Target-invariant aggressive display in a tephritid fly

Fruit flies of the family Tephritidae (Diptera) use specialized wing displays in aggressive encounters with conspecifics and predators. These displays, called supination displays, have been thought to deter attacks from one of their main predators, spiders of the family Salticidae. However, there is no information whether the display is qualitatively or quantitatively different when the target is a conspecific or a predator. In this study, we sought to determine whether flies vary their displays depending on the display target. Using the Mexican fruit fly Anastrepha ludens, we compared the characteristics of the display that male and female flies use against conspecifics and spiders. Flies did not distinguish between spiders and conspecifics in terms of display rates and bout duration. In general, flies are more likely to retreat faster from spiders after performing a display. We suggest that supination is a generalized aggressive behavior that is independent of the target.

Escape of Mexican Fruit Flies from Traps Baited with CeraTrap and Effect of Lure Feeding on Reproduction and Survival

McPhail type traps are commonly used to catch tephritid pests using liquid baits as attractants. Unfortunately, these traps allow that some flies escape after feeding on the bait. Recently, a long-lasting and nontoxic enzymatic-hydrolyzed protein, known commercially as CeraTrap, has been introduced as a novel liquid bait. Because feeding on hydrolyzed proteins can improve reproduction in many tephritids, questions remain as to whether CeraTrap could provide a nutritious meal to flies that ingest the bait but escape the trap. In this study, we analyzed the efficacy of CeraTrap baited traps in capturing Anastrepha ludens flies of two different physiological states and two different diets. We also explored the effect of feeding on CeraTrap on the mating performance of males, ovarian development and fecundity of females and fly survival. Results demonstrated that CeraTrap attracted more protein-deprived and immature flies of both sexes and 2-30% of flies that entered the trap managed to escape. However, after feeding on the bait for 24 h, males exhibited lower mating success, longer latency to mate and longer copula durations than males fed on either sugar or sugar+ protein. Interestingly, females fed CeraTrap for 24 h developed ovaries as large as those females fed on sugar+ protein, however, they laid no eggs. When feeding continuously on CeraTrap, flies exhibited shorter lifespans and females laid no eggs. These findings indicate that, although some flies can ingest the bait and escape from the trap, their reproductive traits are negatively affected.

Determination of the Host Status of the 'Persian' Lime (Citrus latifolia Tanaka) for Anastrepha ludens (Loew) (Diptera: Tephritidae)

Field and laboratory no-choice oviposition tests were performed to determine whether the 'Persian' lime (Citrus latifolia Tanaka) is a host of Anastrepha ludens Loew (Diptera: Tephritidae). Trapping and fruit sampling were performed to determine adult population densities and the level of infestation in the two lime orchards. Additionally, unharvested and harvested limes were exposed to sexually mature flies and the number of eggs laid and the immature developmental rates were determined. As a control, parthenocarpic 'Ataulfo' mangoes (Mangifera indica L.), a suitable host for A. ludens, were exposed to similar experimental procedures. The fecundity and fertility of adults obtained from limes and mangoes were compared. Our results demonstrate that A. ludens, under forced infestation conditions, oviposit on limes and also on control fruit. However, differences were detected in unharvested and harvested fruit, as unharvested limes were not infested. In the case of harvested fruit, the numbers of eggs laid and survival rates of immatures were significantly lower for 'Persian' limes compared with mangoes. Egg clutches were larger in limes than in mangoes, and most were deposited in the albedo rather than in the pulp. Moreover, oviposition rates were much higher in limes than in mangoes. Despite the fact that few of the immatures reached adulthood, the females obtained from limes were as fecund and fertile as those obtained from mangoes. Although adult A. ludens flies were captured in the two orchards, fruit sampling showed a complete absence of natural infestation among 'Persian' limes. We discuss the importance of our findings for determining the host status for 'Persian' limes.

