Using mathematical models to describe aerial dispersal and silk ball formation of peanut red spider mite, Tetranychus ogmophallos (Acari: Tetranychidae).

Peanut red spider mite, Tetranychus ogmophallos, exhibits a peculiar dispersal behavior using silk balls, which involves clustering of mites and spinning of webs at the top of plants. Such a dispersal mechanism has not been studied for this species yet. Therefore, this study aimed at using mathematical models to describe aerial dispersal and silk ball formation of peanut red spider mite on peanut plants. The influence of wind speed, generated by a wind tunnel, on the dispersal of mites was studied in two experiments, one with 500 mites per plant and one with 1000 mites per plant, and six wind speeds (5, 10, 15, 20, 25, and 30 km h-1) for each mite density. The proportion of displaced mites and the distance they were blown were measured. Another series of experiments considered the formation of silk balls to assess how fast balls were formed as a function of time and the number of mites present on a peanut plant. Data from the wind tunnel experiments were analyzed by logistic regression and multiple regression to assess the proportion of displaced mites and the distance moved, respectively, as functions of wind speed and the initial density of mites on the donor plant. The distribution of dispersal distances from the donor plant was fitted by a mathematical model proposed by Ricker (J Fish Res Board Can 11:559-623, 1954). The number of mites moving upwards on a plant to be involved in silk ball formation was modeled as a function of time based on the initial number of spider mites and their estimated birth, death and movement rates per capita. Logistic regression was used to analyze the presence of balls as a function of time elapsed since a plant was infested with spider mites. Finally, non-linear regression was applied to link ball size to the total number of mites occupying the ball. The data analyses revealed that wind speed had a significant positive effect on take-off probability and distance moved by individual mites, whereas mite density had little influence. Ricker's model adequately described the distribution of dispersal distances. The models describing silk ball formation also described data very well. Ball size was found to increase almost linearly with the number of mites found in the ball. We expect that the knowledge provided by the present study will help to develop efficient management strategies against T. ogmophallos in peanut crops as dispersal seems to be a key factor in the species' capability to become a serious pest.

Spatial distributions of the red palm mite, Raoiella indica (Acari: Tenuipalpidae) on coconut and their implications for development of efficient sampling plans.

The red palm mite (Raoiella indica), an invasive pest of coconut, entered the Western hemisphere in 2004, then rapidly spread through the Caribbean and into Florida, USA. Developing effective sampling methods may aid in the timely detection of the pest in a new area. Studies were conducted to provide and compare intra tree spatial distribution of red palm mite populations on coconut in two different geographical areas, Trinidad and Puerto Rico, recently invaded by the mite. The middle stratum of a palm hosted significantly more mites than fronds from the upper or lower canopy and fronds from the lower stratum, on average, had significantly fewer mites than the two other strata. The mite populations did not vary within a frond. Mite densities on the top section of the pinna had significantly lower mite densities than the two other sections, which were not significantly different from each other. In order to improve future sampling plans for the red palm mite, the data was used to estimate the variance components associated with the various levels of the hierarchical sampling design. Additionally, presence-absence data were used to investigate the probability of no mites being present in a pinna section randomly chosen from a frond inhabited by mites at a certain density. Our results show that the most precise density estimate at the plantation level is to sample one pinna section per tree from as many trees as possible.

A comparative study of development and demographic parameters of Tetranychus merganser and Tetranychus kanzawai (Acari: Tetranychidae) at different temperatures.

