1. Please state project objectives and what work was done this quarter to address them:
Objective 1: Document laboratory and field biology of Bulimulus bonariensis in Florida citrus
Continuous biweekly field monitoring has been conducted at 3 commercial citrus groves in central Florida since June 2023. This monitoring is conducted using two types of traps- flat and pyramid, as described in our previous report.
Comparison of traps: In a preliminary analysis of trap type, we found that in the two sites with moderate to high levels of vegetation on the ground, the more snails were found under the flat traps compared to pyramid traps (moderate ground cover trap comparison: .2 = 12.767, df = 1, p = 0.004; high amount of ground cover: .2 = 140.247, df =1, p <0.0001), and in the grove with minimal vegetation on the ground, more snails were found on the pyramid traps (.2 = 231.195, df = 1, p < 0.0001). Data are based on cumulative counts, and this may have seasonal influences, that will be determined later.
Field patterns from trapping: While observationally in groves, it appears that there tend to be pockets of snails consistently in specific locations, the bi-weekly monitoring data show that this is unlikely. Below are three trapping time points from the same site (Fig 1). You can see that there are differences in the pattern of snail density over time. These data have not yet been analyzed in the context of temperature or moisture, which may explain the patterns better. However, one conclusion that we can draw from these early data are that we are unlikely to be able to manage this pest at the edge of groves unless management actions can be taken prior to infestation, and that management will need to occur throughout the entire field, particularly during dry periods.
Objective 3: Field evaluation of baits and exclusion
Field evaluation of chemistries: A large-scale bait trial had been planned for summer 2023, however not all baits arrived on time (some still have not arrived). As a proxy, we designed an assay to test direct toxicity in contained arenas in the grove. We are also expanding to include insecticides that several growers have reported potential efficacy from. In our initial trial, the assay design appears to work well for evaluating products as snails are treated in the grove, half returned to optimal conditions in the lab, and half remaining post-treatment to see if impacts on snail mortality are greater in the groves than in the lab. Mortality from treatments is 50-90% higher in groves than in the lab (F= 52.521,22, p < 0.0001), in which mortality is zero post-treatment. We believe that chemical treatments combined with field temperatures results in increased mortality of snails. One unanticipated challenge of this design is that fire ants attacked snails in the control assays and less so in the pesticide assays. We will be updating the arena design to exclude ants in future tests.
Of the chemistries tested in this first round of materials, Malathion had the greatest mortality in the field (94%). This chemistry is not yet labeled for this pest, nor is it labelled for ground application, so we cannot recommend this material for ground management, however it lays the ground for exploring other chemistries and working with chemical companies to seek expanded labelling.
Exclusion: We tested various forms of copper available for potential snail exclusion including copper bands, copper tape, and copper mesh. This snail, unlike other species appears undeterred by physical copper barriers. This was an unexpected find as copper is well-documented to deter snails and slugs in many cropping systems.
Objective 4: Determine if Bulimulus bonariensis predators exist in groves
Informally, our trials in Obj. 3 have demonstrated that fire ants can and will kill snails, however this may be a predator of opportunity that is only successful when the snails are confined within the arenas and are not able to climb/move away from their foraging trails.
Camera trapping for predators. Camera traps are nearly ready for formal deployment and data collection. We are currently fine tuning our camera settings and arena set up for optimal data capture (Figs. 2,3). Initial testing indicates that we are capturing high quality images under a variety of weather and environmental conditions (e.g. dark, bright, rainy, and dry). The battery life of the camera is sufficient to capture at least 24 hours of video when adjusted in accordance with our preliminary testing. We are also optimizing snail retention methods, so that the snails remain within view of the camera for the duration of recording. We plan to begin formal data collection within the next few weeks pending some additional testing and appropriate weather conditions.
Predatory mites: The mites collected earlier in the year were submitted to FDACs for formal identification by a mite specialist. Initially, these mites were thought to be a more commonly occurring species. Surprisingly, this mite is a new species from a very rare genus. Prior to our discovery, this genus of mites only consisted of a single species that has only been observed on a small island off the coast of New Zealand. We plan to collect more of these mites to have the species formally described. In the meantime, we will refer to this mite as Austreynetes sp. nov. This is an exciting development that represents a unique opportunity. We currently do not know the extent of the mite's distribution within Florida's Bulimulus population nor its role in Bulimulus success or mortality. It is possible that this species may impede the reproduction or survival of Bulimulus, as has been observed in similar mites in other snail species. However, its role in regulating the Bulimulus population is completely unknown.
Rearing snails for predation assays. We recently produced another generation of snail eggs and neonates (Fig. 4). These specimens will be used in experiments addressing their suitability to various natural enemies commonly found in citrus groves. Increasing the mortality of eggs and young snails represents a high potential return on investment. Eggs and young snails may be more vulnerable to various sources of mortality, especially natural enemies, given their size and relative lack of defenses. Snails eliminated at any stage will not contribute to crop losses or injury. Attacking them when they are young and potentially more vulnerable is potentially efficient and cost-effective. More work needs to be done however to determine their susceptibility.
Nematodes: While we await approval of the permit that would allow for the study of exotic nematodes in our laboratory, we intend to study the new mite species and generalist natural enemies in the laboratory and the field in order to begin to identify the natural enemy complex of Bulimulus bonariensis in citrus groves, with the goal of improving biological control of this injurious species.
2. Please state what work is anticipated for next quarter:
Obj. 1: We will continue biweekly monitoring of populations at all three sites (field). We are anticipating the arrival of two growth chambers in the coming weeks and plan to begin developing life tables to explain the developmental periods of this pest at temperatures relevant to field conditions (lab).
Obj.2:(a) We will begin troubleshooting methods for this objective that we plan to fully deploy in the spring. (b) We are evaluating the relationship between snail density and plant damage. Damaged trees will be used after this initial test to look at attraction of snails to damaged vs undamaged trees.
Obj.3: We will continue with pesticide and bait evaluations in our new arena design as long as active snail populations are available in groves to work with (we do not know if they will overwinter at some point).
Obj. 4: The first set of camera traps are being deployed today (10/10/23) and we will be collecting data at a minimum of 5 time points, which we intend to complete this next quarter, however that could be impacted by temperatures if they continue to cool as insects and molluscs are generally not very active in cooler temperatures.
3. Please state budget status (underspend or overspend, and why): We are currently underspent in part due to delays in onboarding students/staff. We will request to carry forward our balance into year 2 as much of this budget was intended for objectives we had planned to complete during the summer of 2023 if we had the students/staff onboarded.
4. Please show all potential commercialization products resulting from this research, and the status of each: Not yet, though in a year or so the traps might be worth considering