Changes in Antioxidative, Oxidoreductive and Detoxification Enzymes during Development of Aphids and Temperature Increase

Pest management facing warming and chemical stresses: Multi-stress effects on the biological agent Trichogramma oleae

Global change is affecting plant-insect interactions in agroecosystems and can have dramatic consequences on yields when causing non-targeted pest outbreaks and threatening the use of pest natural enemies for biocontrol. The vineyard agroecosystem is an interesting system to study multi-stress conditions: on the one hand, agricultural intensification comes with high inputs of copper-based fungicides and, on the other hand, temperatures are rising due to climate change. We investigated interactive and bottom-up effects of both temperature increase and copper-based fungicides exposure on the important Lepidopteran vineyard pest Lobesia botrana and its natural enemy, the oophagous parasitoid Trichogramma oleae. We exposed L. botrana larvae to three increasing copper sulfate concentrations under two fluctuating thermal regimes, one current and one future. Eggs produced by L. botrana were then exposed to T. oleae. Our results showed that the survival of L. botrana, was only reduced by the highest copper sulfate concentration and improved under the warmer regime. The development time of L. botrana was strongly reduced by the warmer regime but increased with increasing copper sulfate concentrations, whereas pupal mass was reduced by both thermal regime and copper sulfate. T. oleae F1 emergence rate was reduced and their development time increased by combined effects of the warmer regime and increasing copper sulfate concentrations. Size, longevity and fecundity of T. oleae F1 decreased with high copper sulfate concentrations. These effects on the moth pest and its natural enemy are probably the result of trade-offs between the survival and the development of L. botrana facing multi-stress conditions and implicate potential consequences for future biological pest control. Our study supplies valuable data on how the interaction between pests and biological control agents is affected by multi-stress conditions.

Silencing of catalase reduces unfavorable low-temperature tolerance capacity in whiteflies

BACKGROUND

Temperature is a primary factor that determines the eco-geographical distribution and population development of invasive insects. Temperature stress leads to various negative effects, including excess reactive oxygen species (ROS), and catalase (CAT) is a key enzyme against ROS in the antioxidant pathway. The whitefly Bemisia tabaci MED is a typical invasive pest that causes damage worldwide. Our previous studies have shown that CAT promotes whitefly adaptation to high temperature by eliminating ROS. However, the mechanism underlying the low-temperature adaptation of whiteflies is still unknown.

RESULTS

In this study, we investigated the role of CAT in the low-temperature tolerance of B. tabaci MED by analyzing its survival rate, reproduction, and ROS levels at 25 °C (as a control, suitable temperature), 20 °C (moderately decreased temperature), and 4 °C (severely decreased temperature). Silencing of BtCAT1, BtCAT2, or BtCAT3 reduced the viability of whiteflies under a short-term severely decreased temperature (4 °C), which manifested as decreases in survival and fecundity accompanied by significant increases in ROS levels. Moreover, even at a moderately decreased temperature (20 °C), silencing of BtCAT1 led to high ROS levels and low survival rates in adults.

CONCLUSION

Silencing of BtCATs significantly increased the sensitivity of B. tabaci MED to low temperatures. BtCAT1 is likely more essential than other BtCATs for low-temperature tolerance in whiteflies. © 2024 Society of Chemical Industry.

Lipopeptides from Bacillus velezensis ZLP-101 and their mode of action against bean aphids Acyrthosiphon pisum Harris

BACKGROUND

Natural products are important sources for the discovery of new biopesticides to control the worldwide destructive pests Acyrthosiphon pisum Harris. Here, insecticidal substances were discovered and characterized from the secondary metabolites of the bio-control microorganism Bacillus velezensis strain ZLP-101, as informed by whole-genome sequencing and analysis.

RESULTS

The genome was annotated, revealing the presence of four potentially novel gene clusters and eight known secondary metabolite synthetic gene clusters. Crude extracts, prepared through ammonium sulfate precipitation, were used to evaluate the effects of strain ZLP-101 on Acyrthosiphon pisum Harris aphid pests via exposure experiments. The half lethal concentration (LC50) of the crude extract from strain ZLP-101 against aphids was 411.535 mg/L. Preliminary exploration of the insecticidal mechanism revealed that the crude extract affected aphids to a greater extent through gastric poisoning than through contact. Further, the extracts affected enzymatic activities, causing holes to form in internal organs along with deformation, such that normal physiological activities could not be maintained, eventually leading to death. Isolation and purification of extracellular secondary metabolites were conducted in combination with mass spectrometry analysis to further identify the insecticidal components of the crude extracts. A total of 15 insecticidal active compounds were identified including iturins, fengycins, surfactins, and spergualins. Further insecticidal experimentation revealed that surfactin, iturin, and fengycin all exhibited certain aphidicidal activities, and the three exerted synergistic lethal effects.

CONCLUSIONS

This study improved the available genomic resources for B. velezensis and serves as a foundation for comprehensive studies of the insecticidal mechanism by Bacillus velezensis ZLP-101 in addition to the active components within biological control strains.