We investigated the effect of temperature on development and demographic parameters such as the intrinsic rate of natural increase (r (m)) of the two spider mite species Tetranychus merganser Boudreaux and T. kanzawai Kishida at eleven constant temperatures ranging from 15 to 40°C at intervals of 2.5°C. Both male and female T. merganser and T. kanzawai completed development from egg to adult at temperatures ranging from 15 to 37.5°C. The longest developmental duration of immature stages was found at 15°C and the shortest developmental duration was found at 35°C for both species. Using linear and non-linear developmental rate models, the lower thermal thresholds for egg-to-adult (female and male) and egg-to-egg development were estimated as 12.2-12.3°C for T. merganser and as 10.8°C for T. kanzawai. The highest developmental rates were observed at around 35°C, whereas the upper developmental thresholds were around 40°C for both species. In fact, at 40°C, a few eggs of either species hatched, but no larvae reached the next stage. The r (m)-values of T. merganser ranged from 0.072 (15°C) to 0.411 day(-1) (35°C), whereas those of T. kanzawai ranged from 0.104 (15°C) to 0.399 (30°C). The r (m)-values were higher for T. kanzawai than for T. merganser at temperatures from 15 to 30°C, but not at 35°C (0.348 day(-1)). Total fecundity of T. merganser was also higher than that of T. kanzawai at 35°C. These results indicate that higher temperatures favor T. merganser more than T. kanzawai.

Reproductive performance of seven strains of the tomato red spider mite Tetranychus evansi (Acari: Tetranychidae) at five temperatures.

The tomato red spider mite Tetranychus evansi Baker et Pritchard occurs on solanaceous plants, and causes serious damage to a variety of crops in Africa and Europe. In 2001 this species was also found in Japan, on nightshade (Solanum nigrum L.), and its invasion to solanaceous of agricultural importance is feasible. To evaluate its potential severity as a pest, the present study assessed the life-history parameters, such as the rate of development and the intrinsic rate of natural increase (r(m)), on S. nigrum for T. evansi collected on seven sites worldwide. Increasing temperatures between 15 and 32.5°C significantly increased the developmental rate of the seven strains while immature developmental duration was about the same at 32.5-40°C. The rate of egg-to-adult development [(% hatch) × (% survival)] exceeded 88% at temperatures between 15 and 37.5°C. The lower thermal thresholds (LT) were 11.9-12.5°C for both egg-to-adult and egg-to-egg development. The optimum developmental temperatures ranged from 36.7 to 43.8°C and the upper developmental threshold (UT) ranged from 45.2 to 59.4°C. The r (m)-values became higher with temperature increasing from 15 to 35°C. The r (m)-values at 25°C ranged from 0.265 to 0.277 which are relatively high for species of the genus Tetranychus. These results indicate that T. evansi after invasion into Japan has the potential to become a serious pest on solanaceous crops, just the same as in Africa and Europe.

Temperature-Dependent Functional Response of Spalangia cameroni (Hymenoptera: Pteromalidae), a Parasitoid of Stomoxys calcitrans (Diptera: Muscidae).

The effects of host density, temperature, and burial depths on the functional response of the synovigenic parasitoid Spalangia cameroni (Perkins) attacking pupae of the stable fly Stomoxys calcitrans (L.) were examined. Five temperatures (15, 20, 25, 30, and 35°C), six host densities (2, 4, 8, 16, 32, and 64 pupae per 19.64 cm(2)), and three burial depths in whole wheat grains (0, 8, and 16 cm) were used. It was demonstrated that temperature had a profound effect on the functional response, whereas burial depths of the pupae played a minor role. For all temperatures, the functional response was of type 2 with an upper asymptote that depends on the temperature. Data were fitted by a functional response model where only the maximum attack rate is temperature dependent. The model shows that the optimal temperature for S. cameroni for attacking S. calcitrans pupae is 28.6°C, where the maximum attack rate is 20.2 pupae day(-1). The lower and upper temperature thresholds for attacks were found as 8.1 and 36.6°C, respectively. The temperature range for attacks that resulted in successful parasitism was narrower, namely, 15.0 and 35.5°C. Maximum rate of successful parasitism was estimated to be 18.2 progeny day(-1) occurring at 27.9°C. The proportion of attacks resulting in successful parasitism increased steeply with temperatures >15°C and declined steeply at temperatures >30°C.

Modeling the Effects of Constant and Variable Temperatures on the Vital Rates of an Age-, Stage-, and Sex-Structured Population by Means of the SANDY Approach.

