Effects of social conditions on Juvenile Hormone mediated reproductive development in Bombus terrestris workers

Abstract. During the annual life cycle of the bumble bee Bombus terrestris (L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) release in vitro , ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.     

Effect of juvenile hormone on caste determination and colony processes in the bumblebee Bombus terrestris

To investigate the role of juvenile hormone (JH) in caste determination, first and second instar larvae of Bombus terrestris were topically treated with one of three doses (2, 10, or 20 g/larva) of JH dissolved in acetone. Treated larvae belonged to very young colonies that had just been started by their queen. Therefore, all larvae were supposedly destined to develop into workers. Our study demonstrates that a single application of JH in the first or second instar can lead to the development of queens and that this effect is dose- and instar-dependent. The brood (second, or third brood of the colony) to which the larvae belonged also had an effect. A clear size dimorphism of the female castes exists in B. terrestris. In this study, however, intermediates also developed from treated larvae. In fact, even untreated larvae in a treated colony developed into queens and intermediates, depending on the total dose of JH applied to the colony. There are no indications that a larva, once determined to become a queen, can be forced to become a worker by means of malnutrition. Treatment with JH also had an influence on colony processes. For instance, the appearance of queen larvae resulted in the advanced start of reproduction by workers and egg robbery, the so called competition point. This indicates again the close relationship between queen rearing and the queen-worker conflict. However, the ultimate function of this casual connection is still unclear. Further, the queen reacted to the treatment by switching to the laying of haploid eggs at an earlier date in the colony development compared to untreated colonies.     

Juvenile Hormone titre and vitellogenin gene expression related to ovarian development in primary reproductives compared with nymphs and nymphoid reproductives of the termite Reticulitermes speratus

To elucidate the reproductive cycle of termite queens, incipient colonies of Reticulitemes speratus (Isoptera: Rhinotermitidae) are established under laboratory conditions, and the transition of colony development is observed at 0.5, 1.5, 2.5, 3.5, and 7.5 months (stages I–V, respectively) after colony foundation. Ovarian development, vitellogenin gene expression and Juvenile Hormone (JH) titres are examined in the queens and in nonphysogastric nymphoids collected from natural colonies. A reproductive cycle in queens is observed, in which the oviposition rate is relatively higher during stages I and II, and then decreases during stages III and IV. Vitellogenic oocytes are not observed in the ovaries during stages III and IV, and the expression level of the vitellogenin gene is low, suggesting that egg production in queens is repressed during these stages. However, vitellogenin gene expression and egg deposition in queens resumes during stage V. Juvenile Hormone levels rise during the transition from nymphs to stage I queens, and elevated JH titres are observed also during stages III and IV. The decrease in JH titre in queens at stage II precedes the decline in vitellogenesis at stages III and IV. Thus, JH titre and vitellogenesis are correlated in an offset pattern. However, nonphysogastric nymphoid reproductives do not have vitellogenic oocytes in their ovaries, and their JH titre is two‐fold higher than that of queens, suggesting that elevated JH titre precedes vitellogenesis, as in queens.     

Larval juvenile hormone treatment affects pre-adult development,but not adult age at onset of foraging in worker honey bees (Apis mellifera)

Previous research has shown that juvenile hormone (JH) titers increase as adult worker honey bees age and treatments with JH, JH analogs and JH mimics induce precocious foraging. Larvae from genotypes exhibiting faster adult behavioral development had significantly higher levels of juvenile hormone during the 2nd and 3rd larval instar. It is known that highly increased JH during this period causes the totipotent female larvae to differentiate into a queen. We treated third instar larvae with JH to test the hypothesis that this time period may be a developmental critical period for organizational effects of JH on brain and behavior also in the worker caste, such that JH treatment at a lower level than required to produce queens will speed adult behavioral development in workers. Larval JH treatment did not influence adult worker behavioral development. However, it made pre-adult development more queen-like in two ways: treated larvae were capped sooner by adult bees, and emerged from pupation earlier. These results suggest that some aspects of honey bee behavioral development may be relatively insensitive to pre-adult perturbation. These results also suggest JH titer may be connected to cues perceived by the adult bees indicating larval readiness for pupation resulting in adult bee cell capping behavior.     

