California Tree Fruit Agreement Research Report 2002 SAN JOSE SCALE AND ITS NATURAL ENEMIES: INVESTIGATING NATURAL OR AUGMENTED CONTROLS Project Leaders: Kent M. Daane Cooperators: Glenn Y. Yokota, Walter J. Bentley, Karen Sime, and Brian Hogg ABSTRACT San Jose scale (SJS) and its natural enemies were studied from 1999 through 2002. Natural populations were followed in stone fruit and almond blocks, with orchard management practices divided into “conventional” and “sustainable” practices, based on dormant and in-season insecticide use. Results generally show higher fruit damage at harvest-time in sustainably managed fields, although, these results are not consistent among orchards and exceptions to this pattern were found. In conventionally managed blocks, later harvest dates resulted in higher SJS fruit damage, although this did not hold true in sustainably managed orchards. Results from SJS pheromone-baited traps show a predominant seasonal pattern of SJS densities progressively increasing and parasitoid (Encarsia perniciosi) densities progressively decreasing. These data are discussed with respect to SJS fruit damage and parasitoid establishment and efficiency. SJS and parasitoid sampling methodology and distribution were investigated. Comparing SJS pheromone trap data to numbers of crawlers on double-sided sticky tape and SJS infested fruit at harvest show a significant correlation between pheromone trap counts of SJS males and numbers of SJS crawlers. Results suggest that there is a small window in the season (April-May) when sticky tape provides important information on crawler abundance and damage. Results show a negative correlation between the early season abundance of Encarsia (as measured by pheromone traps) and SJS damage at harvest. These results suggest that early-season ratios of parasitoid : SJS can not be used to predict fruit damage or biological control (these data require more analysis). Three SJS parasitoids were common: Encarsia perniciosi, Aphytis aonidiae, and Aphytis vandenboschi. Encarsia was the dominant parasitoid; however, the relative abundance of Aphytis species, as compared with Encarsia, was higher in collections of live SJS than on SJS pheromone traps. These results suggest that SJS pheromone traps overestimate Encarsia abundance and underestimate Aphytis abundance. SJS and parasitoid distribution in the tree canopy was studied with destructive sampling and placement of sticky card traps throughout the canopy. Results show Encarsia capture was significantly higher on the lower, interior canopy sections. In contrast, SJS males captured were significantly higher in upper canopy sections. Aphytis spp. were found throughout the canopy. Combining these results suggests that a low, interior trap placement will overestimate Encarsia abundance in relationship with SJS. Parasitoid biology studies are being conducted to better understand low levels of summer parasitism in all sampled orchards. Laboratory studies of Aphytis vandenboschi show the parasitoid prefers third instar SJS but will attack second instar SJS as well. First instars (crawlers) and male SJS are rarely attacked. These data suggest that this parasitoid will not optimally increase when the preferred SJS stage (third instars) is not present (which occurs commonly in Central Valley orchards). Temperature cabinet studies provide the most relevant 1 California Tree Fruit Agreement Research Report 2002 data for SJS biological control in the Central Valley. Results show Aphytis vandenboschi has lower and upper temperature thresholds and, in our trials, it could not develop at constant temperatures ≤15ºC or ≥33ºC. These results appear to corroborate results from field studies that show a decrease in parasitoid activity from June through August. Augmentation studies were conducted in small cages and in open field release trials. Results show an increase in percentage parasitism during a 4-week period (1-generation). Parasitism rates varied between trials, with Encarsia parasitizing more SJS but Aphytis “killing” more SJS through a combination of host feeding and parasitism. Comparing augmentation results to field densities of parasitism suggests that early-season augmentative release of Encarsia would not appreciably add to already present field levels. We conducted tests with “soft” insecticides (Success®, Dimilin®, Confirm®) to determine their impact on the target moth pests and orchard beneficial insects. Results show all materials can kill peach twig borer and oriental fruit moth. We tested for potential non-target impact of these soft insecticides on beneficial insects to determine if these materials could negatively impact SJS biological control. In 2000, parasitoids tested were adult Aphytis vandenboschi, Encarsia perniciosi, and