Diapause Larvae Research Articles

In vitro synthesis and secretion of lipophorin by the fat body of nondiapause and prediapause larvae of the southwestern corn borer, Diatraea grandiosella

The capacity of the fat body of nondiapause, prediapause and diapause larvae of the southwestern corn borer, Diatraea gradiosella, to synthesize and release lipophorin was examined in vitro using [ 3H]leucine as the radiotracer. Synthesis and release of [ 3H]lipophorin by the fat body peaked in 11–13 day-old fifth instar nondiapause larvae, which coincided with their feeding period. The rate of lipophorin synthesis in the fat body of newly ecdysed pupae was extremely low. Synthesis and release of [ 3H]lipophorin by the fat body of prediapause larvae occurred at the highest rates in 20–35 day-old fifth and sixth instars, and declined to virtually undetectable levels after larvae entered diapause around 40 days-of-age. Immunoprecipitation of [ 3H]lipophorin from fat body of 13 day-old nondiapause larvae that had been pulse-labeled with [ 3H]leucine showed that the half life of lipophorin synthesis and processing was about 40 minutes. Release of total protein and lipophorin from the fat body of 13 day-old nondiapause larvae into Grace's medium was inhibited by 56 and 60%, respectively, when 10 μg/ml tunicamycin was incorporated into medium.

Parasitization of Diatraea lineolata Pupae and Diapausing Larvae by Several Exotic Parasites

The neotropical cornstalk borer (NCB), Diatraea lineolata (Walker), is a widely distributed species of the economically important genus Diatraea (Lepidoptera: Pyralidae) (Rodriguez-del-Bosque et al. 1988). A recent study on the parasitization of NCB in the corn agroecosystem of northern Tamaulipas, Mexico, revealed a minimal impact of native parasites. No pupal parasites were detected, and only three larval parasites appeared sporadically causing negligible levels of parasitization. The braconid larval parasite Cotesia flavipes (Cameron) was introduced into the corn agroecosystem of northern Tamaulipas in 1985, and rapidly became the most important parasite of both NCB and the sugarcane borer, D. saccharalis (F.) (Rodriguez-del-Bosque 1988). However, the impact of this exotic parasite was greatest on D. saccharalis, dictating the need for introduction of additional natural enemies against NCB. The successful establishment of potential parasites in this area could be limited by their ability to develop on diapausing NCB larvae, which are present during both summer and winter. Diapause of NCB is characterized by a change from a spotted to an immaculate morph, triggered by host plant maturation (Rodriguez-del-Bosque 1988). We investigated the suitability of NCB pupae and diapausing larvae to several exotic parasites. This report serves as a precursor for further detailed investigations and as a guide for selecting the best parasites for trial colonization. Small-scale laboratory tests were conducted from January to May 1988 to determine the host suitability of NCB to several exotic larval and pupal parasites, cultured at the Biological Control Facility, Department of Entomology, Texas A&M University, as part of a biological control program aimed at graminaceous stalkborers in Texas. Diapausing NCB larvae used in the tests were field collected from maturing cornstalks in Rio Bravo, Tamaulipas, Mexico, placed in 20-ml cups with artificial diet (Martinez et al. 1988), and transported to College Station, Texas. Pupae (1-2 days old) were obtained from a NCB colony maintained in College Station (Rodriguez-del-Bosque 1988). Larval parasites tested included the braconids Digonogastra kimballi (Kirkland) and Allorhogas pyralophagus Marsh from Mexico, C. flavipes and Rhacanotus roslinensis Lal from Pakistan, Apanteles minator Muesebeck from Bolivia, and the bethylid Goniozus natalensis Gordh from South Africa. The braconids all developed successfully on nondiapausing (spotted) NCB larvae in preliminary trials. Goniozus natalensis was not tested against nondiapausing NCB larvae. Pupal parasites were the eulophids Trichospilus diatraeae Cherian & Margabandhu from India (founder culture obtained from Florida, U.S.A.) and Pediobiusfurvus Gahan from Kenya, and the ichneumonid Xanthopimpla stemmator Thunberg from Asia (founder culture obtained from Mauritius). Although T. diatraeae has previously been reared from NCB pupae (Bennett & PschornWalker 1970), information on parasitization, emergence, progeny, and developmental time was not reported. Twenty hosts (pupae or diapausing larvae) were used to determine NCB suitability and developmental time (host exposure to adult parasite emergence) for each parasite, except X. stemmator, in which 81 pupae were used. Host larvae and pupae were held at constant 26-+?0.5?C and 14:10 (L:D) photoperiod during and after exposure to parasites. Host larvae were exposed for 24 h to >20 parasite females held in Plexiglas cages

