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Aiming at the application of fruit and vegetables precooling, an innovative wet precooling system with ice slurry as a cooling medium was proposed. A small wet precooling room performance test platform was built. With apples as the precooling subject, the temperature and relative humidity in precooling room, the cooling rate and weight loss of apples as indexes, by changing the weight concentration of ice slurry additives (0%-8%), the ice fraction (0%-10%) and the ice slurry flow rate (50-150 L h−1), the precooling experiments were carried out. The results showed that increasing the concentration of ice slurry additives (NaCl) could effectively reduce the equilibrium temperature in precooling room. For the ice slurry solution with the additive concentrations of 0%, 2%, 4%, 6% and 8%, the equilibrium temperature in precooling room were 4.3°C, 1.7°C, 0.4°C, 0.0°C and -0.7°C, respectively. When the ice fractions increased from 0% to 10%, the precooling time decreased from 165 min to 96 min, and the weight loss decreased from 2.11% to 0.42%. When the ice slurry flow rate increased, the relative humidity in precooling room increased, and the cooling rate of apples firstly increased rapidly and then leveled off. When the flow rate reached 100 L h−1, the relative humidity remained above 90%. The precooling system has a strong applicability, easy to realize the stable environment of low temperature and high relative humidity (0°C, >90%), so it has a large application space in the precooling and fresh-keeping of fruit and vegetables.

Free-standing reduced graphene oxide (rGO) papers were prepared by chemical reduction, thermal reduction and combined chemical-thermal reduction, respectively. Four-point probe and nanoindentation experiments were conducted to investigate the electrical and mechanical properties of rGO papers. The rGO paper prepared by soaking in L-ascorbic acid and thermal annealing in argon at 1000 °C (labeled rGO-AsA-T) showed superior electrical and mechanical properties when compared with rGO papers prepared merely by chemical reduction or thermal reduction. The as-prepared rGO-AsA-T paper exhibited an electrical conductivity of 5.7 × 104 S/m, showing an increase of 90% compared to that in the thermally annealed rGO paper and nearly 40 times that of rGO paper reduced by L-ascorbic acid. It was also found that the rGO-AsA-T paper had the lowest elastic modulus of 288 MPa, showing enhanced flexibility. The nearly free voids in rGO-AsA-T paper proved by scanning electron microscopy (SEM) were due to the capillary action in chemical reduction and were significant in improving the electrical conductivity and flexibility of the paper. The rGO-AsA-T paper with high conductivity and flexibility has a promising application in flexible electronics.

Insects entertain intricate and mutualistic relationship with an array of microorganisms, which significantly influence their fitness, ecology and evolution. In recent decades, there has been increasing interest toward studying the effects of microbiome on many host insects (Dipterans, Lepidopterans, and Coleopterans). Studies so far realized indicate that gut microbiome contribute to host nutritional ecology, defense, immunity and lifespan. Bactrocera dorsalis (Tephritidae: Diptera) is a polyphagous fruit fly which attacks a huge variety of fruits and vegetables worldwide and has been placed as a quarantine species by many countries. To investigate the specific functions of the gut endosymbionts, it is a prerequisite to know the composition of gut bacterial communities whose manipulation will help to decipher their ecological relevance. Here, we used the culture-dependent technique to isolate and identify gut bacteria from B. dorsalis at different developmental stages. The results revealed 11 bacterial species from the third instar larvae, 18 and 12 from female and male populations, respectively. These bacteria were assigned to six families, namely, Enterobacteriaceae, Enterococcaceae, Staphylococcaceae, Streptococcaceae, Micrococcaceae and Bacillaceae. Bacterial species from these families were differentially represented in various samples, except Klebsiella oxytoca , Enterobacter cloacae, Pantoea dispers and Enterococcus faecalis that were detected at all developmental stages. Overall, Enterobacteriaceae was the most dominant family in females and third instar larvae accounting for 57.89% and 26.32%, respectively, while Enterococcaceae was dominant in males with 75% of the total bacterial taxa. These results suggest that B. dorsalis possesses a huge variety of cultivable bacteria that could be used to explore their specific functions on host physiology and fitness.

