Deltamethrin‐induced feeding plasticity in pyrethroid‐susceptible and ‐resistant strains of the maize weevil,Sitophilus zeamais

Phenotypic plasticity contributes to the adaptative evolution of populations exposed to new or altered environments. Feeding plasticity is a component of phenotypic plasticity not usually considered in insect strains adapted to insecticide‐altered environments, but which may either accentuate or mitigate insecticide resistance. This is a concern in the pyrethroid‐resistant strains of the maize weevil Sitophilus zeamais Motsch. (Col., Curculionidae), and the reason for this study. A pyrethroid‐susceptible and two pyrethroid‐resistant strains of maize weevil were subjected to free‐choice and no‐choice tests with maize grains sprayed with increasing doses of the pyrethroid, deltamethrin. The insects from the pyrethroid‐resistant strains exhibited higher feeding avoidance with increased deltamethrin doses than insects from the susceptible strain when subjected to free‐choice tests. The strains of maize weevil physiologically resistant to pyrethroids were also behaviourally resistant to deltamethrin – an additional management concern. The resistant strains avoid deltamethrin‐sprayed grains and are less nutritionally affected by this compound, with divergent responses from the susceptible strain with increased doses of deltamethrin. Furthermore, the higher relative growth rate and consequently higher efficiency of food conversion observed in the insecticide‐resistant strains were significant even without insecticide exposure, indicating that these traits are stimulus‐independent and may persist even without further insecticide selection, potentially limiting the options available for their management.     

Pyrethroid-Acarophenax lacunatus interaction in suppressing the beetle Rhyzopertha dominica on stored wheat

Any biocontrol agent used against stored grain insects will have to interact with insecticides used as grain protectants due to their heavy use especially in tropical areas. Therefore, the interaction between the pyrethroid insecticides bifenthrin and deltamethrin and Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae), an egg parasite of the stored cereal pest Rhyzopertha dominica(F.) (Coleoptera: Bostrichidae), was assessed in a range of mite densities and insecticide doses for each compound. Despite the mite species presence on all insecticide doses, the lowest instantaneous rate of increase of A.lacunatus was recorded with the highest doses of insecticides. The presence of the biological control agent at all doses of both insecticides suggests its tolerance to these compounds. A. lacunatusshowed higher parasitism rate with bifenthrin than with deltamethrin indicating a higher selectivity of the first compound to the biocontrol agent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reproductive and developmental costs of deltamethrin resistance in the Chagas disease vector Triatoma infestans

Effective chemical control relies on reducing vector population size. However, insecticide selection pressure is often associated with the development of resistant populations that reduce control success. In treated areas, these resistant individuals present an adaptive advantage due to enhanced survival. Resistance can also lead to negative effects when the insecticide pressure ceases. In this study, the biological effects of deltamethrin resistance were assessed in the Chagas disease vector Triatoma infestans. The length of each developmental stage and complete life cycle, mating rate, and fecundity were evaluated. Susceptible and resistant insects presented similar mating rates. A reproductive cost of resistance was expressed as a lower fecundity in the resistant colony. Developmental costs in the resistant colony were in the form of a shortening of the second and third nymph stage duration and an extension of the fifth stage. A maternal effect of deltamethrin resistance is suggested as these effects were identified in resistant females and their progeny independently of the mated male's deltamethrin response. Our results suggest the presence of pleiotropic effects of deltamethrin resistance. Possible associations of these characters to other traits such as developmental delays and behavioral resistance are discussed.     

Water transport by the eversible abdominal vesicles of Petrobius brevistylis

The uptake of fluid by the eversible ventral abdominal sacs of Petrobius brevistylis from a wet substrate is described. On lightly wetted filter paper the insects do not drink, and an insect with an initial fresh weight of 15mg can regain a 30% weight loss due to dehydration in 7 min when allowed access to filter paper wetted with distilled water. A similar insect would need 39 min to become replete when taking up fluid from a 0.33 osmole kg^?1 NaCl solution. The length of time taken to become replete with distilled water was related to the size of the insect and the amount of water loss. Between 15 and 30% of the sodium ions present in each μl of an external NaCl solution entered with each mg of weight increase when the insects were allowed access to both a dilute and a stronger NaCl solution. Artificially everted sacs of anaesthetized insects absorbed fluid when in contact with NaCl or sucrose solutions that were hyperosmotic to the blood. The presence of an active transport mechanism for fluid in the eversible vesicles is discussed.     

