Red-eyed Nymphs Research Articles

Effectiveness of Parasitoids of Bemisia tabaci (Hemiptera: Aleyrodidae) on Cotton Cultivars Differing in Leaf Morphology

ABSTRACT Field and laboratory experiments were conducted to determine resistance of cotton Gossypium hirsutum L. cultivars differing in leaf morphology (shape and pubescence) to the B biotype of sweetpotato whitefly Bemisia tabaci (Gennadius) and impacts on its parasitoids. Five cotton cultivars were evaluated in a field-plot experiment at Hastings, Florida. The pubescent cultivars, DP DES 119 and Stoneville 453, were significantly hairier than moderately hairy okra-leaf cultivar, Gumbo 500, and smooth-leaved cultivars NU COTN 33B and DP 51. There were significant differences among cultivars in eggs laid on the second and fifth node leaves. DP DES 119 and Stoneville 453 had greater numbers of whitefly eggs than did the glabrous cultivars. The okra-leaf cultivar, Gumbo 500, had greater numbers of eggs than the 2 glabrous varieties. There were significant differences among cultivars in numbers of first and second instars (young instars), third instars, unparasitized fourth instars and red-eyed nymphs on fif...

MANAGEMENT OF THE SILVERLEAF WHITEFLY ON FRESH MARKET TOMATOES WITH SOIL AND FOLIAR INSECTICIDE APPLICATIONS, SPRING 2002

On 28 Feb, transplants were set 18 inches apart on raised beds of EauGallie fine sand soil covered with white on black low density polyethylene mulch. Plots were three, 21-ft-long rows on 10-ft aisles and 5-ft centers and were irrigated by a seepage sub-irrigation system. Treatments were replicated four times in a RCB design. Admire, Platinum and V-10112 were applied on 28 Feb to each plant in 4 oz of water. Activol, Aza-Direct and Hexacide were applied weekly. The remaining products were to have been applied at the pre-determined density of five whitefly sessile nymphs and/or pupae/10 leaflets (Table 1); however, on 9 May only treatments with Oberon were applied before uncontrollable circumstances stopped spraying. All treatments were applied on 26 May. Foliar applications were made with a high clearance, self-propelled sprayer operated at 200 psi and 3.4 mph. It was fitted with eight Albuz orange nozzles per row and delivered 90 (six nozzles open) or 120 (eight nozzles open) gpa. Because of a heavy population of southern armyworm larvae, Javelin (2 lb/acre), XenTari (2 lb/acre), Confirm 2F(16 oz/acre) or Avaunt 30WG (3.5oz/acre) were applied weekly. The number of plants in each plot with definite visual symptoms of whitefly-vectored geminivirus, primarily tomato yellow leaf curl virus (TYLCV), were recorded weekly beginning 19 Mar. The numbers of sessile nymphs (2nd and 3rd instars) and pupae (4th instar or red eye nymphs) of the silverleaf whitefly were counted on the terminal leaflet from the 7th to 8th leaf counting from the top of each of ten plants in the center row of each plot about weekly beginning on 31 Mar. Fruit were harvested on 4 Jun from the middle 10 plants of the middle row of check plots and plots treated only with either Admire or Platinum. Fruit with zippering, cat-facing or large blossom-end scars were culled as defective and counted and weighed. The remaining fruit were graded for size by machine where extra large fruit were > 2.75 inches in diam, large were 2.51 to 2.75 inches in diam, medium were 2.26 to 2.5 inches in diam and small were ≤ 2.25 inches in diam. All size categories were counted and weighed. Small fruit are considered too small for marketing and are culled.