Toxicity of acephate to larvae of gypsy moth as a function of host plant and bioassay method

We examined toxicity of acephate to third-instar gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), under different conditions of administration method, availability of food to larvae during bioassay, host plant, and activity of detoxifying enzymes. Larvae that had been fed field-collected foliage of white alder (Alnus rhombifolia Nutt.) were less susceptible 48 h after treatment with topically applied acephate if they were allowed to continue feeding on foliage during the bioassay period (LD₅₀= 60.6 μg/g larva ) than if they were not (LD₅₀= 13.5 μg/g larva ). All surviving larvae were replaced on their original food plant after the 48-h bioassay; of these, 14.4% of the larvae not fed during treatment died before pupation, compared with 1.3% of the larvae fed alder during treatment. The LD₅₀ obtained for topically treated larvae reared and treated on Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, (51.1 μg/g larva) was comparable to that obtained for larvae fed alder (60.0 μg/g larva) throughout treatment. Larvae treated orally with acephate, however, were slightly more susceptible when reared on Douglas-fir (LC₅₀, 20.3 ppm ) than when reared on alder (LC₅₀, 27.0 ppm ). Post-treatment mortality in orally treated larvae was 10.3% in those fed alder and 9.5% in those fed Douglas-fir. Higher cytochrome P-450 activities in larvae reared on Douglas-fir apparently did not enhance tolerance to acephate. Both sexes of orally treated larvae took significantly longer to pupate than did controls on both foliage types, as did topically treated males fed Douglas-fir. Pupal weight generally was slightly, but not always significantly, higher in treated than untreated larvae under all dietary and treatment regimes.     

Effect of juvenile hormone treatment on caste differentiation in the honeybee, Apis mellifera

Synthetic juvenile hormone (methyl trans,trans,cis-10-epoxy-7-ethyl-3,11-dimethyl-2,6-tridecadienoate, 1 μg/μl acetone per animal) (JH) was topically applied to 2- to 3-day-old worker honeybee larvae in the hive. Eighty per cent of the hormone-treated larvae were removed from their brood cell before pupation. Only 1 out of 42 adults showed characteristics of an intercaste. Fifty per cent of the control larvae (1 μl acetone) developed to adults, all of which were workers.After topical application of JH and feeding on royal jelly under in vitro conditions, the rate of survival is high (up to 85 per cent adults), but up to 67 per cent of queens and 44 per cent of workers exhibit eye malformations with characteristics of somatic mutation. Formation of a more solid web by the spinning larvae, shortening of the diapause by 1 to 2 days, and unusual shapes of mandibles, legs, and abdomen are a consequence of hormone treatment. The effects are less marked after application of 0·1 instead of 1 μg hormone or after its addition to the food (2 μg/g royal jelly). Treatment of the 2- to 3-day-old worker larvae and subsequent rearing on royal jelly is followed by a shift in caste differentiation from queens and workers to intercastes. In no case, are more queens developed after juvenile hormone treatment.Queen bee determinator, partially purified from royal jelly, induces a concentration-dependent shift from workers to queen differentiation. A threefold increase in the natural determinator concentration of royal jelly results in an almost exclusive (98 per cent) queen formation from 2- to 3-day-old worker larvae. In contrast to this direct effect, the influence of JH is explained as an indirect morphogenetic effect not directly coupled with honeybee caste differentiation.     