We present a general and flexible mathematical model (called SANDY) that can be used to describe many biological phenomena, including the phenology of arthropods. In this paper, we demonstrate how the model can be fitted to vital rates (i.e., rates associated with development, survival, hatching, and oviposition) of the two-spotted spider mite (Tetranychus urticae (Koch)) exposed to different constant temperatures ranging from 15°C to 37.5°C. SANDY was incorporated into an age-, stage- and sex-structured dynamic model, which was fitted to cohort life-tables of T. urticae conducted at five constant temperatures (15, 20, 25, 30, and 35°C). Age- and temperature-dependent vital rates for the three main stages (eggs, immatures, and adults) constituting the life-cycle of mites were adequately described by the SANDY model. The modeling approach allows for simulating the growth of a population in a variable environment. We compared the predicted net reproductive rate (R0) and intrinsic rate of natural increase (rm) at fluctuating temperatures with empirical values obtained from life-table experiments conducted at temperatures that changed with a daily amplitude (±0, ±3, ±6, ±9, and ±12°C) around an average of 22°C. Results show that R0 decreases with increasing amplitude, while rm is more robust to variable temperatures. An advantage of SANDY is that the same simple mathematical expression can be applied to describe all the vital rates. Besides, the approach is not confined to modeling the influence of a single factor on population growth but allows for incorporating the combined effect of several limiting factors, provided that the combined effect of the factors is multiplicative.

Effect of Mutual Interference on the Ability of Spalangia cameroni (Hymenoptera: Pteromalidae) to Attack and Parasitize Pupae of Stomoxys calcitrans (Diptera: Muscidae).

We investigated the effect of mutual interference on the attack efficiency and the rate of successful parasitism on the parasitoid Spalangia cameroni (Perkins) attacking pupae of the stable fly Stomoxys calcitrans (L.). Female parasitoids (2, 4, 8, 16, or 32) were exposed to 100 fly pupae during 24 h. The number of pupae that were attacked and the number successfully parasitized increased with the parasitoid density and reached a maximum of ∼70 and 50, respectively. Parasitoid-induced mortality (PIM) was about 20 pupae, irrespective of parasitoid density. The per capita rates of attack, successful parasitism and parasitoid-induced mortality declined monotonously with parasitoid density. Progeny sex ratio was female biased for all parasitoid densities, but declined significantly with increasing parasitoid density from ∼70% females at the lowest density to ∼60% at the highest. Mutual interference was incorporated into a functional response model to predict the attack rate and the rate of successful parasitism at different temperatures, host densities and parasitoid densities. The model explained 93.5% of the variation in the observed number of attacked pupae and 91.5% of the variation in the number of successfully parasitized pupae. The model predicts that increasing parasitoid densities will increase the percentage of killed hosts, but only up to a certain density. Above this density, a further increase in parasitoid abundance will actually lead to a decline in the percentage parasitism. These findings may have some implications for using S. cameroni in biological control against flies using inundative releases.

Will climate change affect outbreak patterns of planthoppers in Bangladesh?

Recently, planthoppers outbreaks have intensified across Asia resulting in heavy rice yield losses. The problem has been widely reported as being induced by insecticides while other factors such as global warming that could be potential drivers have been neglected. Here, we speculate that global warming may increase outbreak risk of brown planthopper (Nilaparvata lugens Stål.). We present data that demonstrate the relationship between climate variables (air temperature and precipitation) and the abundance of brown planthopper (BPH) during 1998-2007. Data show that BPH has become significantly more abundant in April over the 10-year period, but our data do not indicate that this is due to a change in climate, as no significant time trends in temperature and precipitation could be demonstrated. The abundance of BPH varied considerably between months within a year which is attributed to seasonal factors, including the availability of suitable host plants. On the other hand, the variation within months is attributed to fluctuations in monthly temperature and precipitation among years. The effects of these weather variables on BPH abundance were analyzed statistically by a general linear model. The statistical model shows that the expected effect of increasing temperatures is ambiguous and interacts with the amount of rainfall. According to the model, months or areas characterized by a climate that is either cold and dry or hot and wet are likely to experience higher levels of BPH due to climate change, whereas other combinations of temperature and rainfall may reduce the abundance of BPH. The analysis indicates that global warming may have contributed to the recent outbreaks of BPH in some rice growing areas of Asia, and that the severity of such outbreaks is likely to increase if climate change exaggerates. Our study highlights the need to consider climate change when designing strategies to manage planthoppers outbreaks.

