Microbial larvicides for mosquito control: Impact of long lasting formulations of Bacillus thuringiensis var. israelensis and Bacillus sphaericus on non‐target organisms in western Kenya highlands

The microbial larvicides Bacillus thuringiensis var. israelensis and Bacillus sphaericus have been used extensively for mosquito control and have been found to be effective and safe to non‐target organisms cohabiting with mosquito larvae. Recently developed long lasting microbial larvicides (LLML), although evading the previous challenge of short duration of activity, increase the risk of persistence of toxins in the treated larval habitats. This study monitored the impact of LLML FourStar^® and LL3 on non‐target organisms cohabiting with mosquito larvae in an operational study to control malaria vectors in western Kenya highlands. A total of 300 larval habitats were selected in three highland villages. The habitats were first monitored for 5 weeks to collect baseline data on non‐target organisms cohabiting with mosquito larvae and then randomized into two treatment arms (respective FourStar^® and LL3) and one control arm. Non‐target organisms were sampled weekly for 5 months after treatment to assess the impact of LLML intervention. Before treatment, the mean density of all non‐target organisms combined in the control, LL3 and FourStar^® treated habitats was 1.42, 1.39 and 1.49 individuals per habitat per sampling occasion, respectively. Following treatment, this density remained fairly unchanged for 21 weeks at which time it was 1.82, 2.11, and 2.05 for the respective control, LL3 and FourStar^® treated habitats. Statistical analysis revealed that LL3 and FourStar^® did not significantly alter abundance, richness or diversity of the 11 taxa studied, when comparing the intervention and control larval habitats. However, both FourStar^® and LL3 significantly reduced the density of malaria vectors. In conclusion, one round of label rate application of FourStar^® or LL3 in natural larval habitats did not alter richness, abundance or diversity of the monitored aquatic non‐target organisms cohabiting with mosquito larvae to an ecologically significant level.     

Quarantine host range of Bikasha collaris,a potential biological control agent of Chinese tallowtree (Triadica sebifera) in North America

Chinese tallowtree, Triadica sebifera (L.) Small (Euphorbiaceae), is one of the worst invasive weeds of the southeastern USA impacting coastal wetlands, forests, and natural areas. Traditional mechanical and chemical controls have been unable to limit the spread, and this invasive species continues to expand its range. A proposed biological control candidate, the flea beetle Bikasha collaris (Baly) (Coleoptera: Chrysomelidae), shows high specificity for the target weed Chinese tallowtree. Results from a series of no‐choice and choice feeding tests of B. collaris adults and larvae indicated that this flea beetle was highly specific to Chinese tallowtree. The larvae of B. collaris feed by tunneling in the roots, whereas the adults feed on the leaves of Chinese tallowtree. A total of 77 plant taxa, primarily from members of the tallow plant family Euphorbiaceae, were tested in numerous test designs. Larval no‐choice tests indicated that larvae completed development only on two of the non‐target taxa. Of 80 B. collaris larvae fed roots of Hippomane mancinella L. and 50 larvae fed roots of Ricinus communis L., two and three larvae completed development, respectively. The emerging adults of these five larvae died within 3 days without reproducing. Larval choice tests also indicated little use of these non‐target taxa. Adult no‐choice tests indicated little leaf damage by B. collaris on the non‐targets except for Ditrysinia fruticosa (Bartram) Govaerts & Frodin and Gymnanthes lucida Sw. When given a choice, however, B. collaris adults consumed much less of the non‐targets D. fruticosa (7.4%) and G. lucida (6.1%) compared with the control leaves. Finally, no‐choice oviposition tests indicated that no eggs were produced when adults were fed all non‐target taxa, except those fed G. lucida. These B. collaris adults fed G. lucida leaves produced an average of 4.6 eggs compared with 115.0 eggs per female when fed Chinese tallowtree. The eggs produced from adults fed G. lucida were either inviable or the emerging larvae died within 1 day. These results indicate that the flea beetle B. collaris was unable to complete its life cycle on any of the non‐target taxa tested. If approved for field release, B. collaris will be the first biological control agent deployed against Chinese tallowtree in the USA. This flea beetle may play an important role in suppressing Chinese tallowtree and contribute to the integrated control of this invasive weed.     