Effects of size, sex and teneral resources on the resistance to hydric stress in the tephritid fruit fly Anastrepha ludens

Water availability is recognized as one of the most important factors in the distribution and activity of terrestrial organisms. In the case of insects, hydric stress imposes a major challenge for survival because of the small surface-area-to-volume ratio they exhibit. In general, stress resistance is expected to co-vary positively with size; however, this pattern can become obscured in insects that exhibit sexual size dimorphism, as sexes differ in size and/or shape and have dissimilar resource allocations. In the present study, we use an allometric-based approach to (i) assess the desiccation and starvation stress resistance of teneral Anastrepha ludens flies, (ii) disentangle the relationships between resistance, size and sex and (iii) examine the adult fly body differences in water and lipid contents before and after exposure to stress. After controlling for sexual size dimorphism, an allometric increase of resistance with overall size was observed for all stress-based treatments. The scaling exponents that define the proportion of increase resistance varied with size traits and with type and degree of hydric stress. In this allometric relationship, and also in the relationships between mass and wing length and between size and teneral resources, the sexes maintained similar scaling exponents but differed in the intercepts. Males were more resistant to stress than females; this competitive advantage is probably linked to greater amounts of teneral lipids and more water use during stress.

Fitness cost implications of PhiC31-mediated site-specific integrations in target-site strains of the Mexican fruit fly, Anastrepha ludens (Diptera: Tephritidae)

Site-specific recombination technologies are powerful new tools for the manipulation of genomic DNA in insects that can improve transgenesis strategies such as targeting transgene insertions, allowing transgene cassette exchange and DNA mobilization for transgene stabilization. However, understanding the fitness cost implications of these manipulations for transgenic strain applications is critical. In this study independent piggyBac-mediated attP target-sites marked with DsRed were created in several genomic positions in the Mexican fruit fly, Anastrepha ludens. Two of these strains, one having an autosomal (attP_F7) and the other a Y-linked (attP_2-M6y) integration, exhibited fitness parameters (dynamic demography and sexual competitiveness) similar to wild type flies. These strains were thus selected for targeted insertion using, for the first time in mexfly, the phiC31-integrase recombination system to insert an additional EGFP-marked transgene to determine its effect on host strain fitness. Fitness tests showed that the integration event in the int_2-M6y recombinant strain had no significant effect, while the int_F7 recombinant strain exhibited significantly lower fitness relative to the original attP_F7 target-site host strain. These results indicate that while targeted transgene integrations can be achieved without an additional fitness cost, at some genomic positions insertion of additional DNA into a previously integrated transgene can have a significant negative effect. Thus, for targeted transgene insertions fitness costs must be evaluated both previous to and subsequent to new site-specific insertions in the target-site strain.

Evaluation of the Host Status of Mature Green Papayas 'Maradol' for the Mexican Fruit Fly (Diptera: Tephritidae)

The suitability of mature green 'Maradol' papaya as a host of Anastrepha ludens (Loew) was studied under field and laboratory conditions. Field tests were conducted on commercial-ripened and spot-ripened fruit in two orchards and during two seasons in the state of Chiapas. Fruits at exportation ripeness are in "commercial ripeness", while fruits that are harvested immediately preceding exportation ripeness are in "spot ripeness." The field tests consisted of forced infestation experiments that evaluated papayas at two ripeness stages: the commercial- or exportation-ripened fruit (green fruits with one or two yellow stripes) and fruit before exportation ripeness called "spot ripeness." These tests were conducted in two orchards and during two seasons in the state of Chiapas, Mexico. Laboratory trials were performed with commercial-ripened fruit only. Fruit from four different postharvest periods (3, 24, 48, and 72 h) were exposed to groups of gravid flies. No larvae emerged from the fruit that was collected in the field experiments. However, some larvae and several fertile flies were obtained from the commercial-ripened fruit 72 h postharvest but not 3, 24, and 48 h postharvest in the laboratory. The results of this study indicate that the commercially ripe fruits of papaya Maradol were resistant to or free from infestation of A. ludens flies under field conditions, though these fruits must be considered nonnatural, conditional host because they became infested in the laboratory.

Effect of multiple endogenous biological factors on the response of the tephritids Anastrepha ludens and Anastrepha obliqua (Diptera: Tephritidae) to multilure traps baited with BioLure or NuLure in mango orchards

