[Evidence of long distance migration of diamondback moth (DBM) Plutella xylostella: a review].

As cruciferous plants have been cultivated northwards due to climate warming, diamondback moth (DBM) Plutella xylostella is becoming a major pest in North China. The long distance migration of DBM not only induces its sudden outbreak over extensive areas, but also leads to its insecticide resistance by the spread of resistant genes in large area. To elucidate the long distance migration of DBM is of significance for early warning and decision-making in integrated pest managements. So far, the migration of DBM has not yet been systematically investigated in China. Here, we reviewed the literatures about the long distance migration of DBM at home and abroad, and summarized the related evidence: 1) DBM cannot overwinter in cold regions such as northern Japan, western Canada, and northeast China, where the DBM outbreak is presumed from elsewhere by long distance migration, 2) DBM adults are captured from seas, mountain tops, sea islands, and sky, etc., and the collection of large quantity of DBM presents the powerful direct evidence of DBM long distance migration, 3) the sudden increase of DBM in fields is consistent with the meteorological conditions such as the presence of nocturnal temperature inversion layer and the front passage, suggesting that these meteorological conditions supply suitable backgrounds for the insect migration, 4) the target insect characters identified by vertical insect looking radar is consistent with the measured DBM characters in laboratory and the trapping data from fields, confirming the long distance migration of DBM, 5) the biological characteristics and genetic variations of different DBM populations have no correlations with geographic distance, suggesting the frequent gene flows among the populations in different positions, and 6) the flight test of DBM indicates its long distance flight capacity, and the decreasing fitness of host plants is probably one of the trigger factors for the migration of DBM. Some future research directions are prospected: the construction of track model for DBM long distance migration to clarify the DBM long distance migration pathways in China; the further understanding on the physiological, biochemical, and ecological bases of DBM long distance migration; the strategies for the population insecticide resistance management based on the long distance migration of DBM.

[Identification of endophytic actinomycete St24 tomato plants from and its application in biocontrol of gray mold disease].

An endophytic actinomycete strain St24 with acaricidal activity was isolated from the root-stem junction of tomato plants, with the taxonomic position of the strain and its control effect against gray mold disease investigated. The St24 was identified as Streptomyces vinaceus, and its broth's petroleum ether extracts could inhibit a variety of pathogens. The inhibitory effect of the extracts on Botrytis cinerea was the strongest, with the EC50 of inhibiting B. cinerea mycelia growth being 11.78 mg x L(-1). After treated with the extracts, the amount of the mycelia decreased, and the mycelia became crenate or broken, with the protoplast extravasated and the tuberculate malformation appeared. The B. cinerea culture treated with the extracts showed the maximum absorption at 260 nm, which was absent in the control, indicating that the St24 extracts increased the pathogens cell membrane permeability. Pot experiment showed that the extracts could protect tomato plants against B. cinerea. Foliar spraying the extracts at 100 mg x L(-1) had the best protective effect, with the controlling effect reached 94.3% after 24 h and 85.4% after 120 h.

[Bioactivity of the metabolites from endophytic actinomycete Fq24 against Tetranychus cinnabarinus].

An endophytic actinomycete strain Fq24 was isolated from healthy tomato plants. The acaricidal substances in the metabolites from Fq24 were collected and identified by the methods of extraction, column chromatography, and gas chromatography-mass spectrometry (GC-MS), and their bioactivities against Tetranychus cinnabarinus were measured with slide-dip and leaf-residue methods. Among the extracts, petroleum ether extract had high bioactivity in contact toxicity and oviposition deterrent against T. cinnabarinus. Its lethal concentration of 50% (LC50) was 52.57 mg x L(-1), and its oviposition deterrent concentration of 50% (ODC50) was 43.18 mg x L(-1). The identification with GC-MS showed that the main chemical component of fraction S11 was methyl hexadecanoate, whose molecular formula was C17H34O2, being one of the substances with acaricidal activity in the metabolites from Fq24. The 24 h corrected mortality rate of female mite at 5 mg x mL(-1) of methyl hexadecanoate was 78.3%, and the oviposition deterrent rate was 81.6%.

[Effects of sub-lethal dosages abamectin on food intake and digestive enzyme activities of silkworm Bombyx mori L].

Mulberry leaves treated with sub-lethal dosages (LC5, LC10 and LC20) abameetin were fed to the 5th instar larvae of silkworm (Bombyx mori L.), and the food intake and digestive enzyme activities of the larvae were studied by using gravimetric method and measuring enzyme activities. The results showed that sub-lethal dosages abameetin significantly inhibited the growth and food intake of the larvae, with their body mass and its increase rate as well as their relative growth rate being significantly lower than the control, and accompanied with the decreases of food intake, its relative consumption rate, and feces amount. The efficiency of the conversion of ingested food (ECI) and that of the conversion of digested food (EDI) also reduced, but the approximate digestibility (AD) increased significantly. The amylase and sucrase activities in the midgut of the larvae treated with abameetin decreased significantly for a longer time at the beginning, and then recovered to the same as or a higher level than the control, whereas the trehalase activity decreased significantly for a shorter time at the beginning, then increased significantly, and finally recovered to the normal. It was suggested that sub-lethal dosages abameetin had definite toxicity to the silkworm, and the toxic effect was increased with increasing dosage, which could result in the turbulence of silkworm's digestive system, and further, affect its food intake and its growth and development.