Differential Antioxidant Enzyme Gene Expression and Functional Analysis of Pyridaben-Susceptible and -Resistant Strains of Tetranychus truncatus (Acari: Tetranychidae) under High Temperature Stress

Tetranychus truncatus (Acari: Tetranychidae) has caused serious economic losses on some crops (soybean, corn, and cotton) in China, and has developed resistance to most acaricides. Our laboratory study found that T. truncatus was resistant to pyridaben and also adapted to high temperature (34-40 °C). High temperature stress may cause arthropods to produce a large amount of reactive oxygen species (ROS), causing oxidative damage. Antioxidant enzymes, as the main antioxidants, can reduce the damage caused by excessive ROS in arthropods. In order to study the adaptation mechanism of the pyridaben-resistant strain of T. truncatus to high temperature and the role of antioxidant enzyme genes under high temperature stress, four antioxidant enzyme genes, TtSOD, TtPOD3, TtPOD4, and TtGSTs2, were screened according to the transcriptome sequencing data of pyridaben-susceptible and -resistant strains in T. truncatus. Firstly, the phylogeny and structure analyses of these four genes were carried out. Then, real-time quantitative PCR (RT-qPCR) technology was used to analyze the gene expression patterns of antioxidant enzymes in two strains of T. truncatus at three different high temperature ranges (34 °C, 38 °C, and 42 °C). The results showed that the expression levels of four antioxidant enzyme genes of two strains of T. truncatus were induced by high temperature stress, and the expression levels of antioxidant enzyme genes were significantly different in each development state. The gene expression of antioxidant enzyme genes in resistant strains at the adult stage was significantly higher than that in susceptible strains. After the TtSOD and TtPOD4 genes of adult mites of the resistant strain were silenced by RNA interference (RNAi) technology, the mortality rate of mites with TtPOD4 gene silencing reached 41.11% after 96 h at 34 °C, which was significantly higher than that of the control and TtSOD gene silencing. It has been confirmed that the TtPOD4 gene plays a key role in the adaptation of pyridaben-resistant strain of T. truncatus to high temperature. It lays a theoretical foundation for revealing the thermal adaptation mechanism of T. truncatus.

Two distinct aphid diapause strategies: slow development or development arrest

Aphids adapt to unfavourable environmental conditions, such as low temperatures in winter, by laying diapausing eggs that overwinter. Diapause is a stress-resistant and developmentally arrested stage that can be adopted in order to increase the chance of survival in adverse environmental conditions. The diapause process of aphids is still very poorly understood. We followed the development of two species of aphids, Brachycorynella asparagi and Appendiseta robiniae, using the immunostained embryos of the aphids to identify mitotic cell divisions. Two different models of aphid diapause were demonstrated for the first time. In the first strategy, the embryo developed continuously during winter diapause, while in the second case, there was an embryonic arrest. The possibility of slow development of the whole body during diapause is a characteristic feature of aphids. The link to the plant's phenology appears to be a key factor in determining the diapause strategy in aphids.

Formica fusca ants use aphid supplemented foods to alleviate effects during the acute phase of a fungal infection

The modulation of nutritional intake by animals to combat pathogens is a behaviour that is receiving increasing attention. Ant studies using isolated compounds or nutrients in artificial diets have revealed a lot of the dynamics of the behaviour, but natural sources of medicine are yet to be confirmed. Here we explored whether Formica fusca ants exposed to a fungal pathogen can use an artificial diet containing foods spiked with different concentrations of crushed aphids for a medicinal benefit. We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented foods during the acute phase of the infection, reducing the mortality caused by the disease. However, the benefit was only attained when having access to a varied diet, suggesting that while aphids contain nutrients or compounds beneficial against infection, it is a part of a complex nutritional system where costs and benefits of compounds and nutrients need to be moderated.

Detoxification enzyme is involved in the temperature effect on the toxicity of tetrachlorantraniliprole to Plutella xylostella

The efficacy of insecticides is usually influenced by temperature. Insecticides can be divided into "positive", "negative" and "non-effect" temperature coefficient insecticides (TCI). To assess the temperature-dependent effect of tetrachlorantraniliprole (TET) on Plutella xylostella Linnaeus and to elucidate the mechanism of temperature affects TET toxicity, we determined the toxicity of TET against P. xylostella from 15 °C to 35 °C by leaf dipping method. Moreover, we compared the transcriptome data of the third-instar larvae treated by TET, chlorfenapyr (CHL, non-effect TCI), and the control group at 15, 25, 35 °C, respectively. The results showed that the toxicity of TET against P. xylostella increased with increasing temperature from 15 °C to 35 °C. A total of 21 differential expressed genes (DEGs) of detoxification enzymes were screened by RNA-seq, in which 10 up-regulated genes (3 UGTs, 2 GSTs, 5 P450s) may involve the positive temperature effect of TET, and their expression patterns were consistent with qPCR results. Furthermore, the enzyme activities of GSTs and UGTs significantly increased after TET was treated at 15 °C. Especially, the temperature coefficient (TC) of TET was significantly reduced mixed with UGTs enzyme inhibitor 5-NI. Overall, TET showed higher insecticidal activity with increasing temperature, in which detoxifying enzymes associated with regulation of the positive temperature effect of TET on P. xylostella, such as UGTs, GSTs and P450s, are strongly involved. The transcriptome data provide in-depth information to understand the TET mechanism against diamondback moth. Most importantly, we identified detoxification enzymes that might be involved in regulating TET's positive temperature effect process, and contributed to efficient pest management.