The physiological state of an insect is likely the most important endogenous factor influencing resource-oriented behavior, and it varies considerably among individuals. Trials were conducted in mango orchards to study the effect of multiple endogenous biological factors on the response of two fly species, Anastrepha ludens (Loew) and Anastrepha obliqua Maquart (Diptera: Tephritidae), to BioLure and NuLure baits. The biological factors of the two fly species that were tested were the following: 1) fertility status-sterile (irradiated) and fertile flies; 2) two types of diets (only sugar and a 3:1 mixture of sugar and hydrolyzed yeast protein; 3) sex, and 4) two sexual maturity conditions (2-4- and 15-18-d-old flies, representing immature and sexually mature flies, respectively, and 2-4-d-old flies treated with methoprene as an artificially induced sexually state male condition). The laboratory-treated flies were released into three different mango orchards. The trials were conducted in four blocks per orchard using eight traps in each block (50:50 BioLure: NuLure). The traps were replaced every 2 d during the 12-d period and the flies per trap per day values were calculated. More protein-fed, fertile, female, immature, and A. obliqua flies were caught compared with the other flies tested. In addition, the traps baited with NuLure attracted more flies than those baited with BioLure. Interaction analyses indicated that the type of bait and the sexual maturity status were the most important factors affecting the responses of the flies. Our study demonstrated that lures attract only a small segment of the fly population, those that have a specific hunger for amino acids-immature flies-and those that were protein-starved. The implications for improved trapping system designs are discussed.

The effect of irradiation and mass rearing on the anti-predator behaviour of the Mexican fruit fly, Anastrepha ludens (Diptera: Tephritidae)

Fruit flies (Diptera: Tephritidae) are major pests worldwide. The sterile insect technique, where millions of flies are reared, sterilized by irradiation and then released, is one of the most successful and ecologically friendly methods of controlling populations of these pests. The mating behaviour of irradiated and non-irradiated flies has been compared in earlier studies, but there has been little attention paid to the anti-predator behaviour of mass-reared flies, especially with respect to wild flies. Tephritid flies perform a supination display to their jumping spider predators in order to deter attacks. In this study, we evaluated the possibility of using this display to determine the anti-predator capabilities of mass-reared irradiated, non-irradiated flies, and wild flies. We used an arena setup and observed bouts between jumping spiders (Phidippus audax Hentz) and male Mexican fruit flies (Anastrepha ludens Loew). We show that although all flies performed a supination display to their predator, wild flies were more likely to perform a display and were significantly more successful in avoiding attack than mass-reared flies. We suggest that this interaction can be used to develop a rapid realistic method of quality control in evaluating anti-predator abilities of mass-reared fruit flies.

Susceptibility of 15 mango (Sapindales: Anacardiaceae) cultivars to the attack by Anastrepha ludens and Anastrepha obliqua (Diptera: Tephritidae) and the role of underdeveloped fruit as pest reservoirs: management implications

We evaluated the susceptibility of 15 mango cultivars to the attack of Anastrepha ludens (Loew) and Anastrepha obliqua (Macquart) (Diptera: Tephritidae), the main tephritid pests of this crop in Mexico. In a field experiment, bagged fruit-bearing branches were exposed to gravid females of both fly species. Infestation rates, developmental time, adult eclosion, and F1 adult longevity, fecundity, and fertility were recorded, ranking cultivars in terms of susceptibility to fly attack and development. We also compared the volatile profile in selected resistant and susceptible cultivars in search of possible correlations. In a second experiment, clutch size for A. ludens was determined in each cultivar. Infestation rates, developmental time, and F1 demographic parameters varied sharply among cultivars and between fly species for bagged fruit. Cultivars 'Vishi,' '74-82,' and 'Brooks' were most susceptible to A. ludens infestation while "Tommy,' 'Sensation,' and 'Ataulfo "niño"' (parthenocarpic fruit) were most susceptible to A. obliqua infestation. 'Edward,' 'Kent,' 'Brooks late,' 'Palmer, and 'Ataulfo' exhibited tolerance to attack of both fly species. Fruit of susceptible and resistant cultivars exhibited unique volatile profiles. Fly development and F1 adult demographic parameters varied significantly among cultivars. A. ludens females laid larger clutches in larger and harder fruit. We highlight the important role of Ataulfo "niño" as pest reservoir if fruit is left unharvested on trees. We discuss the possible use of highly resistant cultivars as trap crops or egg sinks.

Insecticidal activity of raw ethanolic extracts from Magnolia dealbata Zucc on a tephritid pest

Ethanolic extracts from Magnolia dealbata (Zucc.) (Magnoliaceae); leaves, bark, seeds, sarcotesta and flowers were evaluated for insecticidal activity against adults of the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae). Using feeding bioassays composed from sugar-extract mixtures, only the extract from sarcotesta indicated insecticidal activity against the flies. The extracts from the other four plant tissues (leaves, bark, seeds and flowers) did not manifest any biological activity. The most effective extract was obtained from oven-dried sarcotesta, whereas extracts from fresh sarcotesta were inactive. Our results suggest that M. dealbata sarcotesta contains secondary metabolites with insecticidal activity against A. ludens adults. These metabolites are as potent as natural pyrethins and represent a potential substance for controlling this type of pest.