FOLIAR AND SOIL APPLICATIONS OF INSECTICIDES FOR CONTROLLING SILVERLEAF WHITEFLY ON FRESH MARKET TOMATOES, FALL 2000

On 21 Sep, transplants were set 18 inches apart on raised beds of EauGallie fine sand soil covered with white polyethylene mulch. Plots were three-21-ft long rows on 5-ft centers and were irrigated by seepage, subsurface irrigation system. Treatments were replicated four times in an RCB design. Admire and Platinum were applied on 21 Sep to each plant in 4 oz of water. Applaud and Knack were applied once on 15 Nov as the controlling effects of Admire diminished and whitefly densities approached or reached 3 5 whitefly sessile nymphs and/or pupae/10 leaflets. Foliar applications were made with a high-clearance, self-propelled sprayer operated at 200 psi and 3.4 mph. It was fitted with eight Albuz orange nozzles per row and delivered 60 (four nozzles open), 90 (six nozzles open) or 120 (eight nozzles open) gpa, depending upon plant height. Because of a moderate population of southern armyworm larvae, Mattch (2 qt/acre), Javelin (2 lb/acre) or SpinTor (6 oz/acre) were applied weekly. The number of plants in each plot with definite symptoms of whitefly-vectored geminivirus, primarily tomato yellow leaf curl virus, were recorded weekly. The numbers of sessile nymphs (2nd and 3rd instars) and pupae (4th instar or red eye nymphs) of the silverleaf whitefly were counted weekly on the terminal leaflet from the 7th to 8th leaf counting from the top of each of 10 plants in the center row of each plot.

Effect of Storage Temperature and Duration on Survival of Eggs and Nymphs of Bemisia argentifolii (Homoptera: Aleyrodidae) and Pupae of the Whitefly Parasitoid Encarsia formosa (Hymenoptera: Aphelinidae)

Bemisia tabaci (Gennadius) and Bemisia argentifolii Bellows & Perring are found on a broad range of plant hosts in the tropics and subtropics and in greenhouses in many temperate zones. Their distribution indicates a strong limitation by cold temperature. The effects of incubation temperature and duration on the survival of B. argentifolii eggs and red-eyed nymphs, and on the survival of Encarsia formosa Gahan, an aphelinid parasite of the whitefly, were studied. Eggs stored at 10°C for 3–28 d on rooted cabbage leaves responded with 94–56% hatch, respectively, whereas the viability of eggs incubated at 5°C declined rapidly after 3 d. Control eggs on rooted cabbage leaves held at 24°C had 96% hatch. Considerably lower survival was observed on nonrooted leaves and leaf disks. Survival of red-eyed nymphs incubated at 2, 5, and 10°C for 3–13 d declined rapidly at all 3 temperatures. Pupae of E. formosa held at 10°C for 3–13 d responded with 90–55% eclosion, respectively, whereas survival of those held at 2 and 5°C declined rapidly after 3 d. Results of our studies indicate that short-term storage of whitefly parasitoids in cold temperatures is possible without excessive detrimental effect. The role of cold temperature storage of eggs in intermittent rearing of Bemisia colonies is discussed.

Suitability of Bemisia argentifolii (Homoptera: Aleyrodidae) Instars for the Parasitoid Eretmocerus mundus (Hymenoptera: Aphelinidae)

Studies were conducted to assess the suitability of nymphal instars of Bemisia argentifolii Bellows & Perring [=sweetpotato whitefly, Bemisia tabaci (Gennadius), Biotype B] attacked by Eretmocerus mundus Mercet. Host mortality, parasitoid survival, development time, and progeny longevity were recorded. E. mundus parasitized all instars; however, 2nd instars had the highest percentage of parasitism (66.4%) and the late 4th instars (red-eyed nymphs) the lowest (8.6%). Second instars exhibited the highest proportion of host mortality and parasitoid survival. The greatest rate of parasitoid emergence (93.8%) was from 2nd-instar hosts; the lowest emergence (35.7%) was from late 4th-instar hosts. Parasitoid development was longest when parasitized in the 1st instar (16.3 d). The longevity of unfed female progeny that emerged from hosts attacked in the 2nd instar was significantly greater (2.6 d) than those from late 4th instars (1.5 d). When E. mundus parasitized 1st or 2nd instars, the parasitoid can be referred as a koinobiont, because after parasitization, the host continues to feed, grow, and develop. However, when E. mundus parasitized 3rd or 4th instar nymphs, they evidently stop development (idiobiont).

