Effects of temperature,photoperiod and soil humidity on induction of pseudopupal diapause in the bean blister beetle Epicauta gorhami

Larvae of the bean blister beetle Epicauta gorhami Marseul (Coleoptera: Meloidae) feed on grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis in meloid beetles. The effects of temperature, photoperiod and soil humidity on larval development of E. gorhami are examined in a population in Miyazaki, Japan, using egg pods of Locusta migratoria L. as food. At lower temperatures (20 and 22.5 °C), all larvae become pseudopupae, regardless of the photoperiod. By contrast, at higher temperatures (27.5 and 30 °C), almost all larvae pupate at the end of the fourth instar, again regardless of the photoperiod. A long‐day photoperiodic response occurs only at an intermediate temperature (25 °C): under an LD 12 : 12 h photocycle, all larvae enter diapause, although the diapause incidence tends to decrease as the day length becomes longer. Pseudopupae are immobile and remain in diapause for ≥120 days when they are kept under the same conditions, except that diapause terminates within a relatively short time at 30 °C. Although lower soil humidity retards post‐feeding development, soil humidity has no effect on the diapause incidence. On the basis of the short developmental period and diapause avoidance under summer conditions, it is suggested that this beetle partially produces two generations a year in southwestern Japan.     

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.     

大菜粉蝶颗粒体病毒对菜粉蝶幼虫取食、生长、发育的影响

菜粉蝶幼虫在一、二、三、四龄初期饲以大菜粉蝶颗粒体病毒(PbGV),食量减少99.3—38.4%;四龄末或五龄初饲毒,食量反而比健虫高出36.3%和87.2%。幼虫感病后取食期的缩短或延长是食量变化的主要原因。幼虫病死前脱皮过程先被抑制,其结果往往使得死亡时所处的龄期明显延长。幼虫在四龄末饲毒后,由于五龄期延长,食量增加,其死亡前达到的最高体重平均为357.9毫克,远高于健虫化蛹前的最高体重。PbGV对菜粉蝶化蛹也有明显影响。幼虫在五龄前饲毒,一般不能化蛹。五龄第1—3天饲毒,化蛹率26.4—87.9%,第4天饲毒对化蛹无影响。本文结果对应用PbGv防治菜粉蝶幼虫危害以及对该病毒的大量增殖均具指导意义。     

Food availability controls the onset of metamorphosis in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

In nature, larvae of the dung beetle Onthophagus taurus (Schreber 1759) are confronted with significant variation in the availability of food without the option of locating new resources. Here we explore how variation in feeding conditions during the final larval instar affects larval growth and the timing of pupation. We found that larvae respond to food deprivation with a reduction in the length of the instar and premature pupation, leading to the early eclosion of a small adult. To achieve pupation, larvae required access to food for at least the first 5 days of the final instar (= 30% of mean third‐instar duration in control individuals), and had to exceed a weight of 0.08 g (= 58% of mean peak weight in control individuals). Larvae that were allowed to feed longer exhibited higher pupation success, but increased larval weight at the time of food deprivation did not result in increased pupation success except for larvae weighing > 0.14 g. Larvae responded to food deprivation by initiating and undergoing the same sequence of developmental events, requiring the same amount of time, as ad libitum‐fed larvae once those had reached their natural peak weight. Our results reveal a striking degree of flexibility in the dynamics and timing of larval development in O. taurus. They also suggest that premature exhaustion of a larva's food supply can serve as a cue for the initiation of metamorphosis. Premature metamorphosis in response to food deprivation has been documented in amphibians, but this is, to the best of our knowledge, the first time such a behaviour has been documented for a holometabolous insect. We discuss our findings in the context of the natural history and behavioural ecology of onthophagine beetles.     