Goniozus legneri (a navel orangeworm parasitoid); predators tested were adult Stethorus sp. and larval green lacewing. Initial results showed green lacewings were relatively tolerant to all materials, while parasitoids were negatively impacted. These results were questioned and, in 2002, we repeated the work with Aphytis, Goniozus and green lacewings. Results again show Success had a negative impact on parasitoid adults, while Dimilin had a negative impact on green lacewing larvae. INTRODUCTION San Jose scale, Diaspidiotus (formerly Quadraspidiotus) perniciosus (Comstock), is a “hard” or “diaspid” scale. It is so small that its first development stage is often hard to see on fruit or branches. It has a large range of susceptible host plants that include stone fruit, pears, apples and many nut crops (Gentile and Summers 1958, see UC IPM website). It is most likely of Asian origin, brought into California in the 1870s on peach trees shipped from China (Gentile and Summers 1958). Because it has wide geographic and host ranges, it quickly became a key pest of most deciduous fruit orchards in North America and remained so until an Integrated Pest Management (IPM) program was developed, based largely on insecticide controls. Much of the development work towards a SJS program was completed in California. From the 1950s-90s, when SJS populations flared up, control was often easily achieved through a well-timed insecticide application of a dormant oil, which was typically combined with an organophosphate, or spring and summer applications of organophosphates (Dowing and Logan 1977, Westigard 1977, 1979, Rice et al. 1979). The dormant season oil and organophosphate application targeting peach twig borer, Anarsia lineatella, also provided SJS control. More recently, the use of higher grade oils or bacterial-by-products (Success®) offers promise for spring and summer suppression of SJS. Walt Bentley and Rich Coviello are working on improved controls with oils and other products (W. J. Bentley, pers. comm.). 2 California Tree Fruit Agreement Research Report 2002 Because insecticides work best against the smaller scale, insecticide applications are often timed to periods of peak crawler emergence. Phenology models of SJS development have been used to improve application timing. Because the crawlers are hard to monitor and count, their emergence patterns are best determined based on “phenology” or development models that use the adult male flights to fix important periods in the SJS development patterns (Jorgenson et al. 1981). Sampling for SJS utilizes pheromone traps that attract adult male SJS – the only development stage and sex that flies. SJS pheromone traps can also attract one of the primary SJS parasitoids – a small “aphelinid” wasp named Encarsia perniciosi (formerly called Prospaltella perniciosi Tower) (McClain et al. 1990, Rice and Jones 1982). Two other SJS parasitoids, Aphytis aonidiae (Mercet) and Aphytis vandenboschi Rosen can also be found on the SJS pheromone traps. The combination of good sampling methods, a phenology model to time insecticide applications, and reliable insecticide products has been the standard for most IPM programs. For the above reasons, it was unusual when high densities of SJS were reported in the 1990s on stone fruit and almonds throughout the Central Valley and in particular in Fresno, Tulare and Kern counties. This past year, SJS infestations have been reported in more northern counties and in almonds and walnuts (Nick Mills and Roger Duncan, pers. comm..). This is particularly unusual because most almond and stone fruit growers with farms in Merced, Modesto and Stanislaus counties have rarely had to apply treatments for SJS (except on nectarine cultivars on which SJS readily settle on the fruit and even small populations can result in noticeable cosmetic damage). The exact causes of these outbreaks are not known but insecticide resistance, insecticide disruption of SJS natural enemies, poor insecticide application methods (e.g., poor coverage), and natural between-season fluctuations have been questioned. In response to grower concerns, the California Tree Fruit Agreement (CTFA) organized a SJS research team to investigate possible reasons for increased SJS pest status and to develop better control practices. Research areas have been prioritized and include studies of chemical controls, sampling methods, SJS insecticide resistance, SJS field biology studies and biological controls. Here, we summarize 1999-2002 studies of (1) the population dynamics (or the change in density over time) of SJS and its natural enemies, (2) seasonal changes in SJS and parasitoid densities between orchards with different management strategies, (3) within tree distribution of SJS and its parasitoids,