FY2000-2001 Progress and Findings: (Report accomplishments toward each objective; include data summaries, and graphs as appropriate; include comments on collaboration and technology transfer; confine text to two pages.)
Continued rearing of field collected populations at lower temperatures to determine lower developmental threshold. First instars observed in the field until early July. Adults first observed in late May. A first instar nymph and an adult were observed on the same tree (May 26th 2001). This helps confirm staggered generations. First instars seen again in late July, most likely representing a second generation, based on the presence of adults in May.
Monitoring & Distribution: Field sampling, March 2001 until present of approx. 3000 acres of navels & valencias confirmed clumped distribution of S. furcata populations. Continued review of three years collection data showed populations remained consistent in ranches from year to year (i.e., hot spots remain hot spots).
Feeding damage: late instar nymphs observed feeding on fruit slightly smaller than golf-ball-size; the oldest nymphs inflict deeper wounds as fruit becomes larger. The tree may not abort severely wounded fruit. Damaged fruit occurs in clusters and near damaged foliage on a tree.
Temperatures were hotter in May than the 30 yr. average in the San Joaquin Valley (7-8 days at or above 100F) leading to a slight acceleration in development of eggs as evidenced by the presence of a larger second
generation. Field work this spring and summer (2001) showed a second generation hatching as early as late July (first instars observed at a ranch near Arvin area on July 18th, 2001 & first and second instars have been observed since that time). Katydids emerging as a part of a second generation can damage remaining susceptible fruit, including smooth skinned citrus varieties (i.e., Thompson Improved (T.I.) navels and some valencias) no fruit larger than golf-ball-size has been observed with fresh katydid damage. Second generation katydids comprise the breeding population that lays the eggs for the following year’s population.
Smaller trees, and non-harvested trees managed for intense vegetative growth, showed high katydid populations after about two to three year’s growth. Katydids were easier to find on smaller trees; they were observed feeding on new flushes. Initial spring searching for newly emerged katydids on young trees, if present, would likely reveal populations relatively easier than on larger trees.
Field Mortality: Thrips treatments following petal fall appear to be successful at controlling katydids. No natural enemies were observed in the field.
CONCLUSIONS & CONCERNS BASED ON 2001 FIELD STUDIES:
Spray applications have limited success because of the prolonged hatching period during the spring and the prolonged period that fruit is susceptible to katydid damage. A degree-day model may have limited field application based on the potential daily emergence of first instars for a period of about 2 -3 months in the spring. The growth and development of katydids will be most successfully monitored in a manner consistent with lepidopteran pest sampling in citrus: visual inspection during the spring for early instars and sweep net counts. Following thrips treatments, timing of any ensuing katydid applications may be initiated by visual observation of katydids or their damage within a block.
500 Word report on the 2001 Results
Population growth and development:
Field and laboratory studies have shown the fork-tailed katydid consistently has two generations per year and up to three generations per year. Further, these generations have a staggered stage-class distribution, or stage overlap, due to several factors: multiple oviposition episodes per female, variable embryonic development, variable eclosion and late season oviposition (February to May). A third generation may develop due to oviposition by females from earlier generations in warmer than normal seasons, as in 2001. Field observations in 2001 showed a second generation emerging in early June 2001 and third generation emerging in late July 2001. There is strong seasonality with katydids in the San Joaquin Valley due to the egg being the only stage that survives the coldest months in winter.
The majority of katydid damage occurs during spring and early summer months. Egg hatch usually begins weeks before citrus petal fall and continues into the summer. First instars hatching before petal fall prefer to feed upon flushes of newer leaves, flowers, and terminal shoots. Katydids feeding on flowers and newly developing fruit can cause scarring and fruit abortion in addition to natural fruit abscission. All katydid instars prefer to feed on all parts of the flower (stamen, pistil, petals, and ovary), taking small bites from these tissues. First through fourth instars are most abundant during flower formation and through petal fall and feed on blooms and fruit until fruit is ca. 3.0 cm in diam. (about golf ball-size) and the outer rind hardens. Later instars (fifth through adult) prefer newer leaf growth and younger fruit, but their larger and presumably stronger mouthparts allow them to feed on the harder surfaced, larger fruit. Therefore, the potential period of fruit susceptibility is about five months long: from eclosion as early as late March and continuing into late August.
However, the first generation causes the most economic damage. There are no flowers present on trees at the time of the second generation and the majority of citrus fruit has passed the period of susceptibility; thus, early instars are limited to feeding on new foliage. Third generation katydids were observed to feed strictly on foliage as well; fruit size at the time of third generation emergence was well beyond susceptibility to early instar feeding.
Fig. 1. Typical feeding damage on spring flush. Pictured is a second instar nymph. Examination of foliage at chest-height or lower is an effect way to determine presence of katydid during spring scouting activities.