Development of Asian parasitoids in larvae Of Drosophila Suzukii feeding on blueberry and artificial diet

In just a few years, the Asian fly Drosophila suzukii has invaded several continents and has become a very serious pest of many fruit crops worldwide. Current control methods rely on chemical insecticides or expensive and labour‐intensive cultural practices. Classical biological control through the introduction of Asian parasitoids that have co‐evolved with the pest may provide a sustainable solution on condition that they are sufficiently specific to avoid non‐target effects on local biodiversity. Here, we present the first study on the development of three larval parasitoids from China and Japan, the Braconidae Asobara japonica and the Figitidae Leptopilina japonica and Ganaspis sp., on D. suzukii. The Asian parasitoids were compared with Leptopilina heterotoma, a common parasitoid of several Drosophilidae worldwide. The three Asian species were successfully reared on D. suzukii larvae in both, blueberry and artificial diet, in contrast to L. heterotoma whose eggs and larvae were encapsulated by the host larvae. All parasitoids were able to oviposit one day after emergence. Asobara japonica laid as many eggs in larvae feeding in blueberry as in artificial diet, whereas L. heterotoma oviposited more in larvae on the artificial diet and the Asian Figitidae oviposited more in larvae feeding on blueberry. Ganaspis sp. laid very few eggs in larvae in the artificial diet, suggesting that it may be specialized in Drosophila species living in fresh fruits. These data will be used for the development of a host range testing to assess the suitability of Asian parasitoids as biological control agents in invaded regions.     

Preference of Bt‐resistant and susceptible Busseola fusca moths and larvae for Bt and non‐Bt maize

The sustainability of genetically engineered insecticidal Bacillus thuringiensis Berliner (Bt) maize, Zea mays L. (Poaceae), is threatened by the evolution of resistance by target pest species. Several Lepidoptera species have evolved resistance to Cry proteins expressed by Bt maize over the last decade, including the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The insect resistance management (IRM) strategy (i.e., the high‐dose/refuge strategy) deployed to delay resistance evolution is grounded on certain assumptions about the biology and ecology of a pest species, for example, the interactions between the insect pest and crop plants. Should these assumptions be violated, the evolution of resistance within pest populations will be rapid. This study evaluated the assumption that B. fusca adults and larvae select and colonize maize plants at random, and do not show any preference for either Bt or non‐Bt maize. Gravid female B. fusca moths of a resistant and susceptible population were subjected to two‐choice oviposition preference tests using stems of Bt and non‐Bt maize plants. Both the number of egg batches as well as the total number of eggs laid on each stem were recorded. The feeding preference of Bt‐resistant and susceptible neonate B. fusca larvae were evaluated in choice test bioassays with whorl leaf samples of specific maize cultivars. Although no differential oviposition preference was observed for either resistant or susceptible female moths, leaf damage ratings indicated that neonate larvae were able to detect Bt toxins and that they displayed feeding avoidance behaviour on Bt maize leaf samples.     

Observations of parasitoid behaviour in both no‐choice and choice tests are consistent with proposed ecological host range

The solitary larval endoparasitoid Eadya daenerys Ridenbaugh (Hymenoptera: Braconidae) is a proposed biocontrol agent of Paropsis charybdis Stål (Coleoptera: Chrysomelidae, Chrysomelinae), a pest of eucalypts in New Zealand. Eadya daenerys oviposition behaviour was examined in two assay types during host range testing, with the aim of improving ecological host range prediction. No‐choice sequential and two‐choice behavioural observations were undertaken against nine closely related species of New Zealand non‐target beetle larvae, including a native beetle, introduced weed biocontrol agents, and invasive paropsine beetles. No behavioural measure was significantly different between no‐choice and two‐choice tests. In sequential no‐choice assays the order of first presentation (target–non‐target) had no significant effect on the median number of attacks or the attack rate while on the plant. Beetle species was the most important factor. Parasitoids expressed significantly lower on‐plant attack rates against non‐targets compared to target P. charybdis larvae. The median number of attacks was always higher towards target larvae than towards non‐target larvae, except for the phylogenetically closest related non‐target Trachymela sloanei (Blackburn) (Coleoptera: Chrysomelidae, Chrysomelinae). Most non‐target larvae were disregarded upon contact, which suggests that the infrequent attack behaviour observed by two individual E. daenerys against Allocharis nr. tarsalis larvae in two‐choice tests and the frass of Chrysolina abchasica (Weise) was probably abnormal host selection behaviour. Results indicate that E. daenerys is unlikely to attack non‐target species apart from Eucalyptus‐feeding invasive paropsines (Chrysomelinae). Non‐lethal negative impacts upon less preferred non‐target larvae are possible if E. daenerys does attack them in the field; however, this is likely to be rare.     

