Determination of insecticidal effects of Ricinus communis crude extracts and blood baited traps with castor oil adhesive on phlebotomine sand flies (Diptera: Psychodidae)

Abstract

Sand flies are small haematophagous insects that transmit Leishmania parasites. Infection with Leishmania results in diseases known as leishmaniases which infects 14 million people worldwide with 2 million new cases occurring annually. The drawbacks for pentamonials and synthetic chemical insecticides have necessitated the search for new therapies against leishmaniasis and Phlebotomus duboscqi ((Diptera: Psychodidae, Phlebotominae)). This study aimed at assessing the effects of Ricinus communis (castor oil plant) extracts on P. duboscqi pre-emergent stages and adults in the laboratory. The study also sought to assess the potential of an improved sand fly trap incorporated with castor oil and baited with animal blood, urine and fruit attractants in the field. This trap could help solve the problems of the center for disease control (CDC) light trap since it is a simple and inexpensive trap which is light independent. Aqueous, methanol and ethyl acetate extracts were prepared from R. communis plant collected from Suswa (Narok County), Juja (Kiambu) and Nyanchwa (Kisii County). Freshly laid eggs were moistened with 1 ml of each extract separately during the incubation period. Larvae were also fed on larval food mixed with the powdered crude extract and adults were fed on the extracts through cotton wool pads which were soaked in the extracts and placed on the screen tops. Further, defibrinated blood (from cattle, goat, sheep and chicken); urine (from cattle, sheep and goat) and ripe fruits (bananas, apples, grapes and mango) were placed inside each trap to act as sand fly attractants. The study was carried out using a completely randomized design with three replicates. Median survival times were calculated using SPSS version 17.0. The efficacy of the different treatments was compared using the final cumulative mortalities. Differences in mortality rates, rate of pupation, and adult longevity were analyzed by analysis of variance and probability values of <0.05 were considered significant. 250 µg/ml and 500 µg/ml of methanol R. communis leaf extracts from Narok eroded all the chorionic membranes of the egg shell while egg hatchability was significantly inhibited with 9% (13.33 ± 1.67, P<0.001) of eggs hatching at 500 µg/ml of methanol R. communis extract. This was in comparison to 84% (96.67 ± 7.26) of eggs hatching in the untreated control group (P<0.001). Larval mortality was 100% at 500 µg/ml methanol R. communis extract (both leaf and bark) that was obtained from Narok. The larval period was prolonged to 87 days with the life cycle lasting for 101 days, a significantly long duration (P=0.002). R. communis extracts from Narok showed insecticidal effects against adults. At 48 hours post treatment, the LC50 was 121.15 µg/ml and 126.21 µg/ml for methanol bark and leaf extracts respectively. P. duboscqi adults were found to be highly susceptible to methanol extracts. The modified trap collected 1302 sand flies within three trapping nights. Goat blood baited trap yielded more sand flies (202.33 ± 2.85) while chicken blood baited traps caught the least (65.00 ±1.53). Among the fruit baited traps, bananas attracted the highest number of sand flies (94.33 ± 4.63) followed by mango baited trap (89.67 ± 2.33) although the difference was not significant (P=0.682). 64.3% of the collected sand flies belonged to the genus Sergentomyia and 35.7% to Phlebotomus with Phlebotomus martini (35.7%), Sergentomyia schwetzi (34.1%) and S. antennata (15.7%) being the dominant species. Volatiles from plant and animal hosts may be used instead of light or carbon dioxide to improve the efficiency of traps for haematophagous insects. Further, R. communis extracts have deleterious effects on hatching of eggs, larval and pupal development and adult emergence of P. duboscqi; hence R. communis should be used against sand flies and Leishmania in situ. The knowledge of phlebotomine ecology gained in this study will increase the ability to develop effective integrated vector control programs in visceral leishmaniasis (VL) endemic areas in Kenya.