Sustainable management of two Sitophilus species infesting wheat grains using crude extracts from botanicals.

This study investigates the bioactivities of the leaf extract of Acalypha godseffiana (Muell Arg.) and the stem bark extract of Alstonia boonei (De Wild) against Sitophilus oryzae (Linnaeus) and Sitophilus zeamais (Motschulsky) at different concentrations (2.5, 5.0, 7.5, 10.0, and 12.5% %). The relative growth rate (RGR), relative consumption rate (RCR), and efficiency of conversion of ingested food (ECI) of both Sitophilus species were assessed using extract-treated wheat flour discs. The contact toxicity and effects of both extracts on the adult emergence of both weevils were also determined. Control experiments were set up for all the bioassays. Phytochemical compounds (tannins, saponins, anthraquinones, cardiac glycosides, flavonoids, and alkaloids) in each botanical extract were checked. Except for anthraquinones, which was lacking in A. boonei but marginally present in A. godseffiana, both extracts contain all the tested phytochemicals in either low, moderate, or high amounts. The LC50 values showed that both extracts had higher toxicity to S. zeamais at 24 and 48 h and to S. oryzae at 72 and 96 h. Both extracts at 12.5% significantly decreased adult emergence and evoked higher inhibition in adult emergence of both Sitophilus species relative to controls. RGR, RCR, and ECI generally decreased as extract concentrations increased. At 12.5%, A. boonei and A. godseffiana considerably decreased the RCR of S. oryzae and S. zeamais, respectively. Additionally, the ECI of both species was significantly lower relative to controls. Conclusively, the two extracts evoked insecticidal, anti-nutritional, and significantly reduced adult emergence of both Sitophilus species relative to controls. [ABSTRACT FROM AUTHOR]