Inoculation of susceptible and resistant potato plants with the late blight pathogen Phytophthora infestans: effects on an aphid and its parasitoid

Plants are exposed to microbial pathogens as well as herbivorous insects and their natural enemies. Here, we examined the effects of inoculation of potato plants, Solanum tuberosum L. (Solanaceae), with the late blight pathogen Phytophthora infestans (Mont.) de Bary (Peronosporales: Pythiaceae) on an aphid species commonly infesting potato crops and one of the aphid's major parasitoids. We observed the peach‐potato aphid, Myzus persicae Sulzer (Hemiptera: Aphididae), and its natural enemy, the biocontrol agent Aphidius colemani Viereck (Hymenoptera: Braconidae), on potato either inoculated with water or P. infestans. Population growth of the aphid, parasitism rate of its natural enemy, and other insect life‐history traits were compared on several potato genotypes, the susceptible cultivar Désirée and genetically modified (GM) isogenic lines carrying genes conferring resistance to P. infestans. Effects of P. infestans inoculation on the intrinsic rate of aphid population increase and the performance of the parasitoid were only found on the susceptible cultivar. Insect traits were similar when comparing inoculated with non‐inoculated resistant GM genotypes. We also tested how GM‐plant characteristics such as location of gene insertion and number of R genes could influence non‐target insects by comparing insect performance among GM events. Different transformation events leading to different positions of R‐gene insertion in the genome influenced aphids either with or without P. infestans infection, whereas effects of position of R‐gene insertion on the parasitoid A. colemani were evident only in the presence of inoculation with P. infestans. We conclude that it is important to study different transformation events before continuing with further stages of risk assessment of this GM crop. This provides important information on the effects of plant resistance to a phytopathogen on non‐target insects at various trophic levels.     

Two experimental designs generate contrasting patterns of behavioral differentiation along a latitudinal gradient in Lestes sponsa—Common‐garden not so common after all?

Understanding why and how behavioral profiles differ across latitudes can help predict behavioral responses to environmental change. The first response to environmental change that an organism exhibits is commonly a behavioral response. Change in one behavior usually results in shifts in other correlated behaviors, which may adaptively or maladaptively vary across environments and/or time. However, one important aspect that is often neglected when studying behavioral expressions among populations is if/how the experimental design might affect the results. This is unfortunate since animals often plastically modify their behavior to the environment, for example, rearing conditions. We studied behavioral traits and trait correlations in larvae of a univoltine damselfly, Lestes sponsa, along its latitudinal distribution, spreading over 3,300 km. We compared behavioral profiles among larvae grown in two conditions: (a) native temperatures and photoperiods or (b) averaged constant temperatures and photoperiods (common‐garden). We hypothesized latitudinal differences in behavioral traits regardless of the conditions in which larvae were grown, with northern populations expressing higher activity, boldness, and foraging efficiency. When grown in native conditions, northern larvae were bolder, more active and more effective in prey capture than central and low latitude populations, respectively, as well as showed the strongest behavioral correlations. In contrast, larvae reared in common‐garden conditions showed no differences between regions in both individual traits and trait correlations. The results suggest different selective pressures acting on the studied traits across populations, with environment as a central determinant of the observed trait values. Common‐garden designed experiments may evoke population‐dependent levels of plastic response to the artificial conditions and, hence, generate results that lack ecological relevance when studying multi‐population differences in behavior.     

Sublethal effects of Bt toxin and chlorpyrifos on various Spodoptera exigua populations

