Ross H. Miller

Automated identification of optically sensed aphid (Homoptera: Aphidae) wingbeat waveforms.

Abstract An optical sensor was used to make digital recordings of wingbeat waveforms for the five most common aphids found on Guam: Aphis craccivora Koch, A. gossypii Glover, A. nerii Fonscolombe, Pentalonia nigronervosa Coquerel, and Toxoptera citricida (Kirkaldy). Wingbeat frequencies for each species overlapped all other species. However, mean wingbeat frequencies were significantly different for all species. Wingbeat frequencies and harmonic patterns were extracted from the recordings and submitted to cluster analysis, which failed to separate species completely. Several nearest neighbor and probabilistic neural network classifiers were built using time series, frequency spectra, wingbeat frequencies, and harmonic patterns as input variables. These classifiers were evaluated by having them identify wingbeat waveforms from aphids collected and recorded after their construction. The best performing classifier model was a probabilistic artificial neural network trained using 256-bin frequency spectra as input. Sixty-nine percent of the waveforms presented to this network were identified correctly. This study demonstrates the feasibility of developing an insect flight monitor that automatically counts and identifies individual flying insects. Essential components of the monitoring system are a photosensor, a multimedia personal computer, and software that identifies wingbeat frequency spectra using an artificial neural network.

‘Natural experiment’ Demonstrates Top-Down Control of Spiders by Birds on a Landscape Level

The combination of small-scale manipulative experiments and large-scale natural experiments provides a powerful approach for demonstrating the importance of top-down trophic control on the ecosystem scale. The most compelling natural experiments have come from studies examining the landscape-scale loss of apex predators like sea otters, wolves, fish and land crabs. Birds are dominant apex predators in terrestrial systems around the world, yet all studies on their role as predators have come from small-scale experiments; the top-down impact of bird loss on their arthropod prey has yet to be examined at a landscape scale. Here, we use a unique natural experiment, the extirpation of insectivorous birds from nearly all forests on the island of Guam by the invasive brown tree snake, to produce the first assessment of the impacts of bird loss on their prey. We focused on spiders because experimental studies showed a consistent top-down effect of birds on spiders. We conducted spider web surveys in native forest on Guam and three nearby islands with healthy bird populations. Spider web densities on the island of Guam were 40 times greater than densities on islands with birds during the wet season, and 2.3 times greater during the dry season. These results confirm the general trend from manipulative experiments conducted in other systems however, the effect size was much greater in this natural experiment than in most manipulative experiments. In addition, bird loss appears to have removed the seasonality of spider webs and led to larger webs in at least one spider species in the forests of Guam than on nearby islands with birds. We discuss several possible mechanisms for the observed changes. Overall, our results suggest that effect sizes from smaller-scale experimental studies may significantly underestimate the impact of bird loss on spider density as demonstrated by this large-scale natural experiment.

Antibiosis and Antixenosis to Aphis gossypii (Homoptera: Aphididae) in Colocasia esculenta

Abstract Fifty cultivars of taro, Colocasia esculenta (L.) Schott (Araceae), collected from islands in Micronesia and Polynesia, eight cultivars from the University of Hawaii’s taro germplasm collection, and a closely related aroid, Xanthosoma sagittifolium (L.) (Araceae), were screened for antibiosis and antixenosis to Aphis gossypii Glover. Life history data for A. gossypii were collected by assessing survivorship and fecundity of aphids caged on taro leaves in the field. Significant differences in aphid reproductive rate and longevity were observed among the taro cultivars, and cultivars were ranked from most resistant to most susceptible. Antixenosis was assayed in the laboratory in a multiround choice test where A. gossypii were offered four leaf discs excised from different taro cultivars. Additionally, field observations of aphid abundance on taro cultivars were made to corroborate clip cage studies and laboratory experiments. ‘Iliuaua’, ‘Rumung Mary’, ‘Maria’, ‘Ketan 36’, and ‘Agaga’ were the most resistant in terms of reducing aphid fecundity and survivorship, whereas the Iliuana, ‘Purple’, ‘TC-83001’, and ‘Putih 24’ were least preferred in aphid choice tests. X. sagittifolium consistently exhibited strong aphid resistance. Resistant cultivars identified in this study may form the basis of breeding programs seeking to combine aphid resistance with other desirable agronomic traits in taro.

Efficacy of pheromone trapping of the sweetpotato weevil (Coleoptera: Brentidae): based on dose, septum age, attractive radius, and mass trapping.

