New repellent effective against African malaria mosquito Anopheles gambiae: implications for vector control.

Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) is a vector for Plasmodium, the causative agent of malaria. Current control strategies to reduce the impact of malaria focus on reducing the frequency of mosquito attacks on humans, thereby decreasing Plasmodium transmission. A need for new repellents effective against Anopheles mosquitoes has arisen because of changes in vector behaviour as a result of control strategies and concern over the health impacts of current repellents. The response of A. gambiae to potential repellents was investigated through an electroantennogram screen and the most promising of these candidates (1-allyloxy-4-propoxybenzene, 3c{3,6}) chosen for behavioural testing. An assay to evaluate the blood-host seeking behaviour of A. gambiae towards a simulated host protected with this repellent was then performed. The compound 3c{3,6} was shown to be an effective repellent, causing mosquitoes to reduce their contact with a simulated blood-host and probe less at the host odour. Thus, 3c{3,6} may be an effective repellent for the control of A. gambiae.

Sugar deprivation reduces insemination of Anopheles gambiae (Diptera: Culicidae), despite daily recruitment of adults, and predicts decline in model populations.

Our research tests the hypothesis that the inability to sugar-feed reduces the insemination rate in mosquito populations. To test this, we measured the effects of sugar availability on cumulative insemination performance of male Anopheles gambiae Giles s.s. (Diptera: Culicidae) during 10-d periods of continual emergence of equal numbers of both sexes, and we evaluated the implications at the population level with a matrix population model. On each day of each of four replicates, 20 newly emerged mosquitoes of each sex were recruited into the populations within two mesocosms, large walk-in enclosures with simulated natural conditions. Each mesocosm contained a cage to replicate the experiment on a small scale. Scented sucrose was absent or present (control). A human host was available nightly as a bloodmeal source in both mesocosms. Sugar availability and enclosure size significantly influenced female insemination. In the mesocosms, with sugar 49.7% of the females were inseminated, compared with 10.9% of the females without sugar. In the small cages, the insemination rates were 76.0 and 23.5%, respectively. In the mesocosms, cumulative survival of females after 10 d was 51.6% with sugar and 25.6% without sugar. In the cages, female survival was 95 and 73%, respectively. Sensitivity analysis of the population projection matrix shows that both reduced male survival and reduced mating capability due to a lack of sugar contributed to lower insemination rates in females, and in the absence of sugar the insemination rate was lowered to an extent that led to population decline.

Influence of habitat structure and resource availability on the movements of Rhagoletis indifferens (Diptera: Tephritidae).

Habitat structure and resources availability may differentially influence movement between habitat patches. We examined fly movement decisions (stay or leave) at the scale of individual trees by measuring the response of marked Rhagoletis indifferens (Diptera: Tephritidae) to sweet cherry trees (Prunus avium) that were manipulated by changing the shape of the tree (structure treatment = normal or reduced) and the fruit load (fruit treatment = augmented, normal, or reduced). More than 600 observations were made at two field sites that differed in the average inter-tree distance: Senger site, 10.1 +/- 4.5 m; Tuemp site, 29.0 +/- 19.3 m. At the Senger site, flies were resighted most often in the normal structure-augmented fruit trees. At the Tuemp site, however, there were fewer transfers between trees, unusual tree preferences, and significant treatment interaction terms. Using a first principles diffusion model of attraction and by varying fly perceptual range to limit tree choice, we generated unusual tree preferences based on differential attraction to individual trees. Our results suggest that manipulating tree attractiveness may be a viable pest management strategy for closely spaced trees but not for dispersed trees. Further study into the relationship between the spatial arrangement of trees and the flies' ability to detect specific tree characteristics is warranted.

Host antibodies in mosquito bloodmeals: a potential tool to detect and monitor infectious diseases in wildlife.

