Phil A. Phillips

Foreign exploration for Scirtothrips perseae Nakahara (Thysanoptera: Thripidae) and associated natural enemies on avocado (Persea americana Miller)

Scirtothrips perseae Nakahara was discovered attacking avocados in California,USA,in 1996. Host plant surveys in California indicated that S. perseae has a highly restricted host range with larvae being found only on avocados,while adults were collected from 11 different plant species. As part of a management program for this pest,a ‘‘classical’’ biological control program was initiated and foreign exploration was conducted to delineate the home range of S. perseae,to survey for associated natural enemies and inventory other species of phytophagous thrips on avocados grown in Mexico,Guatemala,Costa Rica,the Dominican Republic, Trinidad,and Brazil. Foreign exploration efforts indicate that S. perseae occurs on avocados grown at high altitudes (>1500 m) from Uruapan in Mexico south to areas around Guatemala City in Guatemala. In Costa Rica, S. perseae is replaced by an undescribed congener as the dominant phytophagous thrips on avocados grown at high altitudes (>1300 m). No species of Scirtothrips were found on avocados in the Dominican Republic,Trinidad,or Brazil. In total,2136 phytophagous thrips were collected and identified, representing over 47 identified species from at least 19 genera. The significance of these species records is discussed. Of collected material � 4% were potential thrips biological control agents. Natural enemies were dominated by six genera of predatory thrips (Aeolothrips, Aleurodothrips, Franklinothrips, Leptothrips, Scolothrips,and Karnyothrips). One genus each of parasitoid (Ceranisus) and predatory mite (Balaustium) were found. Based on the results of our sampling techniques,prospects for the importation of thrips natural enemies for use in a ‘‘classical’’ biological control program in California against S. perseae are not promising. 2002 Elsevier Science (USA). All rights reserved.

Disruption of foraging by argentine ants,Iridomyrmex humilis (mayr) (hymenoptera: Formicidae), in citrus trees through the use of semiochemicals and related chemicals.

Foraging in trees by the Argentine ant,Iridomyrmex humilis (Mayr), was disrupted by a variety of synthetic chemicals, with the most effective chemical being farnesol. Testing of substrates for presentation of the disruptant chemicals gave some success with rubber or Tygon tubing, although best results were obtained through incorporation of the material into Stikem, which was then banded around tree trunks. Amounts of farnesol used for effective, long residual ant control were between 0.8 and 2 g per tree.

Effects of Aerial Spray Volume, Coverage, and Abamectin on Scirtothrips perseae (Thysanoptera: Thripidae)

Abstract Helicopter applications using abamectin in different spray volumes were made against Scirtothrips perseae Nakahara in Ventura County, CA. On small (2.2 m tall) trees, spray coverage on water-sensitive papers was 24–48% and 43–97% for 468 and 935 liter/ha volume treatments, respectively. On large (6.2–8.1 m tall) trees, spray coverage was lower and quite variable, from 1 to 28% and 10 to 70% for 468 and 935 liter/ha treatments, respectively. On small trees, 468, 701, and 935 liter/ha with a high abamectin rate (26 g [AI]/ha) were equally effective against larvae from 13 to 27 d after treatment (DAT). On medium (4.2 m tall) trees, 468 and 935 liter/ha with the high rate were equally effective from 23 to 113 DAT. On large (6.5–8.1 m tall) trees, 468 and 935 liter/ha with a low abamectin rate (13 g [AI]/ha) were ineffective in three tests. In a fourth large (6.8 m tall) tree test, 468 and 935 liter/ha with the high rate were effective at 3 and 37 DAT. In a fifth large (6.2 m tall) tree test, 468-1, 403 liter/ha with the high and 935 liter/ha with the low rate were equally effective 2-22 DAT. After all effective treatments, thrips numbers were lower than in controls for 1–3 mo. However, stable and highest reductions in populations were sometimes delayed until 20–23 DAT even when coverage was high. The variability in spray coverage on the lower levels of large trees and the delayed effect may explain inconsistencies in the reporting of or in actual aerial application results.

Phenology of Arthropod Pests and Associated Natural Predators on Avocado Leaves, Fruit, and in Leaf Litter in Southern California

Abstract Abundance of Scirtothrips perseae Nakahara (Thysanoptera: Thripidae), Oligonychus perseae Tuttle, Baker & Abbatiello (Acari: Tetranychidae), predators, and associations among their population trends on avocado leaves and fruit were determined in three untreated avocado orchards in Ventura and Santa Barbara Counties, CA, from 1998 to 2000. Objectives were to understand pest-predator dynamics and to assess which predators have potential as biological control agents. Numbers of S. perseae and predators from leaf litter/soil were also determined in one orchard from 1998 to 2000. On leaves, O. perseae was the most abundant pest, followed by S. perseae, and Oligonychus puniciae (Hirst) (Acari: Tetranychidae). Phytoseiid mites and spiders were the most abundant predators. The predatory thrips Franklinothrips orizabensis Johansen and Aeolothrips kuwanaii Moulton (Thysanoptera: Aeolothripidae) were also relatively abundant compared with at least 13 other species of predators on leaves. On immature avocado fruit, S. perseae was the most abundant pest and phytoseiid mites, F. orizabensis, and A. kuwanaii were the three most abundant predators. No consistent positive associations between pests and predators were seen on leaves, but F. orizabensis, A. kuwanaii, and phytoseiid numbers on fruit and S. perseae numbers on fruit were positively and significantly associated in all three orchards. In addition, there were significant positive associations between S. perseae and predatory thrips populations from leaf litter in two of the 3 yr. These pest-predator interactions may play a role in developing new control strategies and the importance of these relationships needs to be experimentally investigated.