Evidence for the presence of a threshold weight for entering diapause in the yellow-spotted longicorn beetle, Psacothea hilaris

Under long-day conditions larvae of Psacothea hilaris (Coleoptera: Cerambycidae) pupate after the 4th or 5th instar, while under short-day conditions they undergo 2-4 nonstationary supernumerary molts and eventually enter diapause. To explore the possibility of a threshold weight for entering diapause, P. hilaris larvae were deprived of food on days 0 (day of ecdysis), 4 or 8 of the 4th, 5th and 6th instars under short-day conditions. Within the first 40 days of starvation, 60% of the larvae starved starting on day 0 of the 4th instar died, but all the larvae starved at later stages survived. The incidence of diapause in these survivors was determined by the occurrence of pupation after a temporary chilling at 15 degrees C for 15 days. Diapause incidence increased as the onset of starvation was delayed; from 11% in the larvae starved on day 0 of the 5th instar to 100% in the larvae starved on day 4 and day 8 of the 6th instar. Analysis of the relationship between the initial weight of a respective larva at the onset of starvation and its pupation success revealed that none of the larvae weighing 690 mg did. This finding suggests the presence of a threshold weight (about 600 mg), below which larvae are incapable of entering diapause. We discuss these findings with reference to the life history of P. hilaris.     

Contrary food requirements of the larvae of two Curtonotus (Coleoptera: Carabidae: Amara) species

The larvae of carabids that are granivorous as adults can be granivorous, omnivorous or carnivorous. The differences in larval food preferences of Amara aulica and Amara convexiuscula, two closely related species of the subgenus Curtonotus, were studied. Survival and duration of development of non‐diapausing first and second instar larvae were compared. The third instar larvae were not studied because they go into diapause prior to pupation. The larvae were fed diets consisting of insect larvae (Tenebrio molitor), seeds of Artemisia vulgaris, Tripleurospermum inodorum, Urtica dioica or Cirsium arvense and a mixed diet consisting of insect larvae and seed. Larvae of A. aulica required seeds for successful development, whereas those of A. convexiuscula developed on both an insect diet and seeds of Artemisia. The difference in larval food requirements facilitates the coexistence of these closely related species, which frequently share the same habitat.     

Effects of temperature and photoperiod on termination of pseudopupal diapause in the bean blister beetle, Epicauta gorhami

Larvae of the bean blister beetle, Epicauta gorhami (Coleoptera: Meloidae), feed on grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis in meloid beetles. This pseudopupal diapause is maintained for a long period if the larvae are kept under continuous diapause-inducing short-day conditions. In the present study, the effects of temperature and photoperiod on termination of pseudopupal diapause in E. gorhami were examined using pseudopupae obtained under 12L-12D at 25°C. Diapause was terminated by exposure to low or high temperature, but not by transfer to long-day conditions. The pseudopupal stage comprises diapause and post-diapause phases despite its unchanging appearance. The optimum low temperature for diapause termination was 10-15°C, and a higher or lower temperature was less effective. There was an individual variation in the low temperature requirement for diapause termination and post-diapause development may not occur until this requirement is satisfied. Although under natural conditions pseudopupae may encounter low temperatures that are effective for diapause termination at different ages, our results show that pseudopupae at various ages respond similarly to low temperature exposure. This response may ensure that resumption of development synchronizes in a population.     

Juvenile hormone changes associated with diapause induction, maintenance, and termination in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

At 22°C and under a long-day photoperiod of L:D 16:8, all the last fifth instar Loxostege sticticalis larvae undergo prepupal stage and pupate without diapause. Under a short-day photoperiod of L:D 12:12, in contrast, they all enter diapause with approximately 36 days diapause maintenance and then terminate diapause spontaneously, although only 44% of the larvae terminated diapause successfully. Changes in hemolymph juvenile hormone (JH I) titers of diapause-destined larvae across diapause induction, maintenance and termination were examined using HPLC, and were compared with those of non-diapause-destined larvae from the fifth instar through pupation. JH I titer of the earliest fifth instar diapause-destined larvae remained at a high level with a peak of 220.4 ng/ml, though it decreased continuously to a minimum of 69.0 ng/ml on day 5 in the fifth instar when the larvae stopped feeding to enter diapause. During the diapause maintenance, JH I titer of the mature larvae increased significantly and maintained a high level until day 31 in prepupae. JH I titer declined and fluctuated at low level from 5 days before pupation. In contrast, JH I titer of both the fifth instar non-diapause-destined larvae and prepupae remained and fluctuated at low level consistently, as well as decreased before pupation. These results indicate that diapause induction and maintenance in this species might be a consequence of high JH, whereas diapause termination can be attributed to low JH titer, which was in agreement with the hormonal regulation observed in many other larval-diapausing insects.     

