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Project description

Development of an economic injury level and monitoring methods for cottony cushion scale Icerya purchasi, and the predatory beetle vedalia beetle Rodolia cardinalis. (02DS022)
Program UC IPM competitive research grants program
Principal
investigators
E.E. Grafton-Cardwell, Entomology, UC Riverside/Kearney Agricultural Center
J.T. Trumble, Entomology, UC Riverside
Host/habitat Citrus
Pest Cottony Cushion Scale Icerya purchasi
Discipline Biological Control
Beneficial
organism
Vedalia Beetle Rodolia cardinalis
Review
panel
Decision Support
Start year (duration)  2002 (Three Years)
Objectives Determine the life cycle and number of generations of cottony cushion scale produced in the San Joaquin Valley.

Develop an economic injury level for cottony cushion scale in mature navels

Develop a user-friendly sampling method for cottony cushion scale.

Develop a sampling method for vedalia beetle

Determine the upper and lower developmental threshold of vedalia beetle

Final report We have evaluated cottony cushion scale populations (CCS) in 10 San Joaquin Valley citrus orchards and determined that the populations consist of mixed stages during the fall and winter, but becomes uniformly adult females in April and May. This is the ideal time for sampling by PCAs and growers since the adult female scales are easy to see and this is the peak period of activity of its predator the vedalia beetle.

By May 15 to June 15 (depending on temperature), all of the adult female scales die, scale populations are primarily 1st instars which are not suitable for vedalia egg laying, and summer heat arrives and suppresses vedalia. We documented a reduction in vedalia egg laying, egg hatch, and larval survival when exposed to temperatures of 93 to 100 degrees Fahrenheit.

Our data suggests that growers should move vedalia into their orchards in March, and if for some reason vedalia do not control the scale, wait until the vedalia is no longer effective and the scale stages are primarily 1st instars (June) to use insecticides. There are three generations of scale per year, however, the spring generation shows the greatest growth.

Third-year
progress
We have evaluated cottony cushion scale (CCS) populations in 10 San Joaquin Valley citrus orchards and determined that the populations consist of mixed stages during the fall and winter, but becomes uniformly adult females in April to May. This is the ideal time for sampling by PCAs and growers since the adult female scales are easy to see and this is the peak period of activity of its predator the vedalia beetle. By May 15 to June 15 (depending on temperature), all of the adult female scales die, scale populations are primarily 1st instars which are not suitable for vedalia egg laying, and summer heat arrives and suppresses vedalia. We documented a reduction in vedalia egg laying, egg hatch, and larval survival when exposed to temperatures of 93 to 100oF. Our data suggests that growers should move vedalia into their orchards in March, and if for some reason vedalia do not control the scale, wait until the vedalia is no longer effective and the scale stages are primarily 1st instars (June) to use insecticides. There are three generations of scale per year, however, the spring generation shows the greatest growth.

Second-year
progress
During 2003, we evaluated cottony cushion scale populations (CCS) in six San Joaquin Valley citrus orchards. During the winter, CCS were primarily younger instars that gradually developed into adults during March through May. Predatory vedalia beetles arrived as early as March 15, and as late as May 15 in these orchards. Vedalia is most effective in controlling CCS during March-May when it can lay eggs on adult female scales and the temperature is not too hot or cold. By June, the adult female scales had died, scale populations were primarily first instars which are not suitable for vedalia egg laying, and the summer heat arrived and suppressed egg production in vedalia. Uniformity of the scale population in March through May makes it an excellent time for pest control advisors (PCAs) to sample for both scale and predator. Additionally, we found that the CCS populations were uniformly first instars during June, which is the stage that is most successfully controlled with insecticides. Thus, growers should move vedalia into their orchards in March, and if for some reason vedalia do not control the scale, wait until the vedalia is no longer effective (June) to use insecticides. CCS development was rapid during the summer (three months). In September, the cottony cushion scale population was again primarily first instars, allowing another opportunity for insecticidal control. All stages were present in the fall months, allowing another opportunity for vedalia releases. In laboratory experiments, we determined that the vedalia beetle has a lower developmental threshold of 10oC.

First-year
progress
We conducted experiments to determine the upper developmental threshold of vedalia beetle and found that while adults can easily survive constant high temperatures (93-99oF), they deposit very few eggs at a 93oF and eggs do not hatch at 99oF. Their sensitivity to high temperature explains the nearly complete disappearance of vedalia beetle populations in the San Joaquin Valley during the summer months. We also began sampling three citrus orchards to determine which stages are present during each month of the year. In October, the three populations consisted primarily of females and first instar nymphs. In November and December the populations gradually developed into 2nd and 3rd instar nymphs. We will continue to follow these populations for several years to see if they grow during all months of the year and to see if there are certain times of the year when eggs are common (a good time for predatory vedalia beetle releases), or young instars on leaves (a good time for insecticide treatments), or adult females (a good time for sampling the population of pest and beneficial vedalia beetles.

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