Springtail postmolt vulnerability to pseudoscorpion predation: Mechanisms and implications

Arthropod prey are expected to be more vulnerable to their predators immediately following molt. The effects of springtail (Isotoma carpenteri) postmolt vulnerability on interactions with a pseudoscorpion predator were examined in the laboratory. Springtails exposed to vials pretreated with pseudoscorpions (Apochthonius minimus) delayed molting compared to those prey that were exposed to vials pretreated only with springtails. Although their escape ability (measured as distance jumped) was unaffected by molt condition, postmolt springtails were more profitable in terms of reduced predator handling time following capture. Despite this,A. minimus did not distinguish between postmolt and intermolt prey presented at either end of a T-maze.     

Decreased JH biosynthesis is related to precocious metamorphosis in recessive trimolter (rt) mutants of the silkworm, Bombyx mori

In recessive trimolter (rt) mutants of the silkworm, Bombyx mori, that have four larval instars rather than five larval instars of normal B. mori, a decrease after a small increase in the hemolymph ecdysteroid titer during the early stages of the last (fourth) larval instar appeared to be a prerequisite for larvae to undergo precocious metamorphosis. The present study was carried out to investigate the possible mechanism underlying this decrease in the ecdysteroid titer. It was found that juvenile hormone (JH) biosynthetic activity of the corpora allata (CA) increased during the first day of the last larval instar, but its absolute JH biosynthesis activity was relatively lower compared to that of normal fourth-instar larvae in tetramolters. This lowered JH biosynthetic activity appeared to be related to a decrease in prothoracic gland ecdysteroidogenesis during the second day of the last instar, because hydroprene application prevented this decrease in prothoracic gland ecdysteroidogenesis, leading to the induction of a supernumerary larval molt. The in vitro incubation of prothoracic glands with hydroprene showed that hydroprene did not directly exert its action on prothoracicotropic hormone (PTTH) release. Further study showed that the application of hydroprene enhanced the competency of the glands to respond to PTTH. From these results, it was supposed that the lowered JH biosynthesis of the CA during the first day of last instar in rt mutants was related to decreased ecdysteroidogenesis in the prothoracic glands during the second day, thus playing a role in leading to precocious metamorphosis.     

Entomogenous fungus Nomuraea rileyi inhibits host insect molting by C22-oxidizing inactivation of hemolymph ecdysteroids

The entomogenous fungus Nomuraea rileyi reportedly secretes a proteinaceous substance inhibiting larval molt and metamorphosis in the silkworm Bombyx mori. We studied the possibility that N. rileyi controls B. mori development by inactivating hemolymph molting hormone, ecdysteroids. Incubation of ecdysone (E) and 20-hydroxyecdysone (20E) in fungal-conditioned medium resulted in their rapid modification into products with longer retention times in reverse-phase HPLC. Each modified product from E and 20E was purified by HPLC, and identified by NMR as 22-dehydroecdysone and 22-dehydro-20-hydroxyecdysone. Some other ecdysteroids with a hydroxyl group at position C22 were also modified. Injection of the fungal-conditioned medium into Bombyx mori larvae in the mid-4th instar inhibited larval molt but induced precocious pupal metamorphosis, and its injection into 5th instar larvae just after gut purge blocked pupal metamorphosis. In hemolymph of injected larvae, E and 20E disappeared and, in turn, 22-dehydroecdysone and 22-dehydro-20-hydroxyecdysone accumulated. These results indicate that N. rileyi secretes a specific enzyme that oxidizes the hydroxyl group at position C22 of hemolymph ecdysteroids and prevents molting in B. mori larvae.     

Change in significance of feeding during larval development in the yellow-spotted longicorn beetle, Psacothea hilaris

Larvae of the west-Japan type yellow-spotted longicorn beetle, Psacothea hilaris (Coleoptera: Cerambycidae), show a long-day type photoperiodic response at 25 degrees C; under long-day conditions, larvae pupate after the fourth or fifth instar, while under short-day conditions, they undergo a few nonstationary supernumerary molts and eventually enter diapause. In the present study, the effect of food on the development and photoperiodic response of the larvae was examined with special reference to molting and pupation. Although the pupal body size was greatly affected by the food quality and the length of feeding, the critical day length for induction of metamorphosis at 25 degrees C was always between 13.5 and 14 h. Exposure to starvation of larvae reared on the standard diet revealed that the capability to pupate is acquired after a few days of feeding in the fourth instar. In the larvae that had acquired the capability to pupate, premature pupation was induced by exposure to starvation, indicating that feeding becomes dispensable long before it is normally terminated.     