Interactions of ecdysteroid and juvenoid agonists in Plodia interpunctella (Hübner)

The influence of non-steroidal ecdysteroid agonists on Indianmeal moth larvae was assessed by rearing last instar larvae on diet treated with RH-5992 (tebufenozide) or RH-2485 (methoxyfenozide). Larvae were monitored for effects of the ecdysteroid agonists on weight, metamorphosis and mortality. Larvae treated with either of the ecdysteroid agonists at a concentration of 5 ppm or higher gained less weight and had greater mortality than did larvae reared on control diet. For example, the weights of control larvae increased approximately 400% by day 2, compared with only a 50% increase in weight when the larvae were treated with 25 ppm of RH-2485 or RH-5992. Similarly, mortality in control larvae was less than 10%, but was as much as 90–100% in larvae reared on diet treated with one of the ecdysteroid agonists. We also examined the effects of simultaneous treatment with a juvenile hormone (JH) mimic, either methoprene or fenoxycarb. The JH mimics prevented adult emergence, and the larvae continued to feed throughout the month-long observation period. However, larvae treated with a juvenile hormone mimic gained weight despite the presence of an ecdysteroid agonist in the diet. On diets treated with 0.1 ppm of RH-2485 or RH-5992, JH-treated larvae gained even more weight than did untreated controls. Interestingly, although the addition of a JH mimic to ecdysteroid-treated diet resulted in increased weight, it did not lead to reduced mortality. In fact, combinations of a JH mimic with 10 ppm RH 2485 or RH 5992 resulted in nearly 100% mortality compared with 40–70% mortality without the JH compounds. These results indicate that JH mimics overcome the inhibitory effects of ecdysteroid agonists on weight gain; however, they also resulted in increased mortality compared with moderate doses of ecdysteroid agonists alone. One specific action of these compounds at the cellular level was noted in that RH 5992 mimicked ecdysteroids by increasing uptake of ¹⁴C-GlcNAc in a Plodia interpunctella cell line, while fenoxycarb was inhibitory. Arch. Insect Biochem. Physiol. 38:91–99, 1998. Published 1998 Wiley-Liss, Inc.     

Granulovirus prevents pupation and retards development of Adoxophyes honmai larvae

Abstract Larvae of Adoxophyes honmai (Lepidoptera: Tortricidae) infected with granulovirus (AdhoGV) do not pupate; instead, they undergo prolonged larval development and die during the final stadium. Non-infected larvae, however, pupate after five larval stadia. Insect metamorphosis is regulated by fluctuations of ecdysteroid and Juvenile Hormone (JH). JH esterase activity and titres of ecdysteroid must be measured to understand fully the interaction of an insect virus and its host. JH esterase activity is consistently low in AdhoGV-infected larvae, which suggests that JH in AdhoGV-infected larvae is not degraded during the final stadium. The ecdysteroid titre in non-infected larvae showed a large peak in the final stadium before pupation, whereas that in AdhoGV-infected larvae increased from day 2 to day 5 in the final stadium, and then remained at a high level until death. Furthermore, an ecdysteroid UDP-glucosyltransferase (EGT) assay showed that this activity occurs in haemolymph from AdhoGV-infected larvae, but not in haemolymph of non-infected larvae. PCR and sequencing analysis revealed that the AdhoGV genome contains an egt gene, which encodes a protein of 445 amino acids, located approximately 1 kbp upstream from the granulin gene. These results suggest that AdhoGV-infected larvae are prevented from pupating because JHE activity is suppressed and EGT expression inactivates ecdysteroid in the haemolymph.     

Intergenerational effect of juvenile hormone on offspring in <Emphasis Type="Italic">Pogonomyrmex</Emphasis> harvester ants

Parents can influence the phenotypes of their offspring via a number of mechanisms. In harvester ants, whether female progeny develop into workers or daughter queens is strongly influenced by the age and temperature conditions experienced by their mother, which is associated with variation in maternal ecdysteroid deposition in fertilized eggs. In many insects, juvenile hormone (JH) is antagonistic to ecdysteroid release, suggesting that seasonal and age-based variation in maternal JH titers may explain maternal effects on offspring size and reproductive caste. To test this hypothesis, we artificially increased maternal JH titers with methoprene, a JH analog, in laboratory colonies of two Pogonomyrmex populations exhibiting genetic caste determination. Increasing maternal JH resulted in a 50% increase in worker body size, as well as a sharp reduction in total number of progeny reared, but did not alter the genotype of progeny reared to adulthood. The intergenerational effect of JH manipulation was not mediated by a reduction in ecdysteroid deposition into eggs; instead, changes in egg size, trophic egg availability or brood/worker ratio may have altered the nutritional environment of developing larvae. Egg ecdysteroid content was significantly negatively correlated with natural variation in worker body size, however, suggesting that there are multiple independent routes by which queens can modify offspring phenotypes.     