Coping with an unpredictable and stressful environment: the life history and metabolic response to variable food and host availability in a polyphagous tephritid fly

The way energy resources are used under variable environmental conditions lies at the heart of our understanding of resource management and opportunism in many organisms. Here we sought to determine how a time-limited, synovigenic and polyphagous insect with a high reproductive-potential (Anastrephaludens), copes behaviourally and metabolically with environmental unpredictability represented by constant and variable regimes of host availability and variation in food quality. We hypothesized that an adaptive response to a windfall of nutritious food would be the rapid accumulation of energy metabolites (whole body lipids, glycogen and proteins) in the female. We also studied patterns of oogenesis as an indicator of egg-reabsorption under stressful environmental conditions. As predicted, patterns of energy metabolites were mainly driven by the quality and temporal pattern of food availability. In contrast, patterns of host availability had a lower impact upon metabolites. When given constant access to high quality nutrients, after an initial increase early in life, whole body lipids and glycogen were regulated downward to a steady-state level and somatic protein levels did not vary. In contrast, when food uncertainty was introduced, whole body lipid, glycogen and protein oscillated sharply with peaks associated with pulses of high-quality food. Production of eggs was highest when offered continuous access to hosts and high quality food. Importantly, females fully recovered their reproductive capacity when fruit became available following a period of host deprivation. With no evidence of egg resorption and high levels of egg dumping, it appears that egg dumping may favour the continuous production of eggs such that the female's reproductive tissues are ready to respond to rapid changes in the availability of hosts. Our results exemplify the capacity of insects to maximize reproduction under variable and stressful environmental conditions.

Light conditions affect sexual performance in a lekking tephritid fruit fly

Sensory systems are very susceptible to early environment experience. Mating success depends on the transmission of information from the signaller to the receiver, which means that sensory biases caused by developmental environment are likely to affect sexual selection. We investigated the impact of the developmental visual environment (light spectrum) on male copulation behaviour and female preference in the lekking tephritid Anastrepha ludens. We reared flies in four different light spectrum conditions - red light, blue light, shaded light and darkness - during their first 16 days after emerging from pupae. We found that the light environment experienced during early adulthood affected mating frequency and, in some cases, the latency to copulate, but not copulation duration. Males exposed to any of the three light treatments (red, blue or shaded light) were more frequently chosen as mating partners than dark-reared males. Flies reared under dark conditions exhibited the lowest mating performance out of any of the rearing environments. Under field cage conditions, a slight assortative mating between blue- and red-light-reared flies was detected. Additionally, females reared in blue light and darkness mated less compared with females reared in red and shaded light. Our data demonstrate that male mating behaviour is flexible in response to light environment. The findings suggest that light spectrum only weakly affects the direction of sexual selection by female choice; however, dark rearing environments deeply affect mating success.

Reverse positional orientation in a neotropical orb-web spider, Verrucosa arenata

Most orb-web spiders face downwards in the web. A downward orientation has been proposed to be the optimal strategy because spiders run faster downwards and thus can catch prey quicker. Consequently, orb-web spiders also extend their web in the lower part, leading to top-down web asymmetry. Since the majority of orb-web spiders face downwards, it has been difficult to test the effect of orientation on prey capture and web asymmetry. In this study, we explored the influence of reverse orientation on foraging efficiency and web asymmetry in Verrucosa arenata, a neotropical orb-web spider that faces upwards in the web. We show that reverse orientation does not imply reverse web asymmetry in this species. V. arenata spiders captured more prey in the lower part of the web but more prey per area on the upper part. The average running speeds of spiders did not differ between upward and downward running, but heavier spiders took longer to capture prey while running upwards. We discuss these findings in the context of foraging efficiency and web asymmetry.