Age‐specific maternal effects interact with larval food supply to modulate life history in Coleomegilla maculata

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Extra molting,cannibalism and pupal diapause under unfavorable growth conditions in Atrophaneura alcinous (Lepidoptera: Papilionidae)

Atrophaneura alcinous adopt multiple strategies such as extra molting, cannibalism and pupal diapause under unfavorable growth conditions. The conditions under which these strategies are adopted have been separately verified, but their relationship has often been overlooked. We examined which strategy A. alcinous adopted and the relative advantages of strategies using four experimental groups under different food quantity and individual density conditions. Our results indicated that A. alcinous often extra‐molted, prolonged the larval period, and larval and pupal weights were lighter under food shortage. Cannibalism and disease often occurred under the high density and food shortage condition. We also showed that individuals cannibalized during the prepupal or pupal period were less likely to extra molt before they were killed. Extra molting tended to occur more frequently in females than in males under a shortage of food. In addition, we showed that, when food was insufficient, A. alcinous might initiate pupal diapause under low densities, but not under high densities. These results suggest that A. alcinous prolongs the larval period by engaging in extra molting during times of unfavorable food conditions. This strategy might decrease the risk of cannibalization because surrounding larvae who could potentially cannibalize others pupate before larvae who prolong the larval period pupate. Our results also suggest that diapausing pupae under a shortage of food can only survive when there are few surrounding conspecifics, due to a lower cannibalization risk. In conclusion, there is a complex interaction between extra molting, cannibalism and pupal diapause strategies.     

Brain-independent development in the moth Sesamia nonagrioides

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1-3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1-2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal-adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.     

Temporal and developmental aspects of diet-induced food preferences in larvae of the tobacco hornworm, Manduca sexta

Diet‐induced changes in food preferences in an oligophagous caterpillar were studied in order to characterize the conditions under which this induction occurs. The time course of acquisition and extinction of induced food preferences by larvae of the tobacco hornworm, Manduca sexta (Johan.) (Lepidoptera, Sphingidae), was examined by varying the food and duration of larval food experience. Larvae were given feeding experience with the host plant tomato, Lycopersicon esculentum (Mill.) (Solanaceae), or the acceptable non‐host plant cowpea, Vigna unguiculata (Walp.) (Fabaceae), or switched from one to the other during different instars. Food preferences for V. unguiculata by the fourth or fifth instar larvae were measured individually in two‐choice tests with discs of V. unguiculata and moist filter paper. The acquisition or extinction of an induced food preference for V. unguiculata was indicated by larvae preferring V. unguiculata to filter paper or the reverse, respectively. Results showed that: (1) the period required for the acquisition of induced preference for V. unguiculata can be short (36 h), (2) food experience in either the third or fourth instar period is sufficient, and (3) the most recent feeding experience appears to be important. In contrast, the period required for extinction of induced preference for V. unguiculata appeared to be longer (1–3 instars), and both the most recent feeding experience and total duration of larval experience with the inducing food seem to play a role. Experience is not restricted to a particular instar period to acquire or extinguish such an induced food preference. The induced food preference for V. unguiculata was not very rigid and could be reversed by having one instar of feeding experience on L. esculentum. The findings indicate that diet‐induced food preferences in M. sexta contains elements of habituation and associative learning, but do not support food imprinting and induction of oligophagy.     

Co‐expression of the proteinase inhibitors oryzacystatin I and oryzacystatin II in transgenic potato alters Colorado potato beetle larval development

Colorado potato beetle (CPB; Leptinotarsa decemlineata Say, Coleoptera: Chrysomelidae) has shown a remarkable adaptability to a variety of control measures. Although oryzacystatin I and II (OCI and OCII) have potential in controlling pests that use cysteine proteinases for food digestion, expression of a single OC gene in potato exhibited a minimal or no effect on CPB fitness traits. The aim of this study was to examine the effect of coexpressed OCI and OCII in potato (Solanum tuberosum L.) cultivars Desiree, Draga?evka and Jelica on CPB larvae. Growth parameters, consumption rates and food utilization, as well as activity of proteases of CPB larvae were assayed. Second and third instar larvae fed on transformed leaves molted earlier and had higher relative growth and consumption rates than larvae fed on nontransformed leaves, while efficiency of food utilization was unaffected. In contrast, fourth instar maximum weight gain and amount of leaves consumed were about 20% lower for the larvae fed on transgenic potato. Analysis of total protease activity of third instar larvae revealed reduction in overall proteolytic activity measured by azocasein hydrolysis, accompanied with inhibition of cysteine proteinase activity 24 h after ingestion of potato leaves expressing OCI and OCII. However, after long‐term feeding on transformed leaves proteolytic activities of larvae became similar to the controls. Although feeding on OCI/OCII leaves did not affect larval survival, coexpression of OC genes reduced the development time and thus significantly decreased plant damage caused by CPB larvae.     

