Susceptibility of Helicoverpa armigera from different host plants in northern China to Bacillus thuringiensis toxin Cry1Ac

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a serious pest of cotton and many other crops in northern China. To evaluate the contribution of alternative hosts as an effective refuge for transgenic cotton expressing the Bacillus thuringiensis (Bt) Cry1Ac toxin, the susceptibility to this toxin was measured in progeny derived from field-collected H. armigera larvae and pupae from different hosts in the Xiajin’s region of the Shandong Province in northern China. During 2008-2010, progeny from a total of 258,56,184 and 160 single-pair crosses derived from wheat (first-generation), Bt cotton (second-generation), Bt cotton (third-generation), and corn (third-generation) were screened on Cry1Ac diets, respectively. Based on relative average development rates (RADR) of H. armigera larvae in these F₁ tests, the second and third-generation moths emerging from Bt cotton fields were more tolerant to the Bt toxin than the first and third-generation moths emerging from wheat and corn each year. These results suggest that there is significant variation in susceptibility to Bt toxins among H. armigera populations derived from different host crops. Alternate crops, such as corn, that maintain Bt susceptible populations of H. armigera could be used as refugia to minimize the evolution of resistance to Bt cotton.     

Monitoring resistance of Helicoverpa armigera to different insecticides used in cotton in Spain

Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD₅₀'s were estimated by probit analysis and resistance factors (RF) were calculated at the LD₅₀ level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discussed.     

Frequency of Bt resistance alleles in Helicoverpa armigera in 2007-2009 in the Henan cotton growing region of China

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key insect pest of cotton in the Henan cotton growing region of China. In this region, cotton is grown on small acreages in rich agricultural landscapes, contrary to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt plants) may be sufficient to prevent H. armigera resistance development to Bt toxins. In order to gain a timely understanding of the evolution of resistance of H. armigera to Bt toxin after continuous cultivation of Bt cotton for c. 10 years, we assessed the frequency of alleles conferring resistance to Cry1Ac toxin in field populations of H. armigera sampled from Xinxiang County in Henan province during 2007-2009. Screening F₁ and F₂ generations from isofemale lines, derived from female moths trapped in the field, were used with a discriminating dose of Cry1Ac diet to estimate the frequency of resistance alleles. Totals of 625, 516 and 488 isofemale lines were screened for the F₁ generation in 2007, 2008 and 2009, respectively. Resistance gene frequency in Xinxiang fluctuated between 0.0000 and 0.0005, and it did not increase significantly from 2007 to 2009. Based on the relative average development rates (RADR) of H. armigera larvae in F₁ tests, no substantial increase in Cry1Ac tolerance was found in the Xinxiang region over the 3-yr period.     

Susceptibility of Cry1Ab-susceptible and -resistant sugarcane borer to transgenic corn plants containing single or pyramided Bacillus thuringiensis genes

Multiple independent trials were conducted to evaluate the performance of Cry1Ab-susceptible (Cry1Ab-SS), -heterozygous (Cry1Ab-RS), and -resistant (Cry1Ab-RR) genotypes of the sugarcane borer, Diatraea saccharalis (F.), on eight commercial hybrids and six experimental corn lines. The commercial varieties included two non-Bt and six Bt corn hybrids that expressed a single Bt protein (either Cry1Ab or Cry1F) targeting above-ground lepidopteran pests. The six experimental lines consisted of two non-Bt and four Bt corn lines, two expressing just the Cry1Ab protein and two containing the pyramided-genes Cry1A.105 and Cry2Ab2 (event MON 89034). Larval mortality on non-Bt corn leaf tissue ranged from 6 to 45% after 12 d across insect genotypes. The 12 d mortality of Cry1Ab-SS on leaf tissue of commercial Cry1Ab or Cry1F corn was 96-100%, whereas it was 80-96% for Cry1Ab-RS and 68-78% for Cry1Ab-RR. On intact plants, 39-64% of larvae survived on non-Bt corn plants after 21-25 d. Larval survivorship on intact plants of commercial Cry1Ab or Cry1F corn was 0-8.1% for Cry1Ab-SS, 1.3-34% for Cry1Ab-RS, and 19-51% for Cry1Ab-RR. Larvae of Cry1Ab-RR and -RS also caused significant plant injury to most of the commercial Bt corn hybrids, especially to the Cry1Ab corn. Cry1Ab resistance in D. saccharalis was incompletely dominant on commercial Bt corn hybrids. However, both experimental lines with pyramided genes of Cry1A.105 and Cry2Ab2 provided complete control of all three insect genotypes in both leaf tissue and intact plant tests. Results of this study suggest that MON 89034 should offer a means for Bt resistance management in D. saccharalis.     

