Number Of Instars Research Articles

Host stage preference ofDolichogenidea tasmanica(Cameron, 1912) (Hymenoptera: Braconidae), a parasitoid ofEpiphyas postvittana(Walker, 1863) (Lepidoptera: Tortricidae)

Epiphyas postvittana (Walker, 1863), or light brown apple moth (LBAM), is a highly polyphagous native Australian species and a major insect pest in Australian vineyards. Dolichogenidea tasmanica (Cameron, 1912) is the most abundant parasitoid of the larval stages of LBAM. The prime objective of our study was to determine the parasitism success of D. tasmanica on different larval stages of E. postvittana. Additionally, we aimed to find out if larval head capsule width could be used to determine the instar number by examining the variability in head capsule size of each instar of LBAM and the effect of rearing temperature on larval head capsule size. To determine which of the first three larval stages of LBAM parasitised is most effectively by D. tasmanica, choice and no-choice tests were conducted in a wind tunnel. Head capsule widths varied with rearing temperature, especially in the final fifth or sixth instar. We showed that the ranges of head capsule widths overlaps between successive instars three through six, which makes it impossible to distinguish these instars of LBAM using head capsule size alone. We showed that first, second and third instars of LBAM are parasitised by D. tasmanica. No-choice and choice tests revealed that there are significant differences in parasitism among the three susceptible instars, with the highest percentage of parasitism found in second instars in no-choice and choice tests (65.1% and 65.8%, respectively) compared with first instars (61.1% and 45.1%) and third instars (27.3% and 37.5%). Wasps developed faster in third instars, but the wasp female's size was not significantly different among the instars attacked. These data confirm that D. tasmanica is capable of parasitising early larval instars, which is important for minimising damage through biological control.

Developmental constraints in cave beetles.

In insects, whilst variations in life cycles are common, the basic patterns typical for particular groups remain generally conserved. One of the more extreme modifications is found in some subterranean beetles of the tribe Leptodirini, in which the number of larval instars is reduced from the ancestral three to two and ultimately one, which is not active and does not feed. We analysed all available data on the duration and size of the different developmental stages and compared them in a phylogenetic context. The total duration of development was found to be strongly conserved, irrespective of geographical location, habitat type, number of instars and feeding behaviour of the larvae, with a single alteration of the developmental pattern in a clade of cave species in southeast France. We also found a strong correlation of the size of the first instar larva with adult size, again regardless of geographical location, ecology and type of life cycle. Both results suggest the presence of deeply conserved constraints in the timing and energy requirements of larval development. Past focus on more apparent changes, such as the number of larval instars, may mask more deeply conserved ontogenetic patterns in developmental timing.

Determining the instar of a weevil larva (Coleoptera: Curculionidae) using a parsimonious method

Tracking the larval development of an insect is important in both applied and basic ecology. Yet, it is difficult to discriminate between the different larval instars of holometabolous insect species, particularly in the field. The methods currently available are of limited use as they rely on an a priori determined size distribution of every immature instar and are irrelevant whenever the distributions of two instars actually overlap. We developed a model that computes, for a given species, the most probable instar of a larva based on its individual head capsule width and the size distribution of the last larval instar. The model presented here is specifically for species of curculionid that develop through four immature instars, but can be adapted for species of weevil with a different number of instars or insects of other taxonomic units. Our method computes the risk error associated with assigning a larva to any of the possible instars and might not assign a larva if its size falls within the overlapping zone of the size distributions of two successive instars. Thus, this parsimonious method might be widely used, notably for wild-caught larvae, and can be readily used thanks to the R package CINID that we developed for that purpose.