Modifications to a molt‐based ageing system proposed by Wolfe et al. (2010)

ABSTRACT Wolfe et al. (2010 . Journal of Field Ornithology 81: 186–194) proposed a coding system for ageing birds based on the sequence of molts and plumages, which is more practical than a calendar‐based system, especially in tropical and southern latitudes where species often breed across 1 January. The Wolfe–Ryder–Pyle (hereafter, W–R–P) three‐letter system is based on recognition of molt cycle (first, second, third, definitive, and so on) and plumage phase (juvenile, supplemental, formative, alternate, and basic). For example, a bird in First Cycle Formative plumage is coded as FCF. We propose the use of two additional code options that further refine age brackets. First, we suggest the use of an “after” or “A” code in place of the “C,” or cycle code, where an earlier molt cycle or plumage can be ruled out. For example, a bird that exhibits Staffelmauser might be aged as after‐third cycle basic, or TAB. Second, we suggest using “pre” or “P” in place of the “C,” or cycle code, when birds are actively molting, such as for birds undergoing the second prebasic molt or SPB. For both codes, we discuss their applicability using examples based on actual banding data. Our proposed codes will improve the utility of the W–R–P system by better refining age brackets and by expanding its applicability to a diverse array of taxa.     

Timing of events on the breeding grounds for five species of sympatric warblers

ABSTRACT On the breeding grounds, migratory birds have limited time to breed and molt before autumn migration. However, few studies of long‐distance migrants have examined the phenology of these events to determine what life‐history trade‐offs might result if these activities overlap. From 2000 to 2007, I used banding data to determine the timing of migration, breeding, and primary molt for Yellow Warblers (Dendroica petechia), Yellow‐rumped Warblers (D. coronata coronata), American Redstarts (Setophaga ruticilla), Ovenbirds (Seiurus aurocapilla), and Canada Warblers (Wilsonia canadensis) at a study site in Alberta, Canada. Hatching date did not differ among species (P= 0.63), with means ranging from 27 June to 3 July. All species began primary molt between 12 July and 18 July, near the expected fledging date of offspring, and therefore all species exhibited overlap between postfledging parental care and molt. The duration of primary molt ranged from 28 d for Canada Warblers to 69 d for Yellow‐rumped Warblers. Yellow Warblers, Yellow‐rumped Warblers, and American Redstarts began autumn migration having completed about 50% of their primary molt. However, Ovenbirds departed when 21% of molt was complete, and Canada Warblers departed 2 d after completing molt. For all five species of warblers, molt did not overlap with nest‐bound breeding activities. However, molt did overlap with both postfledging care and migration. This suggests that initiating migration as soon as possible is important, possibly because earlier arrival on the wintering grounds may improve access to high quality winter habitat. Overall, warblers may maximize individual fitness by combining life‐history events that result in overlapping portions of the breeding cycle, molt, and migration.     

The trade-off between molt and parental care: a sexual conflict in the blue tit?

Breeding activities and molt are generally thought to be mutuallyexclusive in birds since both are energetically costly and arenormally separated in time. However, sometimes molt overlapswith breeding to some degree. A trade-off between adult somaticmaintenance functions (feather renewal) and parental care isthen to be expected. The consequences of this are largely unknown,and there are few studies that have shown any fitness costsof molt-breeding overlap. We investigated the consequences ofmolt-breeding overlap by removing first clutches of blue titParus casruleus pairs, thereby inducing late repeat clutches.Among the delayed pairs, a high proportion of males and somefemales started their molt already during incubation or nestlingfeeding. Molting males fed their nestlings to a lesser extentthan non-molting ones, and nestling mortality increased as adirect result of the early timing of male molt. Furthermore,the ability to raise an experimentally enlarged brood was negativelycoupled to the molt stage of the male. Our data thus provideevidence that molt-breeding overlap leads to fitness costs,and we discuss the results within the context of sexual conflictand the implications for optimization of avian reproductivedecisions     

Late breeding season definitive prebasic molt in males,and late breeding season brood care by females,in central California Wilson’s warblers

I made observations of a central California population of Wilson''s Warbler, Cardellina pusilla, after July 1 over 10 breeding seasons. I sighted males in definitive prebasic molt from July 4 (in 2007) to September 1 (in 1999). Most territorial males molted on their breeding territories, and individual molt lasted up to 46 days. Following prebasic molt, territorial males engaged in subdued “post‐molt singing,” which lasted about 7 days in some males, and which I first heard on August 13 (in 2004) and last heard on September 6 (in 1999). I sighted no female in definitive prebasic molt, or in fresh basic plumage, during the study. Of 13 females sighted ≥ July 21, 11 were in late breeding season uniparental brood care, and I could not rule out late brood care for the other two. Most, and possibly all, females not engaged in late season uniparental brood care apparently vacated their breeding territories before July 21. This departure was much earlier than for resident males, the last of which I sighted on September 10 (in 1999). Early‐departing females presumably underwent prebasic molt after July 21 at locations not known. Remaining late‐nesting females must have molted much later than resident males and likely later than early‐departing females, and at locations unknown. I last sighted two uniparental brood‐tending females, still in worn plumage, on August 26 and 29, respectively. Two unique findings of this study are a male/female difference in location of prebasic molt, and a likely dichotomy of prebasic molt timing between females leaving their breeding territories early and those remaining in uniparental brood care. Another finding, post‐molt singing in most and possible all territorial males, is a largely unrecognized behavior, but one previously reported in several passerine species. Post‐molt singing may reliably indicate completion of prebasic molt.