Proof of concept for a novel insecticide bioassay based on sugar feeding by adult Aedes aegypti (Stegomyia aegypti)

Aedes aegypti L. (Stegomyia aegypti) (Diptera: Culicidae) is the principal vector of dengue and yellow fever viruses in tropical and subtropical regions of the world. Disease management is largely based on mosquito control achieved by insecticides applied to interior resting surfaces and through space sprays. Population monitoring to detect insecticide resistance is a significant component of integrated disease management programmes. We developed a bioassay method for assessing insecticide susceptibility based on the feeding activity of mosquitoes on plant sugars. Our prototype sugar‐insecticide feeding bioassay system was composed of inexpensive, disposable components, contained minimal volumes of insecticide, and was compact and highly transportable. Individual mosquitoes were assayed in a plastic cup that contained a sucrose‐permethrin solution. Trypan blue dye was added to create a visual marker in the mosquito's abdomen for ingested sucrose‐permethrin solution. Blue faecal spots provided further evidence of solution ingestion. With the sugar‐insecticide feeding bioassay, the permethrin susceptibility of Ae. aegypti females from two field‐collected strains was characterized by probit analysis of dosage‐response data. The field strains were also tested by forced contact of females with permethrin residues on filter paper. Dosage‐response patterns were similar, indicating that the sugar‐insecticide feeding bioassay had appropriately characterized the permethrin susceptibility of the two strains.     

Interactions of dietary protein and carbohydrate determine blood sugar level and regulate nutrient selection in the insect Manduca sexta L

The non-homeostatic regulation of blood sugar concentration in the insect Manduca sexta L. was affected by nutritional status. Larvae maintained on diets lacking sucrose displayed low concentrations of trehalose, the blood sugar of insects, which varied from 5 to 15 mM with increasing dietary casein level between 12.5 and 75 g/l. These insects were glucogenic, as demonstrated by the selective 13C enrichment of trehalose synthesized from [3-13C]alanine, and de novo synthesis was the sole source of blood sugar. The distribution of 13C in glutamine established that following transamination of the 13C substituted substrate, [3-13C]pyruvate carboxylation rather than decarboxylation was the principal pathway of Pyr metabolism. The mean blood trehalose level was higher in insects maintained on diets with sucrose. At the lowest dietary casein level blood trehalose was approximately 50 mM, and declined to 20 mM at the highest casein level. Gluconeogenesis was detected in insects maintained on sucrose-free diets at the higher protein levels examined, but [3-13C]pyruvate decarboxylation and TCA cycle metabolism was the principal fate of [3-13C]alanine following transamination, and dietary carbohydrate was the principal source of glucose for trehalose synthesis. Feeding studies established a relationship between nutritional status, blood sugar level and dietary self-selection. Insects preconditioned by feeding on diets without sucrose had low blood sugar levels regardless of dietary casein level, and when subsequently given a choice between a sucrose diet or a casein diet, selected the former. Larvae preconditioned on a diet containing sucrose and the lowest level of casein had high blood sugar levels and subsequently selected the casein diet. Larvae maintained on the sucrose diet with the highest casein level had low blood sugar and self-selected the sucrose diet. When preconditioned on diets with sucrose and intermediate levels of casein, insects selected more equally between the sucrose and the casein diets. It is concluded that blood sugar level may be intimately involved in dietary self-selection by M. sexta larvae, and that in the absence of dietary carbohydrate, gluconeogenesis provides sufficient blood sugar to ensure that larvae choose a diet or diets that produce an optimal intake of dietary protein and carbohydrate.     

