Maize (Zea mays L.) is one of the main cereals grown around the world. It is used for human and animal nutrition and also as biofuel. However, as a direct consequence of global climate change, increased abiotic and biotic stress events have been reported in different regions of the world, which have become a threat to world maize yields. Drought and heat are environmental stresses that influence the growth, development, and yield processes of maize crops. Plants have developed dynamic responses at the physiological, biochemical, and molecular levels that allow them to escape, avoid and/or tolerate unfavorable environmental conditions. Arthropod herbivory can generate resistance or tolerance responses in plants that are associated with inducible and constitutive defenses. Increases in the frequency and severity of abiotic stress events (drought and heat), as a consequence of climate change, can generate critical variations in plant-insect interactions. However, the behavior of herbivorous arthropods under drought scenarios is not well understood, and this kind of stress may have some positive and negative effects on arthropod populations. The simultaneous appearance of different environmental stresses and biotic factors results in very complex plant responses. In this review, recent information is provided on the physiological, biochemical, and molecular responses of plants to the combination of drought, heat stress, and the effect on some arthropod pests of interest in the maize crop.

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The recent appearance of the disease known as huanglongbing (HLB) in Colombia has caused the demand for alternative control methods for Diaphorina citri (i.e., the disease vector). Specifically, the use of nutrients, such as calcium (Ca), potassium (K) and silicon (Si), may provide some degree of plant defense against herbivory. One set of experiments (in the form of two separate experiments) was conducted on two different farms in the municipality of Jerusalén to study the effects of foliar and soil applications of nutrients (Ca, K and Si) on controlling the population dynamics of Diaphorina citri. Tahiti lime trees were treated as follows: i) untreated trees (absolute control); ii) clothianidin at a dose of 50 g active ingredient per hectare (chemical control); iii) Ca, K and Si foliar applications (at doses of 3 mL, 3 g and 2 mL of the commercial compound used per liter of H2O, respectively); and iv) soil application of potassium nitrate and potassium silicate (1 kg of commercial fertilizer per tree). Foliar sprays were carried out at 0 and 4 weeks after treatment (WAT) began; meanwhile, soil fertilization occurred at the beginning of the trial (i.e., 0 WAT). The results showed that differences were observed only in adults at 7 WAT, and the foliar calcium and silicon applications resulted in the lowest number of individuals (i.e., 1.13 per flush) compared with untreated trees (i.e., 3.13 per flush). The foliar clothianidin, Ca, Si and K sprays also affected the total number of nymphs. Additionally, Tahiti lime trees treated with either silicon or insecticide had fewer eggs than did trees in the other treatments. The use of these mineral nutrients showed a similar efficacy when compared to clothianidin, indicating that these mineral nutrients can enhance plant resistance. These observations suggest that foliar applications of K, Ca and Si could be considered as complementary tools within an integrated management program for D. citri in Colombia.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the most serious threat to the global citrus industry, and its management has depended mainly on the application of chemical insecticides. The application of plant elicitors can contribute to the insect management and also enhance plant physiology. A set of three different experiments was carried out to evaluate the efficacy of foliar applications of synthetic elicitors [salicylic acid (SA), brassinosteroids (Br), chitosan, or thiamine] on the population dynamics of D. citri and their effects on the physiology of Tahiti lime trees. The treatments were as follows: trees were sprayed separately with thiamine, SA, or chitosan at a dose of 100 ppm, respectively; trees were treated with foliar brassinosteroid applications at a dose of 1 ppm; and untreated trees (control). By the end of the experiment, the elicitors reduced (75%) the number of adult psyllids compared with the control, where trees treated with chitosan had ≈0.5 adult individuals accumulated per flush shoot, whereas the control showed around two individuals. Salicylic acid and thiamine also reduced the number of nymphs compared with the control in the 4 weeks after treatment (WAT) (5.5 vs. 10.08 nymphs, respectively). Treatment with synthetic elicitors also caused a 30% reduction in oviposition by D. citri. The foliar applications with Br promoted a greater relative growth rate (RGR) (44 mm·cm−1·d−1) compared with the control treatment and chitosan (24 and 26 mm·cm−1·d−1, respectively). Chitosan sprays favored proline synthesis in both flush shoots and leaves. These results suggest that the use of synthetic elicitors can be considered as a tool to reduce the number of applications of chemical insecticides and decrease the development of resistances by D. citri because these synthetic elicitors showed an efficacy between 40% and 60% in all its stages in field conditions.