Semiochemicals for aphid control

The ‘Inclusion of Nature in Self' scale (INS) was applied to monitor shifts in reported connectedness with nature within the framework of a school-based environmental education programme. One hundred and twenty-three German students (sixth-graders) participated in a one-day module, which included hands-on indoor (classroom) and outdoor (nearby woods) implementation. Additionally, a control group (n?=?116) did not participate in our intervention at all. Seven types of shifts in students' subjective connectedness with nature before and after project participation were analysed and discussed. Individual initial connectedness and a variety of short- and long-term connectedness shifts indicate the necessity of a needs-oriented environmental education. The reliability of the INS scale as a rapid assessment for improving school-based fieldwork settings is confirmed.     

Prospects for malaria control

Malaria control strategies have to be established locally according to epidemiological situations, including socio-economic factors and to resources available for their implementation. It has been stressed that all antimalaria activities be integrated in PHC.Stratification of malaria is the introduction to malaria control and serves as a basis for the planning which should be established by a body of experts on malaria at the central level (epidemiologist, entomologist, specialists in social sciences, sanitary engineer) who later will guide, supervise and evaluate the activities.Case treatments, sometimes presumptive, are the most basic activities of control. They are cheap and they can be carried out by PHC which insures the coverage of the entire population at risk. Drug resistance of Plasmodium falciparum is a growing and threatening problem. In a number of areas cheap and harmless chloroquine has to be replaced by drugs or combinations of drugs which can only be delivered by experienced personnel. Chemoprophylaxis is recommended for pregnant women but questioned for infants and young children because the risk of side-effects and resistance selection and the difficulties of maintaining a good coverage for a long time.Vector control by house-spraying remains the best means of reducing transmission and is still the basis of malaria control in countries in Asia and America where the disease has been seriously reduced. In some areas resistance to DDT lead to the use of more expensive organophosphates and/or carbamates. Resistance to these compounds has also been reported in several countries. House-spraying is probably one of the malaria activities which is the most difficult to integrate in PHC. Some attempts have been successful.Integrated vector control with community participation is not a simple task nor a panacea. To be efficient it needs to be established on a strong scientific basis. Tools and technics have to be selected for each area according to the vector ecology and socio-cultural habits of the population. Maintaining community interest in a long lasting activity is a problem which has never been really explored. Self-protection against vectors (mainly by using impregnated mosquito nets) has shown promise and is currently being evaluated at an operational scale with community involvement. There is great hope for a vaccine but more advances are necessary before its place in malaria control can be established.Intersectorial approach is the best way to counteract undesirable effects of development schemes like irrigation. There is a need for training in the scope of interdisciplinary actions for high level personnel. PHC agents need special training whatever they are, specialized or multipurpose. Special attention must be paid to malaria in health education for communities at risk. Some researches dealing with the most immediate problems are suggested.     

Baculoviruses-- re-emerging biopesticides

Biological control of agricultural pests has gained importance in recent years due to increased pressure to reduce the use of agrochemicals and their residues in the environment and food. Viruses of a few families are known to infect insects but only those belonging to the highly specialized family Baculoviridae have been used as biopesticides. They are safe to people and wildlife, their specificity is very narrow. Their application as bioinsecticides was limited until recently because of their slow killing action and technical difficulties for in vitro commercial production. Two approaches for the wider application of baculoviruses as biopesticides will be implemented in future. In countries where use of genetically modified organisms is restricted, the improvements will be mainly at the level of diagnostics, in vitro production and changes in biopesticide formulations. In the second approach, the killing activity of baculoviruses may be augmented by genetic modifications of the baculovirus genome with genes of another natural pathogen. It is expected that the baculoviruses improved by genetic modifications will be gradually introduced in countries which have fewer concerns towards genetically modified organisms.     

Prospects for using pyroproxyfen-treated targets for tsetse control

Using¹⁴C cholesterol as a marker a positive correlation was established between the amount of oil (a chlorinated n-alkane containing 43–46% chlorine, ‘cereclor S45’) picked up by an adult tsetse fly exposed by tarsal contact to a treated surface and the duration of such exposure. Only a poor uptake was achieved from netting surfaces treated with less than 50% oil in acetone. Terylene netting treated with radioactive pyriproxyfen, [1-methyl-2-(4-phenoxyphenoxy)ethoxy] pyridine, dissolved in cereclor, was exposed in the field for a year. After 9 months 20% of the original radioactivity remained and was shown to be 95% authentic pyriproxyfen. Brief tarsal contact (up to 5 seconds) with such netting, by adult females ofGlossina morsitans morsitans Westwood, reduced the viability of their offspring to 28–43% of untreated control values. The effect was greatest in the reproductive cycle immediately following contact. Between 10 and 12 months after treatment of the fabric the radioactivity fell to only 7% of the original level but was associated mainly (>80%) with intact pyriproxyfen. Exposure of female flies to this netting resulted in a positive correlation between the duration of exposure and the extent of suppression of offspring viability, such that 2 min was sufficient to reduce offspring viability to zero for the life of the female. Traps or targets impregnated with conventional formulations of pyrethroids to kill tsetse would have lost all their activity by this time. Results are discussed in terms of the prospects for using pyriproxyfen-treated targets to sterilize female tsetse directly and also indirectly through the contamination of males prior to mating through contact with such targets.     

