Secretory laccase 1 in Bemisia tabaci MED is involved in whitefly-plant interaction.

The whitefly Bemisia tabaci is a phloem-feeding pest that lives predominantly on herbaceous species and causes serious damage to hosts. Whitefly saliva is thought to contain proteins that modulate plant defences and facilitate feeding. A predicted secreted protein, laccase 1 (LAC1), was found in the salivary gland transcriptome of B. tabaci and might be existed in the watery saliva of B. tabaci. As LAC1 has a potential role in detoxification of secondary plant compounds in insects, we speculated that it may participate in the insect's response to plant defences. Here, we cloned the complete cDNA of LAC1 and found that (1) LAC1 was highly expressed in the salivary gland (SG) and midgut; (2) LAC1 transcript level in head (containing SG) was 2.1 times higher in plant-fed than in diet-fed whiteflies and 1.6 times higher in the head and 23.8 times higher in the midgut of whiteflies that fed on jasmonic acid (JA)-sprayed plants than on control plants; and (3) silencing LAC1 decreased the survival rate of plant-fed whiteflies but had a marginal effect on whiteflies raised on an artificial diet. These results indicate that LAC1 enables whiteflies to overcome the chemical defences of host plants and might act as an effector in saliva.

Effect of temperature on the occurrence and distribution of colorado potato beetle (Coleoptera: Chrysomelidae) in China.

Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most destructive pest of potato in many countries of the world. It first invaded China from Kazakhstan in 1990s and now is a major pest of potato in many areas of Xinjiang Uygur Autonomous Region (Xinjiang). The objective of this study was to determine the effect of temperature on the spread of Colorado potato beetle in China after its invasion. Cold temperature in winter (December) and high temperature in summer (July) were analyzed in accordance with the absence and presence of Colorado potato beetle in Xinjiang. The boundary between the absence and presence of Colorado potato beetle in Xinjiang nearly coincided with the -8°C isotherm of monthly mean minimum temperature in winter. The stress of the low temperature in winter for Colorado potato beetle basically disappeared in the southeastern Hexi Corridor in Gansu Province of China, suggesting that the Hexi Corridor is the best channel to prevent any long-distance invasions of Colorado potato beetle into the Central Plains region. However, in Turpan City in northeastern Xinjiang, the extremely hot weather in the summer prevents the local colonization of Colorado potato beetle. Furthermore, according to our monitoring, high temperature in summer also limited Colorado potato beetle to diffuse eastward through Turpan. Results of this study suggest that it is essential to strengthen inspection and quarantine measures to prevent any artificial transmissions of Colorado potato beetle spreading eastward and thus to ensure the sustainable production of potato and other Solanaceae crops in northwest regions of China.

Impact of wheat-mung bean intercropping on English grain aphid (Hemiptera: Aphididae) populations and its natural enemy.

The effects of intercropping wheat, Triticum aestivum L., with mung bean, Vigna radiate L., on the populations of English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), and its natural enemies were evaluated by field and laboratory experiments. The population densities of aphids and their natural enemies were evaluated in the intercropped field against different row ratio combinations of wheat-mung bean. Results showed that wheat-mung bean intercropping caused a drop in aphid densities, and the ratio 12 wheat: 4 mung bean brought about the largest drop (> 8%). In addition, the population densities of coccinellids (ladybirds) and parasitoids and the species diversity of all the natural enemies of aphid were higher in the intercropped field than in the field planted only with wheat. However, intercropping did not influence the community indices (evenness and index of dominance concentration) of the natural enemies. Y-tube olfactometer bioassays were carried out in the laboratory to test whether odor blends of host and nonhost plants affect the host selection of S. avenae. Bioassays indicated that both apterous and alate aphids significantly preferred host plant odor over odor blends of host and intercropped species. Hence, the olfactory-based host location of aphids in the field might be affected by intercropping. The intercropping experiment clearly showed that increased crop species diversity suppresses aphid population growth and preserves the population of natural enemies of aphids. Our results also provide support for the "resource concentration hypothesis" and the "enemies hypothesis".

Discovery of English grain aphid (Hemiptera: Aphididae) biotypes in China.

The English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), is an important pest insect of wheat, Triticum aestivum (L.), in China. Grain aphid biotypes are necessary to breed aphid-resistant wheat varieties; however, none have currently been identified. Here, we describe a method to identify grain aphid biotypes and survey the aphid biotype variation in the wheat growth area of China. Clones of S. avenae were collected from 11 locations in China and used to establish culture populations. These populations were then used to assess the resistance of 12 wheat varieties. Based on resistance responses, seven differential hosts were selected to identify the biotype of S. avenae: Amigo, 'Fengchan No. 3', Zhong 4 wumang, JP1, L1, 885479-2, and 'Xiaobaidongmai'. S. avenae was ultimately classified into five biotypes: EGA I, EGA II, EGA III, EGA IV, and EGA V. These methods provide a mechanism to detect the variation and evolution of grain aphids in different wheat-growing locations and also allow for selection of appropriate aphid-resistant germplasm for wheat breeding of commercial wheat cultivars.

Activation of defense mechanism in wheat by polyphenol oxidase from aphid saliva.