Monitoring and Management:
Chemical treatments for katydid are typically conducted in the spring. Our studies have shown that management with a chemical treatment should also focus on the fall oviposition period, concurrent with the fall flush – generally from late September through mid-November. Our data and data we’ve examined from other scouting reports show that katydid populations remain high irrespective of the treatment regime in the spring. Females that survive through to the fall contribute to the next spring’s generation. Most chemical treatments in the spring help reduce populations of nymphal katydids causing economic damage, but are not effective in reducing populations from one year to the next. A reduction in the number of egg-laying females in fall is the best long-term control option. Future studies will attempt to use recordings of male katydid mating calls in an “attract and kill” management tactic.
Longevity - At 26.7C (80F), ~75% R.H. and 14:10 L:D photoperiod, katydids developed from eclosion to adult in 40.60 ± 1.77 days (n = 35). Females lived longer than males 108.06 ± 14.75 days (n = 18) and 99.56 ± 13.19 days (n=17), respectively (Table 1).
Table 1. S. furcata Instar Development and Longevity (days) at 26.7C (80F), ~75% R.H. and 14:10 L:D photoperiod.
5 - 7
6 - 8
5 - 8
5 - 8
6 - 8
5 - 7
5 - 8
Eclosion to Mortality
5 - 9
6 - 11
45 - 94
87 - 135
5 - 9
5 - 14
44 - 85
85 - 129
Longevity was recorded at low temperatures to determine cold tolerance and growth rates. At 1.11C (34F), ~75% R.H. and 14:10 L:D photoperiod, all katydid instars and the adult perished within 24 hours (n = 2 at each lifecycle stage). At 3.0C (37.4F), ~75% R.H. and 14:10 L:D photoperiod, first through fifth instars perished within 36 hours (n = 2 at each lifecycle stage). At 5.0C (41F) ~75% R.H. and 14:10 L:D photoperiod, first through third instars perished within four days (n = 2 at each lifecycle stage); fourth instars through the adult perished within seven days (n = 2 at each lifecycle stage). Longevity of first through fourth instars reared at 4.5C (40.1F), 7.5C (45.5F), and 9.0C (48.2F) ~75% R.H. and 14:10 L:D photoperiod (n = 5 at each lifecycle stage at each temperature) presented in Table 2.
Table 2. S. furcata Mean Longevity (days) at low temperatures, ~75% R.H. and 14:10 L:D Photoperiod (n = 8 each 1st through 4th instars)
Field Population Dynamics See above for population growth and number of generations per year. Figure 2 details the staggered stage-class distribution for katydids in the San Joaquin Valley. The line indicating (blue dots) the number of instars present on each sampling date corresponds to the lines below the chart, thus showing which instars were observed. Fruit is susceptible to katydid feeding damage until it reaches about 30 mm in diam. Thus, fruit are susceptible until early August. In some years three generations of katydids have developed by early August. However, it is the first generation (April through July) that causes the most damage to developing fruit.
Fig. 2. Growth and development of citrus fruit and range of instars present at field sites in the San Joaquin Valley.
We developed a preliminary degree day model based on development rates at various temperatures. The biofix date is set at 50% egg hatch in the field. The first generation is considered to inflict the most economical damage, especially first through fourth instars. Fruit susceptibility decreases as the fruit hardens and reaches golf-ball size, thus later instars or subsequent generations feed mainly on foliage.
We used the line intercept method to estimate degree days for development from eclosion to fourth instar nymph. The lower developmental threshold is 10 ºC.
Eclosion to 4th instar nymph = 425 DD.
Individual - All stages of S. furcata commonly exhibit a basking behavior. All stages can be found during daylight hours resting around the perimeter of trees and at all heights. Younger instars move slowly, but as instars mature, they exhibit coy behavior; hiding behind leaves or jumping into foliage when disturbed. Late instars and adults are easily disturbed and are quick to escape a disturbance, such as a shadow or movement.
Mating - In captivity paired males and females mated readily. Mating occurred late evenings and after sunset. Males and females were paired together as soon an adult of each sex was available. Cages containing pairs were removed from growth chambers and placed in a greenhouse. Males and females were separated following successful mating periods, no pairs were partnered more than 48 hours. All but one pair in captivity engaged in copulation during the late evening or night (n = 17 pairs). Copulation was prefaced by male stridulating, in each successful mating. Stridulating began at sunset and continued until males copulated with females. Males having engaged in copulation and successfully transferring the spermatophore to the female were never observed to mate again, although stridulating continued by a majority of the males. Males began stridulating in the evening hours of the day, within 24 hours following each male adult molt. Stridulating was in the form of rasping noises emitted in sequences. Copulation lasted 21.88 9.74 minutes (n = 17).