Growth and development in a lepidopteran with variable instar number, Pseudocoremia suavis (Geometridae), under standard rearing conditions and when parasitised by Meteorus pulchricornis (Hymenoptera: Braconidae)

Though extra instars are often associated with poor conditions and thought to be a compensation for a low growth rate, the reasons why they are necessary, and for variable instar number existing under standard rearing conditions, are not yet clear. In standard rearing conditions, approximately half of Pseudocoremia suavis larvae had five instars (Type I larvae), and half six instars (Type II larvae). Type II larvae took longer to pupate and reached higher pupal weights than Type I larvae. The extra instar was not related to sexual size dimorphism; Type II larvae were not more likely to be females. Females of both Types pupated later than males and had higher pupal weights; this weight gain was achieved wholly via an extended final instar. Relative growth rates (RGR), instar durations and larval weights on weigh days were otherwise the same for both sexes. For most of the larval period, Type II larvae had lower RGR and lower weights than Type I larvae. They also had shorter 3 rd , 4 th and 5 th instars than Type I larvae, and the estimated weights at each moult were significantly lower. The Types are discussed in terms of being, in species with weight thresholds for pupation, not optional strategies involving different critical weight ratios for larval moults, but as an inevitable consequence of physiological timing con- straints upon reaching the critical weights for larval moults causing large variation in size after the moult. Small larvae may then need an extra instar to reach pupation. When parasitised in the second instar by Meteorus pulchricornis, P. suavis larvae produced parasitoids in either their fourth (4 th instar emerging (IE)) or fifth instar (5 th IE). The estimated moulting weights at each instar of 4 th IE and 5 th IE hosts were very similar to those of Type I and Type II unparasitised larvae respectively, which, together with similarity of instar dura- tion patterns, is strongly suggestive of Types being present within parasitised larvae. The proportion of 5 th IE hosts in the much slower- growing parasitised treatment was greater than the proportion of Type II larvae in the unparasitised treatment, as might be expected if Type II is associated with lower RGR. The lack of further Types appearing is consistent with extra instars being a compensation for small weight after the moult rather than low RGR per se.

Laboratory biology and field population dynamics of Trichopria columbiana (Hymenoptera: Diapriidae), an acquired parasitoid of two hydrilla biological control agents

The biology and population dynamics of Trichopria columbiana, a native semi-aquatic parasitoid of ephydrid flies of the genus Hydrellia, were investigated in Florida and Texas, USA. Hydrellia pakistanae and Hydrellia balciunasi were introduced for classical biological control of the invasive aquatic weed Hydrilla verticillata in the 1980s and acquired T. columbiana post-release. Several life history parameters of T. columbiana were investigated in the laboratory, including fecundity, egg shape and size, number and location of egg(s) deposited per host, preferred host age, description and number of instars, mode of respiration and host-selection behaviour. Field studies included seasonal abundance of T. columbiana and the introduced Hydrellia spp., parasitism levels, overwintering stage and adult winter sex ratio. T. columbiana is a synovigenic solitary endoparasitoid that developed from egg to adult in 21.9 ± 0.2 days under laboratory conditions. Eggs of T. columbiana are hydropic, hymenopteriform in shape and possess a double membrane. Larvae have three instars; first instars have sclerotised mandibles, bifurcated abdominal appendages and are free floating in the host’s haemolymph. Second and third instars are grub-like and remain attached to the host’s tracheal system until pupation. Individual females produced on average 23.2 ± 0.6 eggs and survived 15.6 ± 1.8 days. Highest parasitism levels of early and intermediate stage pupae occurred when wasps were 8–9 days old. Field parasitism rates of the two introduced Hydrellia spp. averaged 19.1%.

