Life table parameters and digestive physiology of Aulacophora lewisii Baly (Coleoptera: Chrysomelidae) on three Luffa acutangula (L.) Roxb. (Cucurbitaceae) cultivars

Aulacophora lewisii Baly (Coleoptera: Chrysomelidae) is an important pest of Luffa acutangula (L.) Roxb. (Cucurbitaceae) in India. Larvae of A. lewisii feed on the roots, while adults consume leaves of L. acutangula. In the current study, effects of three L. acutangula cultivars (Abhiskar, Debsundari, and Jaipur Long) on the life table parameters by age-stage, two-sex approach, and key digestive enzymatic activities (amylolytic, proteolytic, and lipolytic) of the larvae and adults of A. lewisii were determined. Further, nutrients (total carbohydrates, proteins, lipids, amino acids, and nitrogen content) and antinutrients (total phenols, flavonols, and tannins) present in the roots and leaves of three cultivars were estimated. The development time (egg to adult emergence) was fastest and slowest on Jaipur Long (31.80 days) and Abhiskar (40.91 days), respectively. Fecundity was highest and lowest on Jaipur Long (279.91 eggs) and Abhiskar (137.18 eggs), respectively. The intrinsic rate of increase (r) was lowest on Abhiskar (0.0511 day-1) and highest on Jaipur Long (0.0872 day-1). The net reproductive rate (R0) was lowest on Abhiskar (23.32 offspring female-1). The mean generation time (T) was shortest on Jaipur Long (52.59 days) and longest on Abhiskar (61.58 days). The amylolytic, proteolytic, and lipolytic activities of larvae and adults of A. lewisii were highest and lowest on Jaipur Long and Abhiskar, respectively. The lower level of nutrients and higher level of antinutrients influenced higher larval development time and lower fecundity of A. lewisii on Abhiskar than other cultivars. Our results suggest that Abhiskar cultivar could be promoted for cultivation.

Plant hormesis: Revising of the concepts of biostimulation, elicitation and their application in a sustainable agricultural production

Current research in basic and applied knowledge of plant science has aimed to unravel the role of the interaction between environmental factors and the genome in the physiology of plants to confer the ability to overcome challenges in a climate change scenario. Evidence shows that factors causing environmental stress (stressors), whether of biological, chemical, or physical origin, induce eustressing or distressing effects in plants depending on the dose. The latter suggests the induction of the "hormesis" phenomenon. Sustainable crop production requires a better understanding of hormesis, its basic concepts, and the input variables to make its management feasible. This implies that acknowledging hormesis in plant research could allow specifying beneficial effects to effectively manage environmental stressors according to cultivation goals. Several factors have been useful in this regard, which at low doses show beneficial eustressing effects (biostimulant/elicitor), while at higher doses, they show distressing toxic effects. These insights highlight biostimulants/elicitors as tools to be included in integrated crop management strategies for reaching sustainability in plant science and agricultural studies. In addition, compelling evidence on the inheritance of elicited traits in plants unfolds the possibility of implementing stressors as a tool in plant breeding.

Population Growth of Fall Armyworm, Spodoptera frugiperda Fed on Cereal and Pulse Host Plants Cultivated in Yunnan Province, China

The fall armyworm, Spodoptera frugiperda is a major agricultural pest in China, and has migrated from its continuous breeding area to other parts of China. In our study, the biological behaviors of S. frugiperda fed on maize, wheat, barley, faba beans, and soya beans were evaluated in a growth chamber. Results indicated that maize-fed S. frugiperda larvae performed well, as evidenced by shorter larva-adult periods, adult pre-oviposition period (APOP), total pre-oviposition period (TPOP), and generation time (T), and a higher survival rate, intrinsic (r) and finite (λ) rate of increase, and net reproductive rate (R_o), However, S. frugiperda larvae performed weakly when fed barley and faba bean plants, as indicated by lower survival rates, r, and λ, and longer pre-adult period, TPOP, and T. A heavier pupal weight of both sexes was recorded on faba beans (0.202 g) and a lighter weight on barley (0.169 g). Fecundity was higher when fed faba beans and maize, and lower when fed wheat and barley. Thus, maize was the most optimal and barley was the least optimal host plant, followed by faba beans, for S. frugiperda larvae growth and development. This study enhances our knowledge of S. frugiperda in these host plants and can help in the design of management approaches.