Oviposition - Females readily oviposited in captivity during the day and night (n = 15). Potted valencia seedlings served as a host plant and a single gravid female was enclosed in a cage with a single citrus seedling until egg laying was complete. Females oviposited eggs at all heights of the seedling and did not segregate between new and old growth leaves when selecting foliage for oviposition. Pre-ovipostion periods, the time between copulation and first occurrence of egg laying, lasted 16.93 4.81 days. Ovipositional periods, measured as the total time females spent between the first and last oviposition of eggs, lasted 23.64 6.66 days. Females laid each egg singly and one to seven eggs was deposited during any single ovipositional event. Females laid 24.57 8.84 eggs in a lifetime as a result of mating with a single male.
Egg distribution in the field was quantified in order to develop a sampling method for egg detection and delimiting katydid populations for subsequent spring management treatments.
Table 3. Oviposition sites by tree at two field sites in the San Joaquin Valley.
No. Eggs per Tree
No. Eggs per Leaf
Leaf Length (mm)
Leaf Width (mm)
Leaf Height from Ground (cm)
Of 120 trees examined 33% of eggs were laid in the SE quadrant of trees, 23% in the SW quadrant, 21% in the NE quadrant, and 23% in the NW quadrant. Further, eggs placement in leaves was as follows: 27% of eggs were located in the anterior (tip) section of leaves, 47% in the middle section of leaves and 26% in the anterior (basal) section of leaves.
Fig. 3. Placement of eggs into leaves. Eggs occur singly or in groups of up to 4-5.
See above for details about feeding damage and feeding preferences by instar.
Fig. 4. Feeding damage to fruit by katydids. Feeding took place when the fruit was much younger and the fruit have now developed significant scars. Fruit will abort if katydid feeding takes place early in development.
1. Quantified growth and development of katydid in commercial citrus
Feeding damage and fruit susceptibility periods determined
Monitoring techniques developed and validated
I gave a final presentation to the CRB in July of 2002. Upon completion of the presentation a board member requested that the following statement be officially added to the minutes:
“This research is exactly what we needed, it was executed with a high level of skill and completeness, and provides for our growers much needed and very valuable information. I wish we had more researchers committed to the industry as exemplified by this project.”
As the industry increases the use of natural enemies to control key pests such as California red scale, secondary pests will require thoughtful biologically/ecologically-based management compatible with biological control to avoid pest population upsets.
Successful completion of the katydid research program objectives provides the citrus industry with substantive information with which to develop the most appropriate management tactics in commercial citrus production.
The Citrus Research Board has funded the study of the fork-tailed katydid a secondary pest of citrus for three years, substantiating their commitment to such research. Refining and validating the research findings to ease the transition into mainstream use in the industry is a unique and valuable opportunity for us. Adding to the knowledge base through respected and widely used publications and information outlets such as the UCIPM webpage is an opportunity not to be missed.
Dissemination, publications and presentations of research:
The depth and detail of our findings has led to our being asked to participate in several different types of research information outlets.
We have been asked to place our findings on the University of California Statewide Integrated Pest Management webpage (http://axp.ipm.ucdavis.edu/default.html) and guidelines.
We also are freqently asked to give presentations to industry sponsored grower group meetings.
Our findings also are the most detailed of any species in the subfamily that includes the fork-tailed katydid. We plan to pursue publication of these findings in specialized national and trade publications, and a new encyclopaedia of entomology, edited by John Capinera (Entomology Department Head, Univeristy of Florida).
These extension activities are beyond the funding scope of the original citrus research board proposal, but are part of the intent and aim of applied research. These are important opportunities to bring our research into the hands of those that can benefit from it the most.
1999. Demography and Ecology of the Forktailed Katydid in Citrus. David Headrick and Nick Brandt. Citrus Research Board, September 15, Riverside, CA.
2000. Demography and Ecology of the Forktailed Katydid in Citrus. David Headrick & Nick Brandt. Citrus Research Board, March 9th, Riverside, CA.
2000. Demography and Ecology of the Forktailed Katydid in Citrus. Nick Brandt & David Headrick. Citrus Growers Meeting, May 2000, Visalia, CA
2000. Demography and Ecology of the Forktailed Katydid in Citrus. Nick Brandt & David Headrick. Entomological Society of America Annual meeting, Montreal, Canada, December 3 – 7.
2001. Demography and Ecology of the Forktailed Katydid in Citrus. David Headrick & Nick Brandt. Citrus Research Board, Sept 14th, Riverside, CA.
2001. Demography and Ecology of the Forktailed Katydid in Citrus. David Headrick & Nick Brandt. Citrus Research Board, March 9th, Riverside, CA.
2001. Demography and Ecology of the Forktailed Katydid in Citrus. Nick Brandt & David Headrick. UC Field Day Citrus Growers Meeting, May 2001, Lindcove Field Station, Parlier, CA.
Brandt, N. A. & D. H. Headrick, 2000. Biology of the forktailed katydid: an unfolding story. Citrograph. 84: 3, 12.
The graduate thesis is forthcoming (Winter 2003 graduation).