Comparative susceptibility of Ostrinia furnacalis, Ostrinia nubilalis and Diatraea saccharalis (Lepidoptera: Crambidae) to Bacillus thuringiensis Cry1 toxins

Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) are highly effective against the European corn borer, Ostrinia nubilalis (Hübner), and the closely related Asian corn borer, Ostrinia furnacalis (Guenée). Since the registration of Bt corn hybrids in the U.S. in 1996, there has been a great deal of information generated on O. nubilalis. However, relatively little information exists for O. furnacalis. To help determine whether the information generated for O. nubilalis can be leveraged for decisions regarding the use of transgenic Bt corn against O. furnacalis, experiments were designed to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species. Test insects included laboratory-reared O. furnacalis originating from Malaysia, a Bt-susceptible laboratory colony of O. nubilalis maintained at the University of Nebraska-Lincoln (UNL) and an out-group consisting of the sugarcane borer, Diatraea saccharalis (F.), from Louisiana which represents a different genus from the same family. O. furnacalis and O. nubilalis exhibited a similar pattern of susceptibility to all the Cry1 toxins and were highly susceptible to the range of Bt toxins tested including Cry1Aa, Cry1Ab, Cry1Ac and Cry1F. Both of the Ostrinia species were more tolerant to Cry1Ba compared with D. saccharalis, although sensitivity of O. furnacalis was intermediate and did not differ significantly from that of O. nubilalis and D. saccharalis. D. saccharalis was also susceptible to the range of toxins tested but unlike the two Ostrinia species, was more tolerant to Cry1F and more susceptible to Cry1Ba. These results indicate that both of the Ostrinia corn borer species are similar in sensitivity to the Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F toxins, thus suggesting shared toxin receptors and mechanisms of toxicity for the two species.     

Control of chickpea blight disease caused by Didymella rabiei by mixing resistance inducer and contact fungicide

Elicitors of systemic acquired resistance are well known to reduce severity of several plant pathogenic diseases caused by fungi, bacteria and viruses. Their field applications for management of plant diseases are, however, limited because of yield penalties. Our studies on affect of Benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of systemic acquired resistance, on chickpea blight caused by a fungal pathogen Didymella rabiei showed that multiple foliar applications of the chemical were effective in management of the disease under economic threshold levels. Multiple applications, however, affected chickpea grain yield adversely. The BTH induced yield penalties could be prevented by foliar spray schedule comprised of BTH and a contact fungicide mancozeb. One spray of BTH (50 ppm) followed by another of mancozeb (0.2%) was less effective (8.3% severity) than three sprays of BTH (4.2% severity) in blight control, however, this treatment enhanced grain yield significantly (1.241 t ha⁻¹) over three sprays of BTH (0.922 t ha⁻¹).     