ABSTRACT Pheromone dose, effective trapping distance, and longevity of the rubber septa loaded with sex pheromone of Cylas formicarius (F.) (Coleoptera: Brentidae) were evaluated for their impact on the efficacy of mass trapping of the insect in sweet potato fields in Guam in 2012–2013. The number of adults caught at different distances (10–100 m) was significantly different. Catches declined with increasing release distance from the trap in both downwind and upwind directions. While the maximum radius of attraction of pheromone-baited trap for C. formicarius in the field was 80 m, the effective distance for recapturing marked adults in the pheromone-baited Unitraps was 60 m. Pheromone lures were able to capture adults of C. formicarius after being stored in the laboratory for up to 98 d. The number of catches per trap per week was highest when lures were 0–14- and 15–28-d-old, and longer storage of septa led to a progressive reduction of catches. Pheromone traps baited with 100-µg lures captured significantly more adults compared with those loaded with 10-µg lures. In addition, effectiveness of pheromone trapping on damage to sweet potato was tested at two locations. Number of trapped adults, damage level at different times after trap installation, and yield production were evaluated. The number of C. formicarius adults collected in traps at both locations fluctuated dramatically among sampling dates and peaked on 13 September 2013, after which time the number of captures noticeably declined. This decrease was correlated to the increasing age and depletion of the pheromone lures. Pheromone traps significantly reduced feeding damage caused by weevils (<1 feeding hole per root in treatment; up to 38 feeding holes per root in the control) at both locations. Being consistent with damage levels, sweet potato yields in fields with traps were higher than those in untreated controls. We conclude that pheromone-baited traps are effective in reducing damage due to C. formicarius.

Vertebrate seed dispersers maintain the composition of tropical forest seedbanks

Seed dispersal is considered a key mechanism through which the structure and function of forests is maintained. Testing this can be difficult because the large scale over which dispersal operates makes it difficult to examine in a meaningful way. Using the near complete loss of native vertebrate seed dispersers from the island of Guam we examine the importance of seed dispersal for maintaining forest seedbanks. We find that seed dispersers have a strong influence on the species composition of seedbanks. Without seed dispersers seedbanks no longer serve to increase the species pool for tree regeneration following disturbance.

Contrasting ecological roles of non-native ungulates in a novel ecosystem

Conservation has long focused on preserving or restoring pristine ecosystems. However, understanding and managing novel ecosystems has grown in importance as they outnumber pristine ecosystems worldwide. While non-native species may be neutral or detrimental in pristine ecosystems, it is possible that even notorious invaders could play beneficial or mixed roles in novel ecosystems. We examined the effects of two long-established non-native species—Philippine deer (Rusa marianna) and feral pigs (Sus scrofa)—in Guam, Micronesia, where native vertebrate frugivores are functionally absent leaving forests devoid of seed dispersers. We compared the roles of deer and pigs on seedling survival, seed dispersal and plant community structure in limestone karst forests. Deer, even at low abundances, had pronounced negative impacts on forest communities by decreasing seedling and vine abundance. By contrast, pigs showed no such relationship. Also, many viable seeds were found in pig scats, whereas few were found in deer scats, suggesting that pigs, but not deer, provide an ecosystem function—seed dispersal—that has been lost from Guam. Our study presents a discrepancy between the roles of two non-native species that are traditionally managed as a single entity, suggesting that ecological function, rather than identity as a non-native, may be more important to consider in managing novel systems.

Maintenance of muscle strength retains a normal metabolic cost in simulated walking after transtibial limb loss

Recent studies on relatively young and fit individuals with limb loss suggest that maintaining muscle strength after limb loss may mitigate the high metabolic cost of walking typically seen in the larger general limb loss population. However, these data are cross-sectional and the muscle strength prior to limb loss is unknown, and it is therefore difficult to draw causal inferences on changes in strength and gait energetics. Here we used musculoskeletal modeling and optimal control simulations to perform a longitudinal study (25 virtual “subjects”) of the metabolic cost of walking pre- and post-limb loss (unilateral transtibial). Simulations of walking were first performed pre-limb loss on a model with two intact biological legs, then post-limb loss on a model with a unilateral transtibial prosthesis, with a cost function that minimized the weighted sum of gait deviations plus metabolic cost. Metabolic costs were compared pre- vs. post-limb loss, with systematic modifications to the muscle strength and prosthesis type (passive, powered) in the post-limb loss model. The metabolic cost prior to limb loss was 3.44±0.13 J/m/kg. After limb loss, with a passive prosthesis the metabolic cost did not increase above the pre-limb loss cost if pre-limb loss muscle strength was maintained (mean -0.6%, p = 0.17, d = 0.17). With 10% strength loss the metabolic cost with the passive prosthesis increased (mean +5.9%, p < 0.001, d = 1.61). With a powered prosthesis, the metabolic cost was at or below the pre-limb loss cost for all subjects with strength losses of 10% and 20%, but increased for all subjects with strength loss of 30% (mean +5.9%, p < 0.001, d = 1.59). The results suggest that maintaining muscle strength may prevent an increase in the metabolic cost of walking following unilateral transtibial limb loss, and that a gait with minimal deviations can be achieved when muscle strength is sufficiently high, even when using a passive prosthesis.