Relative importance of predators and parasitoids for cereal aphid control

Field experiments with manipulations of natural enemies of plant-feeding insects may show how a diverse enemy group ensures an important ecosystem function such as naturally occurring biological pest control. We studied cereal aphid populations in winter wheat under experimentally reduced densities of: (i) ground-dwelling generalist predators (mostly spiders, carabid and staphylinid beetles); (ii) flying predators (coccinellid beetles, syrphid flies, gall midges, etc.) and parasitoids (aphidiid wasps), and a combination of (i) and (ii), compared with open controls. Aphid populations were 18% higher at reduced densities of ground-dwelling predators, 70% higher when flying predators and parasitoids were removed, and 172% higher on the removal of both enemy groups. Parasitoid wasps probably had the strongest effect, as flying predators occurred only in negligible densities. The great importance of parasitism is a new finding for aphid control in cereal fields. In conclusion, a more detailed knowledge of the mechanisms of natural pest control would help to develop environmentally sound crop management with reduced pesticide applications.     

Neutral density liquid formulations for nematode-based biopesticides

Entomopathogenic nematodes are widely used as biological insecticides for agricultural and horticultural pests. In the vast majority of cases, commercial products contain nematodes partially dehydrated on to inert solid carriers. Nematode survival in these products is generally poor, they are difficult to handle and are not suitable for use with all nematode species. We have developed a non-viscous, non-adhesive and non-toxic liquid formulation for nematode storage and transport based on neutral density colloidal silica suspensions. Survival and virulence of nematodes stored in this formulation without aeration was superior to nematodes stored in aerated quarter strength Ringer's solution.     

Prospects for fungicidal control of take-all of wheat

A range of fungicides and herbicides was tested against Gaeumannomyces graminis (causal agent of take-all) on agar plates, and on wheat seedlings in pots and in liquid culture. Benomyl, the standard in all tests, was consistently most effective: like iprodione, nuarimol and KWG 0599 , it diminished infection from inoculum placed just below the seeds more effectively when applied as a drench than as a soil-mix. Benomyl as a soil-mix was most effective in soils with least organic matter. Some compounds toxic to the pathogen on agar plates and in plants grown in liquid culture were ineffective as soil treatments. The practical limitations of soil treatment with conventional fungicides and application methods are discussed.     

Horizontally transferred genes as RNA interference targets for aphid and whitefly control

RNA interference (RNAi)-based technologies are starting to be commercialized as a new approach for agricultural pest control. Horizontally transferred genes (HTGs), which have been transferred into insect genomes from viruses, bacteria, fungi or plants, are attractive targets for RNAi-mediated pest control. HTGs are often unique to a specific insect family or even genus, making it unlikely that RNAi constructs targeting such genes will have negative effects on ladybugs, lacewings and other beneficial predatory insect species. In this study, we sequenced the genome of a red, tobacco-adapted isolate of Myzus persicae (green peach aphid) and bioinformatically identified 30 HTGs. We then used plant-mediated virus-induced gene silencing (VIGS) to show that several HTGs of bacterial and plant origin are important for aphid growth and/or survival. Silencing the expression of fungal-origin HTGs did not affect aphid survivorship but decreased aphid reproduction. Importantly, although there was uptake of plant-expressed RNA by Coccinella septempunctata (seven-spotted ladybugs) via the aphids that they consumed, we did not observe negative effects on ladybugs from aphid-targeted VIGS constructs. To demonstrate that this approach is more broadly applicable, we also targeted five Bemisia tabaci (whitefly) HTGs using VIGS and demonstrated that knockdown of some of these genes affected whitefly survival. As functional HTGs have been identified in the genomes of numerous pest species, we propose that these HTGs should be explored further as efficient and safe targets for control of insect pests using plant-mediated RNA interference.     

Phytochemical biopesticides: some recent developments

Synthetic pesticides in general, are highly toxic, persistent and their harmful residues contaminate crops, food commodities and pollute soils and groundwater. They adversely affect non-target organisms like pollinators, fish, birds, animals, and their excessive use results in increased resistance in pests. Phytochemical biopesticides on the other hand are less toxic, least persistent, environment friendly and safe to humans and non target organisms. Several phytochemical biopesticides like azadirachtin, nicotine, pyrethrins, rotenone, veratrum, annonins, rocaglamides, isobutylamides etc. have been successfully commercilalized in the past. In this review pesticidal products based on Madhuca indica (Mahua), Sapindus mukorossi (soapnut), Curcuma longa (turmeric), Pongamia glabra (karanja), Eupatorium adenophorum (Crofton weed), Tagetes erecta (marigold), Rheum emodi (Himalayan Rhubarb) and essential oil bearing plants have been discussed. Natural insecticide synergists derived from Anethum sowa and their semisynthetic derivatives have been used to prolong efficacy and counter resistance in insect pests.     

Prospects for biological control of cactus weeds in Namibia

Australia and South Africa have a long history of sharing successful biocontrol agents for cactus weeds but other countries, such as Namibia, could also benefit. There are four biological control agents that are widely utilised in South Africa and/or Australia for the control of 10 invasive alien Cactaceae in Namibia.     

Potential for augmentative biological control of black bean aphid in California sugarbeet

In northern California, black bean aphid (Aphis fabae Scopoli complex) can be a major pest of sugarbeet, particularly in spring-planted fields. The major natural enemies of the aphid are predators, including the coccinellidsHippodamia convergens Guerin,Coccinella novemnotata Herbst &C. septempunctata L., and the chrysopidsChrysopa oculata Say &C. nigricornis Burmeister. Augmentative releases of eggs of eitherChrysoperla carnea (Stephens) orC. rufilabris (Burmeister) failed to significantly reduce aphid populations under field conditions. This was attributed in part to incompatibility between black bean aphids and lacewing larvae from commercial sources. Application of food sprays containing yeast hydrolysate, sucrose and molasses resulted in increased densities of eggs and adults ofC. carnea in treated plots. These results suggest that the potential for augmentative biological control of black bean aphid through the application of food sprays is greater than that for release of commercially available lacewings. Regardless of method, an holistic approach to augmentation that takes into account the ecological structure of the target agroecosystem will be required. Some aspects of “pre-emptive” biological control are discussed.