Mosquitocidal activity of two Bacillus bacterial endotoxins combined with plant oils and conventional insecticides

The full whole culture (FWC), containing parasporal protein toxins of Bacillus thuringiensis israelinsis (Bti) and Bacillus sphaericus 2362 (Bs), either singly or in combination with plant oils and commercial insecticides, was tested against larval and adult stages of Culex pipiens mosquitoes under controlled laboratory conditions. In terms of LC₅₀ values recorded after 24, 48, 72 and 96 h, the bacterial toxins showed high potency towards both larvae and adults of mosquitoes in a dose-dependent manner. Generally, the Bti toxin seemed to be more potent than the Bs toxin. For example, the Bti toxin showed a 24 h LC₅₀ of 8.2 ppm against mosquito larvae compared to 13.6 ppm for the Bs toxin. In the adult bioassay, the obtained 24 h LC₅₀ values were 0.064 and 0.085 mg/cm², respectively for the two bacterial toxins. The bacterial toxins mixed with plant oils or insecticides at equitoxic doses (e.g., LC₂₅ values) mostly showed potentiation effects, either against larvae or adults of the tested insect. Among a total of 14 paired mixtures, only the joint action estimated for the mixture of malathion + Bti or Bs was accounted as additively. Combining Bti or Bs endotoxins at LC₀ with different plant oils and insecticides at LC₅₀ concentration levels each, has resulted in considerable synergism against either larvae or adults. In the case of larval bioassays, the maximum synergistic factor (SF) obtained (ca. 2.0) was entitled to the mixture of Bti + spinosad. In the adult bioassays, the mixtures containing Curcuma longa or Melia azedarach oil extracts with Bti or Bs toxins achieved a SF accounted to 2.0. The results of the present study may be considered as an additional contribution to the area of joint toxicity of biocidal agents combining bacterial toxins, plant oils and traditional insecticides. The reached findings may encourage future research to elucidate its performance under practical field conditions.     

Combining reflective mulch and host plant resistance for sweetpotato whitefly (Hemiptera: Aleyrodidae) management in watermelon

A study was conducted to evaluate the use of reflective mulch and host plant resistance for the management of the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in watermelon [Citrullus lanatus var. lanatus (Thunberg) Matsum & Nakai]. Whitefly abundance data were collected under both greenhouse (caged and uncaged) and field conditions. Consistently, a reflective mulch (also called silver or metallic) treatment resulted in a lower incidence of adult whiteflies as compared with a standard black mulch treatment. Moreover, two whitefly resistant Citrullus colocynthis (L.) Schrad genotypes, which are wild relatives of cultivated watermelon, reduced whitefly populations as compared with standard watermelon. There was generally no interaction between the mulch and genotype variables. No effect of mulch color was observed on sticky card capture of Delphastus catalinae (Horn), a whitefly predator, or on capture of an Eretmocerus sp. whitefly parasitoid in caged trials, which suggests no adverse effect on these natural enemies when using reflective mulch. Overall whitefly populations were relatively low during four seasons of field trials (2006–2009). Results from this study suggest that a combination of using reflective mulch and host plant resistance can additively suppress whitefly infestations, which have particular importance in the fast-growing organic vegetable production industry.     

Manihot flabellifolia Pohl,wild source of resistance to the whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae)

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P < 0.05). Development time was not significantly different, ranging from 35–40 days on accessions and MEcu72 and 33.5 days on CMC-40 (P < 0.05). In contrast, the population growth rate (r_m) was significantly lower on the M. flabellifolia accessions, with Fla 61 standing out with a growth rate 98 and 99% less than that obtained on MEcu72 and CMC-40, respectively. Once the resistant levels have been identified to A. socialis on the M. flabellifolia accessions, interspecific crosses of M. esculenta subsp. M. flabellifolia and backcross programs could be developed to incorporate the desirable characteristics from the wild relatives into elite progenitors of M. esculenta.     