Population dynamics of stable flies Stomoxys calcitrans (Diptera: Muscidae) at an organic dairy farm in Denmark based on mark-recapture with destructive sub-sampling.

A population of stable flies, Stomoxys calcitrans (L.), was studied on a Danish cattle farm in two successive years. Flies were captured monthly by sweep nettings and marked with fluorescent dust. Absolute population size, dilution rate, loss rate, and adult longevity were estimated by means of a modified version of Bailey's triple catch method. In both years, the abundance of flies peaked in July. Using a statistical model, we were able to explain 86.6% of the variation in the per capita growth rate r as a function of current temperature, precipitation, and population size. Omitting precipitation from the model, it still explained 69.3%. The model predicts that stable flies have a temperature optimum at 21.8°C, and that no development will take place when temperatures inside the stable are below 10.2°C or above 33.5°C. At the optimal temperature the intrinsic rate of natural increase is 0.070 d(-1). The per capita dilution rate increased with temperature and decreased with population size, whereas no effect of these factors on the per capita loss rate could be shown. Mean adult survival time was estimated to 6.3 d with 95% CL ranging from 4.3 to 11.1 d. The study points at the possibility of developing predictive models as tools for achieving better, and more environmentally sound, control of stable flies.

A simulation study of how simple mark-recapture methods can be combined with destructive subsampling to facilitate surveys of flying insects.

Mark-recapture techniques are used for studies of animal populations. With only three sampling occasions, both Bailey's triple-catch (BTC) and Jolly-Seber's (J-S) stochastic method can be applied. As marking and handling of fragile organisms may harm them, and thereby affect their chances of being recaptured, handling should be minimized. This can be achieved by taking a subsample before the main sample at the second sampling occasion. Individuals in the main sample are marked and released, whereas those in the subsample are only used for identifying recaptures. Monte-Carlo simulation was used to compare the subsampling method with the ordinary mark-recapture methods. Model-generated populations were sampled with and without subsampling to provide estimates of population size, loss, and dilution rates. The estimated parameters were compared with their true values to identify biases associated with the sampling methods, using 81 different combinations of population size, dilution rate, loss rate, and sampling effort. Each combination was replicated 1,000 times. In no cases did subsampling perform more poorly than the ordinary methods. J-S was slightly more accurate than BTC to estimate the population size, but only when sampling effort was high. The relative biases associated with estimates of dilution and loss rates were substantial, but declined with increasing population size and sampling effort. Confidence limits for the population parameters generally were reliable and tended to be conservative. We therefore conclude that ordinary mark-recapture methods can be supplemented with subsampling without sacrificing accuracy. Subsampling is especially advantageous in cases where marks are difficult to observe under field conditions.

Biological control of house flies Musca domestica and stable flies Stomoxys calcitrans(Diptera: Muscidae) by means of inundative releases of Spalangia cameroni(Hymenoptera: Pteromalidae).

