Paper presented at the 52nd CFCS Annual Meeting, Guadeloupe, July 10-16, 2016 Conclusion Phalacrococcus howertoni, sometimes called the croton scale, is an invasive pest which was first found in 2008 in South Florida. Since its discovery, it has spread to many more counties in Florida, particularly those along the coast. The most commonly infested hosts in the South Florida landscape include croton (Codiaeum variegatum), gumbolimbo (Bursera simaruba), firebush (Hamelia patens), lignum vitae (Guajacum santum), avocado (Persea americana), carambola (Averrhoa carambola), guava (Psidium guajava), and mango (Mangifera indica) (Mannion and Hodges, 2010). We surveyed several sites in Homestead and Key Biscayne in South Florida and found that gumbo limbo appeared to be the most common host for P. howertoni, which is consistent with surveys by the Florida Department of Agriculture and Consumer Services (FDACS) Division of Plant Industry (DPI) database. A potential biological control agent, the coccinellid beetle Thalassa montezumae, was found in Florida in 2009 feeding on P. howertoni. Because of its potential importance as a biological control agent, we first determined it biology. Under laboratory conditions, development from egg to adult required 34 days and adult males lived an average of 122 days while females lived a little longer (137 days). Females oviposited for approximately three weeks laying an average of 274 eggs. Females were larger than males, but there was no significant difference between males and females when choosing a stage of prey. The second instar nymph was the stage of P. howertoni fed upon most by all stages of T. montezumae, and the stage of scale fed upon by adults in experiments did not significantly affect female fecundity. Effects of the insecticides bifenthrin (contact) and imidacloprid (contact and systemic formulations) on T. montezumae were studied by exposing beetles indirectly to insecticide treated leaves or to P. howertoni scales collected from treated plants. Foliar formulations of bifenthrin killed 50% of adult beetles and imidacloprid killed 40% one day after application to leaves; numbers of dead beetles declined at two and three days, and seven days after application there was no mortality. In comparison, a drench formulation of imidacloprid resulted in 20% mortality after three days but only 5% mortality after seven. However, when fed scales that had fed on the leaves, mortality was slightly higher (20%) for the drench after two days than for the foliar applications (5% each); the significance of this result needs further study as total numbers were too low for meaningful comparison. In addition to problems such as insect resistance and environmental and food contamination, pesticides can lead to a reduction in populations of natural enemies (Garrat and Kennedy, 2006). One objective of this study concerned protection of the natural enemy T. montezumae. At minimum, the data suggest that there should be a four day delay between the application of the insecticides studied and the introduction of the predatory beetle T. montezumae in an IPM program.
Bibliographic references Garratt, J., and A. Kennedy. 2006. Use of models to assess the reduction in contamination of water bodies by agricultural pesticides through the implementation of policy instruments: a case study of the voluntary initiative in the UK. Pest Manag. Sci. 62: 1138–1149. Mannion, C. M. and G. Hodges. 2009. Another new scale in Florida. University of Florida. IFAS, Tropical Research and Education Center. [http://trec.ifas.ufl.edu/mannion/pdfs/Croton%20Scale%20Update%20March%202009.pdf] Ruberson, J.D., and H.K. Priesler. 1992. Pesticide bioassays with arthropods. CRC Press, London. Russell, R. M., J. L. Robertson, and N. E. Savin. 1977. POLO. A new computer program for Probit analysis. Bull. Entomol. Soc. Am. 23: 209–213. SAS Institute 1996. SAS User’s guide. Version 9.1. SAS Institute. Cary, North Carolina.
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