Efficiency of phosphine and combinations of phosphine with carbon dioxide against Khapra Beetle larvaeTrogoderma granarium everts. (Col., Dermestidae)

Investigations conducted in the laboratory for comparing the efficacy of phosphine with that of mixtures of the gas plus carbon dioxide against diapause larvae ofTrogoderma granarium showed that addition of varying concentrations of CO2 (20, 50, 75 and 100%) to fixed PH3-concentrations had a negative influence on phosphine efficacy against diapause larvae of Khapra Beetle at 30°C for short exposure periods of 18 and 24 hours. On the other hand, it was found that for longer exposure periods of 48 and 72 hours, the addition of CO2 to phosphine induced significantly higher larval mortality than that by PH3 alone, whereby an additive effect was proved for mixtures contained PH3+75% and 100% CO2. The addition of 20% and 50% CO2 to PH3 at 20°C did not show any increase in larval mortalities of the mixtures for exposure periods between 24–96 hours. The larval mortalities obtained for an atmosphere contained 20 and 50% CO2 alone at 20 and 30°C was (0–6%) and (10–40%), respectively, after 10 days exposure period.

Phenology and fecundity of maize stalk borer Busseola fusca (Fuller) in Awassa, Southern Ethiopia

Three generations of the maize stalk borer, Busseola fusca (Fuller) per year were observed in maize fields in Southern Ethiopia. However, the third generation was not important on maize. The first generation developed on young maize plants during the wetseason (April–July). The second generation occurred in July and majority of larvae went into diapause from September to February while a small proportion pupated in the months of September and October and gave rise to a third generation. Pupation of the diapause larvae was observed in April.

Imaginal Wing Disks and Larval Diapause of the Southwestern Corn Borer, Diatraea grandiosella (Lepidoptera: Pyralidae)

The development of imaginal wing disks was studied in nondiapause, diapause, and postdiapause larvae of the southwestern corn borer, Diatraea grandiosella Dyar. In nondiapause last instars, the development of wing disks is continuous and fast, whereas in diapause larvae, development is arrested at a stage equivalent to that of nondiapause larvae in day 1 of their last stadium. When diapause larvae (96 d of age, 23°C) were transferred to diapause-terminating conditions, wing disk development resumed 7 d later.

In vitro release of lipophorin from the fat body of nondiapause and diapause larvae of the Southwestern corn borer, Diatraea grandiosella

The release of lipophorin and total protein was examined from the fat body of nondiapause and diapause larvae of the southwestern corn borer, Diatraea grandiosella, incubated in vitro in Grace's medium. The characteristics of the released lipophorin were compared to those of the high-density lipophorin present in the hemolymph of nondiapause and diapause larvae. Over a 4 h incubation period, the fat body of nondiapause larvae released about 1.5 times more total protein and 2 times more lipophorin per mg dry weight than did that of diapause larvae. Lipophorin isolated from the medium in which fat bodies of nondiapause and diapause larvae had been incubated and from the plasma of nondiapause and diapause larvae had similar mean densities of 1.115, 1.112, 1.117 and 1.119 g/ml, respectively. Although the lipid classes detected in lipophorin isolated from the fat body incubation medium and hemolymph were identical, more polar lipids and less diacylglycerol were associated with lipophorin isolated from fat body incubation medium then were associated with lipophorin isolated from the hemolymph. Sterols accounted for about 11% of the total lipids of lipophorin isolated from the fat body incubation medium, whereas they accounted for about 20% of the total lipids of lipophorin from hemolymph. We conclude that the fat body of feeding nondiapause larvae and nonfeeding diapause larvae releases high-density lipophorin.

Relationship between the fatty acids of fat body triacylglycerol and lipophorin diacylglycerol of non‐diapause and diapause larvae of the southwestern corn borer, Diatraea grandiosella

AbstractThe fatty acids of the triacylglycerol reserves in the fat body and of the diacylglycerol of lipophorin in the hemolymph of non‐diapause and diapause larvae of D. grandiosella were compared. For both non‐diapause and diapause larvae palmitate, palmitoleate, oleate, and linoleate were the predominant fatty acids present in fatty body triacylglycerol, and palmitate, oleate, and linoleate were the predominant fatty acids present in lipophorin diacylglycerol. However, differences were detected in the relative amounts of oleate and linoleate present in lipophorin diacylglycerol of non‐diapause and diapause larvae. The relative amount of linoleate in lipophorin diacylglycerol declined during diapause, whereas that of oleate remained relatively high during diapause. The fatty acid profile of lipophorin diacylglycerol from non‐diapause larvae treated with a juvenile hormone analog to induce a diapause‐like state more closely matched that of diapause larvae than that of non‐diapause larvae. The differences detected in the fatty acid composition of lipophorin diacylglycerol in non‐diapause and diapause larvae appear to be due mainly to the different physiological states rather than to the different rearing temperatures employed. The results are discussed in relation to the essential role fatty acids, especially oleate, play in the survival of diapause larvae.