Potassium chloride deters Lygus hesperus feeding behavior

A series of bioassays were conducted to determine the response of adult western tarnished plant bugs, Lygus hesperus Knight (Heteroptera: Miridae), to artificial diets containing potassium chloride (KCl). We first examined the feeding behavior of L. hesperus by direct observation in a no‐choice diet feeding arena. We observed a total of 22 Lygus feeding events lasting an average of 411 ± 64 s on the control artificial diet and only three feeding events lasting an average of 11 ± 3 s on the KCl‐treated diet. We then conducted several multiple diet choice bioassays to determine the feeding response of L. hesperus when exposed simultaneously to five artificial diet treatments containing different amounts of KCl. For the first bioassay, we used standard clear parafilm diet packets and for the second bioassay we used dark green parafilm diet packets to hold the various diet treatments. Regardless of the diet packet color, L. hesperus overwhelmingly selected the 0% KCl diet treatment over diets containing 3, 6, 9, or 12% KCl. The third and fourth multiple diet choice bioassays were identical to the first bioassay, except that concentrations of the KCl‐treated diets were reduced. Lygus hesperus consistently selected the control diet over all diets containing more than 0.5% KCl. However, when the concentration of KCl in the diet was reduced to ≤0.4%, there were no significant differences in feeding activity exhibited by L. hesperus. Finally, to determine if the addition of KCl to the diet influenced their upwind response, we examined the responses of L. hesperus that were simultaneously exposed to a control artificial diet and a diet containing 12% KCl in a Y‐tube olfactometer bioassay. Of the 95 adults tested, 47 selected the arm containing the normal diet and 48 selected the arm containing KCl‐treated diet, indicating that dietary constituents did not preferentially attract or repel L. hesperus. The results from these studies strongly suggest that KCl negatively affects L. hesperus feeding behavior by functioning as a strong gustatory deterrent when concentrations exceed 0.5%. Visual and volatile cues appeared to have no role in mediating orientation or feeding behavior under these test conditions.     

Sugar feeding protects against arboviral infection by enhancing gut immunity in the mosquito vector Aedes aegypti

As mosquito females require a blood meal to reproduce, they can act as vectors of numerous pathogens, such as arboviruses (e.g. Zika, dengue and chikungunya viruses), which constitute a substantial worldwide public health burden. In addition to blood meals, mosquito females can also take sugar meals to get carbohydrates for their energy reserves. It is now recognised that diet is a key regulator of health and disease outcome through interactions with the immune system. However, this has been mostly studied in humans and model organisms. So far, the impact of sugar feeding on mosquito immunity and in turn, how this could affect vector competence for arboviruses has not been explored. Here, we show that sugar feeding increases and maintains antiviral immunity in the digestive tract of the main arbovirus vector Aedes aegypti. Our data demonstrate that the gut microbiota does not mediate the sugar-induced immunity but partly inhibits it. Importantly, sugar intake prior to an arbovirus-infected blood meal further protects females against infection with arboviruses from different families. Sugar feeding blocks arbovirus initial infection and dissemination from the gut and lowers infection prevalence and intensity, thereby decreasing the transmission potential of female mosquitoes. Finally, we show that the antiviral role of sugar is mediated by sugar-induced immunity. Overall, our findings uncover a crucial role of sugar feeding in mosquito antiviral immunity which in turn decreases vector competence for arboviruses. Since Ae. aegypti almost exclusively feed on blood in some natural settings, our findings suggest that this lack of sugar intake could increase the spread of mosquito-borne arboviral diseases.     

Bird pollinators differ in their tolerance of a nectar alkaloid

Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti‐herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar‐feeding birds, both specialist (white‐bellied sunbirds Cinnyris talatala) and generalist (dark‐capped bulbuls Pycnonotus tricolor and Cape white‐eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short‐term feeding patterns in white‐bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose‐dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White‐bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white‐eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white‐eyes are generalist nectar‐feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.     