Intraplant Distribution of Immature Lifestages of Bemisia argentifolii (Homoptera: Aleyrodidae) on Tomato

The intraplant distributions of eggs, sessile nymphs, and pupae (red-eye nymphs) of the whitefly Bemisia argentifolii Bellows & Perring [formerly referred to as strain B of the sweetpotato whitefly, B. tabaci (Gennadius)] were studied on the terminal 3 leaflets of leaves on main and lateral stems of tomato, Lycopersicon esculentum Miller, in field plots. The distributions of specific lifestages depended on the age of leaves. Eggs were most abundant and variation generally low or lowest on leaflets at nodes 4-6 (counting from the terminal), nymphs at nodes 6- 8, and pupae at nodes 8-10. The nodal position of the most infested leaf tended to increase within the above ranges as the season progressed. The distribution of immature lifestages on leaflets at different nodes was independent of stem origination as long as the number of nodes present were similar on main and lateral stems. The b dispersion index from the Taylor power law for each lifestage did not vary significantly over nodes and over main and lateral stems within the above ranges of nodes for each lifestage. Single lna and b values were calculated for each lifestage and were used to estimate minimum sample sizes (a sample unit consisted of the terminal 3 leaflets from the above respective nodes for each lifestage on either a main or lateral stem of 1 plant). Estimated minimum sample sizes at a precision of 0.25 (SEM/mean) increased with increasing density of eggs but decreased with increasing density of nymphs and pupae. The minimum sample size did not exceed 13, 23, and 28 for eggs, nymphs, and pupae, respectively. at a density as low as 1 immature per sample.

Insect Management on Fresh Market Tomatoes, Spring 1997B

Abstract On 12 Mar, transplants were set 18 inches apart on raised beds of EauGallie fine sand covered with black plyethylene mulch. Plots were 3-27-ft-long rows on 5-ft centers and were irrigated by a seepage subirrigation system. Insecticidal treatments were replicated 4 times in a randomized complete block design. CGA-293343 25WG was applied with a high-clearance, self-propelled sprayer on 2, 18 Apr, 5, 9, 16, 23, 30 May, and 6 Jun. The sprayer was operated at 200 psi and 3.4 mph and was fitted with eight Al-buz orange nozzles per row delivering 60 gpa for the first application, 90 gpa for the next two applications, and 120 gpa for the remaining 5 applications. The Admire treatment was applied on 31 Mar and the CGA-293343 2SC treatments were applied on 2 Apr in 4 oz water/plant. Because of a very heavy population of southern armyworm larvae, applications of Mattch and Xentari were alternated weekly. All control and yield data were collected on the middle 10 plants of the middle row of each plot. The terminal leaflet was collected from a leaf from the 7th-8th leaf counting from the top of each often plants on 9, 16, 21, 29 Apr, 8, 13, 21, 28 May, 4 and 11 Jun. The numbers of crawlers (1st instar), sessile nymphs (2nd and 3rd instars) and pupae (4th instar or red eye nymphs) of the silverleaf whitefly were counted. All plants in each plot were examined weekly for symptoms of tomato mottle geminivirus (To-MoV) which is vectored by the silverleaf whitefly. All red ripe fruit were harvested on 27 May, 2 and 11 Jun and the fruit were separated by the presence of southern armyworm, thrips (fruit with five or more oviposition dimples on blossom end) and stink bug damage. Fruit were rated \-4 as follows for increasing severity of external symptoms of irregular ripening: ‘ 1’ = fruit without a pronounced yellow star at the blossom end; ‘2’ = a star at the blossom end radiating toward the calyx; ‘3’ or ‘4’ = <30% or >30% of the fruit surface unripened, respectively.

Management of Insects on Fresh Market Tomatoes, Spring 1996C

Abstract On 1 Mar, transplants were set 18 inches apart on raised beds of EauGallie fine sand covered with black polyethylene mulch. Plots were 3-21 ft long rows on 5 ft centers and were irrigated by a seepage subirrigation system. Insecticidal sprays were replicated 4 times in a RCB design and were applied with a high clearance, self-propelled sprayer on 20, 27 May, 10 and 17 Jun. The sprayer was operated at 200 psi and 3.4 mph and was fitted with eight Albuz orange nozzles per row delivering 120 gpa. The Admire treatment was applied in 4 oz water/plant on 4 Mar. Because of a very heavy population of southern armyworm larvae, weekly applications of Bacillus thuringiensis (Javelin and Xentari alternated weekly) were initiated on 13 May. All control and yield data were collected on the middle 10 plants of the middle row of each plot. The terminal leaflet was collected from a leaf from the upper third of each often plants on 30 May, 3, 6, 12 and 24 Jun. The numbers of crawlers, sessile nymphs and pupae (red eye nymphs) of the silverleaf whitefly were counted. All fruit of marketable size were harvested on 12 and 24 Jun and the fruit were separated by the presence of southern armyworm, thrips (fruit with five or more oviposition dimples on blossom end) and stink bug damage and were counted and weighed.