Landscape-level bird loss increases the prevalence of honeydew-producing insects and non-native ants

Bird exclusion experiments consistently show that birds exhibit strong top-down control of arthropods, including ants and the honeydew-producing insects (HPIs) that they tend. However, it remains unclear whether the results of these small-scale bird exclosure experiments can be extrapolated to larger spatial scales. In this study, we use a natural bird removal experiment to compare the prevalence of ants and HPIs between Guam, an island whose bird community has been extirpated since the 1980s due to the introduction of the brown tree snake, and two nearby islands (Rota and Saipan) that have more intact bird assemblages. Consistent with smaller-scale bird exclosure experiments, we show that (1) forest trees from Guam are significantly more likely to host HPIs than trees from Saipan and (2) ants are nearly four times as abundant on Guam than on both Saipan and Rota. The prevalence of HPIs varied slightly based on tree species identity, although these effects were not as strong as island-level effects associated with bird loss. Ant community composition differed between Guam and the other two islands. These results corroborate past observational studies showing increased spider densities on Guam and suggest that trophic changes associated with landscape-level bird extirpation may also involve alterations in the abundance of ants and HPIs. This study also provides a clear example of the strong indirect effects that invasive species can have on natural food webs.

Supplementary material from "Contrasting ecological roles of non-native ungulates in a novel ecosystem"

Conservation has long focused on preserving or restoring pristine ecosystems. However, understanding and managing novel ecosystems has grown in importance as they outnumber pristine ecosystems worldwide. While non-native species may be neutral or detrimental in pristine ecosystems, it is possible that even notorious invaders could play beneficial or mixed roles in novel ecosystems. We examined the effects of two long-established non-native species—Philippine deer ( Rusa marianna ) and feral pigs ( Sus scrofa )—in Guam, Micronesia, where native vertebrate frugivores are functionally absent leaving forests devoid of seed dispersers. We compared the roles of deer and pigs on seedling survival, seed dispersal and plant community structure in limestone karst forests. Deer, even at low abundances, had pronounced negative impacts on forest communities by decreasing seedling and vine abundance. By contrast, pigs showed no such relationship. Also, many viable seeds were found in pig scats, whereas few were found in deer scats, suggesting that pigs, but not deer, provide an ecosystem function—seed dispersal—that has been lost from Guam. Our study presents a discrepancy between the roles of two non-native species that are traditionally managed as a single entity, suggesting that ecological function, rather than identity as a non-native, may be more important to consider in managing novel systems.

FIELD EVALUATION OF PETROLEUM SPRAY OIL AND CARBARYL AGAINST TETRANYCHUS MARIANAE (ACARI: TETRANICHIDAE) ON EGGPLANT

Abstract Tetranychus marianae McGregor (Acari: Tetranychidae) is a pest of several perennial crops and is widespread in the Pacific Basin, including the Mariana Islands where it was first reported. The mite is also present in the West Indies, Bahamas, southern USA, Nicaragua, Argentina, Brazil and Southeast Asia. Eggplant growers apply carbaryl 10 to 15 times against this pest during each cropping period. Some growers no longer cultivate eggplant and tomato because of uncontrollable mite infestations. Previous indoor studies have shown petroleum spray oil (PSO) to be effective against T. marianae. We therefore examined the comparative effectiveness of PSO (Sun-spray 6E®) at the rate of 5mL/liter, and carbaryl at the rate of 1.5 mL/liter, against T. marianae on eggplant at 2 locations in Guam. The mean percentages of mite infested leaves and the population densities of T. marianae at both the locations were significantly higher in control plots than in treatment plots. PSO treatments with 6 and 15 sprays more effectively reduced the number of T. marianae-infested leaves and populations of T. marianae than carbaryl treatments. Marketable yields of eggplant from PSO treated plots were significantly higher than from the other plots. We recommend 6 applications of PSO at 15, 25, 35, 45, 55 and 65 days of after transplanting for managing T. marianae on eggplant.