**6. Conclusions**

These trials consistently showed that the IPM programs had consistently lower populations of *Liriomyza* spp. than the high input conventional programs. These results were seen be‐ cause the IPM programs were able to conserve the leafminer parasitoids. More importantly for growers, because insecticide applications in the IPM programs were based on scouting results and linked to economic thresholds, fewer insecticide applications were made in the IPM programs than in the conventional programs. By focusing on conservation of leafminer parasitoids, growers can reserve use of the few highly efficacious insecticides for situations where there is a danger of leafminer population outbreaks. Limiting their use to these situa‐

Despite the lower insecticide use, growers were not sacrificing the amount of crop harvested or its quality. Ultimately, these IPM programs based on economic thresholds with the goal of conserving *Liriomyza* spp. parasitoids enable growers to produce high quality crops at lower cost and with typically greater profit than programs with higher insecticide inputs. By including economic comparisons of management programs, these trials provide growers

*Liriomyza* spp. management in protected environments, such as enclosed glasshouse and greenhouse production systems, generally requires greater inputs than for field grown crops. Greenhouses are highly managed environments where growers have extensive control over crop conditions (Shipp et al., 1991). Yet, given the potential value of crops and the high production costs, many growers produce crops year round without periods to sanitize facilities. This continuous production is conducted at optimal temperatures for plant and, consequently, insect development. Therefore, the greenhouse environment is highly conducive to the development of pest populations, but colonization by naturally occurring beneficial organisms is restricted. With the lack of naturally occurring biologi‐ cal control available to most greenhouse systems and the high crop value, growers his‐ torically relied on intensive insecticide use for pest management, and this reliance on insecticides has hindered the development of IPM programs for greenhouse production (Parrella & Jones, 1987). Further complicating adoption of IPM programs in greenhouses are the exceedingly low damage threshold for floriculture and vegetable crops that are

Despite these constraints, there have been successful demonstrations of integrated manage‐ ment of *Liriomyza* spp. and other pests in greenhouse systems. The initial impetus for devel‐ opment of IPM programs has, not surprisingly, been the development of resistance and failure of insecticides to effectively manage pests. IPM programs for greenhouse systems have been widely adopted in northern and western Europe (van Lenteren, 2000). There, nat‐ ural enemies are commercially available for all major pests, including parasitoids in the gen‐ era of *Dacnusa, Diglyphus* and *Opius* for *Liriomyza* management. These parasitoids can be released augmentatively and become established in greenhouses for long term management of leafminers. Because of the high demand for natural enemies to meet the needs of the large European greenhouse industry, mass produced natural enemies are cost effective for Euro‐ pean growers to use. However, while augmentative biological control with parasitoids in the United States and other non-European countries has been shown to be effective in man‐

with an economic rationale to alter their management methods (Reitz et al., 1999).

tions mitigates the risk of resistance developing to these insecticides.

242 Insecticides - Development of Safer and More Effective Technologies

grown in protected environments (Yano, 2004).

Growers around the world have experienced significant problems from *Liriomyza* leafmin‐ ers. They continue to invest considerable resources in the management of these pest flies. Despite the long history of problems with leafminers, many of the lessons that have been learned in one area at one time have, unfortunately, had to be relearned elsewhere. Leafmin‐ ers are classic secondary pests. If the parasitoid complex that attacks leafminers is con‐ served, economic damage from leafminers can be mitigated. Still, there are clearly circumstances where insecticides are needed to suppress leafminer populations below eco‐ nomically damaging levels. In particular, there may be cases where the lag in the increase in parasitoid populations may allow leafminer populations to exceed economic threshold lev‐ els. In such situations, growers should select insecticides that will minimally disrupt the par‐ asitoid complex. First and foremost, though, it is imperative that researchers provide growers with realistic economic action thresholds for different cropping systems so that growers have a clear understanding of when their crop may be at risk. Indeed, insecticide treatments may not always be warranted for seemingly high populations of leafminers. Marketable yield for a crop like tomato may not be lowered until exceedingly high levels of leafmines are reached (Levins et al., 1975).

In a similar vein, when other pests reach economic threshold levels and require therapeutic insecticide treatments, growers are encouraged to consider the effect of those insecticide treatments on leafminer management. Proactive management decisions will reduce the like‐ lihood of inducing severe outbreaks of leafminers. It is possible to produce a crop with few, if any insecticide treatments for leafminers, but this will best be realized if all growers in a community adopt similar IPM programs so that any one grower does not adversely affect neighboring growers. Continuing forward, the basic strategies for leafminer management are clear. However, the practical implementation of such strategies will remain a challenge. There is an ongoing need for development of selective, reduced risk insecticides to incorpo‐ rate into leafminer management programs and to ensure that appropriate resistance man‐ agement programs are developed. Further, there is a clear need for improved diagnostic methods and characterization of biological variation among biotypes and cryptic species of pest *Liriomyza.* Because other species share traits with the major pest species, it may be pos‐ sible that new species of *Liriomyza* may emerge as global threats, as have *L. huidobrensis, L. sativae* and *L. trifolii.*

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Because invasions are most likely to continue into the future, it will be critical to accurately identify new invasive species and populations, and to monitor changes in leafminer popula‐ tion dynamics following invasions. As these leafminers will continue to be important pests of high value crops, insecticides will continue to be an important component of leafminer management. Therefore, it is imperative to continue to refine the use of insecticides that tar‐ get leafminers. Improving application timing and methods will help to conserve insecticide susceptibility and maintain efficacy by mitigating the evolution of resistance. Insecticide re‐ sistance management must remain as a critical component of IPM. Furthermore, improving strategies for the conservation and augmentation of leafminer parasitoids will help reduce the need for insecticide applications. Knowledge gaps in regard to the effects of insecticides on various leafminer parasitoids should continue to be addressed. Leafminer management will best be accomplished through research on, and implementation of, comprehensive IPM strategies.