When a female mosquito bites, it carries away a blood sample containing specific antibodies that can provide a history of the immune responses of its vertebrate host. This research examines the limits and reliability of a technique to detect antibodies in blood-fed mosquitoes in the laboratory. Mosquitoes were fed on blood containing a specific antibody, and then they were assayed using an enzyme-linked immunosorbent assay to determine the limits of detection of antibody over time, at different temperatures and initial antibody concentrations. The antibody, at an initial concentration of 1 microg/ml, could be detected in mosquitoes for 24-48 h after feeding. Blind tests simulating the assay of feral mosquitoes were used to test the reliability of the method and detected positive mosquitoes with few false negatives and no false positives. Specific antibodies also could be detected in mosquitoes that had been air-dried or preserved in ethanol. This research indicates that, in theory, the collection and immunological assay of blood-fed mosquitoes could be developed to detect and monitor infectious disease in wildlife.

Repellency of a wireworm, Agriotes obscurus (Coleoptera: Elateridae), on exposure to synthetic insecticides in a soil-less bioassay.

A soil-less bioassay arena to test repellency of wireworms (A. obscurus) to insecticides and carrier solvents is described. The bioassay and variables measured distinguish between shorter-range (contact and/or volatile) and longer-range (volatile) repellency. Wireworm positions are recorded every 3 s for 20 min, and average speed, rate of slowing, and longer- and shorter-range repellent behaviors calculated. Shorter-range repellency is determined with a Wireworm Repellency Score (WRS, range 0-100), calculated before contact and after contact with test chemicals. Of two carrier solvents tested, wireworms were strongly repelled by acetone (WRS = 57) but not by water (WRS = 1) when introduced to the bioassay arenas immediately after chemical inoculation. When bioassay arenas were assembled/sealed 2 min after inoculation, acetone elicited no repellency (WRS = 2). When dissolved in acetone in bioassays assembled with a 2-min delay, imidacloprid, chlorpyrifos, lindane, and tefluthrin elicited slight to moderate repellency at the highest concentrations tested (WRS = 30, 48, 42, and 49, respectively). Both longer- and shorter-range repellency increased over the duration of the observation period for lindane and tefluthrin, and shorter-range repellency also increased over the duration of the observation period for chlorpyrifos. Removal of volatiles in the bioassay arena by vacuum considerably affected wireworm movement in the arena, with the repellency elicited by acetone and lindane being significantly reduced. Clothianidin elicited no longer- or shorter-range repellency.

Chaotic dynamics can select for long-term dormancy.

Extended dormancy in a population is evolutionarily costly unless some variance in season-to-season fitness (usually driven by variance in environmental quality) makes bet hedging useful. Consequently, dormancy in a population is usually accepted as evidence of environmental variance. Using a Ricker-type model with heritable variation in dormancy, we show that this need not be so. Intrinsic population dynamics can generate chaotic fluctuations in the absence of environmental variance. Chaotic dynamics increase the frequency of a range of dormant strategists under natural selection, even when mortality during dormancy is relatively high. The buffering effect of dormant individuals then eliminates chaotic dynamics or generates periodic orbits of relatively low amplitude. These stabilized populations harbor a high frequency of dormant individuals that express a range of propensities to enter dormancy.

Games among cannibals: competition to cannibalize and parent-offspring conflict lead to increased sibling cannibalism.

Sibling cannibalism occurs in many species, yet understanding of sibling cannibalism as an adaptation currently lags behind understanding of other antagonistic interactions among siblings. Observed sibling cannibalism phenotypes likely reflect the interaction between competitive games among siblings and parent-offspring conflict. Using a game-theoretic approach, we derive optimal offspring cannibalism behaviour and parental modifiers that limit or facilitate cannibalism. The results are compared to contemporary frequency-independent analysis. With the addition of game interactions among siblings or parent-offspring co-evolution, our model predicts increased cannibalism (compared to the frequency-independent prediction), as offspring compete to eat siblings. When infertile eggs are present--strengthening competition--offspring risk eating viable siblings in order to gain access to infertile eggs, intensifying parent-offspring conflict. We use the results to make new predictions about the occurrence of sibling cannibalism. Additionally, we demonstrate the utility of trophic egg laying as a maternal mechanism to promote egg eating.