Comparative overwintering host range of three Adelphocoris species (Hemiptera: Miridae) in northern China

In northern China, Adelphocoris suturalis, Adelphocoris lineolatus and Adelphocoris fasciaticollis (Hemiptera: Miridae) are common pests of cotton and several other crops. These species have vastly diverse geographic distribution, seasonal dynamics and abundance, the underlying causal factors of which are poorly understood. In this study, the importance of a broad range of plant species as overwintering hosts for each Adelphocoris sp. was compared. Nymphal emergence from a total of 126 plant species was monitored at two distinct locations. The eggs of A. suturalis successfully eclosed from un-plowed cotton field soil and 115 plant species, primarily pastures, weeds and agricultural crops. The eggs of A. lineolatus successfully eclosed from 40 plant species, mainly pastures and weeds. Finally, A. fasciaticollis overwintered on 35 plant species, primarily tree species, weeds and agricultural crops. In conclusion, the most common and widely distributed mirid species, A. suturalis, overwintered on a comparatively broader range of plants compared to the other two species. These observations help to understand the differences in geographical distribution and abundance of the three Adelphocoris species, and constitute the basis for forecasting and pest management protocols for Adelphocoris spp. in China.     

Evaluation of actinomycete isolates obtained from herbal vermicompost for the biological control of Fusarium wilt of chickpea

A total of 137 actinomycetes cultures, isolated from 25 different herbal vermicomposts, were characterized for their antagonistic potential against Fusarium oxysporum f. sp. ciceri (FOC) by dual-culture assay. Of the isolates, five most promising FOC antagonistic isolates (CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90) were characterized for the production of siderophore, cellulase, protease, hydrocyanic acid (HCN), indole acetic acid (IAA) and antagonistic potential against Rhizoctonia bataticola, which causes dry root rot in chickpea (three strains viz. RB-6, RB-24 and RB-115) and sorghum (one strain). All of the five FOC antagonistic isolates produced siderophore and HCN, four of them (except KAI-90) produced IAA, KAI-32 and KAI-90 produced cellulase and CAI-24 and CAI-127 produced protease. In the dual-culture assay, three of the isolates, CAI-24, KAI-32 and KAI-90, also inhibited all three strains of R. bataticola in chickpea, while two of them (KAI-32 and KAI-90) inhibited the tested strain in sorghum. When the FOC antagonistic isolates were evaluated further for their antagonistic potential in the greenhouse and wilt-sick field conditions on chickpea, 45-76% and 4-19% reduction of disease incidence were observed, respectively compared to the control. The sequences of 16S rDNA gene of the isolates CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90 were matched with Streptomyces tsusimaensis, Streptomyces caviscabies, Streptomyces setonii, Streptomyces africanus and an identified species of Streptomyces, respectively using the BLAST searching. This study indicated that the selected actinomycete isolates have the potential for biological control of Fusarium wilt disease in chickpea.     

Quantification of Bacillus thuringiensis Cry1Ab protein in tissues of YieldGard (MON810) corn hybrids tested at multiple field locations in India

Transgenically expressed Bacillus thuringiensis insecticidal-protein Cry1Ab was quantified in target tissues of insect feeding of several YieldGard^® corn hybrids. The Cry1Ab protein is intended to protect corn plants from two economically important stem borers, Chilo partellus and Sesamia inferens. A total of seven YieldGard hybrids, all with MON810 event, were field-tested in a total of fourteen locations during the dry season (October–March) of 2005/2006 and wet season (May–October) of 2006. S. inferens and C. partellus oviposit on leaves of young corn plants, 15–60 days after emergence (DAE). The neonates initially feed by scraping the leaf lamina before migrating to bore into the stem. Thus high concentrations of Cry1Ab in whorl leaf and stem tissues would ensure effective control of the borers. The mean tissue Cry1Ab concentrations during the oviposition window of the borers (15–60 DAE), ranged from 50.05 to 21.01 ppm in whorl leaf, and between 9.26 and 3.47 ppm in stem tissue during the same period in the dry season of 2005/06. Similarly, Cry1Ab concentrations in whorl leaf and stem between 15 and 60 DAE during the wet season of 2006 ranged between 19.30 to 11.08 and 14.28 to 4.69 ppm, respectively. The baseline-sensitivity data of these insects to Cry1Ab in laboratory assays was determined. The concentrations of Cry1Ab in the target tissues as studied in seven YieldGard hybrids tested suggest effective management of the two borers. This paper also provides a summary of the expression of the Cry1Ab gene in various genetic backgrounds.     

