Progress 09/01/04 to 08/31/06
Outputs
The Asian Citrus Psyllid (ACP) Diaphorina citri Kuwayama (Homoptera: Psyllidae) is the only known vector of Huanglongbing (HLB) or "greening", a devastating bacterial disease of citrus. The pest was first detected in Florida in 1998 and greening in summer 2005. The disease is spreading rapidly, putting the Florida citrus industry at risk. I detected ACP in Puerto Rico in 2001 but noticed that populations were low on both citrus and the related Murraya peniculata, indicating that biological control may be functioning efficiently on the Island. The hope was that a better understanding of the factors causing this apparent regulation of ACP populations could be utilized to reduce pest levels elsewhere. Toward this end the following objectives were set out. 1. Assess seasonal population trends of ACP and its natural enemies in distinct regions of Puerto Rico. 2. Evaluate all biotic sources of mortality to ACP populations to complement similar studies in Florida. 3. Utilize
results to develop biologically-based management strategy for ACP. It was soon determined that a parasitic wasp, Tamarixia radiata, had been unintentionally introduced along with the psyllid. The wasp likely came from Florida where it had been introduced to help combat the pest. A year-long survey of citrus flush patterns, ACP populations and parasitism by T. radiata was undertaken on 4 experiment stations on the Island: 1. Adjuntas at an altitude of 1500 ft in the citrus growing region, 2. Corozal at 700 ft, 3. Gurabo at 250 ft, and 4. Isabela on the coast. Psyllid populations at Adjuntas were almost non-existant, highest at Isabela similar at Corozal, although the peak was delayed from February to April, lower in Gurabo and peaking in April. Parasitism by T. radiata exceeded 80% on 8 of 11 sample dates at Isabela and reaching 100% on 3 sample dates, reached 100% at Corozal on one sample date but was generally below 60%, and was similar but lower at Gurabo. These levels of parasitism
greatly exceeded those seen in Florida. Lifetable studies conducted in Isabela and on the main UPR campus at Rio Piedras showed that survivorship of ACP was less than 10 percent, and that most mortality was attributable to parasitoids, whereas most mortality is caused by predation, primarily from ladybeetles in Florida. A published study showed that aphid-feeding species were most abundant on citrus in Adjuntas whereas species best able to utilize psyllids for food have become most numerous in Florida. The seemingly effective biological control seen in Puerto Rico may be due to the parasitoid being introduced with the pest and holding it in check from the onset. In contrast, the pest reproduced largely unchecked in Florida until a numerical response by predators began turning the tide. Hopefully, biological control of the pest will continue to increase in Florida although it may be too late to stop greening. Citrus growing regions like California that do not yet have the psyllid would
do well to assure themselves of a supply of T. radiata with which to respond quickly to the inevitable invasion.
Impacts
This study established that Tamarixia radiata is serving as an effective biological control agent of Asian Citrus Psyllid in Puerto Rico. Furthermore, it established that psyllid levels in the citrus growing region of Adjuntas that were low in 2001 when the psyllid was first discovered, are almost non-existant now, obviating the necessity for further control. The study also suggested that the introduction of an effective parasitoid like Tamarixia Radiata coincident or soon after the accidental introduction of a pest can greatly mitigate pest impact. This strategy has also been followed in the campagne against pink hibiscus mealybug. In regard to the psyllid, governmental plant protection agencies have been advised to be ready to introduce T. radiata as soon as possible after first detection of this pest.
Publications
- Pluke, R.W.H., A. Escribano, J.P. Michaud and P.A. Stansly. (2005). Potential impact of lady beetles on Diaphorina Citri (Homoptera: Psyllidae) in Puerto Rico. Fla. Entomol. 88:123-128.
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Progress 10/01/04 to 09/30/05
Outputs
The Asian citrus psyllid (ACP), ACP is a vector of citrus greening disease first detected in 2001 in Puerto Rico, 3 years after being found in Florida. Greening was detected in Florida August, 2005. Preliminarily observations indicated that populations in PR were relatively low in comparison to Florida. This project was established in Puerto Rico to asses the role of biotic mortality in regulating ACP. The impact of coccinellids and the exotic parasitoid, Tamarixia radiata (Waterson) in Puerto Rico were compared to past and present results from Florida. During Sep 04 to Sep 05 4, ACP was found on citrus and Murraya peniculata at 4 experiment stations in P.R. but not at the station in Adjuntas at 1,800 feet altitude. Greatest numbers were found at Isabela on the coast. ACP nymphs were only on new growth and were highest on citrus during the two main flushing events (spring and summer). T. radiata was found parasitizing ACP at high incidence throughout the year at all 3
study sites where its host was present. A total of 8 species of coccinellid were encountered of which Coleophora inaequalis and Cycloneda. limbifer were the most abundant, during the course of a survey in a citrus grove at the Adjuntas from April to early July 2003. The 8 species were evaluated for acceptance and preference of ACP compared to the brown citrus aphid (Toxoptera citricida).. All but one of the coccinellid species consumed significant quantities of ACP in a no-choice situation. In a choice test, the two most abundant species preferred the aphid and 4 showed preference for the psyllid. Cohort studies were conducted in a screenhouse in Puerto Rico where T. radiata had appeared spontaneously and where the plants were isolated from ants. Mortality of uncaged ACP was almost complete, with T. radiata parasitism (50%) and direct parasitoid-induced mortality (35%) playing the dominant roles. At the Isabela research station, T. radiata did not have the same impact, apparently
because of greater mortality to young nymphs, principally ant predation. At University of Florida research station in Immokalee, greater than 90% mortality was observed on uncaged cohorts, mostly to young instars, presumably by coccinellid predation. Thus, The Asian citrus psyllid is well established in Puerto Rico (mostly on Murraya paniculata). It is spatially and temporally patchy in the citrus habitats on the island. Tamarixia radiata is found throughout the year, even during times of low citrus flush activity and low psyllid numbers. Percent parasitism fluctuations did not show seasonal patterns. Coccinellids demonstrated the potential to impact ACP numbers in Puerto Rico but under present conditions the coccinellid guild is dominated by aphid predators In screenhouse cohort studies, T. radiata activities resulted in high levels of ACP mortality. The parasitoid had negligible impact to the Isabela field cohort, presumably because significant mortality had already been achieved
earlier in cohort development. In Florida studies, coccinellids were an important mortality factor, especially on young instars, thereby denying hosts to T. radiata.
Impacts
There is great concern that greening disease could destroy the productive capacity of the citrus industry in Florida and Puerto Rico. Given this atmosphere, overuse of insecticides could easily result in resurgence of the psyllid as well as other pests under biological control such as scale insects. Citrus growers are being apprised of the importance of the natural enemy component of mortality and the necessity of conserving it in their quest to control D. citri and the spread of greening disease.
Publications
- Pluke, R.W.H., A. Escribano, J.P. Michaud and P.A. Stansly. (2005). Potential impact of lady beetles on Diaphorina Citri (Homoptera: Psyllidae) in Puerto Rico. Fla. Entomol. 88:123-128.
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