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Whitefly attraction to rosemary (Rosmarinus officinialis L.) is associated with volatile composition and quantity.

Whitefly (Bemisia tabaci) is an important insect pest, causing severe damage to agricultural crops. The pest was recorded in a commercial rosemary (Rosmarinus officinalis, Lamiaceae) field, colonizing rosemary variety (var.) '2', but not '11'. A series of field and controlled laboratory choice bioassays confirmed the observed phenomenon. Mature potted plants of the two varieties were randomly organized in a lemon verbena (Lippia citrodora) and lemon grass (Cymbopogon spp.) fields. Seven days later var. '2' was significantly more colonized by whiteflies than var. '11'. Under lab conditions, whiteflies were significantly more attracted to var. '2' plantlets than to var. '11' following choice bioassays. Furthermore, cotton plants dipped in an essential oil emulsion of var. '2' had significantly greater colonization than cotton plants dipped in the essential oil emulsion of var. '11'. Similar results were obtained in 'plant-plant', 'plant-no plant' as well as, 'essential oil-essential oil' choice bioassay designs. Analyses of the essential oils of the two varieties identified a set of common and unique volatiles in each variety. Among these volatiles were β-caryophyllene and limonene, two compounds known to be associated with plant-insect interactions. The attraction of B. tabaci to pure (>95%) β-caryophyllene and limonene using a range of concentrations was examined in vitro by choice bioassays. The compounds were attractive to the insect at moderate concentration, but not at the lowest or highest concentrations used, where the insect was not attracted or repelled, respectively. Limonene attracted the insects at rates that were 10-fold lower than β-caryophyllene. The results emphasized the role of host plant volatiles in shaping the structure of B. tabaci populations in nature and in agricultural systems, and provided insights into the factors that contribute to the development of insect populations with unique characteristics. The results could also serve for future development of bio-pesticides and in breeding programs

Whitefly attraction to rosemary (<i>Rosmarinus officinialis</i> L.) is associated with volatile composition and quantity

<div><p>Whitefly (<i>Bemisia tabaci</i>) is an important insect pest, causing severe damage to agricultural crops. The pest was recorded in a commercial rosemary (<i>Rosmarinus officinalis</i>, Lamiaceae) field, colonizing rosemary variety (var.) '2', but not '11'. A series of field and controlled laboratory choice bioassays confirmed the observed phenomenon. Mature potted plants of the two varieties were randomly organized in a lemon verbena (<i>Lippia citrodora</i>) and lemon grass (Cymbopogon spp.) fields. Seven days later var. '2' was significantly more colonized by whiteflies than var. '11'. Under lab conditions, whiteflies were significantly more attracted to var. '2' plantlets than to var. '11' following choice bioassays. Furthermore, cotton plants dipped in an essential oil emulsion of var. '2' had significantly greater colonization than cotton plants dipped in the essential oil emulsion of var. '11'. Similar results were obtained in 'plant-plant', 'plant-no plant' as well as, 'essential oil—essential oil' choice bioassay designs. Analyses of the essential oils of the two varieties identified a set of common and unique volatiles in each variety. Among these volatiles were β-caryophyllene and limonene, two compounds known to be associated with plant-insect interactions. The attraction of <i>B</i>. <i>tabaci</i> to pure (>95%) β-caryophyllene and limonene using a range of concentrations was examined <i>in vitro</i> by choice bioassays. The compounds were attractive to the insect at moderate concentration, but not at the lowest or highest concentrations used, where the insect was not attracted or repelled, respectively. Limonene attracted the insects at rates that were 10-fold lower than β-caryophyllene. The results emphasized the role of host plant volatiles in shaping the structure of <i>B</i>. <i>tabaci</i> populations in nature and in agricultural systems, and provided insights into the factors that contribute to the development of insect populations with unique characteristics. The results could also serve for future development of bio-pesticides and in breeding programs.</p></div

Whitefly mortality (%) following 60 min.

<p>of exposure to the essential oil volatiles of var. 2 (black bars) or 11 (grey bars) in 500 mL flasks. Error bars represent standard error of the mean (SE ()) and upper-case letters represent statistical differences following 2-way ANOVA and mean separation using Tukey-Kramer multiple range test at α = 0.05.</p

Kinetics of whitefly colonization of cotton plants dipped in the essential oil emulsions of vars. 2 or 11.

<p>Control cotton plants were dipped in 80% Tween 20 solution. The colonization of cotton plants dipped in the essential oil emulsion of var. 2 had a 67.4% and 34.8% higher rates than the colonization of cotton plants dipped in the essential oil emulsion of var. 11 or in 80% Tween 20 solution control, respectively. Colonization of the control cotton plants that were dipped in the 80% Tween 20 solution control treatment was 50% higher than the colonization of cotton plants dipped in the essential oil emulsions of var. 11, but not significantly higher (<i>P</i>>0.05). Error bars represent standard error of the proportion ().</p

Colonization kinetics of biotypes Q and B on rosemary varieties 2 (A) and 11 (B) and joint preference (C).

<p>Chi-square analysis indicated that biotype and variety were independent of each other (<i>P</i>>0.05) and that the preference of both biotypes to each rosemary variety was similar. Hence, the data was jointly analyzed indicating that var. 2 was more attractive than 11 (<i>P</i> = 0.0091). Error bars represent standard error of the proportion ().</p

Effect of β-Caryophyllene (A) and Limonene (B) concentrations on whitefly preference <i>in vitro</i>.

<p>The insects had greater preference to moderate concentrations of the compounds, showing lesser preference to the highest and/or lowest concentrations of <i>limonene</i> and β-Caryophyllene, respectively. Furthermore, the similar pattern of attraction was recorded with β-Caryophyllene at concentration 10-fold higher than those experiments of <i>limonene</i>. Histograms present % mean preference. Error bars represent standard deviation of the mean. Upper-case letters represent significant statistical differences among concentrations following ANOVA and mean separation using Tukey-Kramer range test at α = 0.05.</p