Damage and survivorship of fall armyworm (Lepidoptera: Noctuidae) on transgenic field corn expressing Bacillus thuringiensis Cry proteins

Field corn, Zea mays L., plants expressing Cry1Ab and Cry1F insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on considerable acreage across the Southern region of the United States. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an economically important pest during the mid-to-late season on non-Bt and some commercial Bt corn hybrids. The objective of this study was to quantify foliar injury and survivorship of fall armyworm on transgenic corn lines expressing Cry1Ab or Cry1F Bt proteins. Corn lines/hybrids expressing Cry1Ab, Cry1F, and a conventional non-Bt cultivar were evaluated against artificial infestations of fall armyworm in field trials. Larvae (second instars) of fall armyworm were placed on corn plants (V8-V10 stages). Leaf injury ratings were recorded 14 d after infestation. Hybrids expressing Cry1F had significantly lower feeding injury ratings than non-Bt corn plants. Development and survivorship of fall armyworm on Bt corn lines/hybrids were also evaluated in no-choice laboratory assays by offering freshly harvested corn leaf tissue to third instars. Transgenic corn hybrids expressing Cry1Ab or Cry1F significantly reduced growth, development, and survivorship of fall armyworm compared to those offered non-Bt corn tissue. However, 25-76% of third instars offered Bt corn leaf tissues successfully pupated and emerged as adults. These results suggest Cry1Ab has limited effects on fall armyworm; whereas Cry1F demonstrated significant reductions in foliar injury and lower survivorship compared to that on non-Bt corn tissues. Although fall armyworm is not considered a primary target for insect resistance management by the U.S. Environmental Protection Agency, these levels of survivorship could impact selection pressures across the farmscape, especially when considering that transgenic Bt cotton cultivars express similar Cry (Cry1Ac or Cry1F) proteins.     

Effects of host plant on the development, survivorship and reproduction of Dysmicoccus neobrevipes Beardsley (Hemiptera: Pseudoccocidae)

The effects of four host plants (Agave sisalana, Ag. americana var. marginata, Ananas comosus Baili and An. comosus Smooth Cayenne) on the biology of the mealybug Dysmicoccus neobrevipes Beardsley were studied in the laboratory at 26 ± 1 °C, 75-90% RH and 14:10 (L:D) photoperiod. The development, survivorship, longevity, reproduction and life table parameters of D. neobrevipes differed among the host plants. The shortest developmental period (from the first instar nymph to adult) was recorded on An. comosus Smooth Cayenne (22.4 days for females and 21.3 days for males), whereas the longest was recorded on An. comosus Baili (25.6 days for females and 24.7 days for males). The highest survivorship was found on An. comosus Baili (98% for both females and males) and the lowest was on Ag. americana var. marginata (39.6% for females and 50% for males). Meanwhile the sex ratio and fecundity were highest and the pre-lay period was shortest on Ag. sisalana. The longest longevity of females was 62.5 days on An. comosus Baili, whereas the other host plants did not differ significantly with grand mean longevities of 51.0 days for females, while the longest and shortest longevities of males were 4.6 days and 2.3 days on Ag. americana var. marginata and Ag. sisalana, respectively. Values for net reproductive rate, intrinsic rate of increase and finite rate of increase were highest on Ag. sisalana, whereas the mean generation time was shortest on An. comosus Smooth Cayenne. The results indicated that Ag. sisalana is the most suitable host for D. neobrevipes among the four tested plants. When reared on Ag. sisalana, D. neobrevipes had a short developmental period (females 22.7 days and males 23.8 days), high reproduction (418 nymphs/female) and a high intrinsic rate of increase (0.106). Results of this study indicated that host plant can largely influence the population dynamics of D. neobrevipes, and our findings are useful in understanding the roles of host plants in integrated management of this pest, including exploitation of these host plants in push-pull control.     

