Behavior and Development of <I>Pseudacteon curvatus</I> (Diptera: Phoridae) Varies According to the Social Form of Its Host <I>Solenopsis invicta</I> (Hymenoptera: Formicidae) in Its Native Range

Abstract

We assessed the performance of Pseudacteon curvatus Borgmeier with respect to the social form of Solenopsis invicta Buren in Argentina In the field, we studied the effect the parasitoid on size and proportion of ant foragers. In the laboratory, we evaluated P. curvatus oviposition preferences; host size elected; developmental periods; and sexual size dimorphism, sex ratio, and parasitoid survivorship. P. curvatus affected the average size of foraging workers on both social forms diminishing the proportion of big and increasing the proportion of minor workers. P. curvatus required a shorter orientation time and exhibited a greater number of attacks when ovipositing on monogynes workers. In the laboratory, host sizes elected by P. curvatus were similar between social forms. However, attacks on polygyne colonies were more variable, increasing the number of unviable offspring. Developmental times of females and males of P. curvatus were similar for both social forms, but total developmental periods were shorter for males from monogyne colonies. We did not find differences between sexes in emerging adults' size by social form and the female: male sex ratio was 1:1 for both social forms. P. curvatus pupae survival and adult emergence per trial from monogyne colonies were greater than from polygyne colonies. The rarity of polygyne S. invicta in its native range may prevent this phorid from adjusting its life history to that social form. Consequences of applying this phorid in biological control are discussed.

Pseudacteon tricuspis: Its Behavior and Development According to the Social Form of Its Host and the Role of Interference Competition Among Females

“…Monogyne colonies have larger but fewer foragers than polygyne ones, a reverse trade-off pattern previously reported for S. invicta in Chaco (Chirino et al 2009). Trade-offs between offspring size and number are common in many animals (Fox and Czesak 2000) and social insects are no exception (Hö lldobler and Wilson 1990).…”

“…The reasons for this difference could be 1) that polygynic ants are generally smaller than monogynes (0.73 Ϯ 0.01 vs. 0.80 Ϯ 0.01 mm for polygyne and monogyne workers, respectively; P Ͻ 0.001; M.G.C., unpublished data; Greenberg et al 1985, Morrison andGilbert 1998), and/or 2) that polygyne nests have twice as many medium but half the number of large workers than monogyne nests (Table 1). Although, P. tricuspis successfully developed in both social forms, the percentage of inviable pupae was higher in polygyne colonies, which are far less abundant than monogyne ones in Argentina (Wojcik 1983, Ross and Trager 1990, Porter et al 1997, Ross et al 1997, Mescher et al 2003, Chirino et al 2009). Thus P. tricuspis may be poorly adapted to the polygynic form of S. invicta which is 2Ð3 times more abundant than monogyne colonies in some places in the United States (Macom and Porter 1996).…”

“…This interference competition pattern was not observed in P. curvatus, another species already released in the United States along with P. tricuspis Gilbert 2004, Gilbert et al 2008). The aggressive and territorial behavior observed for P. tricuspis females may be unnecessary as P. curvatus mainly attack small workers, which are abundant, and both genders develop in similar host sizes (Chirino et al 2009). Moreover, the number of pupae and adults produced by P. curvatus under similar rearing conditions were four times higher than P. tricuspis (Vazquez et al 2004, Chirino et al 2009).…”

“…For instance, we found that the social form of S. invicta affects development in P. curvatus (Chirino et al 2009), with stronger preference for, and more offspring produced from, monogyne than polygyne Þre ant colonies. Consequently, our Þrst goal was to evaluate whether P. tricuspis prefers the monogyne over the polygyne form, and to study the parasitoidÕs effect on the size and proportion of foragers in the Þeld.…”

“…The monogyne social form of S. invicta is predominant in Argentina and much of the United States, although the polygyne form is dominant from western Louisiana to southern Texas (Greenberg et al 1985;Porter and Savignano 1990;Porter et al 1992Porter et al , 1997Macom and Porter 1996). The number of mated queens inßuences the genotype of workers and the colony social form Ross 1998, Deheer 2002), which determinates the proportion of subcastes (Chirino et al 2009). One consequence is that the mean size of S. invicta monogyne workers is greater than that of polygynes (Greenberg et al 1985, Morrison andGilbert 1998).…”