Red Scale Populations Research Articles

Mating Disruption of the California Red Scale, Aonidiella aurantii (Hemiptera: Diaspididae) in Central California Citrus

A warmer climate and the development of pesticide resistance have led to an increase in the number of generations and higher population densities of California red scale, Aonidella aurantii (Maskell) in central California. Commercial citrus orchard studies were conducted to determine how effective mating disruption using CheckMate CRS was at reducing A. aurantii. In 2016-2017, two replicated trials were conducted in 15.0-15.5 ha orchards and in 2018 and 2019, one half of each of 10 orchards 8-16.2 ha in size were treated with CheckMate CRS. Mating disruption significantly suppressed male captures for up to 8 mo. Average reductions of 90% in cumulative male flight trap catches were recorded, twig and leaf infestations were reduced by 95%, and highly scale-infested fruit were reduced by 75% in the CheckMate CRS plots for the 2018 and 2019 trials. In seven of 12 sites the percentage of highly infested fruit was reduced below 0.5%. Leaf and twig infestations in August and reductions in male captures during the 4th flight were strongly related to the percentage of highly infested fruit at the end of the season and could be used as predictors of the success of mating disruption. The results of the study indicated mating disruption using CheckMate CRS can be an effective method to reduce California red scale populations throughout the 4+ generations that occur in central California. Mating disruption has the potential to reduce or eliminate pesticide applications, especially in low scale density situations.

Dispersion, contagion, and population stability of red scale, Aonidiella aurantii, in citrus orchards with low or zero insecticide use

Red scale, Aonidiella aurantii Maskell (Hemiptera: Diaspididae), has a contagious distribution among fruit and among trees largely due to the fact that most young settle on the same fruit as their mothers. The pattern of distribution and degree of dispersion of red scale within various sets of contiguous citrus trees in several orchards were recorded each autumn for 4 years. Changes in density and site occupancy within trees and within contiguous groups of trees were made to assess the strength of any link between populations and their dynamics on different trees. Aonidiella aurantii was found to have a very clumped distribution whereby trees with a level of scale infestation well above average for their block could be adjacent to trees with few or no detectable scale. However, patches of high density on a given tree usually did not recur for more than 2 years but were replaced with above average infestations on other trees. The stability of the red scale populations varied from block to block. Some blocks had few or no infested trees over the study period whereas others had widely fluctuating levels of infestation. Dispersion coefficients at ‘within tree’ and ‘within block’ levels were similar. Theoretical and statistical models of the relation of average scale levels to the percentage of fruit or trees infested were less precise than they are for other pests because of high variation of clumping intensity of scale within any block.

Role of esterase enzymes in monitoring for resistance of California red scale, Aonidiella aurantii (Homoptera: Diaspididae), to organophosphate and carbamate insecticides.

Eighty-seven populations of California red scale, Aonidiella aurantii (Maskell), from the San Joaquin Valley of California were tested for insecticide resistance by using chlorpyrifos, methidathion, and/or carbaryl in a standard fruit-dip bioassay as well as for general esterase activity by using alpha-naphthyl acetate as a substrate in a colorimetric test. The percentage of individuals that survived a discriminating concentration of methidathion, chlorpyrifos, or carbaryl was significantly correlated with the percentage of individuals showing > 0.4 nmol of esterase activity per minute per microgram of protein in the colorimetric test. Scale survival of the organophosphates showed a higher correlation with esterase activity than survival of carbaryl. These results suggest that the colorimetric test of esterase activity is useful as an indicator of the frequency of organophosphate-resistant and, to a lesser extent, carbamate-resistant individuals in California red scale populations. The results of tests for activity and inhibition of acetylcholinesterase activity suggest that California red scale is using increased amounts of esterase enzymes, including acetylcholinesterase, to sequester organophosphate and carbamate insecticides, rather than modified acetylcholinesterase. Third instars collected from twigs, leaves, and fruit showed similar levels of esterase activity. The colorimetric test of esterase activity is a useful tool to detect organophosphate and carbamate resistance in San Joaquin Valley California red scale because of its speed of testing over a wide range of months, allowing for within-season decision making by citrus growers.

