Differential defense responses of tropical grasses to Mahanarva spectabilis (Hemiptera: Cercopidae) infestation.

The spittlebugs Mahanarva spectabilis economically challenges cattle production of neotropical regions, due to its voracious feeding on tropical grasses. Here, we evaluated biochemical responses of the interaction between M. spectabilis and the widely cultivated tropical grasses Brachiaria spp. (i.e., brizantha and decumbens) and elephant grasses (cvs. Roxo de Botucatu and Pioneiro), regarding lipoxygenases, protease inhibitors, phytohormones, and proteolytic activities in the midgut of M. spectabilis. The M. spectabilis-infested grasses increased lipoxygenases activity, except for cv. Pioneiro. The levels of the phytohormones jasmonic and abscisic acids were similarly low in all genotypes and increased under herbivory. Furthermore, salicylic acid concentration was constitutively higher in Brachiaria sp., increasing only in spittlebug-infested B. decumbens. M. spectabilis infestations did not induce increases of protease inhibitors in any forage grass type. The trypsin activity remained unaltered, and the total proteolytic activity increased only in B. decumbens-fed insects. Our findings revealed that most forage grasses exposed to spittlebugs activate the lipoxygenases pathway, resulting in increased abscisic and jasmonic acids. However, greater amounts of these hormones do not induce protease inhibitory activity in response to spittlebug attack. This knowledge certainly helps to guide future projects aiming at reducing the impact of spittlebugs on forage production.

Protein and phytohormone profiles of Mahanarva spectabilis salivary glands infesting different forages.

Given the importance of pastures for feeding cattle, the study of factors that affect their productivity is essential to get plant material of higher nutritional quality. Thus, the study of insect-plant interaction is important for the development of control strategies. Pasture spittlebugs affect forage grasses causing severe damage. We tested hormone and protein profiles differentially expressed in the salivary glands of Mahanarva spectabilis when fed with different pasture genotypes. The LC/MS approaches combined with bioinformatics tools were used to identify the mains biological processes in the salivary glands. The grouping revealed a greater number of proteins involved in biological processes of metabolic synthesis, biotic/abiotic stress, and ion transport across the membrane. The proteomic profiles were altered when insects were fed with different grasses. We also detected phytohormones in the salivary glands involved in the modulation of defense responses in host plants. These results allowed the analysis of important biological processes such as cell homeostasis, stress proteins, nucleic acid metabolism, regulation of muscle contraction, and transport and export of biomolecules. This represents an important advance in the understanding of the plant-pest interaction and can contribute to the choice of target elicitors, which allow effective strategies in the control of pasture spittlebugs.

Intestinal proteolytic profile changes during larval development of Anticarsia gemmatalis caterpillars.

Soybean is one of most consumed and produced grains in the world, and Anticarsia gemmatalis is a pest that causes great damage to this crop due to severe defoliation during its larval phase. Plants have mechanisms that lead to the inhibition of proteases in the intestine of these herbivores, hampering their development. Understanding this complex protease inhibitor is important for pest control. The objective of this study was to evaluate the enzymatic profiles of the intestinal proteases of the soybean caterpillar at different instars. For this, the proteolytic profile of the gut in the third, fourth, and fifth instars were analyzed. Irreversible inhibitors of proteases were separately incubated with A. gemmatalis enzyme extracts at the third, fourth, and fifth instar to assess the contribution of these proteases to total proteolytic activity. The enzymatic extracts were also evaluated with specific substrates to confirm changes in the specific activities of trypsin-like, chymotrypsin-like, and cysteine proteases at different instars. The results showed that the protease profile of A. gemmatalis gut changes throughout its larval development. The activity of cysteine proteases was more intense in the first instar. On the contrary, the serine proteases showed major activities in the late stages of the larval phase. Zymogram analysis and protein identification by liquid chromatography-mass spectrometry indicated serine protease as the main protease class expressed in the fifth instar. These results may shift the focus from the rational development of the protease inhibitor to A. gemmatalis and other Lepidoptera, as the expression of major proteases is not constant.