Bt cotton (Cry1Ac) has been commercially grown in China since 1997, saving China's cotton production from attack by Bt‐target pests and also tremendously reducing pesticide usage. In recent years, however, Bt cotton, with 4.2 million ha of cultivation, has suffered from a secondary target pest, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). In China, growers have even had to re‐adopt conventional pesticides to control the pest, and this practice has already caused serious pesticide residue. In order to clarify the sublethal effects of chemical pesticide, the responses of a Bt‐susceptible and a Bt‐tolerant (Bt10) S. exigua strain to three treatment combinations were examined, including Bt toxin, sublethal chlorpyrifos, and Bt + sublethal chlorpyrifos. The susceptible and the Bt10 strain responded differently to dual pressure. Bt toxin + sublethal chlorpyrifos treatment lowered larval mortality and stimulated population increase of the susceptible S. exigua, whereas it delayed growth and development of the Bt10 strain. Under dual pressure, although larvae of the Bt10 strain developed faster than larvae of the susceptible strain, the Bt10 population experienced higher larval mortality, prolonged pupal duration, decreased pupal weight, decreased emergence rate, and shortened adult longevity. Compared with the susceptible strain, the Bt10 strain was deleteriously affected by sublethal chlorpyrifos. The Bt‐tolerant/resistant S. exigua population was more vulnerable to chemical pesticides like chlorpyrifos regardless of whether it was exposed to Bt toxin or not. Our study provides a reference for increasing the efficacy of control of S. exigua in Bt‐cotton planting areas.     

Survival of Helicoverpa armigera larvae on and Bt toxin expression in various parts of transgenic Bt cotton (Bollgard II) plants

There is no conclusive evidence that Helicoverpa spp. (Lepidoptera: Noctuidae) in Australia have evolved significant levels of resistance to Bollgard II^® cotton (which expresses two Bt toxin genes, cry1Ac and cry2Ab). However, there is evidence of surviving larvae on Bollgard II cotton in the field. The distribution and survival of early‐instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae were examined on whole Bollgard II and non‐Bt cotton plants in greenhouse bioassays. The expression of Cry toxins in various parts of Bollgard II plants was compared to the survival of larvae in those locations. Only 1% of larvae survived after 6 days on greenhouse‐grown Bollgard II plants compared to 31% on non‐Bt cotton plants. Overall, and across all time intervals, more larvae survived on reproductive parts (squares, flowers, and bolls) than on vegetative parts (leaves, stems, and petioles) on Bollgard II plants. The concentration of Cry1Ac toxin did not differ between plant structures, whereas Cry2Ab toxin differed significantly, but there was no relationship between the level of expression and the location of larvae. This study provides no evidence that lower expression of Cry toxins in the reproductive parts of plants explains the survival of H. armigera larvae on Bollgard II cotton.     

Effectiveness in the field of Bt rice lines against target pests under various cultural regimes

China has a long history of rice cultivation, incorporating several cultural practices known to influence damage by insect pests. Transgenic Bt rice expresses lepidopteran‐specific insecticidal proteins that primarily target lepidopteran insect pests. However, the effectiveness of Bt rice against target insect pests under different cultural regimes has not been evaluated. In this study, the effectiveness of Bt rice lines against rice leaffolder, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), and striped stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), was evaluated under various transplanting densities, crop establishment methods, and planting times. The results showed that Bt rice lines (T2A‐1 and T1C‐19, containing Cry2A and Cry1C, respectively) could prevent damage by these target pests under a range of cultural practices. Injury by C. medinalis or C. suppressalis on rice did not differ with the rice lines under various transplanting densities. Direct‐seeded non‐Bt rice MH63 suffered heavier injury by C. medinalis and C. suppressalis than it did with transplanting, whereas injury to the two Bt rice lines did not differ with planting methods. Planting time significantly affected injury by C. medinalis or C. suppressalis on non‐Bt rice, whereas injury to Bt rice lines did not differ with planting time. These results suggest that transplanting density, planting method, and planting time did not significantly affect the resistance of two Bt rice lines, due to their high insecticidal activity against target insects.     

Effects of prohydrojasmon‐treated corn plants on attractiveness to parasitoids and the performance of their hosts