Glucose Dehydrogenases-Mediated Acclimation of an Important Rice Pest to Global Warming

Global warming is posing a threat to animals. As a large group of widely distributed poikilothermal animals, insects are liable to heat stress. How insects deal with heat stress is worth highlighting. Acclimation may improve the heat tolerance of insects, but the underlying mechanism remains vague. In this study, the high temperature of 39 °C was used to select the third instar larvae of the rice leaf folder Cnaphalocrocis medinalis, an important insect pest of rice, for successive generations to establish the heat-acclimated strain (HA39). The molecular mechanism of heat acclimation was explored using this strain. The HA39 larvae showed stronger tolerance to 43 °C than the unacclimated strain (HA27) persistently reared at 27 °C. The HA39 larvae upregulated a glucose dehydrogenase gene, CmGMC10, to decrease the reactive oxygen species (ROS) level and increase the survival rate under heat stress. The HA39 larvae maintained a higher activity of antioxidases than the HA27 when confronted with an exogenous oxidant. Heat acclimation decreased the H₂O₂ level in larvae under heat stress which was associated with the upregulation of CmGMC10. The rice leaf folder larvae may acclimate to global warming via upregulating CmGMC10 to increase the activity of antioxidases and alleviate the oxidative damage of heat stress.

Differences in Oxidative Stress Markers and Antioxidant Enzyme Activities in Black Bean Aphid Morphs (Aphis fabae Scop.) Fed on the Primary Host Viburnum opulus L

Changes in the level of oxidative stress markers-superoxide anion radical (O2-), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) and the activity of antioxidant enzymes-superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in the black bean aphid occurring on the primary host (viburnum plants) were studied. Among the aphid morphs, the lowest contents of O2-, H₂O₂ and MDA were noted for winged adults (alatae), which were also characterized by the highest activity of antioxidant enzymes. These metabolic features indicate the adaptation of winged morphs to the colonization of new host plants. During spring migration, an increase in the content of oxidative stress markers and antioxidant enzyme activities in wingless females (fundatrigeniae) was observed. The significance of the biochemical adaptation of the black bean aphid to its winter host is discussed.

Highly Efficient Use of Infrared Spectroscopy (ATR-FTIR) to Identify Aphid Species

Aphids are commonly considered to be serious pests for trees, herbaceous and cultivated plants. Recognition and identification of individual species is very difficult and is based mainly on morphological features. The aims of the study were to suggest the possibility of identifying aphids through the use of Fourier-transform infrared (FTIR) spectroscopy, and to determine which absorption peaks are the most useful to separate aphid species. Using FTIR spectroscopy, based on the chemical composition of the body, we were able to distinguish 12 species of aphid. We have shown that using nine distinct peaks corresponding to the molecular vibrations from carbohydrates, lipids, amides I and II, it is possible to accurately identify aphid species with an efficiency of 98%.

Mortality, Enzymatic Antioxidant Activity and Gene Expression of Cabbage Aphid (Brevicoryne brassicae L.) in Response to Trichoderma longibrachiatum T6

Aphids are one of the most common insect pests in greenhouse and field crops worldwide, causing significant crop yields and economic losses. The objective of this study was to determine the mortality, enzymatic antioxidant activity and gene expression of cabbage aphids (Brevicoryne brassicae L.) in response to Trichoderma longibrachiatum T6 (T6) at different time points from Day 1 to 7 after inoculation. Our results showed that the highest mortality of B. brassicae was observed on Day 7 at a concentration of 1 × 108 spores ml−1 (73.31%) after inoculation with T6 compared with the control on Day 7 (11.51%). The activities of the enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and glutathione S-transferase (GST) were increased by 52.98%, 44.77%, 48.26%, 49.39%, 45.13% and 39.67%, respectively on Day 3 after inoculation with T6 compared to the control. Howerver increased days post treatment (dpt) decreased the activities of SOD, POD, CAT, APX, GPX and GST enzymes by 20.79%, 21.05%, 13.75%, 20.45%, 25.38%, and 19.76% repectively on Day 7 compared to control. The transcript levels of SOD, POD, CAT, GPX, and GST genes were increased by 10.87, 9.87, 12.77, 6.22 and 4.07 respectively at Day 3 after inoculation with T6 in comparison to the control. However, the SOD, POD, CAT, GPX, and GST transcription levels decreased by 0.43, 0.44, 0.35, 0.52 and 0.47 respectively, compared to control at Day 7. Our results suggest that the T6 strain has a potential effect on the antioxidant activity and mortality of B. brassicae and therefore could be used as a natural biocontrol agent against B. brassicae in the future.