Biocidal potential of clove oils against Aedes albopictus – A comparative study

The first phase of the study involved evaluation of leaf and bud oils of clove, Syzygium aromaticum for their biocidal (i.e. ovicidal and larvicidal) activity against Aedes albopictus. Eggs and fourth instar larvae were exposed to different concentrations of the oils to investigate their comparative efficacy against the target mosquito species. In the second phase of the study, biocidal activity of ‘test formulation’ derived from the leaf oil and commercial mosquitocide, Prallethrin were estimated by thesame method to compare the efficacy of the former with popular mosquitocides. Mortality data were analyzed by a computerized Log-Probit analysis (StatsDirect). Ovicidal assay of the oil samples recorded EC50 values of 0.37 and 2.0 mg/ml respectively for leaf and bud oil. Larvicidal assay showed LC50 and LC95 values of leaf oil as 5.3 and 7.03 mg/ml respectively, while bud oil recorded LC50 and LC95 values of 17.84 and 23.99 mg/ml, respectively. The ‘test formulation’ recorded EC50 value of 1.63 mg/ml, LC50 of 3.67 mg/ml and LC95 of 13.49 mg/ml respectively, indicating levels comparable to that of prallethrin. Third phase of the study involved chemical characterization of the oil samples using GC-MS.Eugenol constituted the major component of both the oils. The study demonstrated the potential of clove oil as a biocide against A. albopictus and warrants further standardization of the ‘test formulation

Evaluation of synthetic oviposition stimulants to enhance egg collection of the oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae)

Tephritid flies are pests of horticultural importance throughout the globe. The oriental fruit fly, Bactrocera dorsalis (Hendel), is particularly feared because it attacks many commercial fruits and vegetables causing huge economic losses. The sterile insect technique (SIT) can be an effective, target-specific and economically feasible control method. However, implementation of SIT depends on mass production of high-quality insects. Production of superior quality eggs is of foremost importance in insect mass production. However, present protocols make use of fruit juices or fruit domes that attract saprophytic insects or microorganisms, reducing the quality of eggs. Furthermore, fermentation of juices is known to decrease oviposition efficiency, and daily sanitation of oviposition devices is required. Here, in a laboratory-scale study, we evaluate the effectiveness of four synthetic oviposition stimulants (OS) of B. dorsalis for egg production in dual choice tests, using oviposition devices similar to those used in mass rearing. Results indicated that γ-octalactone, benzothiazole, octen-3-ol and ethyl tiglate significantly increased egg laying compared to controls (water). Of these, γ-octalactone was particularly effective and elicited a 263-fold increase in oviposition on treated oviposition devices compared to control. Our findings demonstrate the potential of using OSs to improve the efficiency and cost effectiveness of mass production of B. dorsalis