Pupal colour dimorphism in California Battus philenor: pupation sites, environmental control, and diapause linkage

ABSTRACT.

• 1 Natural pupation sites and corresponding pupal colour (green or brown) were determined for samples of Battus philenor (L.) from two Californian populations.
• 2 Larvae pupate off the ground on trees, shrubs and man-made objects.
• 3 The vertical distribution of pupation sites and relative frequencies of pupae formed on narrow twigs and broad substrates show interpopulation variability, and seem to be determined by habitat-specific and possibly behavioural differences among populations.
• 4 The percentage of‘mismatched’pupae in green leafy environments (brown) is greater than that on wide substrates (green). Heterogeneity in samples of the latter suggest strong but sporadic predation pressure on non-cryptic pupae in exposed areas.
• 5 Green and brown substrates generally promoted formation of cryptic green and brown pupae although rearing conditions modified pupal colour response to substrate colour and larval pupation site choice.
• 6 Warm temperatures and long days increased the production of brown pupae. Short photoperiods increased the tendency of larvae to pupate on narrow twig-like substrates and to form green pupae.
• 7 Green pupae show less tendency to diapause than brown pupae. The difference between percentage diapause in the two colour forms increases under conditions favouring progressively more continuous development.

     

Effects of food nutritive quality and Bacillus thuringiensis onfeeding behaviour, food utilization and larval growth of spruce budworm Choristoneura fumiferana (Clem.) when exposed as fourth- and sixth-instar larvae

Abstract 1 Feeding behaviours, and lethal and sublethal (growth, development and food utilization) effects of Foray 48B, a commercial formulation of Bacillus thuringiensis (kurstaki), were investigated on fourth‐ and sixth‐instar spruce budworm larvae according to food nutritive quality. Nitrogen and soluble sugar content of artificial diets were modified to obtain three different qualities of food, simulating variations in nutritive quality of host tree. 2 Larval development times were longer for Bt‐treated larvae and pupal weights were reduced for sixth‐instar larvae only. Bt‐induced mortality levels were influenced by food quality. Ingested dose of Bt and feeding inhibition times were strongly affected by the Bt treatment, but food quality affected only fourth‐instar larvae. Except for food digestibility, nutritional indices were negatively affected by the Bt treatment and by the reduction in food quality. 3 Contrary to early treated larvae (fourth instar), larvae treated at the beginning of the sixth instar were not able to compensate for Bt injury and were consequently more affected by the Bt‐treatment both in terms of lethal and sublethal effects. 4 Bt efficacy was not directly related to the ingested dose. 5 Increase in larval vulnerability to Bt was more likely a consequence of a general stress induced by a less suitable food than a direct interaction between Bt and food nitrogen or sugar compounds. 6 The application of Bt on late‐instar larvae could be a successful operational strategy at low population levels when field sprays target the insect instead of foliage protection.     

The effect of the granulovirus (PapyGV) on larval mortality and feeding behaviour of the Pandemis leafroller,Pandemis pyrusana (Lepidoptera: Tortricidae)

An indigenous betabaculovirus (PapyGV) of the Pandemis leafroller, Pandemis pyrusana (Kearfott), was studied in the laboratory and greenhouse to determine how the virus affected leafroller mortality and foliar damage. Probability of mortality increased with virus concentration as observed after 7 and 10 days of feeding on virus treated diet in neonates and second instar larvae. LC₅₀ estimates for neonates at 7 and 10 days was 2743 and 389 occlusion bodies (OBs)/mm². For second instars, LC₅₀ was 139,487 and 813 OBs/mm² at 7 and 10 days. There was no biologically significant mortality response to increasing virus concentrations by fourth instar larvae; however, when fourth instar larvae were infected with virus on diet and then fed apple leaves, the leaf area consumed declined up to 50% with higher virus concentrations. In a greenhouse study, neonate larvae that fed on seedlings treated with water showed >90% survival and 80% pupation rate of larvae after being transferred to diet. In contrast, larvae that fed on apple seedlings sprayed with 3×10⁶ OBs/ml showed poor survival when transferred to diet after acquiring the virus and failed to reach the pupal stage. This virus shows promise for population regulation and can produce reduction in feeding damage.     