Effect of cold storage on larval and adult Anastrepha ludens (Diptera: Tephritidae) viability in commercially ripe, artificially infested Persea americana 'Hass'

Commercially ripe 'Hass' avocados, Persea americana Mill, artificially exposed to wild Anastrepha ludens (Loew) (Diptera: Tephritidae) females 24 h after harvest were placed in a cold storage facility to determine the effect of low temperature on larval survival and adult viability. Fruit were left for 3, 6, 9, and 12 d in a cold room at 5 degrees C followed by a 20-25-d period at ambient temperature to allow for larval development and pupation. Hass avocados and grapefruit, Citrus paradisi Macfadyen, maintained at ambient temperature served as controls. Overall, only 0.23% of the Hass avocados and 19.30% of the grapefruit were infested. The number of infested fruit increased with decreasing exposure time to cold. Puparia from cold-treated Hass avocados were significantly smaller than those stemming from cold-treated grapefruit. Hass avocados exposed for 12 d to 5 degrees C yielded no puparia, and those exposed for 6 and 9 d yielded 22 and two puparia, respectively, but no adults. Although Hass avocados exposed to cold temperature for 3 d yielded adults that reached sexual maturity (N = 16), females laid inviable eggs. Grapefruit exposed to cold for 12 d yielded normal-sized puparia (but no adults), whereas those exposed over 9 d yielded females able to lay viable eggs. We conclude that exposing fruit to cold storage after packing and during transport represents an effective risk-mitigating procedure in the highly improbable event that a gravid A. ludens female might lay eggs in a commercially ripe Hass avocado that had been left unprotected in a packinghouse.

Application of feces extracts and synthetic analogues of the host marking pheromone of Anastrepha ludens significantly reduces fruit infestation by A. obliqua in tropical plum and mango backyard orchards

We determined the efficacy of three potential oviposition deterrents in reducing fruit infestation by Anastrepha obliqua in tropical plum and mango orchards. These were: (1) Extracts of feces of Mexican fruit fly, Anastrepha ludens, known to contain the A. ludens host marking pheromone (HMP) and (2) two fully synthetic simplified analogues of the naturally occurring compound, which we have named desmethyl A. ludens HMP (DM-HMP) and Anastrephamide. Two applications of feces extracts 2 or 3 wk before fruit color break reduced A. obliqua infestation in plums by 94.1, 75.9, and 72% when measured 8, 14, and 25 d, respectively, after application. The natural A. ludens-HMP containing extract retained its effectiveness despite considerable rainfall (112.5 mm) and high A. obliqua populations. The synthetic desmethyl HMP derivative (DM-HMP) also reduced infestation in plums by 53.3 and 58.7% when measured, 18 and 26 d, respectively, after application. Finally, applications of Anastrephamide resulted in fruit loss cut by half and an 80% reduction in numbers of fly larvae per fruit. Our results confirm previous findings indicating that there is interspecific cross-recognition of the HMP in two of the most pestiferous Anastrepha species and open the door for the development of a highly selective, biorational Anastrepha management scheme.

Random mating among Anastrepha ludens (Diptera: Tephritidae) adults of geographically distant and ecologically distinct populations in Mexico

The Mexican fruit fly Anastrepha ludens (Loew) (Diptera: Tephritidae) is a polyphagous pestiferous insect with a geographical range encompassing highly variable environmental conditions. Considering that cryptic species have been recently found among South American representatives of the same taxonomic group as A. ludens, we tested whether or not some populations of A. ludens have evolved assortative mating as an isolating mechanism that maintains intrapopulation genetic differences and behavioral adaptations to local conditions. Males and females stemming from widely separated locations with similar environmental conditions and males and females stemming from populations within individual-flight range, but collected in different hosts (a native and an exotic one), mated randomly amongst themselves when placed in a field cage. Despite the fact that sibling males and females from two distinct populations also mated randomly amongst themselves, siblings engaged in significantly longer copulations than non-siblings, indicating that perhaps adults discriminated mates with similar genetic compositions. Our results have important practical implications as A. ludens is the most devastating pest of citrus in Mexico and Central America, and large-scale releases of sterile flies are used to control it.