Environmental consequences of deltamethrin residues in cattle feces in an African agricultural landscape

Pyrethroid insecticides are widely used to control ectoparasites of livestock, particularly ticks and biting flies. Their use in African livestock systems is increasing, driven by the need to increase productivity and local food security. However, insecticide residues present in the dung after treatment are toxic to dung‐inhabiting insects. In a semiarid agricultural habitat in Botswana, dung beetle adult mortality, brood ball production, and larval survival were compared between untreated cattle dung and cattle dung spiked with deltamethrin, to give concentrations of 0.01, 0.1, 0.5, or 1 ppm. Cattle dung‐baited pitfall traps were used to measure repellent effects of deltamethrin in dung on Scarabaeidae. Dung decomposition rate was also examined. There was significantly increased mortality of adult dung beetles colonizing pats that contained deltamethrin compared to insecticide‐free pats. Brood ball production was significantly reduced at concentrations of 1 ppm; larval survival was significantly reduced in dung containing 0.1 ppm deltamethrin and above. There was no difference in the number of Scarabaeidae attracted to dung containing any of the deltamethrin concentrations. Dung decomposition was significantly reduced even at the lowest concentration (0.01 ppm) compared to insecticide‐free dung. The widespread use of deltamethrin in African agricultural ecosystems is a significant cause for concern; sustained use is likely to damage dung beetle populations and their provision of environmentally and economically important ecosystem services. Contaminated dung buried by paracoprid (tunneling) beetles may retain insecticidal effects, with impacts on developing larvae below ground. Lethal and sublethal effects on entire dung beetle (Scarabaeidae) communities could impair ecosystem function in agricultural landscapes.     

Characterization of nicotinic acetylcholine receptors from the insects Aphis craccivora, Myzus persicae, and Locusta migratoria by radioligand binding assays: relation to thiamethoxam action

Thiamethoxam, a new neonicotinoid insecticide acting at nicotinic acetylcholine receptors, was characterized in competition binding assays with [3-H]-imidacloprid, a specific nicotinic ligand, using membranes from the aphids Aphis craccivora and Myzus persicae, and from the locust Locusta migratoria. In all insects, Scatchard analysis suggested two binding sites for imidacloprid with Kd values in the range of 1 nM and 10 nM, respectively. The Hill values were significantly below 1 (range of 0.63 to 0.85). In contrast to imidacloprid and nicotine, the potency of thiamethoxam to displace [3-H]-imidacloprid varied considerably among these insects. Thiamethoxam was more active than nicotine on Aphis receptors but 100-fold less in Locusta, a nontarget insect. Comparable relations were found to nithiazine. In Myzus, the inhibition curve for thiamethoxam was shallow. This suggested a heterogeneous receptor population displaying a range of binding affinities to thiamethoxam in this aphid. In all three insects, the other neonicotinoid insecticides studied competed with [3-H]-imidacloprid in the same order: thiacloprid > imidacloprid > or = acetamiprid > nitenpyram. N-Methylation of imidacloprid strongly reduced the affinity to the imidacloprid site, whereas N-demethylation of thiamethoxam resulted in a comparable increase of affinity. Supplementary assays were performed with (-)-[3-H]-nicotine and [3-H]-alpha-bungarotoxin on locust membranes. Overall, the data suggested that the outstanding insecticidal properties of thiamethoxam may be due to either a different binding site on nicotinic receptors, or receptor isoforms, or specific pharmakokinetic behavior, rather than to exceptional affinity to one of the examined binding sites.     