We investigated the effect of prohydrojasmon [propyl (1RS,2RS)‐(3‐oxo‐ 2‐pentylcyclopentyl) acetate] (PDJ) treatment of intact corn plants, on their attractiveness to the specialist endoparasitoid, Cotesia kariyai Watanabe (Hymenoptera: Braconidae), and on the performance of the common armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae) under laboratory conditions. Attractiveness of C. kariyai to PDJ‐treated plants was studied in a wind tunnel, whereas performance of M. separata larvae was tested in plastic cages. The attractiveness of the treated plants increased with concentrations of PDJ increasing to 2 mm , which was equivalent to the attractiveness of host‐infested plants. PDJ‐treated corn plants emitted 16 volatile compounds (α‐pinene, β‐myrcene, (Z)‐3‐hexenyl acetate, limonene, (E)‐β‐ocimene, linalool, (E)‐4,8‐dimethyl‐1,3,7‐nonatriene, (+)‐cyclosativene, ylangene, (E)‐β‐farnesene, (E, E)‐4,8,12‐trimethyl‐1,3,7,11‐tridecatetraene, α‐bergamotene, γ‐cadinene, δ‐cadinene, α‐muulolene and nerolidol), most of which were observed in the headspace of host‐infested corn plants with some quantitative and qualitative differences. We also tested the effects of PDJ treatment on the performance of M. separata larvae. The survival rates of the larval and pupal stages were significantly lower at 2 mm level of PDJ. A significant decrease in weight at 6th stadium larvae was observed only at 2 mm level of PDJ. In contrast, PDJ treatment at all PDJ concentration levels caused significant reduction in weight of pupal stage as compared to control. These data suggested that PDJ, originally developed as a plant growth regulator, especially to induce coloring of fruits, has the potential to induce direct and indirect defenses in corn plants against common armyworm, M. separata.     

Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

Cotesia kariyai Watanabe (Hymenoptera: Braconidae) is a specialist larval parasitoid of Mythimna separata Walker (Lepidoptera: Noctuidae). Cotesia kariyai wasps use herbivore‐induced plant volatiles (HIPVs) to locate hosts. However, complex natural habitats are full of volatiles released by both herbivorous host‐ and non‐host‐infested plants at various levels of intensity. Therefore, the presence of non‐hosts may affect parasitoid decisions while foraging. Here, the host‐finding efficiency of naive C. kariyai from HIPVs influenced by host‐ and non‐host‐infested maize [Zea mays L. (Poaceae)] plants was investigated with a four‐arm olfactometer. Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) was selected as a non‐host species. One unit (1 U) of host‐ or non‐host‐infested plant was prepared by infesting a potted plant with five host or seven non‐host larvae. In two‐choice bioassays, host‐infested plants fed upon by different numbers of larvae, and various units of host‐ and non‐host‐infested plants (infestation units; 1 U, 2 U, and 3 U) were arranged to examine the effects of differences in volatile quantity and quality on the olfactory responses of C. kariyai with the assumption that volatile quantity and quality changes with differences in numbers of insects and plants. Cotesia kariyai was found to perceive quantitative differences in volatiles from host‐infested plants, preferring larger quantities of volatiles from larger numbers of larvae or plants. Also, the parasitoids discriminated between healthy plants, host‐infested plants, and non‐host‐infested plants by recognising volatiles released from those plants. Cotesia kariyai showed a reduced preference for host‐induced volatiles, when larger numbers of non‐host‐infested plants were present. Therefore, quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested plants appear to affect the decision of C. kariyai during host‐habitat searching in multiple tritrophic systems.     

Detrimental effects of plant compounds on a polyembryonic parasitoid are mediated through its highly polyphagous herbivore host

Plant defensive compounds can have sometimes severe deleterious effects on both herbivores and their natural enemies. Iridoid glycosides (IGs) are defensive compounds that are well established as deterrent to several generalist herbivores and generalist predators. Trichoplusia ni Hübner (Lepidoptera: Noctuidae) is exceptional among generalist herbivores for its ability to tolerate and thrive when feeding upon IG‐producing plant species; however, it is not known whether the compounds themselves have a harmful effect on T. ni and whether the effects in turn affect its oligophagous endoparasitoid Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae). To examine these effects, a semi‐purified extract of the IG‐containing plant Plantago lanceolata L. (Plantaginaceae), containing the IGs aucubin and catalpol, was added to artificial diets at 0, 1, 5, or 10% diet dry weight. These diets were fed to both C. floridanum‐parasitized and unparasitized T. ni. Diets higher in IGs tended to be more toxic to both parasitized and unparasitized larvae: host larvae that did survive were slightly smaller and took longer to develop on higher IG diets and total clutch size and survival of the parasitoid C. floridanum were greatly reduced as the host's dietary intake of IGs increased. Only small amounts of aucubin were detected inside the T. ni hemocoel, suggesting that the negative effect of these compounds on C. floridanum is due to nutritional quality of the host being reduced rather than direct toxic effects of the compounds.     