Increases in Florida Red Scale Populations through Pesticidal Elimination of Aphytis holoxanthus Debach in Florida Citrus

Based on a laboratory study, a field study was designed to determine if the host–parasite relationship of Florida red scale and Aphytis holoxanthus could be disrupted in Florida by carbaryl and dicofol pesticide applications. The mean survival rate of third instar nymphs and gravid females on leaf samples was higher in the carbaryl treatment than in the dicofol and control treatments due to lower rates of parasitism. There were no significant differences in the survival of third instar nymphs and gravid females in the dicofol and control treatments. In September, parasitism of Florida red scale was significantly higher in the control and dicofol treatments than in the carbaryl treatment, and September fruit infestation by Florida red scale was highest in the carbaryl treatment, followed by those in the dicofol and control treatments. Higher fruit infestation in the carbaryl treatment (26%) than in the dicofol (9%) and control (7%) treatments did not result in higher fruit drop. This is the first Florida study that shows that pesticide use can increase Florida red scale populations and it confirms previous laboratory results.

Monitoring for Organophosphate- and Carbamate-Resistant Armored Scale (Homoptera: Diaspididae) in San Joaquin Valley Citrus

Citrus fruits infested with California red scale, Aonidiella aurantii (Maskell), and yellow scale, A. citrina (Coquillett), were collected from a total of 68 orchards in four counties in the San Joaquin Valley of California over three seasons to test for insecticide resistance. California red scale populations were collected from Madera, Fresno, Tulare, and Kern counties. Yellow scale populations were fewer in number and were found only in Tulare County. The results of laboratory bioassays of the infested fruit suggest that resistances to the organophosphate insecticides chlorpyrifos and methidathion are developing in the two armored scale species in this region. Armored scale resistance to the carbamate insecticide, carbaryl, appears to he less intense than for the organophosphates at this time. The populations showing the lowest percentage of mortality to any of the tested insecticides were located in eastern Tulare and Kern counties. An insecticide resistance management strategy for this citrus growing region is discussed.

Suspected Resistance to Methidathion in Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) from Queensland

ABSTRACTThe first indication of resistance to organophosphorus insecticides in red scale, Aonidiella aurantii, from Australia is noted from the Mundubbera region, Queensland. Samples of scale‐infested fruit were dipped in a commercial formulation of methidathion and the mortality of sessile first instars was recorded. Analysis of variance revealed that two populations contained significant numbers of first instars surviving the insecticide treatment. Presence of resistance to methidathion in red scale populations would limit its usefulness in pest management programs and may indicate cross‐resistance to other organophosphates.

A Refuge for Red Scale Under Control by Aphytis: Structural Aspects

Red scale populations in eight grapefruit trees in a grove in southern Cali- fornia were sampled over 18 mo. We established that the interior of the trees was an area of partial refuge from parasitism by the major control agent, the parasitoid Aphytis melinus, and also by Encarsia, which was the second major parasitoid in the system. The refuge (interior) population contained >75% of the scale and >90% of the adult scale in the average tree. Parasitism by Aphytis in the exterior (twigs) was 27 times as high as in the refuge for second-instar scale, and 6 times as high for third instars. The differences in instantaneous parasitism rates were greater. Parasitism by Encarsia in the exterior was about twice that in the refuge. A field experiment showed that Aphytis could search in the interior and that it parasitized scales that had been placed there on lemons. Low parasitism rates in the interior may have been caused by the parasitoids' response to the bark substrate. The refuge population may account for the observed stability of the Aphytis-red scale interaction in some citrus groves.

Impact of Pesticides on California Red Scale Populations on Orange, 1984

Abstract A randomized complete block experiment with 7 replicates was conducted in a field of Valencia oranges (ca 15 ft tall, 20 ft × 21 ft planting) in Riverside, California. The field was divided into 9-tree (3 × 3) plots. Pretreatment densities of California red scale (CRS) were estimated by sampling 120 twigs (9-in terminal twigs) per plot in mid May ’84 and posttreatment densities were estimated by sampling 120 twigs and 120 fruit per plot in mid Oct ’84 and again in early Apr ’85. Fruit counts are an index of how well a treatment prevented the current crop from becoming infested and consequently down-graded. This is the immediate benefit of a CRS control application. Twig counts are an index of how well a treatment suppressed scale population growth. The 120 sample units per plot consisted of 15 randomly selected sample units from each of 8 locations within each plot: on the center tree, the NE, NW, SE, and SW quadrants; and on each of the 4 trees immediately N, S, E, and W of the center tree (rows ran E-W), the quadrant that faces the center tree (the S, N, W, and E quadrants of these trees, respectively). Each sample unit was scored in situ as being infested or not infested with live CRS. Blocks with relatively uniform pretreatment counts were created by assigning plots with similar pre-treatment counts to the same block. The treatments were randomized within each of the 7 blocks. Pesticides were applied with an oscillating boom sprayer (500 psi, 1.4 mph) at a rate of ea 2,038 gal/A on 27 Jun ’84 which was approximately 1 wk prior to the peak of the second generation male flight as estimated from pheromone trap catches in a field ca 20 mi from Riverside.

