Battling the Evil – Recent advances in the war on abbreviatus By Robin J. Stuart and Michael E. Rogers

Diaprepes Diaprepes abbreviatus he root weevil, , could contribute to novel management strategies. was first detected in Florida more than 40 years Recent investigations indicate that entomopathogenic ne - ago and continues to be a major cause of tree de - matodes are much more abundant on the Ridge than in the cline and death in certain growing areas Dflaiatwproeopdess and exert a much higher level of natural control on Tacross the state (Fig. 1). Its persistence as an important larvae PonhytthoepRhtihdogrea (Larry Duncan, UF-IFAS). can be attributed to various factors: The incidence of also differs with Ridge and • the broad range of crop, ornamental, and weedy plants well-drained flPat.wnoicoodtsiagnraoe ves more likely to be infested by it utilizes for adult feeding, egg lay - (Fig. 3) whereas poorly drainePd . ing and larval development; pflaaltmwiovoodrsa groves are more likely to harbor • its often asynchronous, highly (Jim Graham, UF-IFAS). variable and complex life history; SOIL VARIABILITY • a relatively large and long-lived larval stage that can cause severe Even within groves, the distribution of damage to major tree rPohoytst;ophthora root can be heterogeneous, and stud - • the facilitation of Di - aiepsreapreesaddressing relationships between infection by larval feeding; abundance and soil characteristics • the ineffectiveness of many (Fig. 4). In a poorly drained citrus grove in pesticides against soil-dwelling Central Florida, Hong Li and Jim Syvertsen larvae; Di - (aUprFe-pIFeAs S) found that the abundance of • and the limited, often patchy Fig. 1. Adult Diaprepes abbreviatus adults was highest in high elevation distributions of important natural (photograph by Robin Stuart) areas and was negatively correlated with soil enemies. Mg and Ca. The results suggest that soil Here we provide an update on some liming, site elevation, soil flooding, and of the current research contributing to Diaprepes rain or waterDeiraopsrieopnesmight be factors our battle against which influencing distributions might soon reduce this evil weevil to lit - within sites. tle more than a benign and occasionally A study in an east coast grove by viewed visitor to Florida citrus groves. Bob Adair (FLARES), Jim Graham (UF- ECONOMIC IMPACT VARIES IFAS) and Arnold Schumann (UF-IFAS) ACROSS REGIONS showed that soil electro-conductiDvii t-y waparsepreelsated toPhspytaotipahltphaotrtaerns of Fortunately, in certain areas of the and populations, state, most notaDbliyapcreerptaeis n parts of the and to decline of Swingle citrumelo and Central Ridge, populations Cleopatra mandarin rootstocks. generally appear to be under good natu - Fig. 2. A citrus grove in Central Florida ral control, probably by an array of nat - with a heavy Diaprepes infestation and ROOTSTOCK TOLERANCE ural enemies. However, off the Ridge in many trees in decline (photograph by Ian Research by Jude Grosser and Jim Jackson) finer tDexiatuprreedpeasnd less well-drained Graham (UF-IFAS) is directed toward soils, continues to be a major problem (Fig. 2). Research efforts to identify and charac - terize problem areas, and to develop and test new strate - gies or combinations of strategies to suppress the weevil and maintain grove productivity, are continuing. DiaApnreaprees a-wide survey of the seasonal abundance of adult at six sites in different regions of Florida by SDtieavpereFpuetsch (UF-IFAS) found that population densities of were five times higher in orchards growing on shallow soils in the coastal and central flatwoods than in orchards on the deep sandy soils of the CenDtriaalpRreidpgees . These results agree with regional trends in abundance reported by researchers andDciiatrpursepgersowers. The causes of regional variation in abun - dance are unknown but merit research because the feasi - Fig. 3. A tree showing symp - Fig. 4. A teneral adult Dia- bility of most tactics to manage the insect is directly toms of nico - prepes in its pupal cell in the related to pest pressure. Moreover, the determination of tianae infection (Photograph by soil (photograph by Ian the factors that regulate or limit the abundance of the Jim Graham) Jackson)

CITRUS INDUSTRY • September 2006 developing new rootsDtoiackpsretpheast are able to recover from Phyftoeepdh - tihnogrdaanmicaogtei,aanraee resistPa.nptatolmivora and , and can grow into productive trees in a wide range of soils, especially those high in clay and calcareous materials that characterize the flatwoods. Trifoli - ate orange hybrids, such as Swingle citrumelo and CarrPiz.onicciotrtaianngaee, with good resistance to , are P. pnaoltmshivoowraing adequate resistance to Fig. 5. An emergence or cone trap (left) Fig. 6. An adult Diaprepes with bee . Therefore, emphasis is and a Tedders trap (right) (photograph by tag and paint marking (photograph by being placed on non-trifoliate based Ian Jackson) Robin Stuart) somatic and sexual hybrids. ENTOMOPATHOGENIC In field trials on a high pH