Reproductive biology and postembryonic development of a polyphagid cockroach Eucorydia yasumatsui Asahina (Blattodea: Polyphagidae)

Reproductive biology, including mating behavior, ootheca deposition, ootheca rotation, and postembryonic development, were examined and described in a Japanese polyphagid, Eucorydia yasumatsui Asahina, 1971. E. yasumatsui lacks elaborate pre-copulation behaviors, in contrast to most cockroaches. On encountering a female, the male rushes to her, chases her, touching her with his antennae, and finally the pair initiates “tail-to-tail” copulation. The ootheca bears a well-developed, serrated keel along its dorsal median line and a flange on its anterior end, which is grasped with the female’s paraprocts while she carries the ootheca. The ootheca formed in the vestibulum emerges from her caudal end, with its keel upwards. Several hours later, she rotates the ootheca clockwise by 90°, viewed from the female’s side, into a horizontal position. After rotation, she carries the ootheca, maintaining this horizontal position for a few days, and then deposits it on the ground. The number of larval instars was 9 or 10 in females and 8 or 9 in males. Addition of annuli to the antennal flagellum occurs from the 2nd instar molting onwards, and annular division occurs both in the 1st annulus of the flagellum (meriston) and in the annulus following it (called “meristal annulus” from the 3rd instar on): one to several annuli from the former and a single annulus from the latter are added. Sexes can be distinguished from the 3rd instar on according to the changes of the postabdominal structures. Regarding exposed structures, in the female the posterior margin of abdominal coxosternum VIII becomes incised medially, the abdominal coxosterna VIII and IX retract, and the styli of segment IX disappear. The male does not undergo marked externally visible changes.

The influence of per offspring investment (POI) and starvation on larval developmental plasticity within the palaemonid shrimp, Palaemonetes varians

At the inter-specific level, per offspring investment (POI), degree of abbreviated development, and lecithotrophic potential all increase with increasing latitude and freshwater penetration among crustaceans. These traits are considered adaptations to conditions of decreasing growth potential. We hypothesise that this relationship between POI and abbreviated development also occurs at the intra-specific level. We studied the caridean shrimp, Palaemonetes varians, to investigate the hypothesis that under food-limited conditions, higher POI enables development through fewer larval instars. Under starvation stress, larvae from broods of greater POI (measured as hatchling brood average dry weight, DW) generally developed through fewer larval instars. With increasing starvation period, larval development time increased, whilst larval growth rate, juvenile DW, juvenile carbon mass, and juvenile carbon:nitrogen (C:N) ratio all decreased. Larval development time generally decreased with increasing brood average dry weight. In contrast, larval growth rate, juvenile DW, juvenile carbon mass, and juvenile C:N ratio all increased with increasing larval brood average DW. The relationship between POI and larval instar number (abbreviation of development) reported here is consistent with that at the inter-specific level and supports the concept that macro-ecological trends in development modes at the inter-specific level may be driven by selection occurring on POI at the intra-specific level.

Developmental Patterns inStagmomantis limbata(Mantodea: Mantidae): Variation in Instar Number, Growth, and Body Size

Development affects many components of life history and fitness, including body size. The present study examined the influence of developmental pattern, specifically the number of nymphal instars, on body size (pronotum length) in the praying mantid Stagmomantis limbata Hahn. Mantids were reared in the laboratory from hatching, on standardized diet, to examine variation in instar number. These lab data were then used to assess developmental patterns forfield-collected female nymphs. Laboratoryreared males and females varied in number of instars. Most females required 6 nymphal instars to reach adulthood (64%), whereas 36% underwent 7 instars. Seven-instar females reached the 4th, 5 th, and 6th instars faster than six-instar females, but had shorter pronota than the six-instar females at each of these stages. Seven-instar females were longer than six-instar females at adulthood. Interestingly, the total developmental period from hatching to adulthood was similar for lab-reared seven-instar and six-instar females. In the lab, most males (91%) underwent 6 instars, with the remaining 9% following a five-instar pattern. By the 4th instar, differences between the sexes began to appear. From the 4th instar onwards, females typically took less time than males to reach each instar. From the 5th instar onwards, females were longer than the males, and were longer as adults. Variation in developmental pattern (number of instars) was evident among siblings from the same ootheca; such intra-clutch variability in number of instars may be a bet-hedging strategy by ovipositing females in a variable environment. The laboratory data allowed for the detection of six-instar and seven-instar patterns among the field-collected females. The field-collected data suggest that females undergoing 6 nymphal instars reach adulthood later in the season, and at smaller body size, than seven-instar females.

