We previously determined that several diets used to rear Aedes aegypti and other mosquito species support the development of larvae with a gut microbiota but do not support the development of axenic larvae. In contrast, axenic larvae have been shown to develop when fed other diets. To understand the mechanisms underlying this dichotomy, we developed a defined diet that could be manipulated in concert with microbiota composition and environmental conditions. Initial studies showed that axenic larvae could not grow under standard rearing conditions (27 °C, 16-h light: 8-h dark photoperiod) when fed a defined diet but could develop when maintained in darkness. Downstream assays identified riboflavin decay to lumichrome as the key factor that prevented axenic larvae from growing under standard conditions, while gut community members like Escherichia coli rescued development by being able to synthesize riboflavin. Earlier results showed that conventional and gnotobiotic but not axenic larvae exhibit midgut hypoxia under standard rearing conditions, which correlated with activation of several pathways with essential growth functions. In this study, axenic larvae in darkness also exhibited midgut hypoxia and activation of growth signaling but rapidly shifted to midgut normoxia and arrested growth in light, which indicated that gut hypoxia was not due to aerobic respiration by the gut microbiota but did depend on riboflavin that only resident microbes could provide under standard conditions. Overall, our results identify riboflavin provisioning as an essential function for the gut microbiota under most conditions A. aegypti larvae experience in the laboratory and field.

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Polyembryonic wasps are the only parasitoids in which sociality has evolved. Theory implicates both competition and sex ratio manipulation in the evolution of a sterile soldier caste. However, investment in soldiers by males and females is predicted to differ depending upon how offspring are allocated to hosts and the mating system. Here, we compared male and female soldiers in the polyembryonic wasp Copidosoma floridanum. We found that male and female soldiers are morphologically identical. Unlike females, however, male soldiers were non-aggressive towards all competitors. We discuss these results in relation to theory and polyembryonic wasp biology.

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Multiparasitism studies were conducted in the laboratory between the egg‐larval polyembryonic parasitoid Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) and the larval endoparasitoid Microplitis demolitor Wilkinson (Hymenoptera: Braconidae) in the mutual host Pseudoplusia includens (Walker) (Lepidoptera: Noctuidae). Most multiparasitized hosts produced either a C. floridanum brood or died without any parasitoid emergence. Most multiparasitized hosts underwent supernumerary molting; however, multiparasitized hosts that produced a C. floridanum brood exhibited growth characteristics associated with C. floridanum parasitism while multiparasitized hosts that died exhibited growth characteristics more typical of M. demolitor parasitism. Multiparasitized hosts that produced a C. floridanum brood increased in weight, and usually exhibited the behavioral and morphological characteristics associated with initiation of metamorphosis. In contrast, multiparasitized hosts that ultimately died gained little weight and exhibited no characteristics associated with metamorphosis. M. demolitor progeny died in multiparasitized hosts as eggs or first instar larvae, but no direct evidence was found to indicate that physical attack by C. floridanum precocious larvae was responsible for their elimination. Résumé Compétition interspécifique dans Pseudoplusia includens entre Copidosoma floridanum parasitoïde polyembryonnaire et Microplitis demolitor endoparasitoïde solitaire Lors de l'étude au laboratoire du multiparasitisme de Pseudoplusia includens Walker (Lépido. Noctuidae) par le parasitoïde ovolarvaire polyembryonnaire C. floridanum Ashmead (Hyméno. Encyrtidae) et l'endoparasitoïde larvaire M. demolitor Wilkinson (Hyméno. Braconidae), soit les hôtes donnent en majorité C. floridanum, soit ils meurent sans que quoi que ce soit émerge. P. includens non parasité présente 5 stades larvaires; les hôtes parasités par C. floridanum subissent 5 ou 6 stades avant le développement complet du parasitoïde, et les hôtes parasités par M. demolitor muent en stade 5 avant émergence du parasitoïde. Par contre, les hôtes multiparasités muent en stade 7; ceux qui produisent une couvée de C. floridanum ont présenté la croissance caractéristique des hôtes parasités par C. floridanum, tandis que les hôtes multiparasités qui sont morts avaient présenté la croissance caractéristique des hôtes parasités par M. demolitor. La plupart des hôtes multiparasités desquels C. floridanum a émergé ont augmenté de poids et présenté les caractères associés au début de la métamorphose. La descendance de M. demolitor est morte dans les hôtes multiparasités au stade œuf ou chenille du premier stade, mais il n'y avait aucun indice d'attaque physique par des larves de C. floridanum qui auraient été responsables de leur élimination.

Trichoplusia ni parasitized by Copidosorna floridanurn weighed more in the fourth and fifth instar than unparasitized controls. While parasitized and unparasitized fourth-instar larvae molted at the same time, parasitized fifthinstar larvae ceased feeding and initiated wandering 1 day later than unparasitized fifth-instar larvae. Measurement of hernolymph ecdysteroid, juvenile hormone esterase (JHE), and protein titers suggested that the delay in wandering had an endocrinological basis. Ecdysteroid titers of parasitized and unparasitized fourth-instar larvae were similar, but the ecdysteroid titer in parasitized fifth-instar larvae rose about 24 h later than in unparasitized fifth-instar larvae. Two major peaks of JHE activity occurred in unparasitized fifth-instar larvae, but only one occurred in parasitized fifth-instar larvae. ]HE activity coincided on the first day of the fifth instar (L5D1) in both parasitized and unparasitized fifth-instar larvae; however, activity peaked and fell later in parasitized individuals. Few differences were noted in the hernolymph protein levels of parasitized and unparasitized hosts. Ligation of parasitized T. ni between the head and prothorax adversely affected C. floridanurn development. Ligation before or immediately after ecdysis to the fourth instar inhibited differentiation of the C. floridanurn morulae. C. floridanurn ecdysed to the second instar or pupated in hosts ligated prior to wandering in the fifth instar, but the number of progeny that pupated and emerged as adult wasps was reduced relative to unligatured controls.

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