## 3 Results and Discussion
Most of the lactones tested caused the inhibition of growth of the _E. coli_ strain. The highest growth inhibition, \(\Delta\)OD = 0.25-0.57, was shown in compounds **2** and **4**. Lactone **5** limited the increase in the biomass. _P. fluorescens_ strain growth was limited by lactones **3-5**. The increase in the optical density of this strain was in the range 0.39-0.58, whereas in the control culture it was 1.36. It is worth noting that in the culture of the _P. fluorescens_ strain that was conducted in the presence of compound **4**, the diauxic growth was observed. A similar effect was observed earlier for bacteria strain _E. coli_ and yeast strain _C. albicans_[21]. This phenomenon was also reported by other authors [36; 37; 38]. The yeast strain _C. albicans_ was found to be relatively sensitive to lactones **2-4**, wherein only compound **2** completely inhibited growth. The other compounds limited the increase in the biomass. It should be noted that compound **5** stimulated the growth of this yeast resulting in the increase in biomass \(\Delta\)OD equal to 1.26, whereas the control culture yeasts' value was 1.14. In the next step, halolactones **2-4** and hydroxolactone **5** were examined for their deterrent activity against the peach potato aphid _Myzus persicae_ (Sulz.). The results of these tests are presented in Table 4.  
Iodolactone **4** and hydroxolactone **5** did not affect aphid behavior during settling in a significant way. Nevertheless, lactone **4** showed a tendency to inhibit aphid settling, while **5** appeared to be a weak attractant. Chlorolactone **2** and bromolactone **3** caused a significant avoidance of the treated leaves by the aphids later than two hours after exposure but the indices of deterrence (ID) calculated on the 24 th hour reached the relatively high values of 0.5 and 0.4, respectively (Table 4, Figure 8). Similar effects were obtained when studying the effect of piperitone-derived halolactones on _M. persicae_ settling behavior: the incorporation of chlorine, bromine and iodine atoms in the lactone molecule caused a significant increase in deterrent activity [39]. In the cited study, the strongest effects were attributed to chlorine and bromine atoms while the effect of iodine atom on the activity was less pronounced [39]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Lactone**} & \multicolumn{3}{c}{**1 h**} & \multicolumn{3}{c}{**2 h**} & \multicolumn{3}{c}{**24 h**} \\ \cline{2-10}  & \(C\) & \(T\) & \(p\) & \(C\) & \(T\) & \(p\) & \(C\) & \(T\) & \(p\) \\ \hline
**2** & 6.8 \(\pm\) 0.9 & 5.3 \(\pm\) 0.8 & 0.2100 & 7.3 \(\pm\) 1.0 & 5.6 \(\pm\) 1.0 & 0.2602 & 14.4 \(\pm\) 0.8 & 5.0 \(\pm\) 0.7 & 0.0000 \\
**3** & 9.3 \(\pm\) 0.8 & 7.0 \(\pm\) 1.3 & 0.1611 & 9.8 \(\pm\) 1.0 & 6.5 \(\pm\) 1.2 & 0.0507 & 13.0 \(\pm\) 2.1 & 5.4 \(\pm\) 2.1 & 0.0219 \\
**4** & 6.1 \(\pm\) 1.1 & 6.4 \(\pm\) 1.2 & 0.8811 & 7.1 \(\pm\) 0.9 & 6.4 \(\pm\) 1.3 & 0.6546 & 7.6 \(\pm\) 1.5 & 5.6 \(\pm\) 1.9 & 0.4304 \\
**5** & 5.6 \(\pm\) 1.7 & 5.9 \(\pm\) 0.9 & 0.8978 & 6.5 \(\pm\) 1.7 & 5.4 \(\pm\) 0.7 & 0.5571 & 6.1 \(\pm\) 2.0 & 10.6 \(\pm\) 2.3 & 0.1599 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Deterrent activity of lactones **2-5**. Numbers for \(C\) = control and \(T\) = treated represent mean number (\(\pm\)SE) of aphids that settled on the control or the treated leaf (choice-test) 1 h, 2 h, and 24 h after exposure. _p_—significance level (Student’s \(t\)-test; StatSoft, Inc. (2014) STATISTICA)—significant differences (_p_ < 0.05) between the number of aphids settled on either leaf are underlined. Figure 8: Effect of lactones **2–5** on settling preferences of _Myzus persicae_ in the choice test. ID—index of deterrence, \({}^{*}p<0.05\) (Student \(t\)-test).