Simple Summary Nitrogen acquisition strategies mediated by insect symbionts through biological nitrogen fixation (BNF) and nitrogenous waste recycling (NWR) were reviewed and compared in our paper, and a model for nitrogen provisioning in insects was then constructed. In our model, (1) insects acquired nitrogen nutrition from food stuffs directly, and the subprime channels (e.g., BNF or NWR) for nitrogen provisioning were accelerated when the available nitrogen in diets could not fully support the normal growth and development of insects; (2) the NWR strategy was more accessible to more insects due to its energy conservation and mild reaction conditions; (3) ammonia produced by different channels was used for essential nitrogenous metabolites synthesis via the glutamine synthetase and glutamate synthase pathways. Abstract Nitrogen is usually a restrictive nutrient that affects the growth and development of insects, especially of those living in low nitrogen nutrient niches. In response to the low nitrogen stress, insects have gradually developed symbiont-based stress response strategies—biological nitrogen fixation and nitrogenous waste recycling—to optimize dietary nitrogen intake. Based on the above two patterns, atmospheric nitrogen or nitrogenous waste (e.g., uric acid, urea) is converted into ammonia, which in turn is incorporated into the organism via the glutamine synthetase and glutamate synthase pathways. This review summarized the reaction mechanisms, conventional research methods and the various applications of biological nitrogen fixation and nitrogenous waste recycling strategies. Further, we compared the bio-reaction characteristics and conditions of two strategies, then proposed a model for nitrogen provisioning based on different strategies.

In order to understand the role of symbionts for their insect hosts, it is customary to treat them with antibiotics or to sterilize eggs (treatments), resulting in aposymbiotic and axenic insects, respectively. Such axenic insects can then be compared with untreated controls. Fruit flies often bear complex communities which are greatly reduced by such treatments. However, the bacterial community is not completely eliminated. Here, we examine the effect of these procedures on the structure of the remaining bacterial communities in Bactrocera dorsalis (Diptera: Tephritidae) and on the insect longevity. The antibiotics (Norfloxacin and Ceftazedime) were administered to 1-day-old adult flies through sugar meal for 7 days, and eggs were surface sterilized and dechorionated to produce axenic lines. The flies were starved of protein before they were offered full diets or diets containing non-essential amino acids only. Antibiotic and egg disinfection treatments resulted in a significant reduction of the vast majority of gut bacterial populations, especially Proteobacteria, Firmicutes and Bacteroidetes. On the other hand, antibiotic allowed the persistence of Actinobacteria, Cyanobacteria and Acidobacteria populations. In untreated control flies, longevity was extended irrespective of diet quality in comparison to treated flies. Conversely, when gut bacteria were largely reduced (aposymbiotic and axenic flies), longevity was reduced in the non-essential amino acids diet treatment versus slightly improved in the presence of a protein diet. We discuss these results in an ecological–life-history perspective.

The adaptation of phytophagous insects to host defence is an important aspect of plant-insect interactions. The reciprocal adaptability between specialist insects and their hosts have been adequately explored; however, the mechanisms underlying the adaptation of tephritid fruit fly specialists, a group of notorious pests worldwide, to unripen host fruits remain elusive. Here, plant metabolomes and insect transcriptomes were analysed for the first time to explore the interaction between unripe citrus fruits and the Chinese citrus fly Bactrocera minax. Seventeen citrus secondary metabolites, mainly flavones, alkaloids and phenylpropanoids, were identified in the unripe citrus fruit metabolome and they accumulated during larval feeding. Three detoxification genes (1 P450 gene, 2 ABCs genes) were highly expressed in B. minax larvae collected from unripe citrus fruits compared with the ones fed on artificial diets and ripe citrus fruits. Based on omics data, a novel ABC gene was screened through plant allelopathy tests and the gene was significantly upregulated in B. minax larvae treated with defensive secondary metabolites; additionally, the mortality rate of the larvae reached 51% after silencing the ABC gene by RNAi technique. Overall, these results shed light on the mechanisms underlying the biological interactions between tephritid fruit fly specialists and host fruits.

