Arthropod-Plant Interactions

Apolygus lucorum (Heteroptera: Miridae), an important herbivore feeding on a broad range of cultivated and wild plants, always shows a strong preference for flowering host plants. In a prior study, we found A. lucorum fecundity to be higher on flowering plants than on plants still at the vegetative stage. This led us to hypothesize that ovarian development and vitellogenin (Vg) expression in A. lucorum, which are highly correlated with its fecundity, might respond positively to the presence of host plant flowers as food. In this study, two types of plant foods, i.e., cotton terminals and flowers, and cotton terminals only without flowers, were examined. Adult females on terminals with flowers had higher ovarian development levels than those of similar stage held on terminals without flowers. Moreover, adults on terminals with flowers had more follicles per ovary throughout adult life than those held on terminals without flowers, and the length of the most developed ovariole of the former treatment was significantly longer than that of the latter diet. Use of qRT-PCR showed that the expression level of Vg was significantly higher in adults raised on a diet with flowers compared with those raised on the diet without flowers. These results suggest that host plant flowers significantly facilitate ovarian development and Vg gene expression of A. lucorum adults.

Large-scale agriculture has led to a loss of overall biodiversity and ecosystem services (e.g., biological control) within farmland. Native wildflower plantings have been used to restore ecosystem services and increase conservation measures within agricultural areas. In this study, we examined spider (Araneae) communities within small wildflower plots and fallow control plots that were primarily composed of grasses. Utilizing multiple trapping schemes (pitfalls, sweep netting, and pan trapping), spiders were found to be more abundant within the wildflower plots compared to fallow controls but species richness or Shannon–Wiener diversity indices were not different between the two habitats. The sheet web-weaving spider, Ceraticelus tibialis, (Araneae: Linyphiidae) was more abundant within the fallow controls, whereas, some spider families (Lycosidae, and Oxyopidae) were significantly more abundant in the wildflower plots. Categorizing spiders into hunting/web-building guilds showed that ambushers, space, and stalkers were significantly more abundant in the wildflower plots but low-sheet/tangle weavers were significantly more abundant in the fallow controls. Our results suggest that wildflower plantings can be a successful way to increase overall spider abundance within intensive agricultural areas and, thus, may help contribute to biological control of pest insects. However, our results also suggest wildflower plantings may not be a useful conservation tool that increases spider biodiversity within agricultural areas.

Plants require mechanisms of defense to limit the amount of damage by herbivores. Calcium oxalate crystals (COC) in the leaves can serve as inducible defenses against chewing insects, such as Caliroa cerasi larvae. We studied the relationship between leaf COC from Prunus avium and herbivory by C. cerasi larvae, to assess the defensive role of inducible responses. We examined from cafeteria choice experiments the C. cerasi larvae preference towards P. avium cultivars (Bing, Lapins and Van) and larvae preference towards leaves from infested and non-infested trees. The number of damaged leaves per meter of branch and the total non-damaged area and the area removed by the insects was evaluated in the field. We also determined the presence, location, size, and number of crystals in leaves from all studied cultivars. Van and Lapins cultivars were the most preferred by C. cerasi and exhibited a greater number of COC in their leaves, possibly due to being more eaten by the insect. This increase in COC possibly contributes to protect the leaf vein from chewing larvae, maintaining this portion of the vascular transport functionality. Potential manipulations of this induced response could be used in the future as a tool for the pest management against herbivore insects.

Insects might impact communities and ecosystems through processes that are not trophic, via ecosystem engineering. In this study, we experimentally evaluated the role of the caterpillars Pandemis sp. as habitat modifiers in the tropical liana Trigonia rotundifolia. Specifically, we examined their effects on the abundance and richness of arthropods that secondarily colonize leaf-rolls (shelters) built by the caterpillars, as well as indirect effects that influence plant herbivory. Two experiments were conducted in the field to evaluate the role of natural and artificial rolls on community structure and plant damage. Plants with artificial leaf-rolls hosted 2.2 times more arthropods than plants without shelters and they had 1.5 times higher richness compared to control plants. Plants with natural shelters exhibited significantly lower arthropod richness than plants with artificial shelters or control plants, but arthropod abundance did not differ among treatments. Although plants with leaf-rolls hosted significantly more arthropods, arthropod species composition did not differ amongst treatments, as Formicidae was the most frequent group in all treatments. Herbivory was almost 3 times higher in plants with leaf-rolls compared to plants with no rolled leaves, indicating that the effect of increased arthropod abundance, and especially herbivore abundance, might influence leaf damage in plants with leaf-rolls. We demonstrate the strong impact of Pandemis as a habitat modifier on community structure as well as on community processes through indirect effects.

