Immature Density Research Articles

Aedes albopictus (Diptera: Culicidae) population density and structure in southwest Louisiana.

Pupal density, wing length at emergence, host-seeking female abundance, and host-seeking female wing length and parity were determined monthly for a population of Aedes albopictus (Skuse) in a southwestern Louisiana tire dump from January 1988 through January 1989. Pupae and host-seeking females were first collected in April. Pupal densities were consistently high from June through September. Host-seeking female abundance was highest during July and August. Average female wing length was longest during spring, declined in midsummer, and increased slightly during fall. Average wing length was negatively correlated with average pupal density during the month of collection and with average air temperature recorded the previous month. Host-seeking females had consistently longer wings than emerging females, and parous host-seeking females had longer wings than nulliparous host-seeking females. Average wing length of the parous host-seeking females was consistently long throughout the season. Parity of host-seeking females parity was highest during July when approximately 21 parous host-seeking females were collected per hour. These results indicate that seasonal patterns in immature population density influence average body size and parity structure in Ae. albopictus.

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.

Control of Sweetpotato Whitefly in Cantaloupe with Various Pesticides, 1992

Abstract Cantaloupes ‘Topmark’ were direct seeded on 20 Feb 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. Two applications of the fungicide Myclobutanil were made on 14 May and 20 May to suppress powdery mildew. Plots were arranged in a randomized complete block design with 4 replicates. Applications were made with a 4-row high-pressure, electrostatic boom sprayer equipped with stainless steel, hollow-cone nozzles (TX-18) spaced at 50 cm and delivered 563 liter/ha at 320 psi. Applications were initiated when immature whitefly densities reached measurable levels. A total of 5 applications were made on 23, 29 Apr, and 8, 13, and 20 May. The pH of the application water was 7.1. Addition of the Aliette to the water caused the pH of the mixture to decrease to 3.5 pH. A spreader/sticker was not used. Insect data were collected only from the inner two beds of each plot. Plots were sampled on 22, 24 and 30 Apr, and 9, 14, and 21 May. 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) in each plot. The underside of each leaf were carefully turned upward and the number of live adults on the surface was recorded. Counts were made at sunrise between 0500-0600 hrs. Data were analyzed for treatment differences using ANOVA and Ryan’s Q test. Bartlett’s test estimated a heterogeneity of variance and treatment means were log transformed prior to analysis of variance.

Effect of Trialeurodes vaporariorum (Homoptera: Aleyrodidae) on Yield of Fresh Market Tomatoes

Effect of the feeding of immature greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and sooty mold contamination on tomato production was determined using small field plots. Total and grade-A fruit weights harvested were correlated negltively with cumulative immature greenhouse whitefly days (=pest-days). Effects of T. vaporariorum feeding on tomato yield were inlluenced by environmental factors. Percentages of fruit contaminated with sooty mold were correlated positively with cumulative immature greenhouse whitefly days. Cumulative immature greenhouse whitelly days were correlated positively with peak immature whitefly densities during the growth cycle of the plant. Results suggest that tomatoes grown in Hawaii may incur a 5% yield loss in grade-A fruit at about greenhouse whitefly levels as low as 70 cumulative greenhouse whitefly days per cm2 tomato leaflet (=a peak density of 0.7 immature greenhouse whitefly per cm2 tomato leaflet per day) due primarily to the consumption of plant assimilates by T. vaporariorum . Compared with direct greenhouse whitefly feeding, contamination of fruit with sooty mold was less important with respect to reducing overall crop yields. A 5% reduction in grade-A fruit due to sooty mold contamination was estimated at ≈300 cumulative greenhouse whitefly days per cm2 tomato leallet (=a peak density of 8.3 immature greenhouse whitefly per cm2 tomato leaflet).

Developmental Sites and Relative Abundance of Immature Stages of the Stable Fly (Diptera: Muscidae) in Beef Cattle Feedlot Pens in Eastern Nebraska

A 3-yr study was done to determine where and at what relative frequency stable fly, Stomoxys calcitrans (L.), immatures develop in beef cattle feedlot pens and the relationship of stable fly immature versus adult sample densities. Pens within feedlots were divided into five areas (the feed apron, back fence, side fences, mound, and the general lot); from each area, three core samples were randomly taken weekly. In 1986 and 1987, the feed apron yielded the most immature stable flies (62.5%). The mound and side fences yielded a significant percentage of flies (24.6 and 8.4%, respectively). There was a strong correlation (overall r = 0.86) between numbers of immatures and numbers of adults 2 wk later. In 1988, a drought year, low numbers of immatures were collected, and only one correlation between numbers of immatures and adults was significant. In all 3 yr, sample densities of stable fly immatures peaked and began to decline by midseason. Waste management along the feed apron and mound areas could significantly reduce stable fly populations. Sampling immatures from these areas could permit prediction of adult numbers.

Population Trends of a Newly Introduced Species, Thrips palmi (Thysanoptera: Thripidae), on Commercial Watermelon Plantings in Hawaii

Population trends of a newly introduced species, Thrips palmi Karny, are reported on commercial watermelon plantings in Hawaii. Eight plantings were surveyed weekly for thrips on foliage and melon vine tips. Peak infestation levels varied from 2.5 to 53.6 thrips per leaf and from 18 to 97% infested vine tips per planting. Treatments of oxamyl appeared to reduce immature thrips densities, but did not affect adults. No correlation was found between thrips density on foliage and percentage of infested vine tips per planting.

A freeze-fracture study of photoreceptor presynaptic membranes during ribbon synapse formation.

The outer plexiform layer (OPL) of the developing chick retina from 11 embryonic days to 11/2 weeks posthatching has been studied by freeze-fracture to characterize changes in the membrane structure of photoreceptor terminals during synaptogenesis. At early stages, the undifferentiated photoreceptor synaptic base is characterized by a sparse distribution of intramembrane articles on the inner leaflet (P-face). Later, as the synaptic base begins to differentiate by extending filopodia into the OPL, numerous small aggregates of large particles appear between and on filopodial surfaces. Many of the aggregates occupy crater-like expressions, which are seen in cross-fractures through the underlying cytoplasm to be associated with vesicular invaginations of the presynaptic membrane. Corresponding thin sections through these regions at this time reveal immature arciform densities and coated vesicles fusing with the presynaptic membrane adjacent to these densities. At later stages, many of the particle aggregates on the photoreceptor membrane appear to have coalesced into longer arrays overlying ridges surrounded by numerous vesicle fusion sites. These intramembrane changes correlate with the formation of the mature arciform density-synaptic ribbon specialization in the photoreceptor presynaptic terminal and with physiological maturation of the chick retina.

Factors Influencing the Distortion of Sex Ratio in Aedes Aegypti1

A genetic factor, Distorter, causes abnormal segregation ratios, resulting in the excess recovery of males in Aedes aegypti. The following factors were assayed to determine their influence on the production of high male ratios: differential mortality of immature stages, larval density, rearing temperature, parental age and genetic constitution. Genetic factors alone are responsible for high male ratios. The use of inbred lines has provided evidence to support the hypothesis that there are several forms of md with different levels of sensitivity to Distorter. These alleles produce different degrees of sex ratio distortion.