Complete tribal sampling reveals basal split in Muscidae (Diptera), confirms saprophagy as ancestral feeding mode, and reveals an evolutionary correlation between instar numbers and carnivory

With about 5000 species in ca. 180 genera, the Muscidae is the most species-rich family in the muscoid grade of Calyptratae (Diptera: Cyclorrhapha), the others being the Fanniidae, Scathophagidae and Anthomyiidae. Muscidae is remarkable for its young age, high species diversity in all biogeographic regions, and an unusually diverse range of feeding habits at the larval stage (e.g., saprophagy, phytophagy, carnivory, endoparasitism, haematophagy). We here review muscid classification and biology and present a molecular phylogeny based on four mitochondrial genes (12S, 16S, COI, CYTB) and three nuclear genes (28S, Ef1a, and CAD) for 84 species from 40 genera. Our analysis is the first to include species from all biogeographic regions and all currently recognised muscid subfamilies and tribes. We provide strong support for the monophyly of the Muscidae, and for the first time also for the first split within this family. The ancestral larval feeding habit is reconstructed to be saprophagy with more specialised coprophagous saprophagy, phytophagy, and carnivory evolving multiple times from saprophagous ancestors. The origins of carnivory in larvae are significantly correlated with a reduction of the number of larval instars from three (ancestral) to two and one. The genus Achanthiptera which was previously in its own subfamily is shown to be closely related to Azeliini. However, it appears that Azeliinae is paraphyletic because Muscinae is sister-group to the Azeliini while the azeliine Reinwardtiini are polyphyletic. Coenosiinae and Muscinae are monophyletic, but Muscini is paraphyletic with regard to Stomoxyini. Because many subfamilies are apparently para- or even polyphyletic, we review the history of muscid classification in order to reveal how the currently used classification originated.

Development and growth in synanthropic species: plasticity and constraints.

Urbanization poses serious extinction risks, yet some species thrive in urban environments. This may be due to a pronounced developmental plasticity in these taxa, since phenotypically, plastic organisms may better adjust to unpredictable urban food resources. We studied phenotypic plasticity in Nuctenea umbratica, a common European forest and urban vegetation spider. We subjected spiderlings to low (LF), medium (MF) and high (HF) food treatments and documented their growth and developmental trajectories into adulthood. Spiders from the three treatments had comparable numbers of instars and growth ratios, but differed in developmental periods. Longest developing LF spiders (♀ = 390, ♂ = 320days) had the smallest adults, but MF (♀ = 300, ♂ = 240days) and HF (♀ = 240, ♂ = 210days) spiders reached comparable adult sizes through shorter development. While males and females had comparable instar numbers, females had longer development, higher growth ratios, adult sizes and mass; and while males adjusted their moulting to food availability, female moulting depended on specific mass, not food treatment. We discussed the patterns of Nuctenea sex-specific development and compared our results with published data on two other Holarctic urban colonizers (Larinioides sclopetarius, Zygiella x-notata) exhibiting high plasticity and fast generation turn-over. We conclude that despite relatively unconstrained developmental time in the laboratory enabling Nuctenea to achieve maximal mass and size-main female fitness proxies-their relatively fixed growth ratio and long generation turn-over may explain their lower success in urban environments.

Life-history specialization was not an evolutionary dead-end in Pyrenean cave beetles

Research on subterranean organisms has focused on the colonization process and some of the associated phenotypic changes, but little is known on the long-term evolutionary dynamics of subterranean lineages and the origin of some highly specialized complex characters. One of the most extreme modifications is the reduction of the number of larval instars in some Leptodirini beetles from the ancestral 3 to 2 and ultimately a single instar. This reduction is usually assumed to have occurred independently multiple times within the same lineage and geographical area, but its evolution has never been studied in a phylogenetic framework. Using a comprehensive molecular phylogeny, we found a low number of independent origins of the reduction in the number of instars, with a single transition, dated to the Oligocene-Miocene, from 3 to 2 and then 1 instar in the Pyrenees, the best-studied area. In the Pyrenees, the 1-instar lineage had a diversification rate (0.22 diversification events per lineage per million years) significantly higher than that of 3- or 2-instar lineages (0.10), and similar to that seen in other Coleopteran radiations. Far from being evolutionary dead-ends, ancient lineages fully adapted to subterranean life seem able to persist and diversify over long evolutionary periods.

