Sub-lethal aquatic doses of pyriproxyfen may increase pyrethroid resistance in malaria mosquitoes

Background Pyriproxyfen (PPF), an insect growth hormone mimic is widely used as a larvicide and in some second-generation bed nets, where it is combined with pyrethroids to improve impact. It has also been evaluated as a candidate for auto-dissemination by adult mosquitoes to control Aedes and Anopheles species. We examined whether PPF added to larval habitats of pyrethroid-resistant malaria vectors can modulate levels of resistance among emergent adult mosquitoes. Methodology Third-instar larvae of pyrethroid-resistant Anopheles arabiensis (both laboratory-reared and field-collected) were reared in different PPF concentrations, between 1×10−9 milligrams active ingredient per litre of water (mgAI/L) and 1×10−4 mgAI/L, or no PPF at all. Emergent adults escaping these sub-lethal exposures were tested using WHO-standard susceptibility assays on pyrethroids (0.75% permethrin and 0.05% deltamethrin), carbamates (0.1% bendiocarb) and organochlorides (4% DDT). Biochemical basis of pyrethroid resistance was investigated by pre-exposure to 4% PBO. Bio-efficacies of long-lasting insecticide-treated nets, Olyset® and PermaNet 2.0 were also examined against adult mosquitoes with or without previous aquatic exposure to PPF. Results Addition of sub-lethal doses of PPF to larval habitats of pyrethroid-resistant An. arabiensis, consistently resulted in significantly reduced mortalities of emergent adults when exposed to pyrethroids, but not to bendiocarb or DDT. Mortality rates after exposure to Olyset® nets, but not PermaNet 2.0 were also reduced following aquatic exposures to PPF. Pre-exposure to PBO followed by permethrin or deltamethrin resulted in significant increases in mortality, compared to either insecticide alone. Conclusions Partially-resistant mosquitoes exposed to sub-lethal aquatic concentrations of PPF may become more resistant to pyrethroids than they already are without such pre-exposures. Studies should be conducted to examine whether field applications of PPF, either by larviciding or other means actually exacerbates pyrethroid-resistance in areas where signs of such resistance already exist in wild the vector populations. The studies should also investigate mechanisms underlying such magnification of resistance, and how this may impact the potential of PPF-based interventions in areas with pyrethroid resistance.

Sub-lethal aquatic doses of pyriproxyfen may increase pyrethroid resistance in malaria mosquitoes

BackgroundPyriproxyfen (PPF), an insect growth hormone mimic is widely used as a larvicide and in some second-generation bed nets, where it is combined with pyrethroids to improve impact. It has also been evaluated as a candidate for auto-dissemination by adult mosquitoes to control Aedes and Anopheles species. We examined whether PPF added to larval habitats of pyrethroid-resistant malaria vectors can modulate levels of resistance among emergent adult mosquitoes.MethodologyThird-instar larvae of pyrethroid-resistant Anopheles arabiensis (both laboratory-reared and field-collected) were reared in different PPF concentrations, between 1×10-9 milligrams active ingredient per litre of water (mgAI/L) and 1×10-4 mgAI/L, or no PPF at all. Emergent adults escaping these sub-lethal exposures were tested using WHO-standard susceptibility assays on pyrethroids (0.75% permethrin and 0.05% deltamethrin), carbamates (0.1% bendiocarb) and organochlorides (4% DDT). Biochemical basis of pyrethroid resistance was investigated by pre-exposure to 4% PBO. Bio-efficacies of long-lasting insecticide-treated nets, Olyset® and PermaNet 2.0 were also examined against adult mosquitoes with or without previous aquatic exposure to PPF.ResultsAddition of sub-lethal doses of PPF to larval habitats of pyrethroid-resistant An. arabiensis, consistently resulted in significantly reduced mortalities of emergent adults when exposed to pyrethroids, but not to bendiocarb or DDT. Mortality rates after exposure to Olyset® nets, but not PermaNet 2.0 were also reduced following aquatic exposures to PPF. Pre-exposure to PBO followed by permethrin or deltamethrin resulted in significant increases in mortality, compared to either insecticide alone.ConclusionsPartially-resistant mosquitoes exposed to sub-lethal aquatic concentrations of PPF may become more resistant to pyrethroids than they already are without such pre-exposures. Studies should be conducted to examine whether field applications of PPF, either by larviciding or other means actually excercebates pyrethroid-resistance in areas where signs of such resistance already exist in wild the vector populations. The studies should also investigate mechanisms underlying such magnification of resistance, and how this may impact the potential of PPF-based interventions in areas with pyrethroid resistance.

