Rebecca A. Schmidt-Jeffris

Effects of Orchard Pesticides on Galendromus occidentalis (Acari: Phytoseiidae): Repellency and Irritancy

ABSTRACT The effects of repellency or irritancy in Galendromus occidentalis (Nesbitt) were studied for three rates of 16 pesticides commonly used in apple production. Adult female mites were exposed to residues in a series of choice bioassays (treated and untreated half of bean leaf disks). Novaluron, carbaryl, mancozeb + copper hydroxide, and sulfur were the most repellent materials to G. occidentalis, with females consistently avoiding the treated side of the leaf disk. Spirotetramat, flubendiamide, and cyantriniliprole caused an intermediate or inconsistent degree of repellency; azinphosmethyl, lambda-cyhalothrin, acetamiprid, thiacloprid, imidacloprid, spinetoram, spinosad, and chlorantriniliprole caused little to no repellency. Irritancy (running off of the disk, as opposed to resting on the untreated half) was the most pronounced in the acetamiprid and lambda-cyhalothrin treatments. Acute toxicity (within the 6 h test period) was highest in the lambda-cyhalothrin and spinetoram treatments; in the former case, the mortality at all rates tested was substantial enough to interfere with the measurement of behavioral effects. Although irritancy may be considered the more extreme form of repellency, there were several pesticides (carbaryl, cyantraniliprole, mancozeb + copper hydroxide, novaluron) where a moderate to high degree of repellency did not correspond to a high degree of irritancy. Similarly, repellency was not consistently related to acute toxicity; one of the most repellent materials (novaluron) was not acutely toxic. Behavioral effects may help explain instances where lethal or sublethal bioassays do not fully predict the effects of pesticides seen in orchard use.

Comparative biology and pesticide susceptibility of Amblydromella caudiglans and Galendromus occidentalis as spider mite predators in apple orchards

The successful integrated mite management program for Washington apples was based on conservation of the mite predator Galendromus occidentalis (Nesbitt). In the 1960s, this mite was assumed to be the only phytoseiid in Washington commercial apple orchards, due to its preference for the most common mite pest of that period, Tetranychus mcdanieli McGregor, as well as its resistance to organophosphate pesticides. A recent survey of phytoseiids in Washington apple found that another phytoseiid, Amblydromella caudiglans (Schuster) has become common. It is a more generalized predator than G. occidentalis (it is not a Tetranychus spp. specialist) and is not known to be organophosphate-resistant. A series of experiments was conducted to compare the life history, prey consumption, and pesticide tolerance of these two species. Galendromus occidentalis developed more quickly than A. caudiglans, but had slightly lower egg survival. Although A. caudiglans attacked more Tetranychus urticae Koch eggs than G. occidentalis, it could not reproduce on this diet. Both predators performed equally well on a diet of T. urticae protonymphs. Unlike G. occidentalis, A. caudiglans experienced significant mortality when exposed to carbaryl, azinphosmethyl, and bifenazate. Both predators experienced significant mortality due to imidacloprid and spinetoram. These results highlight the key differences between these two predators; the shift away from organophosphate use as well as the change in dominant mite pest to Panonychus ulmi (Koch) may be driving factors for the observed increased abundance of A. caudiglans in Washington apple.

Phytoseiids in Washington commercial apple orchards: biodiversity and factors affecting abundance

Galendromus occidentalis (Nesbitt) is an important biological control agent of spider mites (Acari: Tetranychidae) in Washington apple orchards. It was thought to be essentially the sole phytoseiid existing in this system, due in part to its resistance to commonly used orchard pesticides, and organophosphates in particular. To test this assumption, we conducted a survey of 102 commercial apple blocks in Washington to characterize the community of phytoseiid species. Seven phytoseiid species were found in our samples; G. occidentalis and Amblydromella caudiglans (Schuster) were found in the greatest abundance. We hypothesized that the gradual shift away from the use of organophosphates in recent decades may have caused the change in phytoseiid community structure. The survey data and information regarding the management, location, and surrounding habitat of each block were used to determine what factors affect phytoseiid abundances. Galendromus occidentalis abundance was positively affected by the use of conventional (vs. organic) spray programs, and the use of the acaricide bifenazate. Amblydromella caudiglans abundance was negatively affected by bifenazate use and positively affected by herbicide strip weediness; it was also less prevalent in ‘Golden Delicious’ blocks compared to other cultivars. These results indicate that A. caudiglans reaches higher abundances in orchards that lack certain agricultural disturbances, whereas G. occidentalis can survive in more disturbed environments. Surveys of this nature can provide valuable insight to potential drivers of community structure, allowing for the improvement of integrated pest management programs that incorporate conservation of newly recognized biological control agents such as A. caudiglans.

