Conservation biological control and pest performance in lawn turf: does mowing height matter?

Faunal Diet of Adult Cane Toads, Rhinella marina, in the Urban Landscape of Southwest Florida

We investigated the diet of cane toads (Rhinella marina) inhabiting urbanized areas in southwest Florida to provide high taxonomic resolution of prey items, contrast toad diets between sampling seasons and sexes, and assess this invasive species' ecological role in the urban landscape. A pest control agency collected cane toads from two golf course communities in Naples, Florida, USA during November-December 2018 (early dry season) and June-July 2019 (early wet season), and faunal stomach contents were quantified from a random subsample of 240 adult toads (30 males and 30 females from each community and season). Yellow-banded millipedes (Anadenobolus monilicornis), big-headed ants (Pheidole spp.), and hunting billbugs (Sphenophorus venatus vestitus) were the most frequently consumed prey items and had the highest total numbers and/or volume with corresponding highest indices of relative importance. There was considerable overlap in the seasonal prey importance values for each golf course community and little if any difference in the importance values between toad sexes in each community. Nonetheless, big-headed ants were the most important prey in both communities during the wet season, while yellow-banded millipedes were the most important dry season prey in one community and hunting billbugs the most important in the other. Despite limited spatiotemporal sampling effort, our results indicated that cane toad was consuming arthropod taxa considered pests in the urban ecosystem. Further studies are needed to investigate the potential effects of human activities and environmental variability on the cane toad diet and to determine whether cane toads act as a biological control for pest populations.

Influence of Turfgrass Parameters on the Abundance of Arthropods in Sod Farms

Sod farms, where turfgrass is commercially produced, have a unique system, in which sod is harvested within 2 yr after planting. Understanding the turfgrass factors that influence the abundance of predators, herbivores, detritivores, and parasitoids that inhabit turfgrass paves the foundation for developing effective pest management programs. However, little is known about those factors in sod farms. The objective of the study was to determine the influence of turfgrass height, density, and thatch thickness on abundance of arthropod taxa in sod farms. The study was conducted at 18 and 10 sod field sites in 2019 and 2020, respectively. Four pitfall traps were deployed at each site. In 2019, each site was sampled in May, June, and July, whereas in 2020, each site was sampled in June and August. In 2019, the numbers of predatory heteropterans were two times greater in bermudagrass (Cynodon dactylon L.) than in zoysiagrass (Zoysia spp.). The numbers of predatory mirids, Spanogonicus albofasciatus (Reuter), and carabids significantly decreased with increases in turfgrass height. In 2020, the abundance of staphylinids increased as the thatch thickness increased. The abundance of Sphenophorus spp. adults were significantly greater in bermudagrass than in zoysiagrass in 2020 and were more abundant in the denser turfgrasses in both years. The predatory arthropods were positively correlated with increased densities of cicadellids, whereas predatory mirids were positively associated with cicadellids, delphacids, and chrysomelids. These results have implications on management of arthropod pests in sod farms as abundance of beneficial arthropods are influenced by turfgrass factors.

Caught on camera: Field imagery reveals the unexpected importance of vertebrates for biological control of the banana weevil (Cosmopolites sordidus Col. Curculionidae)

Understanding of ecological interactions is necessary for the application of biological control. Banana is the second most produced fruit worldwide and the banana weevil (Cosmopolites sordidus) is the most important pest of banana and plantain. Its biological control remains challenging because of the robustness and cryptic behaviour of the adult and the hidden development of larval stages. Researchers therefore tend to favour conservation biological control of this pest. The commonly used methods for measuring the effects of natural enemies on the regulation of this pest focus on invertebrates and may underestimate the role of vertebrates on biological control. Using cameras, we recorded the predation of sentinel adult weevils in banana plots in La Réunion island that differed in weevil infestation levels and in animal biodiversity. To facilitate image analysis, we used background subtraction to isolate moving parts of image sequences and thus detect predators and predation events. Our cameras recorded only vertebrates as predators of adult banana weevils. The most important predator appeared to be the Asian shrew (Suncus murinus), which was responsible for 67% of the predation events. Other predators included the house mouse (Mus musculus), the oriental garden lizard (Calotes versicolor), and the guttural toad (Sclerophrys gutturalis). The exact time of predation events were determined from the images metadata. It was thus possible to identify predator foraging periods that coincided with activity of adult weevils. Our results confirm that images provide useful information for biological and ecological studies. Along with other recent studies, our results suggest that the role of vertebrates in biological control may be underestimated. Based on these results, we advocate for several management implications such as the installation of hedges, grasslands, and ponds to favour these vertebrate predators of the banana weevil, possibly also favouring other vertebrate and invertebrate natural enemies.

Vertical Distribution of Arthropod Interactions Within Turfgrass

Arthropod predators are abundant in turfgrass systems, and they play an important role in managing pests. Understanding the vertical distribution of predation is critical to developing cultural strategies that enhance and conserve predatory services. However, little is known on how the predation is vertically distributed within the turfgrass canopy. Thus, the objective of this study was to determine the vertical distribution of predation within the turfgrass canopy. Clay models were used to emulate the general appearance of Noctuidae caterpillars, to estimate the predatory activity. The choice and no-choice experiments were conducted by placing clay models at 2.54, 5.08, and 7.62 cm from the thatch surface and denoted as lower, intermediate, and upper levels, respectively, within turfgrass canopy. The predator-mediated impressions, paired mark, scratch, deep cut mark, deep distortion, prick, dent, stacked surface impression, scooped mark, granulation, and U-shaped mark, were identified on clay models. The incidence and severity of impressions were significantly greater on clay models placed at the lower canopy level than on those placed at the intermediate and upper canopy levels in the choice and no-choice experiments (P < 0.05). Thus, predators are more likely to find their prey at the soil level. This information can be used to refine management strategies, such as mowing height and insecticide use for effectively managing soil-borne and foliar-feeding arthropod pests and beneficial arthropods.