Regulation of Juvenile Hormone synthesis in the blowfly Lucilla cuprina

Abstract. Juvenile Hormone III bisepoxide synthesis by ring gland complexes from third-instar larvae of the blowfly Lucilia cuprina Weidemann (Diptera, Calliphoridae) was measured using a radiochemical assay in vitro. Hormone synthesis is regulated by three distinct mechanisms during development of the final larval instar up to the time of pupariation. The first type of regulation is detected as a rapid decline in hormone release coinciding with the final phase of commitment to pupariation. The second is a neurally mediated inhibition by the brain that acts at all stages of development in third-instar larvae. A protease-sensitive factor from brains of third-instar larvae causes dose-dependent reversible inhibition of Juvenile Hormone III bisepoxide synthesis. The third regulatory signal is a neural inhibition, observed in brain-ring gland complexes of prepupal stages. The first two levels of regulation appear to act early in the synthetic pathway for Juvenile Hormone (JH), whereas the third acts on the final steps of bisepoxide synthesis.     

Caste regulation in the pharaoh's ant Monomorium pharaonis: the influence of queens on the production of new sexual forms

ABSTRACT. In colonies of Monomorium pharaonis (L.), the presence of fertile queens normally prevents the production of new queens and males (sexuals). The inhibitory effect of the presence of fertile queens is not shared by virgin queens or by freshly killed dead queens, but can be substituted by the artificial introduction of eggs. Moreover, fertile queens made sterile by exposure to a Juvenile Hormone analogue lose their ability to prevent the rearing of new sexuals. Thus, the inhibitory action of queens is mediated via the eggs that they lay, such that the rearing of new sexuals is limited to the times when either the number or fecundity of extant queens is reduced. Workers appear able to detect changes in the number of eggs present in the colony. When eggs are plentiful (i.e. when queens are laying at maximum rates), only worker brood is reared, but if egg numbers decline, workers will respond by rearing a new batch of males and queens. This method of caste regulation is highly efficient, and the inhibitory action of eggs on the production of sexuals is comparable to the action of 'queen substances' reported in some other social insects.     

Assimilation of carbon and nitrogen from pollen and nectar by a predaceous larva and its effects on growth and development

Abstract. 1. Predaceous insects may benefit from feeding on non‐prey foods, such as pollen, nectar, and honeydew, because they can provide nutrients that help maintain metabolism and enhance overall nutrient intake. Yet, the extent to which predaceous insects can assimilate non‐prey food and the importance of diet mixing during particular life history stages is poorly understood. In this study the relative contribution of an omnivorous diet to the growth and survivorship of a predaceous larva was tested in a hypothetical situation in which nutritionally optimal prey was not available. The study system comprised a predaceous larva (second‐ and third‐instar larvae of the green lacewing Chrysoperla carnea), nutritionally poor prey (larvae of Drosophila melanogaster), and non‐prey food (pollen suspension, a mixture of bee pollen and artificial nectar (1 M sucrose solution)). Chrysoperla carnea larvae in the mixed diet treatment were provided with both Drosophila larvae and pollen suspension, while those reared on the prey and non‐prey diet treatments received only Drosophila larvae or pollen suspension respectively. 2. The inclusion of pollen and sucrose in their diet enhanced the growth of C. carnea larvae. Second instars reared on the mixed diet developed significantly faster than their cohorts reared on the prey diet, however third instars reared on the mixed diet did not develop faster than their cohorts reared on the prey diet. Larvae reared on the mixed diet became larger adults than did those reared on either the prey or non‐prey diets. Third instars reared on the non‐prey diet completed their development while second instars in the non‐prey diet treatment failed to pupate. 3. Stable isotope analysis indicated that the larvae obtained most of their carbon (55–73%) and nitrogen (71–73%) from Drosophila but acquired only a minor amount of carbon (2–5%) and nitrogen (3–11%) from pollen. Larvae reared on the mixed and non‐prey diets acquired a relatively significant amount of carbon (23–51%) from sucrose. 4. A model, which included a novel fractionation factor to account for the isotopic effect of metamorphosis, was developed to explain the proportion of larval growth attributable to each diet item. It explained the adult δ¹³C values to within 0.2‰ and adult δ¹⁵N values to within 0.7‰ in all treatments. 5. Adults fed ¹⁵N‐labelled pollen as larvae retained the ¹⁵N signal of the pollen as adults. 6. The collective results of this study support the view that, despite their dependence on prey arthropods to obtain most of their dietary nitrogen, omnivorous lacewing larvae can enhance their growth and development by supplementing their diets with alternative non‐prey food resources. This finding is consistent with the notion that omnivory has evolved as a feeding strategy to acquire both additional nitrogen as well as trace nutrients.     

