Greenhouse whitefly, Trialeurodes vaporariorum Westwood, is one of the major insect pests of agricultural crops such as eggplant. Due to various difficulties associated with synthetic pesticides, more environmentally friendly alternative methods are greatly appreciated for controlling pests. In the present study, the induction of resistance was investigated in eggplant using root and foliar application of jasmonic acid, abscisic acid, as well as Nesidiocoris tenuis (Reuter) either individually or in combination against T. vaporariorum. The experiments were carried out under laboratory conditions inside a growth chamber, which was set at 27 ± 2°C, 50 ± 5% relative humidity with a 16 h day length. Our results showed an increase in plant resistance due to the higher immature mortality rates, longer immature periods, lower longevity of adults, and fecundity. In free-choice situation, oviposition on root jasmonic acid (RJA) + N. tenuis and root abscisic acid (RABA) + N. tenuis was similar, but numbers of eggs deposited on these plants were lower than other treatments and control plants. The plant enzyme activity and phenolic content were significantly greater in RJA + N. tenuis and RABA + N. tenuis, intermediate in individual treatments, and the lowest in control plants. Correspondingly, T. vaporariorum longevity, number of eggs produced per female, oviposition preference, all were lowest when the insects fed on these treatments. These findings suggest that the induction of resistance in eggplants with the physiological changes in the host plant leads to a reduction in whitefly damage.

Several elicitors, stimulating induced resistance mechanisms, have potential in preventing or mitigating pathogen infections. Some of these compounds, triggering the production of jasmonic acid (JA), a precursor of herbivore-induced plant volatiles, could also play a central role in indirect resistance to pest species, by improving beneficial arthropod performance, and necrotrophic pathogens. In the current work, Trichoderma gamsii/T. asperellum and silica gel treatments – alone and in combination – were studied to evaluate the plant defence mechanism on grapevines (Vitis vinifera L.) by laboratory and field trials. JA production level was measured before and after Plasmopara viticola infection on potted vines. JA production induced by silica gel was higher than that caused by Trichoderma before infection. In Trichoderma-treated plants, JA production increased after P. viticola inoculation. In vineyard field trials, Mymaridae (Hymenoptera: Chalcidoidea) showed higher captures in transparent sticky traps on silica gel-treated plants, in comparison with control. On the other hand, no significant attraction was detected for Ichneumonoidea and other Chalcidoidea in silica gel and T. gamsii/T. asperellum-treated plants. The potential effects of elicitors are discussed, in the frame of attract and reward strategy.

A 3-year (2011–2013) field trial was carried out in a mature vineyard (Vitis vinifera L., cv. Sangiovese), planted in 2003, to assess physiological responses of grapevines to biodynamic management. Starting in 2007, the vineyard was managed with organic production protocols in accordance with EC Regulations (834/2007). In 2008, the vineyard (2 ha) was divided in two large plots, with each plot having similar soil physico-chemical properties. One of the plots was managed with organic protocols per EC Regulations and the other with biodynamic practices, consisting of spray application of preparations 500, 500 K, fladen and 501. During the 2011–2013 season, the biodynamic preparations were used at least twice per year, with the exception of 501 that was applied only once in 2013. Concentration of hormones and mineral elements in biodynamic preparations were determined. Biodynamically managed vines showed lower stomatal conductance in all years and lower leaf water potential in 2012. Leaf photosynthetic activity was not influenced by cultivation method. Biodynamic management led to an increase in leaf enzymatic activities of endochitinase (EC 3.2.1.14), exochitinase (β-N-acetylhexosaminidase, EC 3.2.1.52 and chitin 1,4-β-chitobiosidase) and β-1,3-glucanase (EC 3.2.1.39), which are typically correlated with plant biotic and abiotic stresses and associated with induced plant resistance. Year effects were observed with 1,3-β-glucanase, whose activity in 2012 was 4.1-fold higher than in 2013. Disease incidence and grape yields were not different between organic and biodynamic treatments. This study provided a strong indication of a stimulation of natural defense compounds in grapes grown under biodynamic cultivation, but subsequent effects on plant protection and productivity require further evaluation.