Production of the bioinsecticide Bacillus thuringiensis subsp. israelensis with deltamethrin increases toxicity towards mosquito larvae

Bacillus thuringiensis subsp. israelensis is a bioinsecticide used for larval mosquito control and it represents a safe alternative to chemical insecticides. Despite its environmental safety, it is less efficient and persistent than chemical insecticides. To bypass these limitations, we propose to combine the advantages of chemical and biological insecticides by producing Bti in a medium supplemented with a chemical insecticide (DDT, deltamethrin, permethrin, propoxur or temephos). Among the investigated insecticides, the addition of deltamethrin in the medium induced a higher toxicity (over 6·72‐fold) of the composite deltamethrin‐Bti towards mosquito larvae as compared to Bti alone. This was mainly due to the insertion of deltamethrin into the membranes of Bti spores, as evidenced by a quantification of membrane‐extracted deltamethrin by HPLC. This composite larvicide is a promising tool to decrease the quantity of chemicals dispersed in the environment, to increase the efficacy of Bti and to facilitate its widespread use as a transition between chemical and biological insecticides. Further experiments are required to characterize the mechanisms that underline the incorporation of deltamethrin into Bti to optimize the production and the toxicity of this composite larvicide.

Significance and Impact of the Study

This study is the first report of an increased efficacy of the mosquitocidal bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) when produced with a chemical insecticide. The results clearly demonstrate that deltamethrin is able to synergize the insecticidal activity of Bti through inclusion into spore membranes, reducing off‐target and nonspecific toxicity occurring when the chemical is used alone as sprays. This new composite chemical–biological insecticide can become an invaluable tool as an intermediate between single chemical usage and the widespread use of Bti, notably in developing countries with limited financial resources for intensive mosquito control campaigns.     

Adipokinetic hormones concentrations in the haemolymph of Schistocerca gregaria,measured by radioimmunoassay

A new procedure for the measurement of adipokinetic hormone (AKH) concentrations in locust (Schistocerca gregaria) haemolymph is described: Haemolymph is extracted with chloroform/methanol/water and the aqueous layer is fractionated with reverse-phase cartridges and HPLC. The fractions corresponding to AKH-I (Lom-AKH-I) and AKH-II (Scg-AKH-II) are then measured in a competitive binding assay using specific antibodies and [3H]AKHs. The procedures could be applied to any peptides containing N-terminal pyroglutamate residues including all members of the adipokinetic/hyperglycaemic/red pigment concentrating hormone family. Results show that the concentrations of both AKH-I and AKH-II increase within 5 min of initiation of flight and are maintained at approx. 15-fold (AKH-I) and 6-fold (AKH-II) the resting levels over flights of at least 60 min. Poisoning of locusts with either the insecticide deltamethrin or with potassium chloride also caused release of hormones. Starvation for 6 h caused elevation of hormone levels in 5th instar nymphs, but starvation for 6 or 20 h had little effect on hormones in adults, despite an increase in haemolymph diacylglycerols at 20 h.     

Is acetylcholinesterase a pertinent biomarker to detect exposure of pyrethroids? A study case with deltamethrin

The possibility to use acetylcholinesterase as biomarker of exposure to deltamethrin insecticide in the honeybee, Apis mellifera were considered. Joined actions of deltamethrin and pirimicarb (carbamate), alone or in association (dual treatment), were investigated on AChE activity in surviving and dead honeybees in order to test its reliability as biomarker. All treatments induced a reduction in tissue AChE activity in dead bees. In surviving bees, deltamethrin treatment induced an important increase of AChE activity that is not abolished by pirimicarb treatment. The analysis of AChE forms revealed an increase in the soluble form in surviving and dead bees and an increase of the membrane form in surviving bees. No direct effect of deltamethrin on soluble and membrane AChE was observed in vitro. The important increase in AChE activity in response to deltamethrin, not altered by pirimicarb treatment, suggests that AChE activity could represent a robust biomarker specific to deltamethrin exposure in living bees.     