Identification, characterization, and developmental regulation of two storage proteins in the bamboo borer Omphisa fuscidentalis

Two insect storage proteins, OfSP1 (75 kDa) and OfSP2 (72 kDa), were purified using three different chromatographies from the hemolymph of Omphisa fuscidentalis larvae during diapause, and their genes were cloned. OfSP1 and OfSP2 concentrations in the hemolymph were high during diapause. During pupation, OfSP1 levels decreased in the male hemolymph and disappeared from the female hemolymph. OfSP1 and OfSP2 mRNA levels in the fat bodies were low during the third instar, but increased greatly during the fourth and fifth larval instars. During diapause, mRNA expression continued at a lower level than during the feeding period. The injection of 20-hydroxyecdysone (20E) into diapausing larvae caused an increase in OfSP1 and OfSP2 mRNA levels 2-3 days post-injection, followed by a decrease in expression until pupation, which occurred 2-4 days thereafter. When larvae were treated with juvenile-hormone analog (JHA), OfSP1 and OfSP2 mRNA levels gradually decreased until the onset of pupation. In Omphisa, OfSP1 and OfSP2 proteins are produced and released by the larval fat bodies in the fourth and fifth-instar larvae, and the proteins accumulate in the hemolymph until the insects enter diapause. OfSP1 may be reabsorbed by the fat bodies at the end of diapause for subsequent re-use during pupation.     

Day‐Night Vertical Distribution and Feeding Patterns of Fourth Instar ofChaoborus Larvae in a Neotropical Reservoir (Socuy Reservoir,Venezuela)

The day‐night vertical distribution, diel feeding activity and diet of fourth instar of Chaoborus larvae were analyzed in lacustrine zone of a neotropical reservoir which shows seasonally contrasting hypolimnetic oxygen conditions. Larvae stayed in sediment and water bottom during day and ascended to surface during night. Results indicate that feeding activity is limited mainly to the plankton population. Phytoplankton, rotifers or remains of Chaoborus larvae were not found in crops. With the exception of ostracods, all crustacean prey available in the zooplankton occurred in the guts. Ceriodaphnia cornuta and Moina micrura were the most frequent food items (about 75% of occurrence frequency) and were positively selected. The remainder crustacean zooplankton taxa were negatively selected by larvae. The most intense feeding activity in larvae occurred near midnight and sunrise, in dates when the hypolimnion was anoxic. When oxygen was available on the bottom, a higher and not changing diel feeding activity was detected. Our results indicate that vertical migration may promote a spatial separation between larvae and zooplankton, and feeding activity of larvae occurred only when both overlapped. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Insights into How Longicorn Beetle Larvae Determine the Timing of Metamorphosis: Starvation-Induced Mechanism Revisited

Larvae of holometabolous insects must determine the timing of their metamorphosis. How they determine this timing has only been studied in detail for a few insect species. In a few species of Coleoptera, starvation is known to be a cue for metamorphosis, leading to the formation of smaller adults (starvation-induced pupation, SiP). We investigated the occurrence of SiP in the beetle Psacothea hilaris. When P. hilaris larvae were starved late in the feeding phase of the last (5th) instar, they exhibited typical SiP characterized by constancy of the time from food deprivation to pupation (TTP) irrespective of the body weight upon food deprivation or the length of prior feeding. In contrast, when larvae were starved early in the feeding phase, TTP decreased by roughly 1 day as the feeding became 1 day longer. The change in the response to starvation was estimated to occur on day 5.9 in the last instar. A series of refeeding experiments suggested that whereas SiP occurred readily in the larvae starved in the late feeding phase, activation of SiP was suspended until day 5.9 in the larvae starved early in the feeding phase. When P. hilaris larvae were fed continuously, they eventually ceased feeding spontaneously and pupated. The time length between spontaneous cessation of feeding and pupation was approximately equal to the TTP in SiP. This suggests that the same mechanism was activated by food deprivation in the late feeding phase and by spontaneous cessation of ad libitum feeding.