Effects of starvation and sucrose feeding on corpora allata of last instar larvae of Manduca sexta: in vitro activity, size, and cell number

Abstract Larvae of the tobacco hornworm moth Manduca sexta starved for the first 3 days of the last (fifth) stadium undergo a supernumerary moult. If they are provided with sucrose during the starvation period, they develop into normal pupae although pupation is delayed. The activities of the corpora allata (CA) from normal, starved, and sucrose fed larvae were followed through the fifth stadium with a radiochemical assay for Juvenile Hormone (JH) biosynthesis. An attempt was made to correlate CA-activity with CA cell number, size, and protein content.
In CA of normally fed larvae the rate of JH synthesis declined to undetectable levels by day 4 which was also the time of exposure of the dorsal vessel. In CA of starved larvae, the rate of JH synthesis at first decreased but began to increase on day 3 and reached a peak value by day 7 , at which time head capsule slippage occurred. In CA of sucrose fed larvae, the rate of biosynthesis declined as in normal larvae but the decline was extended over a longer period. Exposure of the dorsal vessel was delayed in the same manner and occurred on days 7–9. The major JH in all cases was JH-II.
The CA comprise c. 150 cells in the early fifth stadium, and this number remained constant during the fifth stadium in all three feeding regimens. In normal larvae, CA size and protein content increased several-fold during the stadium whereas in starved and sucrose-fed larvae they increased slowly and in agreement with the altered timing of developmental events. In none of the groups was the CA activity pattern correlated with morphometric changes of the CA. The rates of JH biosynthesis were not closely correlated with published JH titre curves. The in vivo mechanisms for regulation of JH production remain to be elucidated.     

Juvenile Hormone biosynthesis and utilization of farnesoic acid during the final larval stadium of the ring-legged earwig

Abstract. The regulation of Juvenile Hormone (JH) HI biosynthesis and release by the corpora allata (CA) was studied in final instar male and female larvae of the earwig, Euborellia annulipes , using a radiochemical assay in vitro. In males, maximal biosyntiiesis of JH IH occurred on day 1, then declined to virtually undetectable levels for the following 12 days of the stadium, and finally increased on days 14–16. In females, peaks of biosynthesis were detected on days 0–1 and on day 12. A further investigation of the 12-day-old larvae demonstrated mat in nonmoulting males and females, JH UJ biosynthesis was undetectable. However, for males and females undergoing ecdysis, the biosynthesis of JH III was detected and quantified.
The addition of 60 μM farnesoic acid to the incubation medium significantly increased the production of JH III by CA taken from females from day 8 until the end of the stadium. Glands from 12-day old females that had initiated ecdysis were stimulated by farnesoic acid. By contrast, we could detect no stimulation of production of JH III by farnesoic acid in CA taken from males, even very late in the stadium. CA from newly emerged adult males and females were more active than those of larvae, and were greatly stimulated by farnesoic acid. CA from females immediately after emergence were stimulated significantly more by farnesoic acid man were glands from newly emerged males. These results suggest fundamental differences in the synmetic activity of CA for males and females in this insect.     