There is no magic fruit fly trap: multiple biological factors influence the response of adult Anastrepha ludens and Anastrepha obliqua (Diptera: Tephritidae) individuals to MultiLure traps baited with BioLure or NuLure

Field-cage experiments were performed to determine the effectiveness of MultiLure traps (Better World MFG Inc., Fresno, CA) baited with NuLure (Miller Chemical and Fertilizer Corp., Hanover, PA) or BioLure (Suterra LLC, Inc., Bend, OR) in capturing individually marked Mexican fruit fly, Anastrepha ludens (Loew), and West Indian fruit fly, Anastrepha obliqua (Macquart) (Diptera: Tephritidae), of both sexes. Experimental treatments involved wild and laboratory-reared flies of varying ages (2-4 and 15-18 d) and dietary histories (sugar only, open fruit, open fruit plus chicken feces, and hydrolyzed protein mixed with sugar). Data were divided into two parts: total captures over a 24-h period and trap visits/landings, entrances into interior of trap ,and effective captures (i.e., drowning in liquid bait or water) over a 5-h detailed observation period (0600-1100 hours). The response to the two baits varied by fly species, gender, physiological state, age, and strain. Importantly, there were several highly significant interactions among these factors, underlining the complex nature of the response. The two baits differed in attractiveness for A. obliqua but not A. ludens. The effect of strain (wild versus laboratory flies) was significant for A. ludens but not A. obliqua. For effect of dietary history, adults of both species, irrespective of sex, were significantly less responsive to both baits when fed on a mixture of protein and sugar when compared with adults fed the other diets. Finally, we confirmed previous observations indicating that McPhail-type traps are quite inefficient. Considering the total 24-h fly tenure in the cage, and independent of bait treatment and fly type (i.e., strain, adult diet, gender and age), of a total of 2,880 A. obliqua and 2,880 A. ludens adults released into the field cages over the entire study (15 replicates), only 564 (19.6%) and 174 (6%) individuals, respectively, were effectively caught. When only considering the 5-h detailed observation period and independent of bait treatment and fly type, of a total of 785 marked flies that landed on traps (519 females and 266 males, respectively), only 10.3% (144 females and 59 males) and 20.8% (25 females and 18 males) A. obliqua and A. ludens individuals, respectively, ended up being effectively captured. We discuss the practical implications of these findings with respect to developing new baits and designing new traps and to the interpretation of capture results in the field.

Comparison of sexual compatibility between laboratory and wild Mexican fruit flies under laboratory and field conditions

The sexual compatibility between laboratory (LF) and wild (WF) strains of the Mexican fruit fly, Anastrepha ludens (Loew), was analyzed using analogous methodologies and experimental arenas under both laboratory and field conditions. Sexual compatibility was quantified with the following indices: the isolation index (ISI), male relative performance index (MRP), female relative performance index (FRPI), and the relative sterility index (RSI). ISI detected a certain level of incompatibility between strains under both laboratory and field conditions, because LF females tended to mate with LF males. LF mating performance was higher under laboratory than under field conditions. The relative performance indices for LF and the relative sterility index were higher in the laboratory than in the field. Differences between LF and WF in the times that males started calling and mating were observed in both environments. Importantly, WF males reduced their sexual activity under laboratory environments, whereas LF maintained similar activity levels in both conditions. The possible applications of the above-mentioned methods, not only to assess fly quality but also to determine the suitability of conditions in mass-rearing facilities, are discussed. Correlating laboratory quality to sexual behavior may contribute in the development of environmental parameters for mass-rearing facilities.

Foraging Behavior of Anastrepha Ludens, A. obliqua, and A. serpentina in Response to Feces Extracts Containing Host Marking Pheromone

Following oviposition, females of many Tephritid flies deposit host marking pheromones (HMPs) to indicate that the host fruit has been occupied. We describe the foraging behavior of these three economically important species (Anastrepha ludens and A. obliqua from the fraterculus species group and A. serpentina from the serpentina species group) when they encounter an artificial fruit (green agar spheres wrapped in Parafilm) marked with intra- and interspecific feces extracts that contain, among other substances, host marking pheromone. When flies encountered fruit treated with either 1 or 100 mg/ml feces extract, there were drastic and statistically significant reductions in tree residence time, mean time spent on fruit, and in the number of oviposition attempts or actual ovipositions when compared to the control treatment (clean fruit). These responses were almost identical irrespective of extract origin (i.e., fly species), indicating complete interspecific HMP cross-recognition by all three Anastrepha species tested. We discuss the ecological and practical implications of our findings.