The ability of a host plant to act as a substrate or media for larval development may depend on how good it is at offering suitable nutrients for bacterial growth. In this study, we hypothesized that the suitability of a fruit type for fruit fly larval development is positively correlated with the ability of that fruit to act as a substrate/media for fruit fly symbiotic bacterial growth. We allowed a single female fruit fly to lay eggs on five different host fruits, then we monitored the larval development parameters across five generations and analyzed the bacterial community structure of larvae developing in 2 of these hosts (apple and banana) at the first and fifth generations. Results indicate that the larval length and dry weight did not vary significantly across experimental generations, but were greatly affected by fruit types and larval stages. The larval development time was extended considerably in apple and tomato but shortened in banana and mango. There was a significant shift in bacterial community structure and composition across fruits and generations. The bacterial community of larvae within the same fruit (apple and banana) clustered and was similar to the parental female (with the predominance of Proteobacteria), but there was a shift at the fifth generation (dominance of Firmicutes). Banana offered a suitable better development and growth to larvae and bacteria, respectively, compared to apple in which reduced larval development and bacterial growth were recorded. Although additional experiments are needed to adequately show that the differences in microbiome seen in fruit fly larval guts are the actual driver of different developmental outcomes of larvae on the different fruits, at the very least, our study has provided intriguing data suggesting interaction between the diets and gut microbial communities on insect development.Importance and Significance of the studyTephritid fruit flies entertain complex interactions with gut bacteria. These bacteria are known to provide nutritional benefits to their hosts, by supplementing missing nutrients from the host diets and regulating energy balance. Foraging for food is a risky exercise for the insect which is exposed to ecological adversities, including predators. Therefore, making beneficial choice among available food substrates is a question of survival for the flies and bacteria as well. Our study demonstrates interactions between the host fly and its intestinal bacteria in sustaining the larval development while foraging optimally on different fruit types. These findings add a novel step into our understanding of the interactions between the gut microbial communities and B. dorsalis and provide avenues for developing control strategies to limit the devastative incidence of the fly.

Background The gut bacteria of tephritid fruit flies play prominent roles in nutrition, reproduction, maintenance and ecological adaptations of the host. Here, we adopted an approach based on direct observation of symbiotic or axenic flies feeding on dishes seeded with drops of full diet (containing all amino acids) or full diet supplemented with bacteria at similar concentrations to explore the effects of intestinal bacteria on foraging decision and fitness of Bactrocera dorsalis. Results The results show that intestinal probiotics elicit beneficial foraging decision and enhance the female reproduction fitness and survival of B. dorsalis (symbiotic and axenic), yet preferences for probiotic diets were significantly higher in axenic flies to which they responded faster compared to full diet. Moreover, females fed diet supplemented with Pantoea dispersa and Enterobacter cloacae laid more eggs but had shorter lifespan while female fed Enterococcus faecalis and Klebsiella oxytoca enriched diets lived longer but had lower fecundity compared to the positive control. Conversely, flies fed sugar diet (negative control) were not able to produce eggs, but lived longer than those from the positive control. Conclusions These results suggest that intestinal bacteria can drive the foraging decision in a way which promotes the reproduction and survival of B. dorsalis. Our data highlight the potentials of gut bacterial isolates to control the foraging behavior of the fly and empower the sterile insect technique (SIT) program through the mass rearing.

An abundant semigroup S is a superabundant semigroup if each $\mathcal{H}^*$-class of S contains an idempotent. We call a superabundant semigroup a left regular cyber-group if the set of its idempotents forms a left regular band. After the investigation of the properties of superabundant semigroups, we establish a structure theorem for the left regular cybergroups by using the newly defined left twist product of semigroups.

As a generalization of quasi-inverse semigroups in the class of regular semigroups, we consider the Q ⁎ -inverse semigroups which are idempotent-connected abundant semigroups with regular bands. In this paper, a construction theorem of Q ⁎ -inverse semigroups is given by using the wreath product of some semigroups. It is proved that a semigroup S is a Q ⁎ -inverse semigroup if and only if S is a spined product of an L ⁎ -inverse semigroup and an R ⁎ -inverse semigroup. Thus the structure of Q ⁎ -inverse semigroups is fully described and the results on quasi-inverse semigroups obtained by M. Yamada in 1973 are extended and amplified.