Movement of Aedes aegypti following a sugar meal and its implication in the development of control strategies in Durán,Ecuador

We evaluated how the presence of sugar sources impacted the distribution of Aedes aegypti in different habitats in Durán , Ecuador. Land cover and normalized difference vegetation index maps were used to guide a random point sampling routine to select study grids (30 m × 30 m) in low vegetation (LV) and high vegetation (HV). Five individual plants, at one home in the LV and HV grid, were treated with a different colored, non‐attractive, 60% sucrose solution to determine mosquito feeding and movement. Sugar alone is not attractive to mosquitoes, so spraying vegetation with a dyed sugar solution can be used for visual determination of sugar feeding. Outdoor collections using BG sentinel traps and indoor collections using aspirators were conducted at the treatment home and with collection points at 20, 40, and 60 m surrounding the treatment home for three consecutive days. A total of 3,245 mosquitoes in two genera, Aedes and Culex, was collected. The proportion of stained Ae. aegypti females was 56.8% (510/898) and 0% for males. For Culex, 63.9% (248/388) females and 36.1% (140/388) males were collected stained. Aedes aegypti and Culex spp. were found up to 60 m stained in both LV and HV grids. Significantly more stained females Ae. aegypti were found inside homes compared to females and males of Culex spp. in both habitats. This study identifies that outdoor sugar feeding is a common behavior of Ae. aegypti and can be targeted as a control strategy in urban habitats in Latin America.     

The impact of mating and sugar feeding on blood-feeding physiology and behavior in the arbovirus vector mosquito Aedes aegypti

BackgroundAedes aegypti mosquitoes are globally distributed vectors of viruses that impact the health of hundreds of millions of people annually. Mating and blood feeding represent fundamental aspects of mosquito life history that carry important implications for vectorial capacity and for control strategies. Females transmit pathogens to vertebrate hosts and obtain essential nutrients for eggs during blood feeding. Further, because host-seeking Ae. aegypti females mate with males swarming near hosts, biological crosstalk between these behaviors could be important. Although mating influences nutritional intake in other insects, prior studies examining mating effects on mosquito blood feeding have yielded conflicting results.Methodology/Principal findingsTo resolve these discrepancies, we examined blood-feeding physiology and behavior in virgin and mated females and in virgins injected with male accessory gland extracts (MAG), which induce post-mating changes in female behavior. We controlled adult nutritional status prior to blood feeding by using water- and sugar-fed controls. Our data show that neither mating nor injection with MAG affect Ae. aegypti blood intake, digestion, or feeding avidity for an initial blood meal. However, sugar feeding, a common supplement in laboratory settings but relatively rare in nature, significantly affected all aspects of feeding and may have contributed to conflicting results among previous studies. Further, mating, MAG injection, and sugar intake induced declines in subsequent feedings after an initial blood meal, correlating with egg production and laying. Taking our evaluation to the field, virgin and mated mosquitoes collected in Colombia were equally likely to contain blood at the time of collection.Conclusions/SignificanceMating, MAG, and sugar feeding impact a mosquito’s estimated ability to transmit pathogens through both direct and indirect effects on multiple aspects of mosquito biology. Our results highlight the need to consider natural mosquito ecology, including diet, when assessing their physiology and behavior in the laboratory.     

Effects of temperature and dietary sucrose concentration on respiration in the silverleaf whitefly, Bemisia argentifolii

A system consisting of a flow-through chamber connected to a commercial infrared gas analysis system was developed to measure homopteran respiration during feeding. Using this system, respiration rates of 202 and 206 μmol CO(2) h(-1) g(-1) (4.96 and 5.04 ml CO(2) h(-1) g(-1)) were determined for whiteflies and cotton aphids, respectively, at 25 degrees C on diets containing 15% sucrose. These rates were considerably higher than those of other stationary insects, indicating that whiteflies and aphids maintain a relatively high metabolic rate when feeding. Whitefly respiration increased with temperature from 25 to 46 degrees C with a Q(10) of about 2 on diets containing 10, 15 and 20% sucrose, but less than 2 on diets containing 2.5 and 5% sucrose. Respiration rates were similar on the diets containing >10% sucrose, but were generally lower on the diets containing <10% sucrose. Respiration rates decreased upon extended exposure to 47 degrees C; the rate of decrease was inversely related to the dietary sucrose concentration up to 15%. The results indicate that whiteflies require a sucrose concentration of between 5 and 10% (i.e. 0.15 and 0.3 M) for maximum rates of metabolism while feeding. Higher concentrations of sucrose in the diet delayed high-temperature mortality, possibly a reflection of the high sucrose requirement for sorbitol synthesis in whiteflies.     

