Eight bacterial isolates from the larval guts of Diamondback moths (Plutella xylostella) were tested for their plant growth-promoting (PGP) traits and effects on early plant growth. All of the strains tested positive for nitrogen fixation and indole 3-acetic acid (IAA) and salicylic acid production but negative for hydrogen cyanide and pectinase production. In addition, five of the isolates exhibited significant levels of tricalcium phosphate and zinc oxide solubilization; six isolates were able to oxidize sulfur in growth media; and four isolates tested positive for chitinase and beta-1,3-glucanase activities. Based on their IAA production, six strains including four that were 1-aminocyclopropane-1-carboxylate (ACC) deaminase positive and two that were ACC deaminase negative were tested for PGP activity on the early growth of canola and tomato seeds under gnotobiotic conditions. Acinetobacter sp. PSGB04 significantly increased root length (41%), seedling vigor, and dry biomass (30%) of the canola test plants, whereas Pseudomonas sp. PRGB06 inhibited the mycelial growth of Botrytis cinerea, Colletotrichum coccodes, C. gleospoiroides, Rhizoctonia solani, and Sclerotia sclerotiorum under in vitro conditions. A significant increase, greater than that of the control, was also noted for growth parameters of the tomato test plants when the seeds were treated with PRGB06. Therefore, the results of the present study suggest that bacteria associated with insect larval guts possess PGP traits and positively influence plant growth. Therefore, insect gut bacteria as effective PGP agents represent an unexplored niche and may broaden the spectrum of beneficial bacteria available for crop production.

Aims:  To evaluate whether the gut bacteria of insecticide‐resistant, insecticide‐susceptible and field‐caught populations of the lepidopteran insect pest diamondback moth (DBM) –Plutella xylostella (L.) – are variable and their role in host protection and nutrition. Methods and Results:  The gut bacterial populations of the three DBM larvae populations were found to be significantly different, irrespective of the developmental stage. The 16S rRNA gene sequence analysis of the DBM gut bacteria revealed that the bacterial population from the prothiofos‐resistant larval gut was more diversified with Pseudomonas sp., Stenotrophomonas sp., Acinetobacter sp., and Serratia marcescens. Meanwhile, the susceptible larvae were associated with Brachybacterium sp., Acinetobacter sp. and S. marcescens and the field‐caught population harboured a rather simple gut microflora of phylotypes belonging to Serratia. The siderophore‐producing Pseudomonas sp. strain PRGB06 showed antagonistic activity towards entomopathogenic fungi, including Beaveria bassiana, Hirsutella thompsonii, Metarhizium anisopliae, Paecilomyces sp., and Paecilomyces tenuipes, while the chitinase‐producing S. marcescens enhanced the larval growth and development. Conclusion:  There was a significant variation in the gut bacteria from the three different populations of DBM. The production of antifungal siderophore compounds, like pyoverdine, may contribute to host antagonism against entomopathogens. The production of chitinase by gut bacteria appeared to contribute to host nutrition. Significance and Impact of the Study:  The results provide the first comprehensive description of the gut microbial communities in three different populations of an important crucifer pest DBM and suggest that the bacteria associated with the insect pest could be of interest for developing a pest management strategy.

No abstract

This study aimed to examine the induction of defense responses in tomato elicited by Methylobacterium oryzae CBMB20 as a consequence of reduced stress ethylene level possibly through its ACC deaminase activity. Significantly increased activities of pathogenesis-related (PR) proteins and defense enzymes such as b-1,3-glucanase, phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase were noted in M. oryzae CBMB20 pretreated and challenged with Pseudomonas syringae pv. tomato (Pst) compared to either control or M. oryzaetreated tomato plants in both growth chamber and greenhouse conditions. Increased PR proteins and defense enzyme activities were correlated with the reduction of stress ethylene level. M. oryzae CBMB20 reduced the stress ethylene level about 27% and 55% when challenged with Pst, in growth chamber and greenhouse on day 7 respectively and the effect was comparable to that of the chemical ethylene biosynthesis inhibitor AVG, L-a-(2-aminoethoxyvinyl)-glycine hydrochloride. As a consequence of reduced stress ethylene level and its effect on defense response in crop plants, the disease severity was reduced 26% in M. oryzae CBMB20-treated plants challenged with pathogen. Therefore, inoculation of M. oryzae CBMB20 would induce the defense enzymes and contribute to the enhanced resistance of tomato plants against the pathogen Pst.

The repellent efficacy of 17 essential oils against the German cockroach, Blattella germanica was examined using a T-tube olfactometer. Five oils repelled B. germanica with good efficacy, ranging from 70.0 to 96.7%. Four of these oils, grapefruit, lemon, lime, and orange, were from the citrus family Rutaceae. These citrus essential oils showed similar repellent activity against two more cockroach species, such as Periplaneta americana and P. fuliginosa. Gas chromatography (GC) and GC-mass spectrometry analyses revealed that the major components responsible for the repellent activity of the citrus oils were limonene, b-pinene and g-terpinene. Limonene appears to be the main component responsible for the repellent activity rather than b-pinene and g-terpinene. The repellent efficacy of these components varied with different doses and the cockroach species tested. It is likely that minor components of the oils also contributed to the overall repellent activity of citrus essential oils, except orange oil. The activity of orange oil is almost solely attributed to the activity of limonene. Also, the repellent activity of citrus oil and that of each of the terpenoids makes little difference to the efficacy of a repellant against the three species of cockroaches.