calcare - that vigoPrhoyutsoprohothtsotroa cks with resist - oDuiaspsriteeptehs at is heavily infested with ance to can better toler - , two pummelo-based so - ate high weevil populations, Commercially produced ento - matic hybrids are outperforming other especially when assisted by strategic mopathogenic nematodes have been material. These hybrids apparently do pesticide use to suppress adult wee - used by Florida growers to help control not share the usual problems associ - vils during critical periods. A limited root weevils for more than 15 years and ated with the use of diploid pummelos pesticide program such as this could are the only recommended control for as rootstocks (i.e., excessively large be cost effective and is likely to be Diaprepes lSatrevinaerfneeemdiangrionbrtareve roots but poor yielding trees). The results less destructive to natural enemies. in the soil. has suggest the potential for pummelo-de - MOVEMENT proven to be one of the best entomo- rived material as an alternative to sour AND LONGEVITY pathogenic nemDatioadperespfeosr use in appli - orange (which has been lost due to Diaprepes cations against , but until CTV qDuiicakprdeepcelis ne) in areas with Although was first de - recently, only a single strain of this heavy pressure. Intensive tected in Florida in 1964, and was species was known. This original strain efforts during the past four years have considered a pest in the Caribbean for was isolated in the Rio Grande Valley generated a large amount of geneti - many years previously, there are still of Texas and Clay McCoy (UF-IFAS), cally diverse material, and the screen - important gaps in our knowledge of Robin Stuart (UF-IFAS), and David ing of this material in greenhouse and the biology of this insect. For exam - Shapiro-Ilan (USDA-ARS) revisited field trials is continuing. ple, we have little idea as to what ex - that area, took soil sampSl.ersi,oabnrdavieso - Diaprepes lated 10 new strains of . STRATEGIC PESTICIDE tent adults move in citrus groves, or how long adults normally Laboratory tests demonstrated that APPLICATIONS ENHANCE some of the new strains were signifi - ROOTSTOCK TOLERANCE Dliviaepurnedpers field conditions. Since Diaprepes adults are highly polypha- cantly more virulent to lar - An ongoing long-term field study gous and prefer citrus flush to older vae than the previous strain. If this in a Central Florida grove on a fine- leaves, they would be expected to increased virulence carries over to field trials, then the new strains might im - textured soil heavily infested with move in response to food availability Dia-prepe prove current products. s has shown that both root - and flushing cycles within groves, Recently, Biocontrol Systems, Inc., perhaps migrating to and from groves stock selection and a limited pesti - (Greendale, IN) licensed two of the in response to food availability. cide application program can be new strains for further product devel - Some observations suggest that important for maintainingDciiatrpursepes opment for citrus and other crops. Ad - adults might move a great deal, espe - grovPeshyutnodpehrthsotrreassnifcromtianae ditional studies by Larry Duncan and (Clay cially at night, and laboratory data in - (UF-IFAS) are examining how nema - McCoy, Robin Stuart, Bill Castle and dicate that adults might sometimes tode applications impact natural wee - live for more than a year (Herb Nigg, MichaelPRhyotgoeprhs,thUoFra-IFAS). In this vil control by endemic nematodes, and grove, resistant root - UF-IFAS). In a current study by how physical habitats and natural ene - stocks such as Swingle citrumelo and Robin Stuart and Michael Rogers mies affect nematode abundance in C35 citrange are outperforming more (UF-IFAS), young weevils are different parts of the state. susceptible rootstocks such as trapped in cone traps (Fig. 5) as they Naturally occurring nematode com - Cleopatra mandarin. Moreover, pesti - emerge from soil, individually munities appear to provide sigDniifaic- cide applications with activity against marked using numbered, color-coded Diaprepes plerveepless of biological control of the egg and adult stages of bee tags and paint marks (Fig. 6), and in certain areas but not in oth - applied twice during the weevil’s released back into the grove at the ers, and it might be possible to develop spring emergence peak effectively site of emergence. The weevils are new strategies to increase nematode suppress weevil populations on later recovered during routine popu - effectiveness in problematic sites by treated trees and enhance the growth, lation monitoring in Tedders traps discovering what factors limit nema - survival and yield of trees on the (Fig. 5) and during tree shaking. In - tode abundance. best performing rootstocks. formation from this study is being EGG PARASITOIDS TPhhisytsotpuhdtyhorerian/fDoiracpersetphees view that used to make preDdiicatpiorenpsers egarding the complex the dynamics of infesta - A classical biological control pro - can kill trees on all rootstocks, but tions and develop control