Management of Insects on Fresh Market Tomatoes, Spring 1996B

Abstract On 1 Mar, transplants were set 18 inches apart on raised beds of EauGallie fine sand covered with black polyethylene mulch. Plots were 3-21 ft long rows on 5 ft centers and were irrigated by a seepage subirrigation system. Insecticidal sprays were replicated 4 times in a RCB design and were applied with a high clearance, self-propelled sprayer on 15, 22 Apr, 1,8, 16, 24, 31 May, 5 and 12 Jun. The sprayer was operated at 200 psi and 3.4 mph and was fitted with Albuz orange nozzles. The number of nozzles per row was increased from 4 to 8 to increase gallonage as the plants grew. Thus, 60 gpa were applied the first two sprays (four nozzles), 90 gpa the next spray (six nozzles) and 120 gpa for the remaining five sprays (eight nozzles). The Admire treatment was applied in 4 oz water/plant on 4 Mar. Because of a very heavy population of southern armyworm larvae, weekly applications of Bacillus thuringiensis (Javeline and Xentari alternated biweekly) were initiated on 13 May. All control and yield data were collected on the middle 10 plants of the middle row of each plot. The terminal leaflet was collected from a leaf from the upper third of each of ten plants on 22 May and from two leaves from each of ten plants on 18 Jun. The numbers of crawlers, sessile nymphs and pupae (red eye nymphs) of the silverleaf whitefly (SLWF) were counted. The plants in the outside two rows of each plot were examined weekly for the presence of virus-like symptoms. There are two viruses present which have nearly indistinguishable symptoms: tomato mottle virus (ToMoV), a geminivirus vectored by the SLWF, and potato virus Y (PVY), a potyvirus vectored by several species of aphids. On 13 May and 18 Jun, a 3—4 leaf terminal was collected from each plant with virus symptoms from the outer two rows of the checks. The samples were frozen and a single leaflet was used later for determining the presence of ToMoV using nucleic acid spot hybridization and the presence of PVY using ELISA. All fruit of marketable size were harvested on 29 May and 14 Jun and the fruit were separated by the presence of southern armyworm, thrips (fruit with five or more oviposition dimples on blossom end) and stink bug damage and were counted and weighed.

Use of Beauveria Bassiana, an Entomopathogen, to Control Nymphs of Bemisia Argentifolii Under Field Conditions, 1995

Abstract Eight pairs of raised beds, 91 cm wide on 180 cm centers, were fertilized and maintained using the standard practices 3 wk before setting eggplant and tomato transplants in adjacent rows at 51 cm spacing. Two plots designated in each row for the trial were 6.5 m long and separated at either end by a 1 m buffer, to give two RCB designs (one for eggplant and other for tomato), each with 2 treatments and 8 replications. The treatment material was Mycotrol WP9504 (Mycotech Stain GHA spores, 22%; 4.4 X 1010 spores/g; Mycotech, Butte, MT) which was applied at a rate of 1.1 kg/ha (1 lb/acre) as recommended five times weekly from 21 Apr until 7 May 1995. Spray was delivered using a high clearance sprayer utilizing an hydraulic pump operating at 200 psi and equipped with drop nozzles, 8 “ATR Yellow” Albuz® hollow cone per row, to deliver 81 gpa. Weekly samples of SWF immatures from 24 Apr consisted of a single, 6th or 7th leaf from the terminal, leaf each from 3 randomly selected plants per plot, collected into plastic zip-lock bags, and brought back to the laboratory. Whitefly immatures (eggs, nymphs and pupae) were examined on four 1-cm2 disks, 2 on each side of the mid-vein. Eggs, young (1 st and 2nd instar) and old (3rd and 4th instar) nymphs and pupae (red-eyed nymphs) of SWF on 12 cm2 leaf area were counted under a stereomicroscope in the laboratory.