Response to rearing in laboratory of the xylophagous grape pest,Xylotrechus arvicola (Coleoptera: Cerambycidae)

Xylotrechus arvicola (Olivier) (Coleoptera: Cerambycidae) is an important pest in vineyards (Vitis vinifera) in the main Iberian wine‐producing regions. Larvae were reared with Semi‐Synthetic Iglesias (SSI) diet over 27 months and two generations in the laboratory. Larval mortality was highest during the first (49.49 %) and second (9.38 %) month of rearing, increasing to 50.52 % during the first month if F2 reared larvae were obtained from an F1 adult female obtained in laboratory. The diet had sufficient nutrients to enable the pest to complete its life cycle within nine months, with F1 larval viability ranging from 23.49 % to 27.97 % and F2 larval viability reduced to 2.07 %. However, the diet did not allow for the completion of additional life cycles and generations (F3, F4,…). Larval mortality increased as the months of rearing (66.13 %, 69.51 % and 89.50 %) and generations (59.10 % and 76.93 % in F1 and F2, respectively) progressed in the laboratory. The larva–adult period of females obtained in the laboratory was longer than for males. In the laboratory, the life cycle was shortened in relation to the life cycle in the field because larvae did not require a cold period to break diapause and start pupation. This indicates that X. arvicola has the potential to complete its life cycle inside grape wood in vineyards of wine‐producing regions with warmer winters.     

Caste Determination in Bombus terrestris: Differences in Development and Rates of JH Biosynthesis between Queen and Worker Larvae

To study the possible role of juvenile hormone in caste determination in Bombus terrestris, we measured development and rates of juvenile hormone biosynthesis in vitro in larvae destined to develop into either workers or queens. Larvae of both castes developed through four instars and had the same growth rates. However, the duration of the instars was longer for queen larvae, and their head width at the third and fourth instars was significantly larger. After validating the well-known radiochemical assay of JH for bumble bee larvae, we show that worker larvae corpora allata exhibited a constant and low rate of JH biosynthesis, never more than 5 pmol JH/h/pair. Queen larvae, in contrast, had two peaks of JH biosynthesis: a small one during the first instar, which has previously been correlated with caste determination; and a large peak, previously undetected, above 40 pmol JH/h/pair, during the second and third instars. We suggest that caste determination in this species is mediated by JH and that the duration of larval instars is a key factor. The possibility that the queen influences caste determination via an effect on instar duration is also discussed. Copyright 1997 Elsevier Science Ltd. All rights reserved     

Juvenile hormone modulation of insect cold hardening: Ice-nucleating activity

Data are presented offering the first evidence for probable endocrine involvement in the control of cold hardening in Eurosta solidaginis. Juvenile hormone (JH) deprivation experiments in which the corpora allata were removed by head ligation resulted in a loss of supercooling (SC) capacity in larvae collected over 2 years. This loss of supercooling capacity is indicative of synthesis of organismal pools of ice-nucleating agents (INA). Larval sensitivity to JH removal (ligation) on SC is seasonally dependent. For example, in 1983, larvae were most sensitive in October, secondarily so in September, and relatively insensitive in December regardless of acclimation temperature. While in 1984, larvae acclimated to +5 °C were most sensitive in November, secondarily so in October, and relatively insensitive in December, and larvae acclimated to +15 °C were most sensitive in October and December and least so in November. Supercooling point elevations as great as 7 °C over controls were observed with maximal responses occurring within 1 day following ligation. In 1983, juvenile hormone replacement following ligation generally resulted in an expansion of supercooling capacity when compared to controls. As with ligation, the sensitivity to JH replacement on SC was seasonally dependent: September and October larvae being the most sensitive with December larvae being insensitive. Larvae collected in 1984 were given a greater dose of JH than those in the previous year and showed no significant change in SC over ligated-acetone controls. Hormone analog potentiation experiments in which unligated larvae collected in 1983 and acclimated to +5 °C were given methoprene resulted in depression of supercooling points for September and October larvae. JH titres appear to play an important role in the regulation of SC capacity in E. solidaginis larvae.     