Whole-tree sap flow is substantially diminished by leaf herbivory

Ecohydrological models consider the relationship between tree size and structure (especially leaf area index) and water use but generally treat herbivory as a source of unwanted noise in the data. Little is known of how insect damage to leaves influences whole-plant water use in trees. Water use is driven by environmental demand and the total leaf area through which transpiration can occur, but the effects of insects are expected to be complex. Different kinds of insects could have different effects; for example, chewing insects reduce leaf area, whereas sucking and tissue mining insects reduce leaf function without reducing area. Further, plants respond to herbivory in a range of ways, such as by altering leaf production or abscising leaves. We examined the effect of insects on Eucalyptus blakelyi in a woodland near Canberra, Australia, using sap flow velocity as a measure of whole-plant water use. We applied insecticide to 16 trees matched to an untreated control group. After 6 months, we examined the effects on sap flow velocity and crown condition. There was a general increase in sap flow velocity as trees produced leaves over the growing season, but the increase in sap flow for trees without insecticide protection was half that of the protected trees (increase: 4.4 vs. 9.0 cm/h, respectively). This dramatic effect on sap flow was consistent with effects on crown condition. Unprotected trees had 20% less leaf mass per unit stem in the crown. In addition, unprotected trees had a 20% greater loss of leaf functional area from necrosis. It should be noted that these effects were detected in a year in which there was not an outbreak of the psyllids (Homoptera) that commonly cause severe leaf damage to this tree species. It is predicted that the effect in a psyllid outbreak year would be even more substantial. This result underscores the significant impact that insect herbivores can have on an ecological process of significance to the ecosystem, namely, the movement of water from the soil to the atmosphere.     

Functional Characterization of the Short Neuropeptide F Receptor in the Desert Locust,Schistocerca gregaria

Whereas short neuropeptide F (sNPF) has already been reported to stimulate feeding behaviour in a variety of insect species, the opposite effect was observed in the desert locust. In the present study, we cloned a G protein-coupled receptor (GPCR) cDNA from the desert locust, Schistocerca gregaria. Cell-based functional analysis of this receptor indicated that it is activated by both known isoforms of Schgr-sNPF in a concentration dependent manner, with EC₅₀ values in the nanomolar range. This Schgr-sNPF receptor constitutes the first functionally characterized peptide GPCR in locusts. The in vivo effects of the sNPF signalling pathway on the regulation of feeding in locusts were further studied by knocking down the newly identified Schgr-sNPF receptor by means of RNA interference, as well as by means of peptide injection studies. While injection of sNPF caused an inhibitory effect on food uptake in the desert locust, knocking down the corresponding peptide receptor resulted in an increase of total food uptake when compared to control animals. This is the first comprehensive study in which a clearly negative correlation is described between the sNPF signalling pathway and feeding, prompting a reconsideration of the diverse roles of sNPFs in the physiology of insects.     

Locust flight activity as a model for hormonal regulation of lipid mobilization and transport

Flight activity of insects provides a fascinating yet relatively simple model system for studying the regulation of processes involved in energy metabolism. This is particularly highlighted during long-distance flight, for which the locust constitutes a long-standing favored model insect, which as one of the most infamous agricultural pests additionally has considerable economical importance. Remarkably many aspects and processes pivotal to our understanding of (neuro)hormonal regulation of lipid mobilization and transport during insect flight activity have been discovered in the locust; among which are the peptide adipokinetic hormones (AKHs), synthesized and stored by the neurosecretory cells of the corpus cardiacum, that regulate and integrate lipid (diacylglycerol) mobilization and transport, the functioning of the reversible conversions of lipoproteins (lipophorins) in the hemolymph during flight activity, revealing novel concepts for the transport of lipids in the circulatory system, and the structure and functioning of the exchangeable apolipopotein, apolipophorin III, which exhibits a dual capacity to exist in both lipid-bound and lipid-free states that is essential to these lipophorin conversions. Besides, the lipophorin receptor (LpR) was identified and characterized in the locust.In an integrative approach, this short review aims at highlighting the locust as an unrivalled model for studying (neuro)hormonal regulation of lipid mobilization and transport during insect flight activity, that additionally has offered a broad and profound research model for integrative physiology and biochemistry, and particularly focuses on recent developments in the concept of AKH-induced changes in the lipophorin system during locust flight, that deviates fundamentally from the lipoprotein-based transport of lipids in the circulation of mammals. Current studies in this field employing the locust as a model continue to attribute to its role as a favored model organism, but also reveal some disadvantages compared to model insects with a completely sequenced genome.     