Suppression of Rust and Brown Eye Spot Diseases on Coffee by Phosphites and By‐products of Coffee and Citrus Industries

The rust and brown eye spot, caused by Hemileia vastatrix and Cercospora coffeicola, respectively, are the most important fungal diseases on coffee in South America. Their management is mainly by chemical treatment, and there is no genetic resistance to brown eye spot known so far. Considering the need for developing alternative products for their control, the goal of this work was to evaluate the effects of phosphites and by‐products of coffee and citrus industries on rust and brown eye spot. Formulations of coffee and citrus industry by‐products, phosphites and their combination with fungicide were evaluated in field experiments, and their effect on fungal urediniospores and conidia was evaluated in vitro. In the field, treatments were applied individually or in combination and the in vitro assays were performed with manganese phosphite (Reforce Mn), potassium phosphite and citrus industry by‐product (Fortaleza), copper phosphite and coffee industry by‐product (Fitoforce Full), and fungicide. The severity and incidence of rust and brown eye spot on coffee leaves, yield, and leaf retention were evaluated in the field. Percentage of spore germination was evaluated in vitro for both fungi, whereas mycelial growth was evaluated for C. coffeicola only. The treatments Fortaleza, Reforce Mn and Fitoforce Full suppressed both diseases with a reduction in defoliation. In the year 2012, the plants treated with Reforce Mn and Reforce Mn + Fortaleza showed a yield increase of 72 and 88%, respectively, which was similar to the results shown by the fungicide treatment. In vitro inhibition of germination of H. vastatrix urediniospores and of C. coffeicola conidia was observed and suggests that the products exert some toxic effects to both fungi. Finally, the results observed indicate that the combined use of by‐products of plant‐processing industries and phosphites is an alternative and can be added efficiently to the management of coffee diseases.     

Bacillus thuringiensis plants expressing Cry1Ac,Cry2Ab and Cry1F are not toxic to the assassin bug,Zelus renardii

Cotton‐ and maize‐producing insecticidal crystal (Cry) proteins from the bacterium, Bacillus thuringiensis (Bt), have been commercialized since 1996. Bt plants are subjected to environmental risk assessments for non‐target organisms, including natural enemies that suppress pest populations. Here, we used Cry1F‐resistant Spodoptera frugiperda (J.E. Smith) and Cry1Ac and Cry2Ab‐resistant Trichoplusia ni (Hübner) as prey for the assassin bug, Zelus renardii (Kolenati), a common predator in maize and cotton fields. In tritrophic studies, we assessed several fitness parameters of Z. renardii when it fed on resistant S. frugiperda that had fed on Bt maize expressing Cry1F or on resistant T. ni that had fed on Bt cotton expressing Cry1Ac and Cry2Ab. Survival, nymphal duration, adult weight, adult longevity and female fecundity of Z. renardii were not different when they were fed resistant‐prey larvae (S. frugiperda or T. ni) reared on either a Bt crop or respective non‐Bt crops. ELISA tests demonstrated that the Cry proteins were present in the plant at the highest levels, at lower levels in the prey and at the lowest levels in the predator. While Z. renardii was exposed to Cry1F and Cry1Ac and Cry2Ab when it fed on hosts that consumed Bt‐transgenic plants, the proteins did not affect important fitness parameters in this common and important predator.     

Long‐term phosphite application maintains species assemblages,richness and structure of plant communities invaded by Phytophthora cinnamomi

The impact of the plant pathogen Phytophthora cinnamomi and the fungicide phosphite on species assemblages, richness, abundance and vegetation structure was quantified at three sites in Kwongkan communities in the Southwest Australian Floristic Region. Healthy and diseased vegetation treated with phosphite over 7–16 years was compared with non‐treated healthy and diseased vegetation. After site differences, disease had the greatest effect on species assemblages, species richness and richness within families. Disease significantly reduced cover in the upper and lower shrub layers and increased sedge and bare ground cover. Seventeen of 21 species assessed from the families Ericaceae, Fabaceae, Myrtaceae and Proteaceae were significantly less abundant in non‐treated diseased vegetation. In diseased habitats, phosphite treatment significantly reduced the loss of shrub cover and reduced bare ground and sedge cover. In multivariate analysis of species assemblages, phosphite‐treated diseased plots grouped more closely with healthy plots. Seven of 17 susceptible species were significantly more abundant in phosphite‐treated diseased plots compared with diseased non‐treated plots. The abundance of seven of 10 Phytophthora‐susceptible species was significantly higher along transects in phosphite‐treated vegetation. Comparison of the floristics of healthy non‐treated with healthy‐treated plots showed no significant differences in species assemblages. Of 21 species assessed, three increased in abundance and only one decreased significantly in phosphite‐treated healthy plots. In three Kwongkan communities of the SWAFR, P. cinnamomi had a profound impact on species assemblages, richness, abundance and vegetation structure. There was no evidence of adverse effects of phosphite treatment on phosphorus‐sensitive species, even after fire. Treatment with phosphite enhanced the survival of key susceptible species and mitigated disease‐mediated changes in vegetation structure. In the absence of alternative methods of control in native communities, phosphite will continue to play an important role in the protection of high priority species and communities at risk of extinction due to P. cinnamomi.     