Nutrition vs association: plant defenses are altered by arbuscular mycorrhizal fungi association not by nutritional provisioning alone

BACKGROUND

While it is known that arbuscular mycorrhizal fungi (AMF) can improve nutrient acquisition and herbivore resistance in crops, the mechanisms by which AMF influence plant defense remain unknown. Plants respond to herbivory with a cascade of gene expression and phytochemical biosynthesis. Given that the production of defensive phytochemicals requires nutrients, a commonly invoked hypothesis is that the improvement to plant defense when grown with AMF is simply due to an increased availability of nutrients. An alternative hypothesis is that the AMF effect on herbivory is due to changes in plant defense gene expression that are not simply due to nutrient availability. In this study, we tested whether changes in plant defenses are regulated by nutritional provisioning alone or the response of plant to AMF associations. Maize plants grown with or without AMF and with one of three fertilizer treatments (standard, 2 × nitrogen, or 2 × phosphorous) were infested with fall armyworm (Spodoptera frugiperda; FAW) for 72 h. We measured general plant characteristics (e.g. height, number of leaves), relative gene expression (rtPCR) of three defensive genes (lox3, mpi, and pr5), total plant N and P nutrient content, and change in FAW mass per plant.

RESULTS

We found that AMF drove the defense response of maize by increasing the expression of mpi and pr5. Furthermore, while AMF increased the total phosphorous content of maize it had no impact on maize nitrogen. Fertilization alone did not alter upregulation of any of the 3 induced defense genes tested, suggesting the mechanism through which AMF upregulate defenses is not solely via increased N or P plant nutrition.

CONCLUSION

This work supports that maize defense may be optimized by AMF associations alone, reducing the need for artificial inputs when managing FAW.

Development of a polyphagous leaf beetle on different host plant species and its detoxification of glucosinolates

Herbivores face a broad range of defences when feeding on plants. By mixing diets, polyphagous herbivores are assumed to benefit during their development by gaining a better nutritional balance and reducing the intake of toxic compounds from individual plant species. Nevertheless, they also show strategies to metabolically cope with plant defences. In this study, we investigated the development of the polyphagous tansy leaf beetle, Galeruca tanaceti (Coleoptera: Chrysomelidae), on mono diets consisting of one plant species [cabbage (Brassica rapa), Brassicaceae; lettuce (Lactuca sativa), or tansy (Tanacetum vulgare), Asteraceae] vs. two mixed diets, both containing tansy. Leaves of the three species were analysed for contents of water, carbon and nitrogen, the specific leaf area (SLA) and trichome density. Furthermore, we studied the insect metabolism of two glucosinolates, characteristic defences of Brassicaceae. Individuals reared on cabbage mono diet developed fastest and showed the highest survival, while the development was slowest for individuals kept on tansy mono diet. Cabbage had the lowest water content, while tansy had the highest water content, C/N ratio and trichome density and the lowest SLA. Lettuce showed the lowest C/N ratio, highest SLA and no trichomes. Analysis of insect samples with UHPLC-DAD-QTOF-MS/MS revealed that benzyl glucosinolate was metabolised to N-benzoylglycine, N-benzoylalanine and N-benzoylserine. MALDI-Orbitrap-MS imaging revealed the localisation of these metabolites in the larval hindgut region. 4-Hydroxybenzyl glucosinolate was metabolised to N-(4-hydroxybenzoyl)glycine. Our results highlight that G. tanaceti deals with toxic hydrolysis products of glucosinolates by conjugation with different amino acids, which may enable this species to develop well on cabbage. The high trichome density and/or specific plant chemistry may lower the accessibility and/or digestibility of tansy leaves, leading to a poorer beetle development on pure tansy diet or diet mixes containing tansy. Thus, diet mixing is not necessarily beneficial, if one of the plant species is strongly defended.