Linking spatial processes to life-history evolution of insect parasitoids.

Understanding the evolutionary transition from solitary to group living in animals is a profound challenge to evolutionary ecologists. A special case is found in insect parasitoids, where a tolerant gregarious larval lifestyle evolved from an intolerant solitary ancestor. The conditions for this transition are generally considered to be very stringent. Recent studies have aimed to identify conditions that facilitate the spread of a gregarious mutant. However, until now, ecological factors have not been included. Host distributions and life-history trade-offs affect the distribution of parasitoids in space and thus should determine the evolution of gregariousness. We add to current theory by using deterministic models to analyze the role of these ecological factors in the evolution of gregariousness. Our results show that gregariousness is facilitated through inversely density-dependent patch exploitation. In contrast, host density dependence in parasitoid distribution and patch exploitation impedes gregariousness. Numerical solutions show that an aggressive gregarious form can more easily invade a solitary population than can a tolerant form. Solitary forms can more easily invade a gregarious, tolerant population than vice versa. We discuss our results in light of exploitation of multitrophic chemical cues by searching parasitoids and aggregative and defensive behavior in herbivorous hosts.

Joining and avoidance behavior in nonsocial insects.

Groups of two or more consexual conspecific adults of many kinds of nonsocial insects have been observed to form at feeding, mating, ovipositional, or sheltering sites. Conversely, adults of these same insects have been observed to avoid joining consexual conspecifics (or their progeny) and to place themselves (or their progeny) at some distance that results in spacing. Examples from various taxa illustrate that mechanisms underlying joining or avoidance behavior differ among species, as do types of benefits and costs to individuals who decide to join or avoid others. Moreover, within a given species, the decision to join or avoid others can be affected markedly by the physiological and informational state of the individual and by contextual response thresholds to resource availability. Decisions that benefit the individual may or may not affect the group in terms of total reproductive output.

Feeding and mating strategies in anopheles (Diptera: Culicidae): theoretical modeling approach.

The effects of various ecological factors, such as the probability of finding mates and hosts and of successfully obtaining a blood meal, on the mating and feeding strategies of domestic female anopheline mosquitoes was investigated using theoretical models. The models calculated the mean fitness of 1,000 nonblood-fed, anautogenous, virgin anophelines. One model simulated females that always mate before blood feeding, whereas another simulated females that are able to feed opportunistically if a host was detected before they mated. The models demonstrated highest fitness for mosquitoes capable of opportunistic feeding under nearly all simulated conditions. This advantage increased as the probability of finding hosts and mates decreased as a function of host and mate availability.

Host response profiles: a new theory to help us understand why and how attractants attract.

Much insect behavior is better described in terms of response profiles than by classical stimulus-response patterns; the response to a particular stimulus may vary with changing internal and external conditions, making it important to qualify statements such as "compound X is an attractant." Because of the large number of conditions that may affect responses, it is crucial to develop a theoretical basis to direct the collection of field and experimental data, and their interpretation. A theory-driven model can help us predict response profiles over a wide range of such conditions. We describe an example of such a model, the assumptions upon which it is based, how the model is constructed, and the types of results that a computer implementation of the model can produce.

Parent-offspring conflict and life-history consequences in herbivorous insects.

We develop an evolutionarily stable strategy theory of parent-offspring conflict in insect herbivores for the case in which offspring can choose to leave host plants on which they have been deposited by their mother. We find that a fundamental parent-offspring conflict in larval leaving rates occurs because individual larvae are more related to themselves than to their siblings whereas mothers are equally related to each of their offspring. Several patterns emerge: (1) The optimal probability of movement from the mother's perspective, P*(mom), is always greater than or equal to the optimal probability of movement from the offspring's perspective, P*(off), (2) a consequence of this difference in optimal probabilities of movement is that the mother's fitness for a given clutch is always greater for P*(mom) than P*(off), (3) as the payoff for leaving a plant decreases, (i) the optimal movement rates decrease and (ii) clutches become smaller, (4) as relatedness increases, optimal movement probabilities increase and this causes an increase in optimal clutches, and (5) the clutch size that maximizes the mother's lifetime fitness will frequently diverge from that which the mother would produce were the offspring to move at her optimal rate (i.e., P*(mom)).