Oviposition deterrents for the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae) from fly faeces extracts

After oviposition, females of the Mediterranean fruit fly Ceratitis capitata Wiedemann deposit a host-marking pheromone on the fruit surface that deters oviposition by conspecifics. Methanolic extracts of fruit fly faeces elicit a similar deterrent effect. The results of laboratory and field experiments using raw methanolic extracts of C. capitata faeces as an oviposition deterrent are reported. Laboratory bioassays revealed a significant positive relationship between concentration of faeces and the inhibition of oviposition responses by C. capitata. Treatment of halves of coffee bushes with methanolic extracts containing 0.1, 1.0 and 10 mg faeces ml(-1) resulted in a significant reduction of infestation only at the highest concentration (P=0.03). Treatment of blocks of coffee bushes with an extract of 10 mg faeces ml(-1) resulted in an 84% reduction in infestation by C. capitata in sprayed plants and a 56% reduction in adjacent untreated coffee bushes surrounding treated plots, probably due to the deterrent effect of host-marking pheromone on fly oviposition. We conclude that faeces contain oviposition deterrent substances that effectively reduce fruit infestations by C. capitata, suggesting a clear potential for the use of this infochemical in integrated management programmes targeted at this pest.

Predatory behaviour and prey-capture decision-making by the web-weaving spider Micrathena sagittata

Optimal-foraging theory predicts how a predator would feed most efficiently when faced with a choice of two types of prey differing in profitability and density in the habitat. The predator should focus only on the more profitable prey, since any prey item eaten by the predator has a cost in terms of the time and resources taken to subdue and eat it. A study of the hunting behaviour and prey-type selection of the web-weaving spider Micrathena sagittata (Walckenaer, 1841) (Araneae: Araneidae) in the field is documented. In the first part of the study, prey of two sizes were offered in four sectors of the web (top, bottom, right, and left). A prey item was provided at one position of the web at a time. Attack time was recorded at each position. Also, choice and no-choice tests were carried out by offering prey in opposing web sectors (top and bottom) simultaneously. Large prey were more successfully captured in the upper parts than in the bottom parts of the web. In the choice test, spiders always preferred large prey to small prey, while in the no-choice test, spiders always responded to the first stimulus received. Two different attack strategies, depending on prey size, were observed. Hunting strategies and prey-size preference can be related to the cost of web construction and profitability of the prey type.

Nonhost status of commercial Persea americana 'Hass' to Anastrepha ludens, Anastrepha obliqua, Anastrepha serpentina, and Anastrepha striata (Diptera: Tephritidae) in Mexico

The objective of this study was to determine the host status in Mexico of commercially cultivated and marketed avocado, Persea americana (Mill.), 'Hass' to Anastrepha ludens (Loew), Anastrepha obliqua (Macquart), Anastrepha serpentina (Wiedemann), and Anastrepha striata (Schiner) (Diptera: Tephritidae). Experiments in Michoacán, Mexico, were carried out in six orchards located at three altitudes above sea level during two times (August-October 2001 and April-June 2002). They included choice ('Hass' avocado plus natural host) and no-choice foraging behavior tests on trees under field cages; no-choice, forced infestation trials on caged, fruit-bearing branches in the field, and with individual fruit under laboratory conditions; infestation trials using 'Hass' avocados left unprotected over 1 and 7 d on the ground of orchards; studies to ascertain depth of oviposition and determine egg hatchability; and experiments to determine susceptibility by using time elapsed since removal of fruit from tree as the experimental variable. We trapped adult Anastrepha (n = 7,936) in all orchards and dissected fruit (n = 7,695) from orchards and packing houses (n = 1,620) in search of eggs or larvae. Most (96.7%) A. ludens, A. obliqua, A. striata, and A. serpentina adults were captured in low-elevation orchards. No eggs or larvae were detected in any of the fruit from foraging behavior studies or dissected fruit from orchards or packing houses. Of 5,200 mature, intact fruit on trees in the field forcibly exposed to no-choice female oviposition activity (five females/fruit), we only found four fruit infested by A. ludens but no adults emerged. 'Hass' avocados only became marginally susceptible to attack by A. ludens (but not A. obliqua, A. serpentina, and A. striata) 24 h after being removed from the tree. Fruit placed on the ground in orchards (n = 3,600) were occasionally infested by Neosilba batesi (Curran) (Diptera: Lonchaeidae), a decomposer, but not Anastrepha spp. Based on our results, commercially cultivated and marketed P. americana 'Hass' should not be considered a natural host of A. ludens, A. obliqua, A. striata, and A. serpentina in Mexico.