Influence of larvae and workers on egg production of queens of the pharaoh's ant,Monomorium pharaonis (L.)

Summary Social regulation of egg production and weight in queens was studied in relation to presence and absence of larvae and workers in the pharaoh's ant,Monomorium pharaonis (L.).Results were obtained by counting eggs and weighing queens under various conditions.The results confirm the existence of a positive feed-back loop between mated queens and their larvae as evident from a correlation (Y = 4.575 * X + 6.452) between the number of large worker larvae (X) and the egg yield (Y). This correlation seems to relate to the queens preferential feeding on larval secretions. Queens without larvae maintained a low level of egg production of about 6 eggs/day. Queens deprived of larvae as well as workers stopped producing eggs within 24 hours.Repletes, special workers, with greatly distended gasters functioned as a buffer retarding decline of egg production by feeding the queens during short periods without larvae.     

Exogenous juvenile hormone and methoprene, but not male accessory gland substances or ovariectomy, affect the blood/nectar choice of female Culex nigripalpus mosquitoes

When newly emerged females of the mosquito Culex nigripalpus Theobald (Diptera: Culicidae) take a sugar meal, they develop both a propensity to seek a host and resting-stage ovarian follicles. As follicle growth is indicative of Juvenile Hormone (JH) activity, we searched for possible roles of JH in the behavioural shift from nectar to blood-host odour preference by Cx. nigripalpus after emergence, using an olfactometer-choice assay. Topically applied or injected methoprene (a JH analogue) resulted in a behavioural shift and follicular growth in unfed females that increased with increasing dosages. Topical methoprene 500 ng and 4 microg resulted in a switch to bird-odour preference. JH III injection resulted in a lesser shift from honey responses to bird responses. Methoprene application caused no detectable changes in glycogen, total sugars or total lipid when assayed 24h after treatment. Additionally, as male accessory glands (MAG) have been shown to synthesize JH, we implanted intact paired MAGs from either conspecific or Aedes aegypti (L.) donors, or injected 1/3 gland pair equivalents of conspecific MAG homogenate into unfed newly emerged females. All MAG treatments failed to induce behavioural or ovarian modifications. Ovariectomy had no effect on the sugar-induced shift from nectar to host preference in the olfactometer. Thus JH, but not MAG, mimicked the effects of a sugar meal by causing both follicular growth and the shift to preference for a host.     

Morphogenetic and gonadotrophic effects of a juvenile hormone analogue ((7S)-hydroprene) in last instar female larvae of Diploptera punctata

ABSTRACT. The effect of treatment of last instar female larvae of Diploptera punctata with a Juvenile Hormone (JH) analogue, (7 S )-hydroprene, has been determined with respect to the ability of the analogue to alter the duration of the stadium and the nature of the ensuing ecdysis. We have also investigated the effects of the analogue on JH release, the growth of the basal oocytes, as well as ecdysteroid titres during the fourth stadium. Analogue treatment prior to day 10 of the stadium results in prolongation of the stadium and desynchronization of ecdysteroid release. Thereafter, treatment with the analogue has little effect. Analogue treatment results also in the formation of supernumerary larvae and intermediates, in a dose-dependent fashion, provided that animals are treated on day 10 or earlier. Thus, the 'critical' period for metamorphosis in last instar D. punctata is between days 0 and 10.
Treatment with (7 S )-hydroprene produces profound effects also on both JH release, and basal oocyte growth. At a dose of 500μg administered on day 1, JH release is stimulated significantly at a time when JH release is normally undetectable. Significant growth of basal oocytes is observed in such treated animals, and appears to precede the peak in JH release. We suggest that the growth of the basal oocytes, as a result of analogue treatment, stimulates the production of JH by CA in these last instar larvae.