Anthranilic Diamide Insecticides Delivered via Multiple Approaches to Control Vegetable Pests: A Case Study in Snap Bean

Abstract Many vegetable insect pests are managed using neonicotinoid and pyrethroid insecticides. Unfortunately, these insecticides are toxic to many bees and natural enemies and no longer control some pests that have developed resistance. Anthranilic diamide insecticides provide systemic control of many herbivorous arthropod pests, but exhibit low toxicity to beneficial arthropods and mammals, and may be a promising alternative to neonicotinoids and pyrethroids. Anthranilic diamides may be delivered to vegetable crops via seed, in-furrow, or foliar treatments; therefore, it would be desirable to identify which application method provides high levels of pest control while minimizing the amount of active ingredient. As a case study, chlorantraniliprole and cyantraniliprole applied via the methods listed above were evaluated for managing seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae), and European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), in snap bean. Chlorantraniliprole and cyantraniliprole delivered as seed and in-furrow treatments reduced D. platura damage to the same level as the standard neonicotinoid seed treatment. Both diamides applied via all three methods significantly reduced O. nubilalis damage, but only the foliar application provided similar control as the standard pyrethroid spray. Results from laboratory bioassays revealed that both diamides applied as seed and in-furrow treatments caused high O. nubilalis neonate mortality up to 44 d after application. While the diamides provided equivalent control of these pests as the neonicotinoid and pyrethroid standards when applied in the same manner, chlorantraniliprole delivered as a seed treatment showed the most promise for managing both pests.

Estimating E-Race European Corn Borer (Lepidoptera: Crambidae) Adult Activity in Snap Bean Fields Based on Corn Planting Intensity and Their Activity in Corn in New York Agroecosystems.

Abstract European corn borer, Ostrinia nubilalis (Hübner), is a major pest of processing snap bean because larvae are contaminants in pods. The incidence of O. nubilalis-contaminated beans has become uncommon in New York, possibly because widespread adoption of Bt field corn has suppressed populations. Snap bean fields located where Bt corn has been intensively grown in space and time may be at lower risk for O. nubilalis than fields located where Bt corn is not common. To manage O. nubilalis infestation risk, growers determine insecticide application frequency in snap bean based on pheromone-trapping information in nearby sweet corn fields; adult activity is presumed equivalent in both crops. Our goal was to determine if corn planting intensity and adult activity in sweet corn could be used to estimate O. nubilalis populations in snap bean in New York in 2014-2015. Numbers of O nubilalis adults captured in pheromone-baited traps located in snap bean fields where corn was and was not intensively grown were similar, suggesting that O. nubilalis does not respond to local levels of Bt corn in the landscape. Numbers of Ostrinia nubilalis captured in pheromone-baited traps placed by snap bean fields and proximal sweet corn fields were not related, indicating that snap bean growers should no longer make control decisions based on adult activity in sweet corn. Our results also suggest that the risk of O. nubilalis infestations in snap bean is low (∼80% of the traps caught zero moths) and insecticide applications targeting this pest should be reduced or eliminated.

Effects of foliar apple trichomes on Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae): preferences, fecundity and prey consumption

Tritrophic interactions may alter the efficacy of biocontrol agents such as Galendromus occidentalis, the primary predator of tetranychids in Washington State apple. Apple cultivars vary in leaf pubescence, which may differentially affect the performance of G. occidentalis. The present study aimed to determine both preference and performance of G. occidentalis on pubescent and glabrous surfaces. Choice tests were conducted on two apple cultivars: ‘Oregon Spur Delicious’ – pubescent and ‘Golden Delicious’ – glabrous, as well as by adding simulated trichomes to a bean leaf disk. No‐choice tests measured oviposition and prey consumption on the two apple cultivars. Galendromus occidentalis consumed more prey on the ‘Oregon Spur Delicious’ side of arenas, although only when arenas were constructed without including the leaf midrib. When the midrib was included, G. occidentalis preferred to oviposit on the ‘Oregon Spur Delicious’ side. The preference of G. occidentalis for simulated trichomes did not lead to a performance difference between cultivars. In the no‐choice test, G. occidentalis did not differ in performance between cultivars. These studies indicate that G. occidentalis may have a slight preference for more pubescent surfaces, although this preference is not sufficiently strong to alter its biocontrol performance. As a specialist, G. occidentalis may be more adapted to tracking populations of its prey than locating ‘ideal’ host plants.

Phenology and structure of a phytoseiid community in an insecticide-free apple orchard

Abstract Commercial orchards have acarine communities that are reduced in biological diversity compared to their undisturbed counterparts. Examining the phenology of an unsprayed orchard allows for the examination of non-pesticide factors that drive changes in populations. This study examined the mite community in a largely unsprayed research orchard in 2013–2014. The phytoseiids Galendromus flumenis (Chant), Amblydromella caudiglans (Schuster), Kampimodromus corylosus Kolodochka, and Galendromus occidentalis (Nesbitt) were found, in addition to Zetzellia mali (Ewing) and Aculus schlechtendali (Nalepa). Although G. occidentalis is typically the dominant phytoseiid in commercial orchards, G. flumenis was much more abundant in this unsprayed block. Aculus schlechtendali appeared to be the main source of prey for all predator species. The availability of this prey item and the lack of pesticides are likely the factors that allowed for G. flumenis to reach high abundances. Tetranychids were scarce, emphasizing the role of these mites as induced pests; without the application of disruptive sprays, the predatory mite community was able to maintain biological control. This study demonstrates that the species complex of generalist phytoseiids that is present in orchard systems undisturbed by pesticides is sufficient to maintain spider mite populations below damaging levels throughout the season.

Assessment of techniques for marking Galendromus occidentalis (Nesbitt)

ABSTRACT The negative effects and duration of an immunomark (egg albumin) and fluorescent powder for marking phytoseiids were examined. Neither mark caused significant mortality, run-off, or reduction in fecundity. The fluorescent powder mark was more durable, but neither mark has sufficient durability to be used in a long-term mark-recapture study.