Fumigant toxicity of plant essential oils in controlling thrips, Frankliniella schultzei (Thysanoptera: Thripidae) and mealybug, Pseudococcus jackbeardsleyi (Hemiptera: Pseudococcidae).
Insecticidal activity of 18 plant essential oils against adults of thrips (Frankliniella schultzei (trybom)) and larvae of mealybug (Pseudococcus jackbeardsleyi Gimpel & Miller) were primarily investigated by using fumigation method. Later, various concentrations of the highly effective essential oils (resulting in more than 80% mortality) were tested. Major constituents in the commonly effective essential oils against both insects were analyzed. Then, fumigant toxicities of the standard chemicals and the selected essential oils were studied and compared. The results showed that the essential oils of clove (Syzygium aromaticum Merr. & L.M. Perry), cinnamon (Cinnamomum bejolghota (Buch.-Ham.) sweet) and lemon grass (Cymbopogon citratus (Dc.ex.Nees)) showed commonly high fumigant toxicity against the thrips and mealybug with the LC50 at 1.14-1.48 and 1.12-1.58 µl/L air, respectively. The major chemicals found were eugenol in clove and cinnamon oils (97.100 and 82.054%, respectively) and citral (trans-citral and cis-citral) in lemongrass (69.730%). In general, the essential oil presented higher fumigant toxicity than the standard chemical. Study revealed that a combination of various compounds resulted in synergism and higher insecticidal activity.