Effect of Trichoderma asperellum and arbuscular mycorrhizal fungi on cacao growth and resistance against black pod disease

Arbuscular mycorrhizal fungi (AMF) and members of the genus Trichoderma have emerged as promising groups of microbial inoculants that can induce plant growth and resistance to disease. This study aimed at investigating the potential of AMF and a strain (PR11) of Trichoderma asperellum to promote cacao growth and induce resistance against Phytophthora megakarya. Cacao seedlings were either non-inoculated, or inoculated with the saprophytic fungus T. asperellum and/or a mixture of two different mycorrhizal fungi, Gigaspora margarita and Acaulospora tuberculata. Eighteen weeks after planting, a series of morphological as well as biochemical changes, which are considered to be part of the plant defense response, were measured after a challenge inoculation of the leaves with zoospores of P. megakarya. Inoculation with AMF and T. asperellum alone was essential for the promotion of plant growth. Significant increase in plant height, root and shoot fresh weights, as well as phosphorous uptake was recorded in comparison to non-inoculated control plants. However, dual inoculation of cacao seedlings with T. asperellum and AMF did not always positively benefit the plants. Leaf inoculation showed variation among the treatments, with the lowest disease index (highest level of resistance) recorded in plants inoculated with either AMF or T. asperellum only. This came along with a high synthesis of amino acids and phenolic compounds in both healthy and infected leaves, suggesting that these metabolites are implicated in disease resistance.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

Overwintering hosts of Apolygus lucorum (Hemiptera: Miridae) in northern China

During the past decade, Apolygus lucorum Meyer-Dür (Heteroptera: Miridae) has become a key pest of cotton in northern China, due to widespread planting of Bt cotton and an associated drop in the use of broad-spectrum insecticides. Because of a lack of management alternatives, A. lucorum outbreaks are presently exclusively controlled with insecticides. In this study, we determined A. lucorum overwintering locations and host plants during the 2006–2009 winter seasons. A total of 126 plant species were screened and nymphal emergence of A. lucorum was monitored over time. Eggs of A. lucorum successfully overwintered in cotton field soils and on 86 plant species, including weeds, fruit trees, pastures and agricultural crops. More specifically, Vitis vinifera L., Ricinus communis L., Momordica charantia L., Artemisia argyi Levl. et Vant., Artemisia annua L., Artemisia lavandulaefolia DC., Isatis indigotica Fort., Artemisia scoparia Waldst. et Kit., Vigna radiate (L.) Wilczek, Ziziphus jujuba Mill., Vigna angularis (Willd.) Ohwi et, Ocimum basilicum L., Onobrychi viciifolia Scop., Pyrus bretschneideri Rehd., Malus domestica Borkh. and Brassica juncea (L.) Czern. et Coss proved optimal overwintering hosts of A. lucorum. Based upon plant species occurrence and distribution in Chinese cotton-growing regions, several weeds and fruit trees, such as V. vinifera, Z. jujuba, P. bretschneideri and M. domestica can be termed key overwintering hosts of A. lucorum. Our findings can form the basis for future formulation of targeted management actions to lower A. lucorum overwintering populations in cotton-growing landscapes of northern China.     

Effects of pigment glands and gossypol on growth,development and insecticide-resistance of cotton bollworm (Heliothis armigera (Hübner))