The saliva of two cereal aphids, Sitobion avenae and Schizaphis graminum in third-instar nymphs, was collected after 24 h of feeding by 30 aphids, separately, on artificial diet sachets, and the salivary enzymes were determined. The result showed that polyphenol oxidase (PPO) existed in the saliva of both aphid species, and the enzymatic activities were 6.2 x 10(-3) U/g for S. avenae and 2.37 x 10(-1) U/g for S. graminum, revealing a 38-fold higher activity in the saliva of S. graminum than in the saliva of S. avenae. It was speculated that the higher PPO activity in S. graminum saliva was a contributing factor to the light yellow spot left on the feeding site of the wheat leaf by S. graminum; no such spot was left by S. avenae. After treatment of a wheat seedling with the saliva of S. avenae and S. graminum and PPO at the concentration of aphid saliva, transcript profiling data showed that aphid saliva and PPO significantly induced expression of the genes aos and fps. Because genes aos and fps encode the key enzymes in the defense signal pathways jasmonic acid and terpene signal pathways, respectively, it was deduced that PPO from aphid saliva, as the main elicitor, triggers an appropriate defense response in wheat through jasmonic acid and terpene signal pathways.

Population forecasting model of Nilaparvata lugens and Sogatella furcifera (Homoptera: Delphacidae) based on Markov chain theory.

Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth) are the two most important long-distance migratory insect pests that cause great yield losses to rice in China. Accurate long-term population forecast is needed to implement effective management strategies for these two rice pests. In this paper, a transition probability matrix of 5-yr steps of Markov chain theory was constructed based on 31-yr light-trapping data of the two pests from 1977 to 2007 in Jiangkou County, Guizhou, China. The weight of each step for the transition probability matrix was calculated according to its prediction accuracy. Insect occurrence levels in the sixth year were predicted based on the occurrences of the previous 5 yr. Nonparametric Wilcoxon paired sample tests showed that there were no significant differences between the actual and predicted occurrences for both N. lugens and S. furcifera. In addition, the models accurately forecasted field occurrence in 2008 in Jinangkou County for both species. The results showed that the Markov models developed in this study offer an effective method for long-term population forecasting of N. lugens and S. furcifera and thus provide plant protection agencies and organizations with valuable information in implementing appropriate management strategies for these two devastating rice pests in Jiangkou and neighboring areas.

Autumn migration of Mythimna separata (Lepidoptera: Noctuidae) over the Bohai Sea in northern China.

The autumn migration of Mythimna separata (Walker) (Lepidoptera: Noctuidae) across the Bohai Sea was observed with a scanning entomological radar and a searchlight trap at Beihuang, an island located in the center of the Bohai Gulf of northern China, in 2003-2006. During the autumn migration, M. separata flew at the altitudes of 50-500 m, with a displacement speed of 4-12 m/s, toward the southwest. Variations of area density of the radar targets and of catches in the searchlight trap through the night indicated that the flight duration of M. separata was approximately 10 h. Based on these observations, M. separata that originated in northeastern China (i.e., Liaoning, Jilin, and Heilongjiang provinces and part of the Inner Mongolia autonomous region) could immigrate into eastcentral China and subsequently to southern China (i.e., Fujian, Guangdong, and Guangxi provinces) within a week for overwintering.

[Effects of wheat leaf surface waxes on the feeding of two wheat aphid species].

By using GC-MS and bioassay techniques, this paper studied the effects of different wheat varieties (cultivars) leaf surface waxes on the feeding of wheat aphids Sitobion avenae and Rhopalosiphum padi. The results showed that the leaf surface waxes of wheat varieties (cultivars) SN80, SN18 and Zimail2 could stimulate the feeding of test aphids, while SN87 could not. GC-MS analysis showed that the chemical composition of leaf surface waxes differed with wheat varieties (cultivars). The main components were long chain alkanes, and others were 7-tetradecene, 8-pentadecanone, ethyl citrate, tetradecanoic acid ethyl ester, and hexadecanoic acid ethyl ester. The bioassay found that alkanes (> C17), 7-tetradecene and 8-pentadecanone could act as strong stimulants to the feeding of the aphids, while ethyl citrate, tetradecanoic acid ethyl ester and hexadecanoic acid ethyl ester didn't have stimulation to S. avenae, neither tetradecanoic acid ethyl ester and hexadecanoic acid ethyl ester to R. padi.

Northward migration of Helicoverpa armigera (Lepidoptera: Noctuidae) and other moths in early summer observed with radar in northern China.

The northward migration of Helicoverpa armigera (Hübner) and other moths in early summer was observed with radar in 2001 and 2002 at Langfang, Hebei province, China. Migratory flights typically occurred at heights up to 1.2 km above ground level (AGL), and high density layer concentrations frequently formed at 200-300 m AGL. Adult moths of local populations took off at dusk and ceased flight approximately 0.5 h before sunrise with area density peaking approximately 35 min after dusk. A strong dumb-bell pattern of echoes on the plan position indicator screen, indicating collective orientation of the targets, was evident in 2001, when targets were typically moving toward the northeast and when layering was associated with a temperature inversion and maximum wind speed. By contrast, there was no notable dumb-bell pattern in 2002, when targets were moving toward the northwest. However, orientations calculated from target and wind velocities showed that downwind common orientation also was occurring in 2002 and that the direction varied with the wind direction. The probable sources of the H. armigera observed at Langfang were deduced to be Henan province in 2001 and Shandong province in 2002, and the destination regions were Liaoning and Inner Mongolia.