Sex pheromone components of the fruit-tree leaf roller,Archips argyrospilus (Walker) (Lepidoptera: Tortricidae), in British Columbia.

In field experiments in the Okanagan Valley, British Columbia, the pheromone blend of (11Z)-tetradecen-1-ol acetate (Z11-14:OAc), (11E)-tetradecen-1-ol acetate (E 11-14:OAc), (9Z)-tetradecen-1-ol acetate (Z9-14:OAc) and dodecan-1-ol acetate (12: OAc) at a 100∶64∶2∶1 ratio (western FTLR blend) attracted significantly more male fruit-tree leaf roller (FTLR),Archips argyrospilus (Walker), than did the previously reported four-component blend and modifications thereof. Addition of (11Z)-tetradecen-1-ol (Z11-14:OH) to the western FTLR blend in a ratio of 4% relative toZ11-14: OAc further significantly enhanced attraction. Compounds were identified and their ratio determined by coupled gas chromatographic-electroantennographic (GC-EAD) and coupled GC-mass spectrometric analyses of female FTLR pheromone gland extracts and by retention index calculations of candidate pheromone components. Determination and use of geographically specific pheromonal blends may be required for optimal, semiochemical-based biorational control of FTLR and other lepidopteran orchard pests.

A general theory for host seeking decisions in mosquitoes.

We develop a theory for host seeking decisions in mosquitoes that explicitly considers the tradeoffs mosquitoes face in allocation to somatic and gametic function. Specifically, we consider conditions under which mosquitoes should seek out nectar and blood hosts upon encountering host odours. Results from development of a dynamic model that considers free and crop energy states suggest that mosquitoes should seek out blood hosts under a wide variety of conditions but that decisions to seek nectar depends upon crop volume, concentration and free energy. This pattern arises because mosquitoes carrying large crop loads are constrained in their ability to obtain large blood meals due to space limitations in the abdomen. The predicted patterns of behaviour are supported by published observations of mosquito behaviour.

Host selection behavior of a thistle-feeding fly: choices and consequences.

Female Canada thistle seed flies (Orellia ruficauda) preferentially oviposit into seed heads which are a single day from opening. When flies are forced to oviposit into flower heads at other stages of development, offspring typically do slightly poorer: they attain a mature mass of about 15% less than do larvae derived from preferred hosts. Larval mass correlates strongly with reproductive success: heavy larvae develop into adults that produce eggs at a faster rate than do those developing from small larvae. After laying a clutch of eggs, flies circumscribe the rim of the flowerhead with their extended ovipositor and deposit a clear fluid. Flies reject previously-attacked hosts, bearing this apparent marking pheromone, significantly more often than they reject unattacked hosts. Costs of superparasitism in this system are relatively small, inasmuch as there is only a weak relationship between clutch size and larval success at the densities measured in this study. We speculate that flies are highly selective, when the apparent costs of making a mistake are rather low, because the information provided by phenological cues and by the putative marking pheromone is highly reliable, and low fecundity and time costs allow sufficient time to express a high level of discrimination.

A Sheep in Wolf's Clothing: Tephritid Flies Mimic Spider Predators.

Mimicry where prey resemble predators to avoid predation is unusual. Snowberry flies, Rhagoletis zephyria Snow, possess striped wing patterns that resemble the legs of jumping spiders. Observations and comparisons of responses of the jumping spider Salticus scenicus (Clerck) to conspecifics, snowberry flies, and other prey flies showed that snowberry flies can avoid predation by jumping spiders through spider mimicry. The mimicry effect was decreased by obliterating snowberry fly wing stripes.