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Project description

Biological control of the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in Southern California. (01BC004)
Program UC IPM competitive research grants program
J.M. Heraty, Entomology, UC Riverside
Host/habitat Citrus; Tree Crops
Pest Citrus Leafminer Phyllocnistis citrella
Discipline Entomology
Ageniaspis citricola; parasitiods
Biological Controls
Start year (duration)  2001 (Two Years)
Objectives Monitor spread of a new pest, the citrus leafminer, in southern California

Evaluate the role of native parasitoids in the control of CLM in southern California

Import and introduce the CLM parasitoid Ageniaspis citricola, if necessary, to complement the role of the native parasitoids in controlling CLM.

Compare several schemes to apply biological control agents: single versus mixed populations and annual versus frequent application.

Final report The citrus leafminer (CLM), Phyllocnistis citrella St. (Lepidoptera: Gracillariidae),was first detected in California in Calexico (Imperial County) in January of 2000. By fall 2000, presence of CLM was limited to backyard citrus and nurseries in the southeast corner of the ImperialValley. In winter 2002, it was confirmed throughout the Imperial County including commercial citrus. During 2002, it was confirmed in Riverside County, in the Coachella Valley. CLM activity in the Imperial Valley was limited to fall, early winter, and late spring. Levels of infestations (flushes with live CLM) reached 10 to 20% in backyard citrus and were below 2% in commercial groves. No CLM activity was recorded in any of the backyard sites from February 2002 to June 2003. Very low activity (two mined leaves/grove) was reported at two commercial groves during fall 2002 (CLM survey, ICAC). The only activity recorded in our monitored groves after February 2002 was in mid-May 2003 (0.8% infestation in one grove). CLM is present in the Imperial Valley, but densities remain very low. In the Coachella Valley, CLM activity was observed during fall 2002, winter and late spring 2003. Infestation incidence peaked (100%) by mid-December. No infestation was recorded during early spring; late spring populations peaked (14%) in early May to later disappear by the end of the month. One parasitoid, Closterocerus utahensis, was found on CLM in backyard citrus in the Imperial Valley during fall and early winter. Parasitization rates were low (<10%). In the Coachella Valley, nine species of parasitoids have been recovered from CLM so far: C. utahensis (42%), Cirrospilus coachellae (10%), C. flavicintus (7%), three Cirrospilus spp. (9%), Pnigalio minio and P. coloni (16%), Sympiesis sp. (1%) and Chrysocharis sp. (14%). All these species were recovered during fall and winter when larval parasitism reached 70% and pupal parasitism 30%. Parasitism levels by Chrysocharis sp., increased again (33% larval, 45% pupal) in late spring at a time when CLM numbers were very low. Although studies on the role of these parasites in declining CLM densities should be continued, protection of these parasites should be considered as the most important method to reduce CLM numbers in commercial citrus groves at this point.

The citrus leafminer (CLM) was first detected in California in Calexico in January of 2000. By fall of 2000 CLM presence was limited to backyard citrus in the Southeast corner of the Imperial Valley. In winter of 2002, presence of CLM was confirmed throughout the Imperial Valley including backyards, nurseries and commercial citrus. CLM reached the Coachella Valley during 2002 and fall activity has been recorded in at least three groves in the southeast of the valley. Dynamics of the CLM have been monitored in backyard and commercial citrus sites in the Imperial Valley during 2001-2002. Activity was observed only during fall. No CLM activity on new growth was observed during spring and summer. Levels of infestations reached 40% at one of the backyard sites in Imperial by December of 2001 and were below 2% in commercial groves. CLM activity in the Coachella Valley has been monitored since October of 2002 in one lemon grove. Infestations reached 96% by November. Two parasitoids have been found on CLM, Closterocerus utahensis in the Imperial and Coachella Valleys, and an unidentified species of Cirrospilus in the Coachella Valley. Parasitization rates remained low (<10%) in the Imperial Valley and reached 28% in the Coachella Valley. Closterocerus was previously known in both areas as a parasite of the citrus peelminer (CPM) and it has moved from CPM onto CLM naturally. Studies are being conducted to test efficacy of Cirrospilus coachellae, the main and most abundant parasitoid of CPM in the Coachella Valley, on CLM.
In 2001, citrus leafminer (CLM) has spread north and west of the Imperial Valley, reaching the commercial groves by Niland and Calipatria. Backyard citrus sites with CLM activity during 2000 were monitored during summer and fall 2001. No CLM activity on new growth was observed during summer. Activity resumed in mid October. The incidence of infestation by CLM reached maximum infestations of 40% at one of the sites in December. Levels of infestation were below 2% in commercial groves (1.3% in one block in the SW of the valley and less than 1% in two groves in the NE). One parasitoid, Closterocerus utahensis, was found on CLM. Parasitization rates remained low in two of the sites(<15%) and reached 35% at another site. Predation by thrips and Chrysopa was common, reaching almost 40% at one of the sites. Citrus peelminer (CPM) has been found in low numbers in all monitored sites during fall, along with two species of parasitoids, Cirrospilus coachellae and Closterocerus utahensis. Closterocerus has moved from CPM onto CLM naturally. Cirrospilus has not been found on CLM in the field but it develops successfully on CLM in laboratory trials. Cage releases have been initiated to assure at least one generation of Cirrospilus on CLM in the field, and increase Cirrospilus acceptance and movement to CLM. CPM and Cirrospilus colonies are being maintained at UCR, and a total of 3,695 parasitoids have been sent to the San Joaquin Valley for releases on CPM during summer and fall 2001.

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