The efficacy of the pupal parasitoid Spalangia cameroni Perkins as a biological control agent was tested against house flies Musca domestica Linnaeus and stable flies Stomoxys calcitrans (Linnaeus) in one dairy cattle and two pig installations in Denmark. Weekly releases of S. cameroni from April through to September-October 1999 and 2000 resulted in significant suppressions of house fly populations to below nuisance level, whereas no effect on stable flies was found. Parasitism was significantly higher in the release years compared to the control years, but was below 25% averaged over the fly season for each farm. A statistical model based on a functional relationship between the innate capacity of increase of the two fly species and three explanatory variables (air temperature, fly density and parasitism) provided a fairly good fit to data with the abundances of house flies and stable flies explained mostly by temperature, but intra- and interspecific competition, and parasitism had a significant effect as well. Overall, the model was capable of explaining 14% and 6.6% of the total variation in data for house fly and stable fly, respectively. Spalangia cameroni was the predominant parasitoid to emerge from exposed house fly pupae, but from mid summer onwards Muscidifurax raptor Girault & Sanders (Hymenoptera: Pteromalidae) was also quite common. The study indicated that biological control of house flies can be an efficient alternative to chemical control.

Short-term changes in consumption and oviposition rates of Neoseiulus californicus strains (Acari: Phytoseiidae) after a diet shift.

Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or protonymphs of Tetranychus urticae Koch placed on excised strawberry leaflet discs and maintained under laboratory conditions (25 +/- 1 degrees C, 75-85% RH, 16L: 8D). The observations were made on the first and the fifth day of the experiment. The phytoseiids came from three long-term mass-reared strains fed on T. urticae, Dermatophagoidesfarinae Hughes, or Quercus spp. pollen, respectively. The fourth strain was collected directly in a strawberry field. Time since diet transfer can be added to the factors (i.e. feeding history and prey density) already known to affect the functional and numerical responses of N. californicus, both when it feeds on prey eggs and protonymphs. If consumption rates were averaged over all strains and densities, 9.04 and 11.41 eggs, and 6.97 and 6.48 protonymphs were consumed on the first and the fifth day, respectively. If the same was done for oviposition rates, predators feeding on eggs produced 1.46 and 2.36 eggs/female/day, whereas predators feeding on protonymphs produced 1.35 and 2.29 eggs/female/day. Time had the greatest impact on the functional response of the strain that had previously fed on tetranychids, while an effect of time on the numerical response was detectable in all strains.

Sexual and physical abuse history in gastroenterology practice: how types of abuse impact health status.

OBJECTIVE: There is an increasing amount of literature pointing to a relationship between sexual and/or physical abuse history and poor health status, although few studies provide evidence concerning which aspects of abuse may impact on health. In female patients with gastrointestinal (GI) disorders, the present study examined the effects on health status of: 1) history of sexual abuse and physical abuse, 2) invasiveness or seriousness of sexual abuse and physical abuse, and 3) age at first sexual and physical abuse. METHOD: The sample included 239 female patients from a referral gastroenterology clinic who were interviewed to assess sexual and physical abuse history. RESULTS: We found the following: 1) 66.5% of patients experienced some type of sexual and/or physical abuse; 2) women with sexual abuse history had more pain, non-GI somatic symptoms, bed disability days, lifetime surgeries, psychological distress, and functional disability compared to those without sexual abuse; 3) women with physical abuse also had worse health outcome on most health status indicators; 4) rape (intercourse) and life-threatening physical abuse seem to have worse health effects than less serious physical violence, and sexual abuse involving attempts and touch; and 5) those with first abuse in childhood did not appear to differ on health from those whose first abuse was as adults. CONCLUSIONS: The authors conclude that asking about abuse should be integrated into history taking within referral-based gastroenterology practices.

Impact of sexual and physical abuse dimensions on health status: development of an abuse severity measure.