Evaluation Of Tomato Cultivars, Isolines And Near-Isolines For Resistance To Silverleaf Whitefly. Spring 1995

Abstract Seeds of 7 tomato cultivars and 12 isogenic or near-isogenic mutants varying for foliar pubescence were obtained from C. M. Rick Tomato Genetics ResourceCenter (Department of Vegetable Crops, University of California, Davis). ‘Sunny’ was the control susceptible cultivar. On 20 Mar, transplants were set 18 inches apart on raised beds covered with blackpolyethylene mulch in Bradenton. The field plot consisted of 2 150ft long rows separate by 5 ft and irrigated by a seepage subirrigation system. Single plants wer replicated 1 times in a completely randomized design On 24 May, 7 Jun, and 20Jun, 2 terminal leaflets from the 6th leaf (counting from the top) and 2 terminal leaflets from the 8th leaf were collected from each plant. The area of each leaflet was measure and the numbers of eggs, nymphs and red-eyed nymphs (pupae) were recorded on a per 10 cm basis. On 1 April and on10 May, numbers of glandular (type VI) and nonglandular (types II, III and V)trichomes were counted per 8 mm2 on terminals from the 6th leaves.

Evaluation of Peanut Breeding Lines for Resistance to Silverleaf whitefly (Homoptera: Aleyrodidae)

Silverleaf whitefly, Bemisia argentifolii Bellows & Perring, n. sp., is a new and occasionally damaging pest of peanut, Arachis hypogaea L., in Florida and other southern states. In 1992 and 1993, elite germplasm from the peanut breeding program at the University of Florida and several commercial cultivars were evaluated for resistance to silverleaf whitefly. In 1992, 52 genotypes that were chosen based on their performance in previous trials were evaluated. Numbers of whitefly red-eyed nymphs on peanut genotypes differed significantly. However, only two genotypes supported fewer whiteflies (although not significantly) than the cultivar ‘Southern Runner’. In 1993, we evaluated selections of crosses between Florida parent material (81206 and 567A) and a North Carolina parent (GP-NC343) with multi-insect resistance. All selections tested had higher numbers of whitefly eggs and red-eyed nymphs than either ‘Florunner’ or ‘Southern Runner’. No resistance to silverleaf whitefly was found in the peanut germplasm tested.

Population Levels and Parasitism of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on Peanut Cultivars

Sweetpotato whitefly, Bemisia tabaci (Gennadius), has recently become a pest of peanut in the southern United States. Limited observations in grower fields had identified differences in infestation among cultivars. We wished to determine whether selected cultivars grown commercially in this region resisted whitefly infestation and whether parasitism by aphelinid parasitoids differed among cultivars. Five cultivars were evaluated in summer 1992 and six in summer 1993. In 1992, ‘Florunner’ supported the greatest populations of red-eye nymphs and ‘Southern Runner’ supported the lowest populations. Encarsia nigricephala Dozier was the most common parasitoid (53.0% of all parasitoids reared), followed by Encarsia transvena (Timberlake) (25.6%), and Encarsia pergandiella Howard (18.3%). Parasitism was uniformly high and species composition on the five cultivars did not differ. In 1993, ‘Southern Runner’ supported the greatest populations of all immature whitefly stages except red-eye nymphs. ‘Marc I’ supported the lowest levels of whitefly infestation. E. nigricephala was extremely abundant in 1993 (85.3% of all parasitoids reared), followed by E. pergandiella (9.8%), and E. transvena (4.7%). Eretmocerus nr. californicus was found in low numbers in both years. Again, in 1993, parasitism was high on all cultivars (up to 100% by the end of September), and no differences were noted in the parasitoid composition among the six cultivars. Whitefly infestation was light in these noninsecticide-treated peanut plots, most likely because of natural control by native aphelinid parasitoids, and other beneficial insects.

Distribution Patterns of Bemisia tabaci (Homoptera: Aleyrodidae) in Cantaloupe Fields in Arizona

Infestations of the sweetpotato whitefly, Bemisia tabaci (Gennadius), in fields of spring-grown cantaloupes, Cucumis melo L., near Yuma, AZ, were measured by counts of eggs, first to mid-fourth instars, late-fourth instars (red-eyed nymphs) and adults. All stages were sampled from leaves at the terminal and crown portions of the plant. Adults were sampled at 0700 and 1300 hours on the entire leaf, and immature stages were counted in a 1-cm2 area from each of four quadrants of a leaf. Adult whiteflies were more abundant on samples collected at 0700 hours and on terminal leaves in all fields. There were no significant differences between leaf sections for any immature life stage, but red-eyed nymphs were more abundant on crown leaves, whereas eggs had higher densities on terminal leaves. The power law and patchiness regressions indicated that all life stages were aggregated, but there were distinct degrees of aggregation between leaf positions.