This study demonstrates that soybean cultivars respond differentially to damage in a herbivore-specific manner, and trigger responses decreasing herbivore performance. Soybean crops are affected by a great number of insect herbivores, resulting in devastating yield losses. Secondary metabolites like proteinase inhibitors and phenolic compounds are part of plants’ defense mechanisms against insect pests. However, the specificity of soybean defense responses to different attacking herbivores is poorly known. To investigate species-specific foliage responses to herbivory, we used two different commercial soybean cultivars (DM 4210 and DM 5.8i) widely used in Argentina with diverse susceptibility to insects’ attack and two species of phytophagous insects, thrips (Caliothrips phaseoli; Thysanoptera) and lepidopteran larvae (Spodoptera frugiperda; Lepidoptera) with a different way of feeding. Benzoic acid derivative levels were increased by damage of both insect species in the foliage of the field-grown soybean cultivars, whereas trypsin protease inhibitors activity was induced in cultivar (cv) DM 4210 by fall armyworm damage and malonyl genistein content in cv DM 5.8i after thrips’ attack. Although survivorship and mass of fall armyworm larvae were not differentially affected in field conditions by soybean cultivars, larvae reared in the laboratory that fed on cv DM 5.8i gained more mass than those on DM 4210. Conversely, thrips performance, natural colonization, and preference of feeding were higher on cv DM 4210 than on cv DM 5.8i. The differential effects of soybean cultivars on insectspecies’ performance were explained not only by induced defenses, but also by differences of constitutive defenses between cultivars. This study demonstrated that soybean cultivars responded differentially to damage in a herbivore-specific manner, and triggered responses decreased herbivore performance.

Under laboratory conditions we have investigated the effect of the application of pro-ecological procedures (effective microorganisms and biostimulant Asahi SL) and plant injury on the production of free phenolic acids in winter wheat and on the feeding and development of Oulema melanopus. Wheat plants before reaching the BBCH 32 stage (the beginning of stem elongation) were treated with effective microorganisms and the biostimulant Asahi SL. Then, for 2 days, some of the plants were injured by O. melanopus and some were uninjured. The influence of factors was investigated in conditions under which the cereal leaf beetle had the possibility to choose their food (no-choice test or choice test). It was found that wheat plants produce on average 0.172% DM of free phenolic acids. It has been shown that O. melanopus males and females preferred wheat previously uninjured. Also, irrespective of whether the plants were previously injured or uninjured, the females of that pest species always that caused areally more extensive leaf losses than the males. Treating plants with effective microorganisms and biostimulant Asahi SL is a secondary factor, as compared to previous wheat injury. Additionally, in choice tests, both males and females O. melanopus much preferred feeding on plants unprovided with preparations, whereas in no-choice tests, the application of pro-ecological procedures does not reduce egg laying by pests, does not adversely affect embryogenesis length and does not reduce hatching L1.

Thrips hawaiiensis is a polyphagous flower-inhabiting insect pest that causes considerable damage to numerous plants worldwide. However, not much is known about the interaction between this thrips species and its host plants. In the present study, laboratory experiments were performed to determine the oviposition and feeding preferences and compare the biological performance of T. hawaiiensis on four host plants with and without supplemental foods. In the choice tests, when compared with mango and tea petals and bean pods, the T. hawaiiensis population showed stronger oviposition and feeding preferences for banana petals. Under laboratory conditions, the T. hawaiiensis population reared on banana petals showed a significantly faster development, longer lifespan, and higher survival and fecundity levels than the populations reared on the other three host plants. Diets with supplemental foods (honey solution or tea pollen) reduced the developmental time, prolonged the longevity and enhanced the fecundity of T. hawaiiensis compared with banana petals alone. These findings indicate that the banana flower is an optimal host to increase the T. hawaiiensis population and suggest that additional foods, such as honey solution or tea pollen, are beneficial to the population performance of this species. More importantly, knowledge of the benefits of supplemental foods on predator–prey interactions and their potential use in biological control programs are also discussed. Overall, the present study improves our understanding of the ecological features of T. hawaiiensis and provides useful information on the interaction of T. hawaiiensis and its host plants. In the future, these contributions can help establish a better integrated pest management (IPM) control program for thrips.