## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{**Statistics**} & \multicolumn{6}{c}{**Time (Ti)**} \\ \cline{3-7}  & & **Treatments (Tr)** & **t0** & **t1** & **t3** & **t8** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Leaf fresh weight \\ \end{tabular} } & Tr 10.92 *** & ABIO & a & a & b & b \\ \cline{2-7}  & Ti 1.40 \({}^{\text{NS}}\) & BIO & a & a & a & a \\ \cline{2-7}  & Bl 6.08 \({}^{\text{*}}\) & COMB & a & a & b & b \\ \cline{2-7}  & TrxTi 1.06 \({}^{\text{NS}}\) & CTR & a & a & a & a \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Leaf dry weight \\ \end{tabular} } & Tr 8.87 *** & ABIO & a & a & b & b \\ \cline{2-7}  & Ti 2.91 \({}^{\text{*}}\) & BIO & a & a & a & a \\ \cline{2-7}  & BI 17.17 *** & COMB & a & a & b & b \\ \cline{2-7}  & TrxTi 1.26 \({}^{\text{NS}}\) & CTR & a & a & a & a \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Leaf water content \\ \end{tabular} } & Tr 3.16 \({}^{\text{*}}\) & ABIO & a & ab & ab & a \\ \cline{2-7}  & Ti 12.01 *** & BIO & a & b & a & a \\ \cline{2-7}  & BI 52.15 *** & COMB & a & b & b & a \\ \cline{2-7}  & TrxTi 1.50 \({}^{\text{NS}}\) & CTR & a & a & a & a \\ \hline \hline \end{tabular}  
* \(0.05<p<0.001\); *** \(p<0.001\); NS not significant.  
\end{table} 
Table 1: Results of two-way ANOVA [Treatment (Tr), time (Ti), block (Bl), TrxTi interaction (TrxTi)] on the morphological traits. Abbreviations as in Figure 1. Statistics: F- and \(p\)-values. Within each morphological traits and time of exposure, the different letters indicated statistical differences among the means of the treatments (\(p<0.05\), test of Tukey). in the highly variable effects observed in different plant-insect combinations. For example, the leaf dry to fresh mass ratio was not changed by _Monsoma pulveratum_ feeding on _Alnus glutinosa_[11] but a weak negative effect in the soybean-natural herbivory interaction was observed [46]. Further, the net photosynthesis was found to be either sharply reduced [47], or even increased [48] or even not modified [49]. In the present study, the infestation of _Tuta absoluta_ could probably have caused 'indirect effects' in leaf tomato such as increase of the photosynthesis and water losses by transpiration rate, resulting in reduced iWUE and leaf water content as also observed in soybean-Japanese beetles and corn earworm caterpillars interactions [49]. However, in a previous study concerning the _Tuta_-tomato interactions, a reduction in leaflet growth was pointed out [50]. Although the plant responses to the individual abiotic stress and herbivory infestation are well understood, the information concerning the effects of stress combination is, in most of the cases, scanty or even absent. In the present study, the combination among the N deficiency and drought, on one side, and herbivory by _Tuta_, on the other side, caused the highest reduction of the tomato morpho-physiological traits respect to the control plants (Figures 1 and 2; Tables 1 and 2). This overstate effect of the combined stress could be due to the interactive responses determined by cross-talk in hormonal signaling and by the transcriptional modulation of defense-related genes. Indeed, in the interaction between _Solanum dulcamara_ and the herbivory by specialist _Leptinotarsa decmelineata_, the antagonism of the specific herbivory-induced salicylic acid on the jasmonic acid (JA) was found to prevail over the synergism of the specific drought-induced abscissic acid (ABA) with consequent reduction of the defense responses observed at transcriptional levels (increase in the cell wall components and secondary metabolism) [51]. Moreover, in tomato plants subjected to both drought and herbivory by _Spodoptera exigua_, an adaptive response was observed by a transcriptional activation of the genes related to the photosynthetic machinery and chlorophyll biosynthesis causing, as a consequence, a reduction of the secondary metabolite production [51].