Larvicidal and insecticidal properties ofRicinus communisseed extracts obtained by different methods againstTribolium castaneumHerbst (Coleoptera: Tenebrionidae)

Ricinus communis seed extract obtained by hydraulic extractor tagged Ricinus hydraulic seed extract (RHSE) and that obtained by cold extraction using analytical grade ethanol tagged Ricinus ethanolic seed extract (RESE) were compared for their relative bioactivity against T. castaneum adult and larva in the laboratory (relative humidity, 70 ± 5%; temperature, 28 ± 2°C). Toxicity tests consisted of exposing T. castaneum adults and larvae to filter papers impregnated with four dosages (0.0, 0.1, 0.3 and 0.5 ml/60 cm2) of the R. communis seed extract or to sorghum seeds administered with same dosages (0.0, 0.1, 0.3 and 0.5 ml/5 g seeds). In the repellency tests, both adults and larvae were exposed to four dosages (0.0, 0.1, 0.3, 0.4 ml/ 30 cm2) of the extracts. Mortality increased with exposure period and concentration of extracts. The susceptibility of the two target stages of T. castaneum was more pronounced in treated sorghum seeds than on impregnated filter papers. All treatments (0.1–0.5 ml/5 g sorghum seed) of RESE caused 100% mortality of 5th–7th instar larvae at 1 day after treatment (DAT), whereas in RHSE, 100% larval mortality was only observed at 3 DAT when extract was applied at 0.3 ml/5 g seed. For filter paper toxicity bioassay, significant mortality was observed in RHSE. Larvae were more susceptible to extracts than adult in both methods of toxicity bioassays. RHSE was more repellent against T. castaneum than RESE with adults more repelled than larvae. At the lowest test concentration of 0.1 ml/30 cm2, 80% repellency of adult was recorded in RHSE, compared with 56.0% repellency of larvae at the same concentration. The results indicate that RHSE has greater potency than RESE for filter paper contact toxicity and repellency.