Predictive Year-end California Red Scale (Homoptera: Diaspididae) Orange Fruit Infestations Based on Catches of Males in the San Joaquin Valley

Aonidiella aurantii (Maskell) infestations on ‘Navel’ and ‘Valencia’ orange fruit at the end of the calendar year were successfully predicted in the San Joaquin Valley based on data developed from catches of male scales in traps, female scales on twigs, and fruit infestations. Fruit infestations at harvest were regressed on the number of males trapped in the first, second, or fourth male scale flights or on the number of adult females on twigs. The equation that best explained the percentage of infested fruit as a function of male catches was a polynomial of the second degree. If the number of trapped males is known for the first, second, or fourth flights, the percentage of fruit infestation (≥1 scale per fruit) at the end of the season can be predicted. By regressing the percentage of fruit with ≥1 scale on that with ≥11 scales per fruit, a direct relationship to the flights was established. The citriculturist can select an acceptable action threshold by either recording total fruits with ≥:1 scale or patchy fruits with ≥:11 scales. Thus, the red scale pheromone trap can be incorporated as a valuable tool in the management of red scale populations.

Parasitism by Aphytis chrysomphali, Mercet and A. melinus Debach of Californian red scale, Aonidiella aurantoo (Maskell), in relation to seasonal availability of suitable stages of the scale

A field study was undertaken to investigate the host-parasite relationship of A. aurantii and two species of Aphytis in north-western Victoria, and to suggest methods for improving and extending the biological control of A. aurantii in Victoria. Monthly samples of scale-infested Valencia oranges from five unsprayed biocontrol properties at Mildura provided information which showed a positive correlation between the percentage of available stages in the host population and the efficiency of parasitism by the Aphytis. This was thought to result from the seemingly inefficient method employed by the Aphytis in selecting a suitable host in which to oviposit; a postulate reinforced by the results of earlier work. The scarcity of suitable hosts at certain times of the year is thought to limit the efficiency of the Aphytis by reducing the chances of the parasite to achieve its reproductive potential. On the basis of this study an improved approach to red scale control is proffered, namely that attempts be made to augment the effectiveness of the established Aphytis by devising methods for increasing the proportion of available stages in red scale populations during late spring and early summer. Field and laboratory evidence indicates that parasitism by Aphytis, rather than variation in weather, is responsible for the considerable seasonal fluctuations in percentage of scales available for parasitism.

Efficacy of Natural Enemies of the California Red Scale on Citrus in Israel1

The interrelations between Aonidiella aurantii (Maskell) and its most important local natural enemies, the aphelinids Aphytis spp. and the coccinellid Chilocorus bipustulatus (L..), were investigated in an orange grove the southern Coastal Plain of Israel. The insecticidal check method was used in this study. It was found that natural enemies play a decisive role in retarding the buildup of California red scale populations on citrus, especially at the onset of summer. Thus, decimation of natural enemy populations at that period causes a marked increase in the percentage of live scales, which is followed by a massive outbreak of the scale’s populations. However, local natural enemies alone were not sufficient to hold the California red scale population below the threshold of economic injury in the test plot.

Effect of DDT on Florida Red Scale Populations

Effect of DDT on Florida Red Scale Populations

Effect of Cultivation on Florida Red Scale Populations

Effect of Cultivation on Florida Red Scale Populations

Changes in California Red Scale Populations Following Sprays of Oils With and Without Derris Resins

Journal Article Changes in California Red Scale Populations Following Sprays of Oils With and Without Derris Resins Get access A. W. Cressman, A. W. Cressman U.S.D.A., Agr. Res. Adm., Bureau of Entomology and Plant Quarantine Search for other works by this author on: Oxford Academic PubMed Google Scholar B. M. Broadbent B. M. Broadbent U.S.D.A., Agr. Res. Adm., Bureau of Entomology and Plant Quarantine Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Economic Entomology, Volume 37, Issue 6, 1 December 1944, Pages 809–813, https://doi.org/10.1093/jee/37.6.809 Published: 01 December 1944