β-Aminobutyric acid (BABA) is known to induce resistance to microbial pathogens, nematodes and insects in several host plant/pest systems. The present study was undertaken to determine whether a similar effect of BABA occurred against the Asian citrus psyllid, Diaphorina citri Kuwayama, in citrus. A 25 mM drench application of BABA significantly reduced the number of eggs/plant as compared with a water control, whereas 200 and 100 mM applications of BABA reduced the numbers of nymphs/plant and adults/plants, respectively. A 5 mM foliar application of BABA significantly reduced the number of adults but not eggs or nymphs when compared with a water control treatment. In addition, leaf-dip bioassays using various concentrations (25–500 mM) of BABA indicated no direct toxic effect on 2nd and 5th instar nymphs or adult D. citri. BABA-treated plants were characterized by significantly lower levels of iron, magnesium, phosphorus, sodium, sulfur and zinc as compared with control plants. The expression level of the PR-2 gene (β-1,3-glucanase) in BABA-treated plants that were also damaged by D. citri adult feeding was significantly higher than in plants exposed to BABA, D. citri feeding alone or control plants. Our results indicate the potential for using BABA as a systemic acquired resistance management tool for D. citri.

Introduction. Concerns about the potentially harmful effects of fungicides on human health and the environment encourage the search for alternative treatments for perishable fruit postharvest disease control. To this end, the potential use of oligochitosan as a natural antifungal compound to control postharvest anthracnose caused by Colletotrichum musae was investigated in banana fruits from the Cavendish group (genome AAA). Materials and methods. The influence of oligochitosan on the growth of C. musae was determined in vitro by micrographic analysis, while its in situ antifungal activity was monitored in banana fruits that were artificially injury-inoculated with C. musae; the activities of several defense-related enzymes were measured. Results and discussion. Oligochitosan at (4 and 8) g·L–1 markedly inhibited radial mycelial growth of C. musae in vitro. The scanning electron micrograph of C. musae treated with oligochitosan at inhibitory concentrations showed distortion and thinning of the hyphal wall and reduction in fungus colony diameter. Dipping banana fruits in oligochitosan solution at (5 to 20) g·L–1 significantly reduced the diameter of the anthracnose lesion, and 20 g oligochitosan·L–1 almost reached the same inhibitory effect as 0.5 g·L–1 of Sportak®, a synthetic fungicide. Activities of defense-related enzymes such as phenylalanine ammonia-lyase (PAL), β-1, 3-glucanase (GLU) and chitinase (CHT), but not polyphenol oxidase (PPO), increased in banana fruits treated with 0.5 g oligochitosan·L–1. Conclusion. The inhibitory effect of oligochitosan on anthracnose development is due to the combination of a direct antifungal effect on the pathogen and an indirect effect, whereby the activities of defense-related enzymes in the banana fruit were enhanced. To control anthracnose in harvested bananas, treatment with oligochitosan above 20 g·L–1 may substitute the use of synthetic fungicide.

In addition to constitutive plant resistance against pests or pathogens, plants can activate protective mechanisms upon contact with an invader or a chemical elicitor. Studies on induced plant resistance to herbivores, especially piercing-sucking insects, are less abundant than those devoted to pathogens. Several experiments under controlled conditions have been conducted to demonstrate that infestations by Macrosiphum euphorbiae induce plant resistance to Bemisia tabaci in susceptible tomato plants. After three days of exposure to 20 apterous adult aphids, the plants acquired a transiently induced resistance to B. tabaci when aphid removal occurred one or 18 hours prior to B. tabaci infestation; the effect disappeared when four days passed between aphid and whitefly infestations. The resistance observed was both locally and systemically induced. Other assays were performed to evaluate the effect of preinfestation with ten adults of B. tabaci during 48 h on the tomato responses to two different clones (Sp and Nt) of M. euphorbiae. The numbers of nymph and adult aphids were counted after the same time interval as the pre-reproductive period and 20 (Sp clone) or 22 (Nt clone) days after adult aphid removal. The tomato responses induced by whitefly feeding depend on the aphid clone. For the Sp clone, the number of aphid nymphs ten days after adult removal was significantly higher on whitefly preinfested plants than on uninfested plants. However, no significant differences were observed when the aphid clone Nt was tested. The duration of plant response to a previous infestation by B. tabaci is apparently limited.

