to provide protection for human residents against fleas and to be of use as a narcotic in fishing (similar to rotenone). We found that powder and hexane extracts from the bark of the Fagara heitzii tree contain insecticidal compounds. Dried powder (14.5 mg) on the bottom of a Petri dish is the residue at 14.494 mg per dish (LD50) for 20 adult maize weevils Sitophilus zeamays after four days. The LD50 of the same material to 20 adult cowpea weevils Callosobruchus maculatus was slightly higher at 16.144 mg/dish (after 48 h). These weevils cause significant economic damage to cowpea and maize in Congo–Brazzaville. Hexane extracts of the bark of Fagara heitzii were also toxic to these weevils. Symptoms of toxicity suggested the extracts were slow‐acting nerve poisons or respiratory inhibitors or both. The time needed to develop full toxicity suggested a respiratory poison. The hexane extract was also toxic to the American cockroach Periplaneta americana. The symptoms in the cockroach were similar, but cockroaches also exhibited apparent escape attempts suggesting they could detect the compounds. Signs of apparent irritation or exaggerated locomotion in all three insects also suggested irritation or nerve effects.

Insecticidal Activities of Bark, Leaf and Seed Extracts of Zanthoxylum heitzii against the African Malaria Vector Anopheles gambiae

“…Seed and leaf extracts produced very low mortalities, compared to the bark extracts, indicating that toxic compounds are mainly present in the bark. This is consistent with previous reports [34]. In our study, mortalities ranged from 97% to 100% in the three mosquito strains (insecticide susceptible and resistant) when exposed to the highest test concentration (1%) of Soxhlet and Accelerated Solvent Extraction (ASE) hexane stem bark extracts.…”

“…Only a few investigations on chemical constituents and biological activity of Z. heitzii have been carried out, but alkaloids, lignans, triterpenes, esters and amides have been reported [30,31,32,33]. Hexane extracts from Z. heitzii bark was shown to be toxic to two weevil species and the American cockroach [34] and having antifilarial effect on the nematode Loa loa [35]. A preparation of Z. heitzii has been patented as an antiviral, antibacterial and immunostimulating remedy with possible anti-AIDS activity [36].…”

Natural products from Zanthoxylum heitzii with potent activity against the malaria parasite

“…In this area, the bark is traditionally used to treat malaria [ 10 ]. Zanthoxylum heitzii bark extracts and major components of the extracts have previously been shown to have insecticidal activity [ 16 – 18 ] but it is unknown if Z. heitzii contains any compounds with significant anti-parasitic activity.…”

Identification of chemical constituents of Zanthoxylum heitzii stem bark and their insecticidal activity against the malaria mosquito Anopheles gambiae

“…& Pellegr., Rutaceae, is a West African species found in forests from Congo to Cameroon [ 3 ]. Some of its local names are olon [ 3 ] and bouboulou [ 4 ]. This tree is used for timber, but has also a considerable ethnopharmacological use.…”

“…Antioxidant effects and activity against sickle cell anemia in vitro are reported [ 8 ], as well as immunorestorative properties of an aqueous bark extract in clinical studies [ 15 ]. The bark extract was also toxic towards agricultural weevil pests and the cockroach Periplaneta americana L. [ 4 ]. The effect of Z. heitzii extracts on adult females of the mosquito Anopheles gambiae Giles, a major vector of malaria, has recently been investigated by us [ 16 ].…”