Postembryonic development of the ground louse Zorotypus caudelli Karny (Insecta: Zoraptera: Zorotypidae)

Based on captive breeding, the postembryonic development of the ground louse Zorotypus caudelli Karny, 1927 (Zoraptera, Zorotypidae) was examined and described in detail. The number of nymphal instars in Z. caudelli is five. During the second molt (2nd to 3rd instar), the number of antennomeres increases from eight to nine by subdivision of the basal flagellomere (meriston). Apterous and winged forms differentiate in the 4th nymphal instar. In the 4th instar of the winged form, small wing pads and small ocular spots appear. In the 5th instar, the wing pads elongate and the ocular spots are widened, and three ocelli are differentiated. Wing dimorphism may be a phenomenon independent of crowding. The two sexes closely resemble each other as in other zorapteran species, and sexual dimorphism does not appear until the final (5th) nymphal instar: in the 5th instar of males, setae increase in number on the 9th and 10 + 11th abdominal terga, and a small posteromedian swelling appears on the 10 + 11th abdominal tergum, the precursor of the mating hook. Key to nymphal instars of Zorotypus caudelli was given. The formation of thoracic pleural sclerites was examined and revaluated.

Developmental changes in the spinning apparatus over the life cycle of wolf spiders (Araneae: Lycosidae)

AbstractSpiders are characterized by their spinning activity. Much of the current knowledge of the spinning apparatus comes from studies on orb web spiders and their relatives, whereas wolf spiders have been more or less neglected in this respect. Therefore, we studied developmental changes in the spinning apparatus of four wolf spiders (Tricca lutetiana, Arctosa alpigena lamperti, Pardosa amentata, and Xerolycosa nemoralis) throughout their life cycles. Each of these lycosids has a stenochronous life cycle, but of varied length (from 1 to 3 years) and number of instars (from seven to ten). Use of the spinning apparatus begins in the first instar, after leaving the egg sac. Secondary ampullate, all piriform, and all but four aciniform glands are tartipore‐accommodated. The tartipores, collared openings through which silk gland ducts pass during proecdysis, appear on the spinning field starting with the second instar. Tartipore‐accommodated glands can function during proecdysis and their evolution corresponds with the way spiders secure themselves when molting. We suggest that the function of aciniform silk in juvenile wolf spiders is to serve as an ancillary “scaffold” supporting the spider's body during ecdysis.

Developmental characteristics of Tenebrio molitor larvae (Coleoptera: Tenebrionidae) in different instars

Tenebrio molitor is a major pest of stored grain, although its larvae have potential for use as food. However, little is known about the characteristics of individual larval instars of this species, and the number of instars remains disputed. Therefore, we assessed T. molitor for the average number of instars and its characteristics at different larval stages. The focus of this study was to establish a foundation for further studies on the characteristics of each larval instar. All of the T. molitor larvae showed incubation periods of 7 to 8 d and a period of 3 to 4 d for the <TEX>$1^{st}$</TEX> instar. Beyond the <TEX>$1^{st}$</TEX> instar, there were relatively large variations in the number of days in each instar period. Before emergence, most of the larvae had typically gone through 15 to 17 instars. The highest rate of pupae formation, 28.32%, was observed in the <TEX>$17^{th}$</TEX> instars. The body length gradually increased with each successive instar, reaching its maximum at the 17th instar. Beyond the <TEX>$17^{th}$</TEX> instar, however, the body length decreased. The larvae were white in the first instar, and gradually turned brown after the <TEX>$2^{nd}$</TEX> instar.

