This study presents comprehensive data about the biology of the rare cleptoparasitic European bee species Epeoloides coecutiens (Fabricius, 1775). The phenology and behavioral patterns observed at several localities are described; new information about floral resources (22 species) of E. coecutiens is presented. A new host bee, Macropis fulvipes Fabricius, 1804, is confirmed for E. coecutiens. The differences in color vision of humans and bees affect the interpretation of E. coecutiens floral preferences.

In the field, paired (in copula) female Japanese beetles (Popillia japonica Newman) tend to be larger than unpaired females. In this study, we investigated whether this size pattern could be explained by a male preference for large females, and whether larger females tended to have more and/or larger eggs than smaller females. In a laboratory study, both small and large males, when given a choice of a large and small female, tended to choose the large female. We dissected field-caught paired and unpaired females, measured their body size, and counted and measured their eggs. Larger females tended to have more and larger eggs than smaller females, indicating that males may benefit from choosing larger females due to the egg characteristics of these larger females. Paired females in the field were consistently larger than single females; paired females also had more and larger eggs, even when body width was statistically controlled. Thus, although body width of the female correlates with her fecundity, males may either use cues in addition to a female's body width to determine her immediate fecundity or fecund females may be more available for or less resistant to male mating attempts.

Sexual dimorphisms in four related species of tephritid flies were shown to be associated with differences in sexual behavior. In two species, Ceratitis capitata and C. catoirii, males and females approach closely head to head and apparently touch aristae, and the male buzzes his wings, probably fanning pheromone toward the female; the males were found to have longer aristae with fewer microsetae, and larger posterior areas of their wings than do females. These dimorphisms were absent in the other two species, C. rosa and Neoceratitis cyanescens, which court at a longer distance and in which the male does not fan pheromone toward the female prior to mounting. All three pairs of legs were proportionally longer in the males of all four species. None of the other sexually dimorphic male signalling traits showed the positive allometric slopes predicted by some theories.

Evidence is presented that females of the cleptoparasite Thyreus ramosus (Lepeletier) insert their eggs into the closed host cells of an Anthophora (Dasymegilla), tentatively identified as A. muscaria Fedtschenko, just as other members of the Melectini whose egg deposition habits are known insert their eggs into host cells. The eggs of both host and cleptoparasite are described and illustrated. Comparison of the eggs of T. ramosus with those of other melectines strongly suggests that the melectines are monophyletic.

Sixteen species of Haliplidae belonging to three genera are recorded from Colorado: *Brychius hornii Crotch, Peltodytes callosus (LeConte), P. edentulus (LeConte), *P. litoralis Matheson, *Haliplus apicalis C.G. Thomson, *H. canadensis Wallis, H. cribrarius LeConte, H. deceptus Matheson, *H. distinctus Wallis, H. fulvus Fabricius, H. immaculicollis Harris, H. leechi Wallis, H. longulus LeConte, *H. stagninus Leech, *H. tortilipenis Brigham and Sanderson, and H. triopsis Say. Seven of these species (*) represent new state records, and H. distinctus is reported from the United States for the first time. Haliplids found in Colorado generally fit one of the following distributional patterns for North America: Western, representing 31% of the species, Northern (31%), Eastern-Midwestern (25%), and Holarctic (13%). Diagnostic characters, habitat information, and both Colorado and North American distributions are discussed for each species. Statewide distributional maps and an identification key are provided for adults recorded from the state. The aedeagus is shown to be the most reliable character for identification of Haliplus males, and a photomicrograph of the aedeagus is provided for each Colorado species. Three species previously reported from Colorado, H. dorsomaculatus, H. salmo and H. robertsi, are unconfirmed, and three additional species, P. dispersus, P. tortulosus, and H. borealis whose known distributions suggest they may occur in Colorado, are discussed.

The first species of the scorpionfly genus Panorpodes found in North America and outside the eastern Palearctic is described and illustrated. A key to North American scorpionflies is provided.

One new species of Palmanura from Chiapas is described and illustrated. A key for the 12 species known in the genus is given.