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Female adults of the migratory locust, Locusta migratoria manilensis (Meyen), can sense seasonal photoperiod changes, which induces embryonic diapause as a key strategy to overwinter. Serine protease inhibitor genes (SPNs) were thought to play key roles during diapause, while few SPNs were functionally characterized. LmSPN2 was one of those genes differentially expressed between diapause and non-diapause eggs; however, its biological function remained to be explored. So, we conducted RNAi knockdown of LmSPN2, resulting in a significant decrease of the egg diapause rate by 29.7%. Using yeast two-hybrid assays, co-immunoprecipitation, and pull-down methods, we found an interaction between LmSPN2 and LmSPN3, which was proved to be mediated by a glutamate (E331) binding site of LmSPN2. RNAi knockdown of LmSPN3 resulted in a significant increase in diapause rate by 14.6%, indicating an inverse function of LmSPN2 and LmSPN3 on diapause regulation. Double knockdown of two SPN genes resulted in a 26.4% reduction in diapause rate, indicating that LmSPN2 was the dominant regulatory signal. Moreover, we found four Toll pathway genes (easter, spätzle, pelle, and dorsal) upregulated significantly after the knockdown of LmSPN2 while downregulated after the knockdown of LmSPN3. Therefore, we speculate that two SPNs regulate diapause through the Toll pathway. Our results indicated that LmSPN2 positively regulates locust egg entry into diapause, while LmSPN3 is a negative regulator of embryonic commitment to diapause. Their interaction is mediated by the binding site of E331 and influences egg diapause through the Toll pathway. This mechanistic understanding of diapause regulation expands our understanding of insect developmental regulation and provides functional targets for developing locust management strategies.

The efficacies of biological and conventional chemical insecticides against two major insect pests of alfalfa (aphids and thrips) were compared in three sites across China’s alfalfa belt. In addition, the persistence of the residues of chemical insecticides in alfalfa and their influence on the quality of alfalfa hay were examined. Efficacy varied among the different biological and chemical insecticides. The chemical insecticides were significantly more effective than biopesticides in a short time-frame. The efficacy period of biopesticides was significantly longer than that of chemical insecticides, and the corrected mortality rate of aphids in all regions was above 50% at 14 days after application. The analysis of pesticide residues showed that the residual doses of all the pesticides were within the allowed ranges after the safe period. The acid detergent fiber and neutral detergent fiber contents in alfalfa hay were higher and the protein content was lower in chemical insecticide treatments than in biopesticide treatments in Hebei. The relative feeding value of alfalfa hay treated with Metarhizium anisopliae IPP330189 was the highest among the treatments. Compared with chemical insecticides, the yield of alfalfa hay was higher in the biopesticides treatments. Biopesticides show a stronger control effect on insect populations and also a better improvement in the quality of alfalfa hay than chemical insecticides. This study provides a basis for exploring and developing a comprehensive control regime for alfalfa insect pests in the different alfalfa-growing regions in China, and for reducing chemical insecticide usage and improving forage quality.

Locusts have caused periodic disasters in the recorded history of humankind. Up to now, locust disaster is still the biggest threat to the world's agricultural production. The desert locust Schistocerca gregaria is one of the most harmful locusts, which has caused massive food crises, economic losses, and ecological disasters. The desert locust is a migratory insect pest that occurs year-round in the tropic and subtropical regions. Under the wind and seasonal alternation, it moves and flies in the African continent and West Asia. Desert locust damages the stems and leaves of more than 300 plants, including Gramineae, Tribulus terrestris, and Euphorbiaceae. Locusts cause devastating disasters to local plants, especially field crops, and significantly threaten food security. To date, voluminous research has been conducted regarding the ecology and management of desert locusts. This review represents an effort to summarize the basic information on the biology and ecology, distribution, damage, and economic impact of desert locusts, examine the recent developments in integrated locust management, and make recommendations for future research.

Maternal photoperiodic response is a key factor that affects offspring diapause in migratory locust, Locusta migratoria L. (Orthoptera: Acridoidea). Although many aspects of insect diapause have been studied, little is known about the molecular mechanisms of maternal photoperiodic response that influence diapause regulation. To gain insight into the possible mechanisms of maternal photoperiod influence on diapause regulation, proteomics data by label-free quantification analysis were generated from non-diapause and diapause eggs. A total of 175 proteins were differentially expressed between diapause and non-diapause eggs. Among them, 24 proteins were upregulated, and 151 proteins were downregulated. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments were performed on all differentially expressed proteins (DEPs) and showed that peroxisome, insect hormone biosynthesis, and longevity regulating pathway may be related to diapause of migratory locust. Furthermore, we used qRT-PCR to verify some results of the proteomic analysis. Proteins such as hexamerin-like protein 4, juvenile hormone epoxide hydrolase 1 (JHEH1), cytochrome P450 and heat shock protein (HSP) 20.7 were predicted to be involved in diapause. This study provides an important reference for future research that will explore the mechanisms of diapause induced by maternal effects in migratory locust.