Cotton bollworm (Heliothis armigera) is a major pest of cotton and other crops. It is important to understand the mechanisms of insecticide tolerance of cotton bollworm on cotton cultivars with host plant resistance to this insect pest. The objectives of this study were to investigate the effects of cotton pigment glands and their gossypol on the growth, development and insecticide tolerance of cotton bollworm. Three pairs of cotton isogenic lines with glanded versus glandless leaves, as well as artificial diets with 5 levels of gossypol, were used to raise cotton bollworm larvae for five generations. The growth, development and insecticide tolerance of larvae were studied. The results indicated that the cotton pigment glands and higher levels of gossypol resulted in a significant decrease in larval weights and moth eclosion rates and delayed the development of larvae and pupae. Larvae that fed on glanded cotton leaves were significantly more tolerant to two insecticides, cyhalothin and monocrotophos, than those fed on glandless cotton leaves. LD₅₀ values were only increased where they were in amount per unit body weight, and not where were calculated in amount per individual. Also the insecticide tolerance of cotton bollworm larvae increased as the gossypol content was raised from 0 to 0.225% in artificial diets. Meanwhile, the activities of two detoxifying enzymes, carboxylesterase and glutathione s-transferase, were significantly higher in the larvae fed on glanded cotton leaves than those fed on glandless cotton leaves. The activities of two enzymes also increased greatly with the increase of gossypol content from 0 to 0.225% in artificial diets. Across 5 generations of feeding and investigation, the significant inhibition effect on larval growth and larval tolerance to two pesticides were found to be only associated with the feeding by current generation, but were not related to previous diets. The activities of two detoxifying enzymes in larvae were also not enhanced significantly when they were fed continuously on glanded cotton leaves or artificial diet with high gossypol. These results indicated that pigment glands and higher levels of gossypol not only inhibited the growth of cotton bollworm larvae but also enhanced their insecticide tolerance. However, the inhibition effect and enhanced insecticide tolerance were inducible but could not be accumulated or inherited. These results will help us better understand the interaction and co-evolution of insecticide tolerance in larvae of cotton bollworm and host chemical components, and also has provided useful information on cotton bollworm management in cotton production, especially in glandless cotton.     

Plant protection potential and ultrastructure of Bacillus subtilis strain 3A25

Strain 3A25 was isolated from Indian soil during a screening study for new plant protecting candidates. The present study further characterized this strain regarding its species identity, cellular ultrastructure and potential for protecting Brassica juncea against exposure to ozone. The strain was identified as Bacillus subtilis by 16S rDNA sequencing. Transmission electron microscopy revealed that strain 3A25 had intact bacterial flagella, endospores were found only occasionally. The growth-promoting capacity of strain 3A25 on B. juncea seedlings was investigated in a series of treatments with or without ozone stress in open top chambers. Chlorophyll content, shoot length, root length and leaf area were significantly increased by the treatment with B. subtilis 3A25. The ozone treatment (150 pbb) had a significant inhibiting effect on the development of B. juncea, however, the number of secondary roots was increased. Application of B. subtilis 3A25 either as foliar spray or directly on the soil significantly reduced the negative ozone effect, indicating that this strain has capacities in plant protection against environmental stress.     

High level of resistance to Sclerotinia sclerotiorum in introgression lines derived from hybridization between wild crucifers and the crop Brassica species B. napus and B. juncea

Sclerotinia rot caused by the fungus Sclerotinia sclerotiorum is one of the most serious and damaging diseases of oilseed rape and there is keen worldwide interest to identify Brassica genotypes with resistance to this pathogen. Complete resistance against this pathogen has not been reported in the field, with only partial resistance being observed in some Brassica genotypes. Introgression lines were developed following hybridization of three wild crucifers (viz. Erucastrum cardaminoides, Diplotaxis tenuisiliqua and E. abyssinicum) with B. napus or B. juncea. Their resistance responses were characterized by using a stem inoculation test. Seed of 54 lines of B. napus and B. juncea obtained from Australia, India and China through an Australian Centre for International Agricultural Research (ACIAR) collaboration programme were used as susceptible check comparisons. Introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum had much higher levels (P < 0.001) of resistance compared with the ACIAR germplasm. Median values of stem lesion length of introgression lines derived from the wild species were 1.2, 1.7 and 2.0 cm, respectively, as compared with the ACIAR germplasm where the median value for stem lesion length was 8.7 cm. This is the first report of high levels of resistance against S. sclerotiorum in introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum. The novel sources of resistance identified in this study are a highly valuable resource that can be used in oilseed Brassica breeding programmes to enhance resistance in future B. napus and B. juncea cultivars against Sclerotinia stem rot.