strategies. gram in which parasitic wasps that CITRUS INDUSTRY • September 2006 effectiveness of various types of genet - ically engineered Bt corn (Monsanto Co., St. Louis, MO) for their effective - ness against root weevil larvae (Michael Rogers, UF-IFAS). A program is also under way to ex - amine the possibility of uDsinagprtehpeeps ro - tein inhibitors of certain digestive enzymes to reduce weevil growth and survival (Charles Powell, Fig. 8. A worker of the ant species UF-IFAS). Pheidole moerens removing a Di - A trypsin inhibitor from mosquitoes Fig. 7. The egg parasitoid Haeckeliania aprepes neonate from an assay inhibits root weevil trypsinDsiyanptrheepseis sperata (photograph by Rita Duncan) dish (photograph by Robin Stuart) and reduces the growth of Diaprepes larvae that feed on transgenic alfalfa attack egg masses within ent ant species in citrus, how the abun - plants that express the inhibitor in lab - their native range in the Caribbean are dance and distribution of different ant oratory tests. Plans are under way to reared and released in Florida has pro - species varies in response to grove test this transgenic alfalfa on weevils duced promising results (JorgeAPpernoas , - management practices, and what ma - in greenhouse studies and to determine tUoFce-ItuFAs vSa)q. Tuiwtaoruwm asp spQecuiaesdr( astichus nipulations might be effective to con - whether it could be used as a trap crop haitiensis and serve or enhance beneficial ant species in citrus groves. ) have become established in (Robin Stuart and Michael Rogers, UF- South Florida where they are responsi - IFAS). This information is necessary to NEW FRONTS ble for weevil egg mortality of 70 per - maximize the effectiveness of ant pre - IN THE BATTLE Diaprepes Diaprepes cent to 80 percent. Unfortunately, dation on and to enable The root weevil has these species are highly tropical, will growers to make informed decisions demonstrated the capacity to spread not survive temperatures below 15˚C, about alternative pest control tactics. and become established in new areas and have not been successful farther PATHOGENS through the movement of ornamentals north in major citrus growing areas. or nursery material and by hitchhiking However, two additional waFspidsiopbeica ies An Iridovirus is currently being in - on or in long-distance transports. Origi - that are more cold tolerant ( Dia- dominica Haeckeliania sperata pvreesptiegs ated for its potential use in nally from the Caribbean, this weevil and ) control (Wayne Hunter, USDA- has spread to at least 23 counties in (Fig. 7) were recently discovered on ARS). This is passed between Florida and a limited area in the Rio the island of Dominica and are sched - weevils during mating and reduces the Grande Valley of Texas. The weevil uled for release across Florida in 2006. lifespan and fecundity of infected indi - has also been intercepted and destroyed Hopefully these species will find citrus viduals. The main obstacle to the use numerous times in shipments of plants groves throughout Florida more to of this virus is the development of a in truck trailers and the cargo holds of their liking. cost effective method for mass produc - aircraft in California, and it turned up PREDATORS tion. However, technological advances in the Mall of America and a botanical could soon remedy this problem and garden in Britain. During the past year are recognized as important make the virus available for biological in California, it was found in residen - predators of insect pests in various control programs. tial areas of Orange, Los Angeles, and agroecosystems, and are managed and GENETIC ENGINEERING San Diego counties, where it is cur - conserved for biological control in in - AND TRANSFERABLE rently the subject of quarantine and tegrated pest management programs. In RESISTANCE eradication programs by the California Florida, ants are among the major pred - Diaprepes Diaprepes DepartmentDoifaFporeopdeas nd Agriculture. ators of eggs, larvae, and Research indicates that is To date, has proven to be adults, and research shows that several Solenopsis in - susceptible to toxins produced by cer - a foDrmiaidparebpleesfoe, but the solution to ant species, especially victa Btaaincisllturasinthsuorfinthgeiebnasics terial pathogen, the problem could be at Pheid(othleemreoderimenps orted fire ant) and , better known as hand in one or more of these research Diapre(Fpiegs . 8), are effective Bt (Allen Weathersbee, USDA-ARS). projects. The battle continues. predators of neonates on the This discovery raises the possibility of Michael Rogers is assistant professor and soil surface (Robin Stuart and Clay genetically engineering rootstocks to Robin Stuart is a Ph.D. and senior biologi - McCoy, UF-IFAS). express the toxin as a means of control - cal scientist, both at University of Florida- Current research is examining the ling root weevil larvae. IFAS, Citrus Research and Education positive and negative impacts of differ - An additional study is testing the Center, Lake Alfred

CITRUS INDUSTRY • September 2006