Feeding behaviour of the horsefly Tabanus nigrovittatus (Diptera: Tabanidae): effects of dissolved solids on ingestion and destination of sucrose or ATP diets

Abstract Wild caught female horseflies, Tabanus nigrovittatus Macq. (Diptera: Tabanidae), were fed solutions containing either sucrose or ATP as a phagostimulant. The sucrose diets were presented as free liquids at room temperature. The ATP in the other diets was dissolved in 0.15 M NaCl, or in 0.3 M or 1 M cellobiose and was presented covered with a Parafilm membrane at 38^oC. The content of dissolved solids in some diets was adjusted with added cellobiose, which had no phago-stimulatory effect. Diets of 1 M or 0.6 M sucrose were ingested in large amounts and were directed to the crop. Diets of 0.3 M or 0.1 M sucrose induced lower levels of ingestion, and the diet was directed to the midgut. The addition of cellobiose to give a 1 M total concentration of dissolved solids in these sucrose diets induced many insects responding to the lower concentrations of sucrose to direct the diet to the crop. Diets of ATP in saline or in 0.3 M cellobiose were directed to the midgut. ATP in 1 M cellobiose caused many of the insects to put the diet in both the crop and the midgut. Two behavioural models are presented that integrate interactions between the level of phagostimulation, the concentration of dissolved solids, and an endogenous feeding factor. The dissolved solids effect is most likely a response to osmotic pressure.     

Changes in nectar concentration: how quickly do whitebellied sunbirds (Cinnyris talatala) adjust feeding patterns and food intake?

Nectarivorous birds encounter varying nectar concentrations while foraging on different food plants and must adjust their consumption to maintain constant energy intake. We determined how rapidly captive whitebellied sunbirds (Cinnyris talatala) adjust their volumetric intake and feeding patterns after changes in diet concentration. On four consecutive days, birds were fed sucrose diets alternating between a standard diet of 16% w/w and test diets of 2.5, 8.5, 16 or 30% w/w, respectively, for 1.5 h periods. Feeding events were recorded with an infrared photo-detection system and food intake and body mass were monitored continuously by electronic balances interfaced to a computer. Generally, birds demonstrated a measurable increase in feeding frequency and food intake within 10 min after a decrease in sucrose concentration. However, individuals responded differently to the most dilute diet (2.5%): while most increased their food intake, others stopped feeding for a short while, appearing to dislike this diet. Furthermore, the number and duration of feeding events increased in the first 5 min after the switch from 2.5% back to 16%, as the birds attempted to compensate for previous reduced sugar intake. Daily sugar intake was lower when birds alternated between 2.5 and 16% diets than on other test days, but birds were able to maintain body mass, presumably through behavioural adjustments.     

Gene silencing in adult Aedes aegypti mosquitoes through oral delivery of double‐stranded RNA

The induction of the naturally occurring phenomenon of RNA interference (RNAi) to study gene function in insects is now common practice. With appropriately chosen targets, the RNAi pathway has also been exploited for insect control, typically through oral delivery of dsRNA. Adapting current methods to deliver foreign compounds, such as amino acids and pesticides, to mosquitoes through sucrose solutions, we tested whether such an approach could be used in the yellow fever mosquito, Aedes aegypti. Using a non‐specific dsRNA construct, we found that adult Ae. aegypti ingested dsRNA through this method and that the ingested dsRNA can be recovered from the mosquitoes post‐feeding. Through the feeding of a species‐specific dsRNA construct against vacuolar ATPase, subunit A, we found that significant gene knockdown could be achieved at 12, 24 and 48 h post‐feeding.     

