Revision of the Mesoamerican species of Calolydella Townsend (Diptera: Tachinidae) and description of twenty-three new species reared from caterpillars in Area de Conservación Guanacaste, northwestern Costa Rica.

BACKGROUND: Twenty-three new species of the genus Calolydella Townsend, 1927 (Diptera: Tachinidae) are described, all reared from multiple species of wild-caught caterpillars across a wide variety of families (Lepidoptera: Crambidae; Erebidae; Geometridae; Hesperiidae; Lycaenidae; Nymphalidae; Pieridae; Riodinidae; and Sphingidae). All caterpillars were collected within Area de Conservación Guanacaste (ACG), in northwestern Costa Rica. This study provides a concise description of each new species using morphology, life history, molecular data, and photographic documentation. In addition to the new species, we also provide a generic redescription and revised key to species of the genus Calolydella from Central and South America. NEW INFORMATION: The following 23 new species of Calolydella are described by Fleming and Wood: C. adelinamoralesaesp. n., C. alexanderjamesisp. n., C. argenteasp. n., C. aureofaciessp. n., C. bicolorsp. n., C. bifissussp. n., C. crocatasp. n., C. destitutasp. n., C. discalissp. n., C. erasmocoronadoisp. n., C. felipechavarriaisp. n., C. fredriksjobergisp. n., C. inflatipalpissp. n., C. interruptasp. n., C. nigripalpissp. n., C. omissasp. n., C. ordinalissp. n., C. renemalaiseisp. n., C. susanaroibasaesp. n., C. tanyadapkeyaesp. n., C. tenebrosasp. n., C. timjamesisp. n., C. virginiajamesaesp. n.Lydella frugale Curran, 1934 is proposed as a new synonym of Pygophorinia peruviana Townsend, 1927, syn. n., under the combination Calolydella frugale (Curran, 1934), comb. n.