The number of parasites colonizing a host (termed ‘multiple infection’) is an important determinant of host-parasite interactions. In theory, multiple infection is determined by random mass action in genetically and spatially homogeneous populations of host and parasite. In real populations, deviations from these assumptions may strongly influence levels of multiple infection. We carried out inoculation experiments in microcosms of the freshwater protozoan Paramecium caudatum and its bacterial parasite Holospora undulata. Increasing parasite dose produced higher levels of (multiple) infection; more susceptible host genotypes also were more multiply infected. An overall pattern of parasite aggregation (excess of uninfected individuals and of individuals carrying larger numbers of parasites) indicated deviations from random mass-action transmission. Homogenizing spatial distributions of parasite and host in our microcosms did not affect aggregation, whereas aggregation was more pronounced in old than in new host clones. Thus, variation in susceptibility may arise over time within clonal populations. When sequentially inoculated, already established infections increased the probability of additional infection in generally resistant host clones, but decreased it in more susceptible clones. Hence, the role of multiple infection as a driver of epidemiological or evolutionary processes may vary among populations, depending on their precise genetic composition or infection history.

Silicon (Si) can improve resistance of plants to insect attack and may also enhance tolerance of water stress. This study tested if Si-mediated host plant resistance to insect attack was augmented by water stress. Four sugarcane cultivars, two resistant (N21, N33) and two susceptible (N26, N11) to Eldana saccharina Walker were grown in a pot trial in Si-deficient river sand, with (Si+) and without (Si−) calcium silicate. To induce water stress, irrigation to half the trial was reduced after 8.5 months. The trial was artificially infested with E. saccharina eggs after water reduction and harvested 66 days later. Silicon treated, stressed and non-stressed plants of the same cultivar did not differ appreciably in Si content. Decreases in numbers of borers recovered and stalk damage were not associated with comparable increases in rind hardness in Si+ cane, particularly in water-stressed susceptible cultivars. Overall, Si+ plants displayed increased resistance to E. saccharina attack compared with Si− plants. Borer recoveries were significantly lower in stressed Si+ cane compared with either stressed Si− or non-stressed Si− and Si+ cane. Generally, fewer borers were recovered from resistant cultivars than susceptible cultivars. Stalk damage was significantly lower in Si+ cane than in Si− cane, for N21, N11 and N26. Stalk damage was significantly less in Si+ combined susceptible cultivars than in Si− combined susceptible cultivars under non-stressed and especially stressed conditions. In general, the reduction in borer numbers and stalk damage in Si+ plants was greater for water-stressed cane than non-stressed cane, particularly for susceptible sugarcane cultivars. The hypothesis that Si affords greater protection against E. saccharina borer attack in water-stressed sugarcane than in non-stressed cane and that this benefit is greatly enhanced in susceptible cultivars is supported. A possible active role for soluble Si in defence against E. saccharina is proposed.

Allomerus octoarticulatus is a plant-ant that colonizes domatia of the understorey tree Hirtella myrmecophila in the Central Amazon and forages for invertebrates, including leaf herbivores, on the host plant. We conducted manipulative experiments to study the ant's recruitment response to damaged leaves and leaf extracts of the host and to extracts of Protium hebetatum, a non-myrmecophytic sympatric tree species. Artificial damage to leaves of H. myrmecophila caused an increase in the number of recruits to the leaf. Ant response was stronger in young than in mature leaves. Recruitment was restricted to damaged leaves. No increment in recruitment rates was observed in undamaged, adjacent leaves. Different levels of leaf damage did not elicit differences in recruitment rates. Aqueous extract of leaves, placed on undamaged leaves of the host plant, also led to increased recruitment compared with water (control), and more ants were recruited to extracts from young than from mature and old leaves. Extracts of both H. myrmecophila and Protium hebetatum induced recruitment. We discuss the evolutionary importance of plant leaf components for maintenance of the ant-plant mutualism.

Orseolia oryzae, the rice gall midge, is a major pest of rice in many areas of tropical Asia and is becoming an important pest in Africa. A chronological review of the progress made in various national programmes on varietal resistance, sources of resistance and breeding for resistance is given. Many resistant varieties have been identified and have been utilized in breeding programmes to develop high yielding varieties with multiple resistance to the gall midge and other insect pests and diseases. Mechanisms and inheritance of resistance in rice varieties are discussed. Rice varieties resistant in various countries and sources of resistance used in breeding programmes are listed. Biotype variations in different countries and within the countries are revealed, and a preliminary classification of gall midge biotypes based on varietal reactions is proposed.