Effect of six carbohydrate sources on the longevity of a whitefly parasitoid Eretmocerus hayati (Hymenoptera: Aphelinidae)

Parasitoid adults often acquire carbohydrates by feeding on floral nectar and honeydew which provides them with energy and prolongs their life span. The concentration and type of saccharide in nectar and honeydew are variable by species of plant and insect. To explore the effects of various sugar type and concentrations on parasitoid fitness, we compared 5%, 10% and 20% (w/v) solutions of six different sugar resources (glucose, fructose, sucrose, trehalose, melezitose and honey) on the longevity of Eretmocerus hayati, a larval parasitoid of the whitefly Bemisia tabaci in China. Male and female longevity was increased by all of the sugar diets, but female wasps survived longer than the males when the same sugar diet was supplied. Female parasitoids feeding on 10% glucose and 10% honey increased longevity, respectively up to 6.2- and 5.9-fold longer than distil water; 5% honey and 10% fructose had the greatest effects on male longevity, up to 3.5- and 3.3-fold. All six sugar diets, no matter which concentration, significantly changed the survival curves. Glucose, sucrose and honey were optimal sugar diets for this wasp, and 10% was the optimal concentration. Our results could provide an insight into the nutritional requirements of E. hayati under laboratory conditions. Such information can be a basis to improve the longevity of this biological control agent by sugar feeding during the indoor mass-rearing process.     

Sex-specific reaction norms to intraspecific larval competition in the mosquito Aedes aegypti

As the relationship between a given life‐history trait and fitness is not necessarily the same for the two sexes, an ‘intersexual ontogenetic conflict’ may arise. We analysed the phenotypic reaction to intraspecific larval competition of the mosquito, Aedes aegypti, asking: (i) Do both sexes pay the cost of competition with the same life‐history traits and are they equal competitors? (ii) Is there a specific cost of competition beyond sharing food resources? We found that competition incurs a specific cost that was expressed differently by the two sexes. Indeed, each sex maintained the more important life‐history trait(s) for their fitness (developmental time for males and body weight and size for females) at the expense of other traits, thus minimizing the effects of competition on their fitness. The competition exerted by females was estimated as being more intense, probably linked with the greater importance of body size for their fitness.     

Diet affects female mating behaviour in a seed‐feeding beetle

In species where males provide nuptial gifts, females can improve their nutritional status and thus increase their fecundity by mating when in need of resources. However, mating can be costly, so females should only mate to acquire resources when the need for resources is large, such as when females are nutritionally‐deprived. Two populations of the seed‐feeding beetle Callosobruchus maculatus, a species that produces relatively large nuptial gifts, are used to test whether female nutritional status affects mating behaviour. Female access to water, sugar and yeast are manipulated and the fitness consequences of these manipulations are examined together with the effects of diet on the propensity of nonvirgin females to mate. Access to water has a small but significant effect on mass loss over time, lifespan and fecundity of females, relative to unfed controls. Access to sugar (dissolved in water) improves female fecundity and lifespan above that of hydrated females but access to yeast has no positive effects on female survival or reproduction. Diet has a large effect on both receptivity of nonvirgin females to a male and how quickly they accept that male. Unfed females are both more likely to mate, and accept a mate more quickly, than females provided access to water, which are more likely to mate and accept a mate more quickly than females provided with sugar. This rank order of behaviours matches the order predicted if females increase their mating rate when nutritionally deprived (i.e. it matches the effect of diet on female fitness). The results obtained also suggest that mate choice may be condition‐dependent: females from one population (Burkina Faso) show a preference for large males when well‐fed but not when unfed, although this result is not found in a second population (South India). It is concluded that nutritionally‐deprived females are more receptive to mates than are well‐fed females, consistent with the hypothesis that females ‘forage’ for nuptial gifts, or at least more willingly accept sperm in exchange for nuptial gifts, when they are nutritionally deprived.     