Interactions Between Rhizoctonia Root Rot and the Foliar Common Bean Diseases Anthracnose and Rust

The effects of co‐inoculation of Rhizoctonia solani and Colletotrichum lindemuthianum or Uromyces appendiculatus at different inoculum levels were studied on the disease dynamics and on the growth of bean plants under greenhouse conditions. Bean seeds were sown in R. solani‐infested soil. Additional experiments in which seedlings were transplanted to infested soil were also carried out. Conidial suspensions of C. lindemuthianum or uredospores of U. appendiculatus were inoculated onto leaves at plant developmental stages V2 and V3, respectively. Interactions between root rot and the aerial diseases were observed depending on the inoculum levels and on the timing of R. solani inoculation. Anthracnose severity tended to be higher on R. solani‐infected plants. Conversely, R. solani infection significantly reduced diameter of pustules and rust severity. When seedlings were transplanted to soil infested with low levels of R. solani, root rot severity and density of R. solani in the soil were magnified at high levels of C. lindemuthianum or U. appendiculatus. In these experiments, a synergistic interaction between root rot and anthracnose was observed to affect the plant dry weight. Antagonistic effects on the plant dry weight were found for the combination root rot/rust only when seeds were sown in infested soil.     

Target and non‐target effects of a spider venom toxin produced in transgenic cotton and tobacco plants

The peptide ω‐Hexatoxin‐Hv1a (Hvt) is one of the most studied spider toxins. Its insecticidal potential has been reported against species belonging to the arthropod orders Lepidoptera, Diptera and Orthoptera. The gene encoding Hvt has been transformed into cotton and tobacco to protect the plants from damage by lepidopteran pests. This study evaluated the expression of the ω‐HXTX‐Hv1a gene in transgenic plants, and the toxicity of plant‐expressed and purified Hvt on target lepidopteran insects and on several non‐target species. Transgenic Bollgard II cotton plants, which produce Cry1Ac and Cry2Ab2 and purified Cry2Ab2 protein were included in the study as comparators. LC₉₅ values of purified Hvt against Spodoptera littoralis and Heliothis virescens were 28.31 and 27.57 μg/ml of artificial diet, respectively. Larval mortality was 100% on Hvt‐transgenic tobacco plants but not on Hvt‐transgenic cotton, probably because of the significantly lower toxin expression level in the transgenic cotton line. Non‐target studies were conducted with larvae of the predators Chrysoperla carnea and Coccinella septempunctata, adults of the aphid parasitoid Aphidius colemani, and adult workers of the honey bee, Apis mellifera. Even at 40 μg/ml, Hvt did not adversely affect the four non‐target species. Purified Cry2Ab2 at 10 μg/ml also did not adversely affect any of the non‐target species. Our results show that Hvt might be useful for developing insecticidal plant varieties to control pest Lepidoptera.     

Insecticidal potential of Bacillus thuringiensis for the biological control of neotropical brown stink bug

Euschistus heros (Hemiptera: Pentatomidae) is considered a major insect pest in soybean production in Brazil. The indiscriminate application of pesticides to fields leads to reduction in biodiversity, selection of resistant populations, emergence of new pest outbreaks, and damage to non‐target organisms. The objective of this research was to evaluate the effects of exposure to Cry proteins present in new isolates of Bacillus thuringiensis Berliner, commercial formulations, and Bt soybean on E. heros development. The feeding preference of E. heros for Bt‐ vs. non‐Bt soybean was also evaluated. All treatments caused significant mortality to E. heros except the Bt soybean. Tests with combinations of isolated Bt‐toxins indicated that combinations had greater efficacy than other treatments (>98% mortality). The results demonstrate that E. heros is susceptible to B. thuringiensis toxins, which may contribute to the management of this insect in soybean agro‐ecosystems.