Survival of maize stalk borer, Busseola fusca (Fuller), in crop residues in Ethiopia

The importance of maize crop residues, stalks and stubble after harvest as sources of maize stalk borer, Busseola fusca (Fuller) survival during the dry season was assessed in 1984 and 1985 on 50 peasant farms in Awassa (Ethiopia). Residues of various length were examined and the presence of diapause larvae was confirmed in all sizes, but significantly more larvae were in longer stalks. Placing infested maize stalks horizontally for 4 weeks, or sorghum stalks horizontally for 2 weeks, was effective in reducing carry-over populations of B. fusca, so the recommended practice of spreading stalks in the field throughout the dry season or burning them completely to kill diapause larvae would not be necessary in Awassa. In contrast, stalks stored upright in stacks immediately after harvest contained the highest number of live larvae during the dry season and proved to be the major source of carry-over populations.

Characteristics of the larval diapause in Ctenucha virginica (Lepidoptera: Arctiidae)

Ctenucha virginica (Esp.), a univoltine species in Québec, overwinters as a late-instar larva. Larvae brought into the laboratory between October and February and placed at 25°C under 16 h light-8 h dark, showed reduced feeding, diurnal movement, diurnal oxygen consumption, and developmental rates when compared to larvae collected in the spring. However, C. virginica displayed no seasonal variation in nocturnal metabolic rates or activity levels. Furthermore, the oxygen consumption of larvae in diapause was temperature dependent, with Q 10s varying from 2.7 (nocturnal) to 4.0 (diurnal). The ability to overwinter in any one of three larval instars may help C. virginica to synchronize its diapause initiation with the onset of low temperatures. This is especially important for C. virginica, as larvae held at 25°C under 16 h light-8 h dark during diapause died, probably due to a high metabolic rate coupled with a reduced food intake.

北海道十勝産マメシンクイガ越冬幼虫の休眠消去条件

北海道十勝産マメシンクイガ越冬幼虫の休眠消去条件

Cold tolerance and factors affecting the duration of diapause in Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The duration of diapause in larvae of Ephestia kuehniella was studied in 10 population samples from flour mills or unheated stores in England, Egypt, Finland and Japan, and a laboratory stock from Japan under 11 combinations of temperature and photoperiod. The length of diapause varied considerably with little synchronization of pupation at any of the constant conditions tested but when larvae were transferred to 15°C LD 9:15 after 1 week at 25°C LD 16:8 there was a marked synchronization of pupation. At a constant 20°C or 25°C, the mean durations of diapause in different photoperiods ranged from 3 to 40 weeks with the majority of larvae spending at least 4 months in diapause. Larvae reared in continuous darkness remained in diapause for the longest periods, up to a maximum of 60 weeks. Cold tolerance was examined by leaving cultures of eight population samples from England, Scotland, Egypt and Japan in an unheated building over winter. All the cultures survived the winter during which a minimum mean monthly temperature of 4°C and a lowest daily minimum of 2°C were recorded. Pupal mortality, however, was high in some stocks. In laboratory experiments on the Scottish strain, 80% of diapausing larvae survived an exposure of 4 weeks at −2.5°C, whilst only 10% of non-diapausing larvae did so. These observations underline the importance of diapause as a factor to be considered when drawing up programmes for the control of Ephestia keuhniella Zeller.

Quantitative structure-activity studies of benzoylphenylurea larvicides: III. Effects of substituents at the benzoyl moiety

The larvicidal activity of 2-substituted- and 2,6-disubstituted-(4-chlorophenyl)ureas against rice stem borers ( Chilo suppressalis) and silkworms ( Bombyx mori) was measured by topical application under conditions in which oxidative metabolism was eliminated using piperonyl butoxide. The substituent effects at the benzoyl moiety on the activity were analyzed quantitatively using physicochemical parameters and regression analysis. The substituent parameter for the electron withdrawal from the side chain was estimated taking into consideration the steric inhibition of the resonance of ortho substituents. The results indicated that the larvicidal activity was enhanced by electron-withdrawing and hydrophobic substituents and lowered by bulky groups. The effect of substituents at the benzoyl moiety on activity was about the same for rice stem borers and silkworms. In vitro inhibition of the same series of compounds against new cuticle formation was also measured using cultured pieces of integument of diapause larvae of the rice stem borer. In vitro activity was linearly related to in vivo activity after allowing for the hydrophobic factor that may contribute to transport.