Development of probiotic diets for the olive fly: evaluation of their effects on fly longevity and fecundity

One possible control strategy against the olive fly, Bactrocera oleae, the most serious olive crop pest, is the Sterile Insect Technique (SIT) application. However, a number of problems associated with this method remain that decrease the effectiveness of SIT, including the quality of reared insects. Taking the importance of the relationship between the olive fly and bacteria into consideration, the effects of probiotic diets enriched with Pseudomonas putida on B. oleae longevity and fecundity were evaluated. First, we found that the probiotic bacterium, P. putida, is conveyed from diets to the oesophageal bulb as well as to the fly midgut after feeding on the probiotic diet. Subsequently, B. oleae adults fed on either: (a) a standard full protein and sugar diet; (b) a sugar only diet; (c) a probiotic standard full protein and sugar diet; or (d) a probiotic sugar diet. Flies fed on probiotic diets were supplied with an inoculated gel containing P. putida; non‐inoculated gel was provided to the flies fed on non‐probiotic diets. B. oleae males and females that fed on sugar diets did not survive as long as those that fed on protein diets. A comparison of the longevity of adults fed on full diet and sugar with their respective probiotic diets revealed no significant difference. Males fed on the sugar only diet survived longer than males fed on probiotic sugar diet, and females fed on the full protein and sugar diet survived much longer than females fed on the full probiotic diet. As regarding fecundity, both full diets resulted in a higher number of eggs laid per female. Females fed on the probiotic sugar diet laid a higher number of eggs than females that fed on sugar only. The inoculated gel of the probiotic sugar diet contained a significantly higher quantity of leucine, isoleucine and proline than the non‐inoculated gel of the sugar only diet. The possible role of dietary bacteria in relation to functional aspects of olive fly physiology is discussed.     

The effects of a phagostimulant and a deterrent on the microstructure of feeding byManduca sexta caterpillars

Caterpillars of the hawkmothManduca sexta Johan. (Lepidoptera: Sphingidae) were offered discs of agar containing one of a range of concentrations of sucrose or of quinine, and the microstructure of the resulting feeding behaviour was quantified. As sucrose concentration increased caterpillars ate more by increasing the rate of biting and the lengths of meals. Bite frequency increased, after a latency of seconds to minutes, over the entire range tested (0.005 M to 0.5 M) whereas meal length reached a maximum at 0.1 M. Larvae spent less time feeding on agar containing 1 mM quinine than on quinine-free agar. This was accomplished by a reduction in the size of meals; numbers of chewing bouts in meals were lower. No other feeding behaviours were affected. In addition there was no orderly relationship between quinine concentration and changes in feeding behaviours. These observations suggested that postingestive effects were important in decreasing feeding. This paper is dedicated to the memory of Vincent G. Dethier     

The impact of uniform and mixed species blood meals on the fitness of the mosquito vector Anopheles gambiae s.s: does a specialist pay for diversifying its host species diet?

We investigated the fitness consequences of specialization in an organism whose host choice has an immense impact on human health: the African malaria vector Anopheles gambiae s.s. We tested whether this mosquito’s specialism on humans can be attributed to the relative fitness benefits of specialist vs. generalist feeding strategies by contrasting their fecundity and survival on human‐only and mixed host diets consisting of blood meals from humans and animals. When given only one blood meal, An. gambiae s.s. survived significantly longer on human and bovine blood, than on canine or avian blood. However, when blood fed repeatedly, there was no evidence that the fitness of An. gambiae s.s. fed a human‐only diet was greater than those fed generalist diets. This suggests that the adoption of generalist host feeding strategies in An. gambiae s.s. is not constrained by intraspecific variation in the resource quality of blood from other available host species.     