A review of the sentinel prey method as a way of quantifying invertebrate predation under field conditions

Sentinel prey can provide a direct, quantitative measure of predation under field conditions. Live sentinel prey provides more realistic data but rarely allows the partitioning of the total predation pressure; artificial prey is less natural but traces left by different predators are identifiable, making it suitable for comparative studies. We reviewed the available evidence of the use of both types of invertebrate sentinel prey. Fifty-seven papers used real prey, usually measuring predation on a focal (often pest) species, with studies overwhelmingly from North America. The median predation was 25.8% d^-1 . Artificial sentinel prey (45 papers) were used in both temperate and tropical areas, placed more above ground than at ground level. The most commonly used artificial prey imitated a caterpillar. Up to 14 predator groups were identified, registering a median of 8.8% d^-1 predation; half the studies reported only bird predation. Predation on real prey was higher than on artificial ones, but invertebrate predation was not higher than vertebrate predation. Invertertebrate but not vertebrate predation was negatively related to prey size. Predation near the Equator was not higher than at higher latitudes, nor in cultivated than noncultivated habitats. The use of sentinel prey is not yet standardised in terms of prey size, arrangement, exposure period or data reporting. Due to the simplicity and ease of use of the method, such standardisation may increase the usefulness of comparative studies, contributing to the understanding of the importance and level of predation in various habitats worldwide.

Video monitoring of brown planthopper predation in rice shows flaws of sentinel methods

Immobilized preys are routinely used in agro-ecological exposure studies to quantify predation of pests under field conditions, but this method has not been validated. Our purpose was to determine the validity of using immobilized adults of the major rice pest Nilaparvata lugens, brown plant hopper (BPH), as sentinels. We used direct observation by video recording to determine the causal agents of removal of field exposed BPH sentinels with two experiments: 1) we recorded removal events of dead, immobilized BPH; and 2) we compared removal of (i) dead, immobilized BPH, (ii) live, immobilized BPH, and (iii) live, mobile BPH. Long-horned grasshoppers were responsible for most removals of dead, immobilized BPH, in both experiments. Predatory ground beetles removed most of the live, immobilized BPH, whereas frogs were the major predators of live, mobile BPH. Overall, we showed that removal of immobilized sentinel prey is not representative for predation of live, mobile prey, stressing the need for a critical assessment of commonly used sentinel methods. In addition, we found that frogs played the major role in predation of BPH in rice. As current strategies to enhance biocontrol of planthoppers in rice focus on arthropod natural enemies, this finding could have major implications.

Fungicides affect Japanese beetle Popillia japonica (Coleoptera: Scarabaeidae) egg hatch, larval survival and detoxification enzymes

BACKGROUND

Larvae of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), have a patchy distribution in soils, which complicates detection and management of this insect pest. Managed turf systems are frequently under pest pressure from fungal pathogens, necessitating frequent fungicide applications. It is possible that certain turfgrass fungicides may have lethal or sublethal adverse effects on eggs and larvae of P. japonica that inhabit managed turf systems. In this study, eggs and first-, second- and third-instar larvae were treated with the fungicides chlorothalonil and propiconazole, and survival was compared with that of untreated controls as well as positive controls treated with the insecticide trichlorfon.

RESULTS

Chlorothalonil reduced survival of first-instar larvae treated directly and hatched from treated eggs. Propiconazole delayed egg hatch, reduced the proportion of eggs that successfully hatched and reduced survival of first-instar larvae treated directly and hatched from treated eggs. Sublethal doses of the fungicides lowered the activities of certain detoxification enzymes in third-instar grubs.

CONCLUSIONS

Fungicide applications to turfgrass that coincide with oviposition and egg hatch of white grubs may have sublethal effects. This work is applicable both to high-maintenance turfgrass such as golf courses, where applications of pesticides are more frequent, and to home lawn services, where mixtures of multiple pesticides are commonly used.

Biology and Management of Billbugs (Coleoptera: Curculionidae) in Turfgrass

Billbugs (Coleoptera: Curculionidae: Sphenophorus spp.) are a complex of weevil pests affecting turfgrass throughout the United States. Billbug larvae cause damage by feeding in stems, on roots, and on the crowns of turf, causing severe discoloration and eventual plant death. Monitoring efforts have focused on nondestructive pitfall sampling of ground-active billbug adults and on destructive sampling using soil cores for larval stages in the soil. Given the cryptic nature of the susceptible larval stages, billbugs are typically managed by preventive applications of long-residual, systemic insecticides, including neonicotinoids and anthranilic diamides. Despite knowledge of effective management practices including pest-resistant turf varieties, irrigation management, and microbial controls that contribute to an IPM approach, billbug management continues to rely heavily on prophylactic synthetic insecticides. This review will summarize the identification and biology of billbugs and strategies for their management.