Relationships Between Scirtothrips perseae (Thysanoptera: Thripidae) Populations on Avocado Leaves, Fruit, and Scarring Damage on Fruit

Abstract Scirtothrips perseae Nakahara causes significant scarring of avocado fruit and is the most serious pest of avocado in southern California. Because it was described only in 1997, no information that can be used for its control exists, including the relationships between its densities on leaves and fruit and scarring damage on fruit. To determine these relationships, percentages of scarring damage on avocado fruit were regressed against thrips numbers/leaf and numbers/fruit using data collected from three orchards in Ventura and Santa Barbara Counties, CA, from 1997 through 1999. Thrips population increases were positively related to leaf growth flushes. Numbers of first and second instars, total larvae, and adults/leaf were all predictive of scarring on fruit. Peaks of three to five larvae/leaf before and during fruit set predicted 6–15% economic scarring damage on fruit from October through December, whereas means of 0.5–1.5 larvae/small fruit predicted 22–51% scarring. Fruit were most susceptible to damage within a 2-wk period during and shortly after fruit set when they measured 0.53–1.42 cm long. Results suggest S. perseae numbers on leaves during fruit set can be used to predict scarring damage on fruit, and that damage thresholds may be ≤5 larvae/leaf during this time. Because low numbers of larvae on fruit within a 2-wk period can result in high scarring damage, early treatments when thrips are on leaves, just before they move onto fruit, may help prevent damage to fruit.

Intraspecific Larval Competition in the Olive Fruit Fly (Diptera: Tephritidae)

ABSTRACT Olive fruit flies [Bactrocera oleae (Gmelin) ] occur at densities in California that can result in intraspecific larval competition within infested fruit. Larval B. oleae densities tracked in the field at six location were found to be highly variable and related to the proportion of fruit infested and adult densities. Egg and larval distribution within the field was generally aggregated early in the season and trended toward random and uniform as the season progressed. To determine whether B. oleae experienced fitness consequences at a range of larval densities observed in the field, olive fruits were infested with one, two, four, and six eggs, and larval and pupal developmental time, pupal weight, and pupal yield were compared. At the highest egg density, all measures of performance were negatively impacted, resulting in fewer and lighter pupae that took longer to pupate and emerge as adults, and even when only two larvae was present per olive, resulting pupae were significantly smaller. Density did not impact the sex ratio of the resulting flies or survive to adults. As field surveys showed, larval densities ranged from 1 to 11 B. oleae per fruit at some sites, and our results suggest that, at high densities, B. oleae do experience competition for larval resources. The impact of intraspecific larval competition North American in field populations of B. oleae is unknown, but the potential for competition is present.

Strong genetic structure among populations of the invasive avocado pest Pseudacysta perseae (Heidemann) (Hemiptera: Tingidae) reveals the source of introduced populations

In 2004, the avocado lace bug (ALB) Pseudacysta perseae, was discovered in San Diego County, CA, USA. Historically, California avocado producers have relied on biological control for suppression of injurious pests. A fundamental step in identifying biological control agents is determining the source of the invasive population, thus allowing a focused search of that area for natural enemies most closely adapted to the invasive pest genotype. In an attempt to determine the geographic area of origin for ALB to assist incipient biological control efforts, mitochondrial and microsatellite markers were used to compare the genetic profile of the California population of ALB with that of populations from the pest’s known range in the US, Guatemala, Mexico and the Caribbean. Both types of marker revealed evidence for strong genetic structure among the sampled populations. Mitochondrial sequences narrowed the geographic origin of the California population, to populations in Texas and several Mexican states. This geographic range was refined further with the analysis of allele frequencies at eight microsatellite loci which identified ALB populations in the state of Nayarit, Mexico, as the most probable origin of the California population. Any effort to identify natural enemies of ALB for use in biological control in California should therefore focus on Nayarit. The strong genetic structure present among the ALB populations studied is discussed with regards to the potential influence of cytoplasmic incompatibility-inducing endosymbionts, host plant variation, and the putative native range of this pest.

Non-target effects of dimethoate and acephate against Eusieus tularensis Congdon and Aphytis melinus DeBach on lemons in California

Abstract Understanding the non-target effects on pesticides used in crop production systems is essential for the development of IPM programmes in those systems. Two organophosphates for control of citrus thrips in citrus were compared at commercial field rates in a lemon orchard for their effect against a predacious mite and a parasitic wasp, both of which have a significant role in coastal lemon IPM. Dimethoate and acephate greatly reduced populations of both beneficial insects, holding them to below detectable levels for 8 weeks post-treatment. Moreover, citrus red mite, a secondary pest, developed beyond the economic treatment threshold in both the dimethoate and acephate plots 10 weeks and 4 weeks post-treatment, respectively. In addition to predatory mite mortality, hormoligosis is suspected in both instances, and especially with acephate, of causing this secondary pest problem.