Life Cycle of a New Bosminid Cladocera: Bosmina (Bosmina) tripurae (Korinek, Saha, and Bhattacharya, 1999)

Bosmina tripurae was first reported as a new species of subgenus Sinobosmina (Cladocera, Bosmina) in 1999 in Tripura, India. However, no further research work was done on this species. The present investigation has been carried out to provide the basic knowledge of life history aspects of B. tripurae on its length increment, instar number, instar duration, fecundity, hatching success, life span and embryonic development. The species was cultured in the laboratory for ten generations. The experiment was conducted under controlled conditions at 20 ± 0.29 °C and animals were fed with Chlorella sp. (2 × 104 cells ml−1). Parthenogenetic female showed three preadult and ten adult instar stages. Female produced around 22 eggs in its total life span of about 25 days. The length of first instar juvenile was 261 μm and the last adult instar was 590 μm. Duration of preadult instars ranged from 1.05 to 1.27 days whereas adult instars ranged from 1.93 to 2.30 days. Age at first reproduction was about 3.65 days. The species showed maximum ten clutches in the present study however, the sixth clutch produced and released significantly (P < 0.05) higher number of both eggs and neonates as compared to other clutches. In laboratory condition, about 89 % eggs were hatched out into neonates. The gestation period of the embryo was around 2.03 days with 12 developmental stages in the brood pouch of the mother.

Correction: The Implications of Temperature-Mediated Plasticity in Larval Instar Number for Development within a Marine Invertebrate, the Shrimp Palaemonetes varians

Correction: The Implications of Temperature-Mediated Plasticity in Larval Instar Number for Development within a Marine Invertebrate, the Shrimp Palaemonetes varians

Per offspring investment implications for crustacean larval development: evolutionary insights into endotrophy and abbreviated development

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 493:207-217 (2013) - DOI: https://doi.org/10.3354/meps10496 Per offspring investment implications for crustacean larval development: evolutionary insights into endotrophy and abbreviated development Andrew Oliphant*, Sven Thatje Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK *Email: andrew.oliphant@noc.soton.ac.uk ABSTRACT: At the inter-specific level, per offspring investment (POI) is associated with larval development mode and follows a macro-ecological trend within the marine environment; higher POI and its associated greater degree of endotrophy and abbreviated development is found in cooler, high latitude regions. Here, the implications of between-brood-variation in hatchling energy content (measured as carbon mass) on larval starvation resistance and developmental plasticity within the caridean shrimp Palaemonetes varians were assessed. Results demonstrate that greater POI provides increased endotrophy and the potential for abbreviated development. In the absence of food, P. varians larvae from broods of higher hatchling energy content developed to more advanced larval stages and survived for longer before succumbing to starvation. In the presence of food, P. varians larvae from broods of higher hatchling energy content developed through fewer larval instars, showed higher growth rates, and had shorter development times. Also, for larvae developing through the same number of larval instars, larvae from broods of higher hatchling energy content developed to greater juvenile dry weight. These data support the hypothesis that macro-ecological trends in development mode are driven by inter-specific variations in POI. At the intra-specific level, phenotypic plasticity allows for environmentally mediated variations in POI. Under differential selection pressures, this flexibility may, thus, eventually permit the evolution of the diverse and complex life cycles observed in the marine environment. KEY WORDS: Carry-over effects · Evolution of lecithotrophy · Larval ecology · Palaemonidae · Palaemonetes varians · POI Full text in pdf format PreviousNextCite this article as: Oliphant A, Thatje S (2013) Per offspring investment implications for crustacean larval development: evolutionary insights into endotrophy and abbreviated development. Mar Ecol Prog Ser 493:207-217. https://doi.org/10.3354/meps10496 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 493. Online publication date: November 20, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Post-Embryonic Development inZaprionus indianus(Diptera: Drosophilidae)