Self-selection of Dietary Threonine in the Rat and the Effect of Taste Stimuli on its Selection

The possible regulation of dietary threonine intake and the effect of a palatable (sodium saccharin) or aversive (quinine sulfate) taste stimulus on the manner of threonine selection were investigated in rats using a self-selection feeding method. Weanling rats were offered the choice of two diets differing only in threonine content for 2 weeks. Both weight gain and food consumption in the rats offered the choice of diets were quite comparable to each other and were the same as those in rats fed one diet containing sufficient threonine. Threonine intake of the self-selecting rats ranged from 0.43 to 1.90% of the food consumed. The threonine concentrations in the plasma and brain of the self-selecting rats increased proportionally with the threonine intake. When rats were offered a choice of two diets containing various amounts of threonine with taste materials, i.e., sodium saccharin or quinine sulfate, neither the dietary threonine nor their growth were ever affected.

These results indicate clearly that rats have an ability to regulate threonine intake to meet their requirement for the l-amino acid, and the threonine selection is not influenced significantly by the dietary addition of palatable or aversive taste materials.     

Oviposition substrate selection by Florida mosquitoes in response to pathogen‐infected conspecific larvae

The impact of the presence of larval mosquito pathogens with potential for biological control on oviposition choice was evaluated for three mosquito species/pathogen pairs present in Florida. These included Aedes aegypti infected with Edhazardia aedis, Aedes albopictus infected with Vavraia culicis, and Culex quinquefasciatus infected with Culex nigripalpus nucleopolyhedrovirus (CuniNPV). Two‐choice oviposition bioassays were performed on each host and pathogen species with one oviposition cup containing infected larvae and the other cup containing uninfected larvae (control). Both uninfected and E. aedis‐infected female Ae. aegypti laid significantly fewer eggs in oviposition cups containing infected larvae. Uninfected gravid female Ae. albopictus and Cx. quinquefasciatus oviposited equally in cups containing uninfected larvae or containing larvae infected with V. culicis or CuniNPV, respectively. Gravid female Ae. albopictus infected with V. culicis did not display ovarian development and did not lay eggs. The decreased oviposition by gravid Ae. aegypti in containers containing E. aedis‐infected larvae may indicate that the infected larvae produce chemicals deterring oviposition.     

Experience‐ and age‐mediated oviposition behaviour in the yellow fever mosquito Stegomyia aegypti (=Aedes aegypti)

In repeated behaviours such as those of feeding and reproduction, past experiences can inform future behaviour. By altering their behaviour in response to environmental stimuli, insects in highly variable landscapes can tailor their behaviour to their particular environment. In particular, female mosquitoes may benefit from plasticity in their choice of egg‐laying site as these sites are often temporally variable and clustered. The opportunity to adapt egg‐laying behaviour to past experience also exists for mosquito populations as females typically lay eggs multiple times throughout their lives. Whether experience and age affect egg‐laying (or oviposition) behaviour in the mosquito Stegomyia aegypti (=Aedes aegypti) (Diptera: Culicidae) was assessed using a wind tunnel. Initially, gravid mosquitoes were provided with a cup containing either repellent or well water. After ovipositing in these cups, the mosquitoes were blood‐fed and introduced into a wind tunnel. In this wind tunnel, an oviposition cup containing repellent was placed in the immediate vicinity of the gravid mosquitoes. A cup containing well water was placed at the opposite end of the tunnel so that if the females flew across the chamber, they encountered the well water cup, in which they readily laid eggs. Mosquitoes previously exposed to repellent cups became significantly more likely to later lay eggs in repellent cups, suggesting that previous experience with suboptimal oviposition sites informs mosquitoes of the characteristics of nearby oviposition sites. These results provide further evidence that mosquitoes modify behaviour in response to environmental information and are demonstrated in a vector species in which behavioural plasticity may be ecologically and epidemiologically meaningful.