Distribution of western and northern corn rootworms (Coleoptera: Chrysomelidae) in Quebec, Canada

Corn rootworms, Diabrotica Chevrolat spp. (Coleoptera: Chrysomelidae), are major pests of corn, Zea mays L. (Poaceae), in North America. Overwintering eggs hatch in the spring, and larvae feed on the root system, where they complete development. Emergent adults feed on vegetative and reproductive aerial structures of corn and oviposit in soil cracks or at the base of plants. Although feeding on silks by adult corn rootworms reduces the yield of corn, most of the damage results from root injury caused by larval feeding (Levine and Oloumi-Sadeghi 1991).

Root- and stem-colonizing insects recovered from eastern white pines with procerum root disease

In 1988, eastern white pines (Pinusstrobus L.) from four southwestern Virginia Christmas tree plantations symptomatic of infection by Leptographiumprocerum (Kendr.) Wingf. were assigned to one of four symptom categories based on crown color and resin exudation at the root collar. A fifth category was added in 1989 and 1990. From each plantation, the root system and the lower stem of one tree in each symptom class was excavated monthly and examined for fungi and insects from June to September in 1988 and 1989 and from April to September in 1990. Larvae of two weevil species, Hylobiuspales (Herbst) and Pissodesnemorensis Germ., were recovered with L. procerum from 23, 17, and 21% of the trees in all symptom classes in 1988, 1989, and 1990, respectively. Pre-emergent adults of both weevil species contaminated with L. procerum were also recovered from excavated stems. Bark beetle genera (family Scolytidae), including Pityogenes, Xyleborus, Orthotomicus, Ips, and Pityophthorus, were recovered with L. procerum from 10, 11, and 8% of diseased trees with advanced symptoms in 1988, 1989, and 1990, respectively. The association of these insects, especially H. pales and P. nemorensis, with L. procerum throughout the decline of the host adds further evidence that they may act as vectors of the fungus.

COILING OF ALFALFA PODS IN RELATION TO RESISTANCE AGAINST SEED CHALCIDS

A nusery of diverse alfalfa populations was attacked by the seed chalcid Bruchophagus roddi Gussakovsky, with 397 of a sample of 30 821 pods possessing emergent adults. Infestation increased as spiraling of the pod decreased. Legume coiling in alfalfa is an indication of the relative parentage of ssp. sativa, which has highly coiled pods, and of ssp. falcata which has uncoiled pods. Resistance of coiled pods to chalcid infestation could reflect any of several of the differences between these subspecies. A hypothesis is presented arguing that resistance is due to pod coiling per se. Alfalfa seeds develop on the ventral portion of the pod, close to the central axis of coiled pods. Coiling may be protective as it tends to make the ventral portion of the pod, and hence the developing seeds, inaccessible to the chalcid’s short ovipositor.

Application of Insecticides on Eggs of Callosobruchus chinensis L. Using Different Types of Pulse Seeds

Experiments were carried out in the laboratory to assess the effectiveness of Nogos, Malathion, Sevin and Limper on lentil, gram, grasspea, greengram and blackgram seeds with eggs of pulse beetle, Callosobruchus chinensis L. Insecticides were sprayed on the seeds along with eggs and found that all the tested insecticides inhibited hatching of eggs resulting in significantly lowest rate of adult emergence. Nogos and Malathion recorded the lower number of emergent adults. The overall 26.35- 100% reduction of seed damage and 40-100% weight losses were achieved in insecticides treated seeds of five different types of pulses showing highest reduction in seed damage and weight losses due to Nogos and Malathion treatments. The treatment of the pulse seeds with the insecticides did not affect the seed germination. Key words: Insecticides, pulse beetle, egg treatment, pulses, seed damage.