A methodology based on insecticide impregnated filter paper for monitoring resistance to deltamethrin in Triatoma infestans field populations

The domiciliary presence of Triatoma infestans (Klug) (Hemiptera: Reduviidae) after control interventions was reported in recent years. Toxicological studies showed high levels of resistance to pyrethroids suggesting resistance as one of the main causes of deficient control. The aim of the present study was to develop a protocol to test resistance to deltamethrin in T. infestans collected from the field by discriminate concentration. To evaluate field insects, the effect of age (early vs. later) and nutritional state (starved vs. fed) on the deltamethrin susceptibility of each developmental stage was studied. Topical and insecticide impregnated paper bioassays were used. Using the impregnated paper, the susceptibility to deltamethrin was not affected by the age of the stadium and the nutritional states, and varied with the post‐exposure time and with the different developmental stages. A discriminant concentration of deltamethrin (0.36% w/v) impregnated in filter paper was established for all developmental stages. Finally, the methodology and the discriminant concentration were evaluated in the laboratory showing high sensitivity in the discrimination of resistance. The present study developed a methodology of exposure to insecticide impregnated papers and proposes a protocol to test T. infestans in field populations with the aim to detect early evolution of resistance to deltamethrin.     

Energetic consequences of repeated and prolonged dehydration in the Antarctic midge, Belgica antarctica

Larvae of the Antarctic midge, Belgica antarctica, routinely face periods of limited water availability in their natural environments on the Antarctic Peninsula. As a result, B. antarctica is one of the most dehydration-tolerant insects studied, surviving up to 70% loss of its body water. While previous studies have characterized the physiological effects of a single bout of dehydration, in nature larvae are likely to experience multiple bouts of dehydration throughout their lifetime. Thus, we examined the physiological consequences of repeated dehydration and compared results to larvae exposed to a single, prolonged period of dehydration. For the repeated dehydration experiment, larvae were exposed to 1-5 cycles of 24 h dehydration at 75% RH followed by 24 h rehydration. Each bout of dehydration resulted in 30-40% loss of body water, with a concomitant 2- to 3-fold increase in body fluid osmolality. While nearly 100% of larvae survived a single bout of dehydration, <65% of larvae survived five such cycles. Larvae subjected to multiple bouts of dehydration also experienced severe depletion of carbohydrate energy reserves; glycogen and trehalose content decreased with each successive cycle, with larvae losing 89% and 48% of their glycogen and trehalose, respectively, after five cycles of dehydration/rehydration. Larvae exposed to prolonged dehydration (99% RH for 10d) had 26% less water, 43% less glycogen, and 27% less lipid content than controls, but did not experience any mortality. Thus, both repeated and prolonged dehydration results in substantial energetic costs that are likely to negatively impact fitness.     

辛硫磷和溴氰菊酯混剂对家蝇抗性发展的影响

以家蝇(Musca domestica vicina Macquart)为试虫,用辛硫磷溴氰菊酯单剂及不同配比的混剂进行汰选试验。所有混剂选育的家蝇抗性发展都很缓慢,而单剂抗性发展都很快。增效试验表明,辛硫磷与溴氰菊酯混配有明显增效作用,特别是对抗性品系。生化分析结果表明,对澳氰菊酯的抗性发展与酯酶的酶活升高有关。对辛硫磷抗性发展与多功能氧化酶的酶活升高和乙酰胆碱酯酶敏感性降低有关。混剂选育的家蝇其对单剂的敏感性的变化及酶系的变化,随着混剂的配比而变化。     

辛硫磷和溴氰菊酯混剂对家蝇抗性发展的影响

以家蝇（ＭｕｓｃａｄｏｍｅｓｔｉｃａｖｉｃｉｎａＭａｃｑｕａｒｔ）为试虫,用辛硫磷溴氰菊酯单剂及不同配比的混剂进行汰选试验。所有混剂选育的家蝇抗性发展都很缓慢,而单剂抗性发展都很快。增效试验表明,辛硫磷与溴氰菊酯混配有明显增效作用,特别是对抗性品系。生化分析结果表明,对溴氰菊酯的抗性发展与酯酶的酶活升高有关。对辛硫磷抗性发展与多功能氧化酶的酶活升高和乙酰胆碱酯酶敏感性降低有关。混剂选育的家蝇其对单剂的敏感性的变化及酶系的变化,随着混剂的配比而变化