OBJECTIVE: Despite the abundant literature showing a relationship of sexual and/or physical abuse history with poor health status, few studies provide evidence about which dimensions of abuse may have a worse impact on health. In female patients with gastrointestinal (GI) disorders, the present study aims to identify which dimensions of abuse history (eg, number of perpetrators, injury) might predict poor current health status, in order to develop an empirically based severity of abuse measure. METHODS: Of a sample of 239 female patients from a referral gastroenterology clinic, this paper primarily focuses on 121 women with a past history of contact sexual abuse (N = 99), and/or life threatening physical abuse (N = 68). RESULTS: Among those with a sexual abuse history, 24% of current health status was explained by serious injury during abuse (p = .0006), victimization by multiple perpetrators (p = .03), and being raped (p = .09). Among the physically abused, rape (in addition to life threat) (p = .0001), and multiple life-threatening incidents (p = .002) explained 39% of the variance in overall health. Among the women with a sexual and/or physical abuse history, the experience of rape, serious injury during sexual abuse, and multiple life-threatening incidents explained one fourth of the variance in current health status. Based on these three dimensions of abuse, we created an abuse severity measure which explained about one fourth of the variance in health status among the subgroup with abuse history, and among the entire clinic sample. CONCLUSIONS: Given the high prevalence of abuse in referral practice, and the potential health impact of previous abuse, it is important that history taking include details concerning the abuse experience. The severity of abuse measure developed in this paper should prove useful for both research and clinical practice.

Sexual and physical abuse in women with functional or organic gastrointestinal disorders.

STUDY OBJECTIVES: To determine the prevalence of a history of sexual and physical abuse in women seen in a referral-based gastroenterology practice, to determine whether patients with functional gastrointestinal disorders report greater frequencies of abuse than do patients with organic gastrointestinal diseases, and to determine whether a history of abuse is associated with more symptom reporting and health care utilization. DESIGN: A consecutive sample of women seen in a university-based gastroenterology practice over a 2-month period was asked to complete a brief questionnaire. MEASUREMENTS: The self-administered questionnaire requested information about demographics, symptoms, health care utilization, and history of abuse. Physicians indicated the primary diagnosis for each patient and whether she had ever discussed having been sexually or physically abused. RESULTS: Of 206 patients, 89 (44%) reported a history of sexual or physical abuse in childhood or later in life; all but 1 of the physically abused patients had been sexually abused. Almost one third of the abused patients had never discussed their experiences with anyone; only 17% had informed their doctors. Patients with functional disorders were more likely than those with organic disease diagnoses to report a history of forced intercourse (odds ratio, 2.08; 95% CI, 1.03 to 4.21) and frequent physical abuse (odds ratio, 11.39; CI, 2.22 to 58.48), chronic or recurrent abdominal pain (odds ratio, 2.06; CI, 1.03 to 4.12), and more lifetime surgeries (2.7 compared with 2.0 surgeries; P less than 0.03). Abused patients were more likely than nonabused patients to report pelvic pain (odds ratio, 4.05; CI, 1.41 to 11.69), multiple somatic symptoms (7.1 compared with 5.8 symptoms; P less than 0.001), and more lifetime surgeries (2.8 compared with 2.0 surgeries; P less than 0.01). CONCLUSIONS: We found that a history of sexual and physical abuse is a frequent, yet hidden, experience in women seen in referral-based gastroenterology practice and is particularly common in those with functional gastrointestinal disorders. A history of abuse, regardless of diagnosis, is associated with greater risk for symptom reporting and lifetime surgeries.

PIP: This study aims to determine the prevalence of sexual and physical abuse among women seen in a gastroenterology clinic. A total of 206 patients, who completed a self-administered questionnaire, were included in the analysis. Results indicated that 89 patients (44%) reported a history of sexual abuse or physical abuse in childhood or later in life; and all except one of the physically abused were also sexually abused. Among them, only 17% had informed their doctors about the abuse. Moreover, the 75 patients (36%) with functional gastrointestinal disorders were more likely than those with organic disease diagnosis to report a history of forced intercourse, frequent physical abuse, chronic or recurrent abdominal pain, and more lifetime surgeries. They were also more likely to be receiving psychological counseling for emotional concerns. Furthermore, abused patients were more likely than nonabused patients to report pelvic pain, multiple somatic symptoms, and more lifetime surgeries. In conclusion, this study discovered that there is a high prevalence of a history of sexual and physical abuse among women seen in a referral-based gastroenterology clinic, particularly those with functional gastrointestinal disorders.