Control of Sweetpotato Whitefly in Cantaloupe with Various Pesticides, 1992

Abstract Cantaloupes, Cucumis melo, ‘Topmark’ were direct seeded on 3 Mar into single row “yuma beds” on 203 cm centers and thinned to 30 cm intervals at the University of Arizona, Yuma Valley Agricultural Center. Plots consisted of 4 beds, 18 m long with a 3.6 m buffer between plots. Plot preparation and seasonal maintenance followed local practices. Plots were arranged in a randomized complete block design with 4 replicates. Applications were made with a 4-row highpressure, electrostatic boom sprayer equipped with stainless steel, hollow-cone nozzles (TX-18) spaced at 50 cm and delivered 563 liters/ha at 400 psi. Admire was applied as a soil drench in 40 oz of water/plant one week after thinning (5 Apr). Foliar applications were initiated when immature whitefly densities exceeded 3 nymphs/leaf. A total of 3 applications of CGA215944 and Fenoxycarb were made on 29 Apr and 5, 14 May. The remaining foliar treatments were applied 5 times on 29 Apr, 5, 14, 20, and 28 May. The pH of the application water was 7.1. A spreader/sticker was not used. Insect data were collected only from the inner two beds of each plot. Plots were sampled weekly beginning on 14 Apr, and terminating on 9 June. Adult SPWF were assessed by randomly selecting 20 leaves from the terminal area on primary vines (4th fully expanded leaf from the apex of the vine) and counting the number of live adults on the bottom surface. Counts were made at sunrise between 0500-0600 hrs. Immatures were assessed by counting the number of eggs, small nymphs, large and red-eyed nymphs, and eclosed pupal cases on two-cm2 disk sections from each of 10 leaves per plot.

Seasonal Abundance and Within-Plant Distribution of Parasitoids of Bemisia tabaci (Homoptera: Aleyrodidae) in Peanuts

Sweetpotato whitefly, Bemisia tabaci (Gennadius), was sampled on peanuts during 1991 and 1992 in Alachua County, FL, to determine parasitoid abundance and levels of parasitism. Common parasitoid species of B. tabaci in 1991 were Encarsia nigricephala Dozier, Encarsia pergandiella Howard, and Eretmocerus californicus Howard. E. nigricephala, E. pergandiella , and E. transvena (Timberlake) were the most abundant parasitoid species in 1992, whereas E. californicus appeared only rarely. E. nigricephala was the most common species in both years and accounted for 91% of adult parasitoids reared from whitefly-infested foliage in 1991, and for 54 and 71% of parasitoids reared from foliage at two sites in 1992. E. pergandiella , E. californicus , and E. transvena were more common during the late season, whereas E. nigricephala was most prevalent during the early season. Parasitism contributed significantly to whitefly mortality und, in 1992, 90% of all fourth instars were parasitized by 10 September at the second site and by 21 September at the first site. Vertical distribution within plants of sweetpotato whitefly stages, unparasitized and parasitized, was assessed in 1992. Red eye nymphs (late fourth instar) were most common on leaves 4, 5, and 6 (from the top of a lateral stem), and 91% were located on the lower leaflet surface. Parasitized fourth instars were most prevalent on leaves 5, 6, and 7 and were found on the lower leaflet surface 79% of the time. All life stages were equally distributed among the four leaflets of the compound leaf. These data indicate that monitoring for whitefly parasitism in peanuts could best be accomplished by examining both surfaces of a leaflet picked from the fifth leaf down from the terminal lateral stemleaf. The conservation of parasitoids to increase natural biological control of sweetpotato whitefly in peanuts is discussed.

Sampling of Bemisia tabaci (Genn.) (Sternorrhyncha: Aleyrodidae) in Sudanese Cotton Fields

The distribution of the red-eye nymphs of the tobacco whitefly, Bemisia tabaci (Gennadius), within the cotton plant was analyzed during the growing season 1980–1981. Whiteflies distinctly aggregate on and around a main stem leaf, whose location varies according to plant growth and cotton variety. Sampling costs were reduced considerably by counting red-eye nymphs on a distal leaf sector only. The mean crowding index was used to define numerical and sequential sampling plans with a given precision level.