AbstractThe objectives of this study were to determine the number of instars of Zaprionus indianus Gupta, 1970, a fly that is considered a pest on fig plantations; analyze the pupation process; and characterize the morphology of the immature stages. This information would fill a gap in the knowledge regarding Z. indianus development. The post-embryonic development of this species was studied by using Dyar's rule to characterize the immature stages of the fly. In addition, the morphological structures were analyzed by scanning electron microscopy. Following Dyar's rule, Z. indianus exhibited three larval instars. Pupae were formed in higher numbers during the morning, and 5 d was the average time until adult emergence. The male:female sex ratio in this population was 1:1, with a higher emergence of females during the first 72 h. During the morphological analysis, the following structures were observed: (egg) chorionic cells, respiratory filaments, and micropyle; (larvae) body segments, intersegmental spines, antennae, the maxillary palp complex, sensilla, tubercles, and anterior and posterior spiracles; and (pupae) filaments that originated in the anterior spiracles and the presence of spines along these filaments. Some of these characteristics were slightly different from those observed in other drosophilids, which provides a taxonomic quality to these characteristics. In addition, these results may facilitate future studies on the biology, ecology, and control of this species.

A meridic diet for laboratory rearing of Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

The red palm weevil (RPW) Rhynchophorus ferruginous (Olivier) was fully developed and reared on a meridic diet consisting of agar, distilled water, commercial yeast as well as laboratory produced amino and fatty acid rich brewer’s yeast (Saccharomyces cerevisiae), wheat meal, corn flour, benzoic acid, ascorbic acid, sorbic acid, vitamin mix and tetracycline hydrochloride. A group of weevils reared on date palm trunk under the same laboratory conditions was used as control. Diet reared female weevils laid fertile eggs which successfully hatched into healthy larvae in 3.6 days. Between the first and last (eighth) larval instars there was a 2311 fold increase in the larval body biomass before pupation. Linear regression analysis involving log of head capsule width of each instar and instar number resulted in a straight line (R2= 0.978) indicating that Dyar's rule is applicable in the case of RPW. Larval development was completed in 43 to 47 days while the pupa reached the adult stage in 31 to 38 days with an average of 35 day. The whole life cycle of the weevil from egg to adult, was completed in 78 to 85 days. The average adult longevity for male and female weevils was 83.3 and 74.8 days, respectively. Besides the above, important biological parameters including pre-oviposition period, incubation period, per cent egg hatchability, fecundity and larval weight gain were recorded. A food-fiber pupation technique was developed with 100% pupation efficiency. Key words: Rhynchophorus ferrugineus, meridic diet, biological parameters, food-fiber pupation technique, larval instar, Dyar's rule.

Occurrence of two different development patterns in Lobesia botrana (Lepidoptera: Tortricidae) larvae during the second generation

Abstract In north‐eastern Italy, the second‐generation larvae of Lobesia botrana (Den. &amp; Schiff.) (Lepidoptera: Tortricidae) can develop with two different time patterns. In particular, in ‘warmer’ areas, the developmental time is shorter than in ‘cooler’ areas and it is associated with an earlier and more economically important third generation. Because the differences in temperature are not sufficient to explain the two patterns, research was carried out aiming to investigate whether the differences in larval development time are the result of a different number of instars and whether the photoperiod is a factor. In the field, second‐generation larvae develop through five instars in a ‘warmer’ area and through six instars in a ‘cooler’ area. Laboratory and field data showed that decreasing photoperiod, which induces diapause, is also an important cue for inducing larvae to develop six instars. In the light of climate warming and subsequent changes in L. botrana phenology over the last 30 years, the two different development patterns are interpreted as a means to ensure the best fit of the moth to environmental conditions. In ‘cooler’ areas, third‐generation larvae might not complete development before frost or harvest, and hence second‐generation larvae develop through six instars before producing overwintering pupae.