Plant breeding for resistance to agricultural pests is an essential element in the development of integrated crop management systems, however, the molecular and genetic mechanisms underlying resistance are poorly understood. In this pilot study, we conducted a transcriptomic analysis of a resistant (R) and susceptible (S) variety of alfalfa, with (+A) or without (–A) aphids (totally four treatments). We used the resistant cultivar Zhongmu 1 and the susceptible cultivar Soca. A total of 3 549 mRNAs were differentially expressed, of which 1 738 up-regulated and 1 307 down-regulated genes were identified in S+A/S–A plants, while 543 up-regulated and 331 down-regulated genes were identified in the R+A/R–A plants. KEGG analysis mapped 112 and 546 differentially expressed genes to 8 and 17 substantially enriched pathways for Zhongmu 1 and Soca, respectively. Six shared pathways were linked to plant resistance traits, including phenylpropanoid biosynthesis associated with salicylic acid synthesis, and linoleic acid metabolism associated with both jasmonic acid and flavonoid biosynthesis. Ultimately, we proposed a preliminary regulatory mechanism of alfalfa cultivar resistance response to aphids feeding based on transcriptome analyses and published documents.

The aphid quantity ratio (AQR) is defined as the number of aphids on each cultivar divided by the number of aphids on all cultivars. AQR is based on the correlation between aphid populations and their host plants and is an important tool that has been utilized in evaluating Medicago sativa (alfalfa) cultivar resistance to aphids. However, assessment of alfalfa resistance to aphids can be confused by the presence of aphid predators, causing the assessment of plant resistance to aphids to be based on incorrect aphid population data. To refine the AQR and account for the effect of predators on aphid population assessments, we introduced a parameter ‘α’, corresponding to the predator quantity ratio, and used αAQR as the ratio to quantify aphid populations. Populations of both aphids (4 species) and their predators (12 species) occurring in 28 M. sativa cultivars were sampled over two years at a research station near Cangzhou, Hebei Province, China. Results showed that the most suitable evaluation period was from May to June, as the aphid population was stable during this period. Compared with the AQR method, the predator population numbers based on the αAQR had a significant inverse relationship with aphid population numbers and the 28 cultivars were clustered into three classes: the resistant class, tolerant class, and susceptible class. In addition, 17 cultivars were reassigned when evaluated using αAQR. All numerical values calculated by αAQR were displayed as a Gaussian distribution, which showed that the 28 cultivars could be clustered into nine groups using a median value (±SE) of 1±0.1. Hence, ongoing alfalfa breeding trials will be assessed using the αAQR to establish a robust system that includes agronomic performance parameters in order to generalize the new method for further studies.

Abstract: Temperate-zone insects typically survive winter by entering diapause. Although many aspects of insect diapause have been studied, the underlying molecular mechanism of insect diapause is not well understood. Here we report the results of the transcriptional and translational differences of migratory locust eggs at different embryonic states using diapause (low temperature) and non-diapause (high temperature) regimes. Compared with non-diapause eggs at 100 degree-days (N2) treatment, 29 671 transcripts and 296 proteins were differentially expressed at the diapause maintenance stage (D2). While compared with 150 degree-days (N3) treatment, 45 922 transcripts and 404 proteins were differentially expressed in the post-diapause stage (D3). Among them, 51 and 102 transcripts had concurrent transcription and translation profiles in D2 vs. N2 and D3 vs. N3 treatments, respectively. Analysis of Gene Ontology categorized these genes and proteins into three categories: biological processes, cellular components, and molecular functions. Biological pathway analysis indicated that three pathways: (1) insect hormone biosynthesis (KEGG: Map 00981), (2) the insulin signaling pathway (KEGG: Map 04910), and (3) the peroxisome proliferator-activated receptor (PPAR) signaling pathway (KEGG: Map 03320) play an important role in locust diapause regulation. Most of these transcripts and proteins were up-regulated in the diapause treatments, and were highly linked to juvenile hormone biosynthesis, insulin and PPAR signaling pathways, suggesting these three pathways may be involved in diapause and development regulation. This study demonstrates the applicability of high-throughput omics tools to identify biochemical pathways linked to diapause in locust egg development. In addition, it reveals that cellular metabolism in diapause eggs is more inactive than in non-diapause eggs, and most of the down-regulated enzymes and pathways are related to reduce energy loss.

The thrips quantity ratio (TQR) model is an important tool for evaluating crop resistance to thrips based on the correlation between thrips quantities and cultivars. Unfortunately, it is inaccurate, and the results appear significantly inconsistent when analysing the same cultivars in the same field study. To improve this model, we first studied the resistance of 28 alfalfa cultivars to thrips in Cangzhou, Hebei Province, north China. The results showed that the most suitable evaluation period was from May to June, as the thrips population was stable during this period. Second, we found that the natural enemy population was significantly positively correlated with the thrips population density (R=0.7275, P