Diapause Prevention in Aphidoletes aphidimyza (Diptera: Cecidomyiidae) by Low-intensity Light

Low-intensity radiation at night prevented diapause in larvae of the predatory midge Aphidoletes aphidimyza (Rondani) under environmental conditions (9:15 [L:D] photoperiod and 2l:l5°C [T:C] thermoperiod) that induced 100% diapause when “night” was dark. Diapause incidence was negatively related to radiation per unit area at levels 50% of larvae within a 10-m radius.

GENETIC SELECTION FOR AND EVALUATION OF NONDIAPAUSE LINES OF PREDATORY MIDGE, APHIDOLETES APHIDIMYZA (RONDANI) (DIPTERA: CECIDOMYIIDAE)

AbstractFour lines of Aphidoletes aphidimyza (Rond.) were selected for nondiapause (one for 50 generations) under L:D 8:16 and 21 ± 1°C. In three selected lines, diapause incidence dropped rapidly in the first four or five generations, with means of 3–11% thereafter. There was no clear response to selection in the fourth line. Neither morphology nor sex ratio was affected by nondiapause selection in any lines, nor was fecundity affected in the longest-reared line. Reciprocal crosses indicated that the diapause trait was dominant; the effect of relaxing selection pressure was a gradual increase in diapause incidence after eight generations. There was a correlation between increased diapause incidence and slower development in selected lines. Diapause larvae took longer to develop than nondiapause larvae from the same line. Selection for nondiapause under L:D 8:16 with fluctuating thermoperiods was unsuccessful.

Immunocytochemical localization of gastrin/CCK- and insulin-like immunoreactive cells in the brain of active and diapause larvae of the pink bollworm [formula omitted] saunders (lepidoptera)

Immunocytochemical localization of gastrin/CCK- and insulin-like immunoreactive cells in the brain of active and diapause larvae of the pink bollworm [formula omitted] saunders (lepidoptera)

TOXICITY OF PHOSPHINE TO TROGODERMA VARIABILE BALLION (COLEOPTERA: DERMESTIDAE)

AbstractThe susceptibility to phosphine of larvae and also whole cultures of the warehouse beetle, Trogoderma variabile, was investigated using strains collected from outbreaks of the pest in Australia. The LD99 for active larvae of 1 strain was found to be 6.7 ghm−3 at 25° C for a 20 h exposure. The LD99 for 3 strains of larvae in diapause was substantially greater than for the active larvae investigated, ranging from 24–59 ghm−3 under the same conditions and 4–6 ghm−3 after 120 h exposure. It took at least 42 d for the batches of larvae in diapause to reach end point mortality after exposure to phosphine. Active whole cultures of T. variabile were completely killed with an exposure of 43 ghm−3 at 20° C for 5 d, while whole cultures of larvae in diapause did not survive 25 ghm−3 under the same conditions. The minimum rate resulting in complete control under those conditions was not determined. The dosage mortality data obtained indicate that the dosages for phosphine currently recommended for stored product pest control in grain in Australia are adequate for control of T. variabile.

Studies on the toxicity of phosphine to tolerant stages of Trogoderma granarium Everts (Coleoptera: Dermestidae)

Tests were conducted at 20 and 30°C at 60% r.h. to find the dosages of phosphine needed for control of diapausing larvae and eggs of Trogoderma granarium. At 20°C, 60% r.h., some larvae from each of four recently acquired field strains of T. granarium survived a 5-day exposure period at a concentration-time ( Ct) product of 164 g hr/m 3. Under these conditions laboratory stock larvae were killed by a 4-day exposure period of about 120 g hr/m 3, and eggs by a 3-day exposure of about 50 g hr/m 3. Eggs, aged 0–1 days, proved the most tolerant stage at 30°C, 60% r.h., surviving a Ct-product of 16 g hr/m 3 over a 2-day exposure period. At 30°C the diapause of larvae became unstable and their tolerance of phosphine was low. Adults emerging after fumigation of larvae appeared normal and if sufficient numbers emerged together a second generation was produced. Complete control of larvae of several stocks (about 20 weeks in diapause) was achieved within a 4-day exposure at 20°C with a mixture of methyl bromide (2.0 g/m 3) and phosphine (1.4 g/m 3), whereas 6 days were required for these stocks using phosphine alone. To ensure elimination of all stages of non-resistant T. granarium, exposures to phosphine should last 7 days at 20°C and 4 days at 30°C.

Early development of Dermacentor variabilis (Acari: Ixodidae) in Nova Scotia

Compared with Massachusetts populations, early development of Dermacentor varibilis is accelerated during the cool spring and summer in Nova Scotia. At 15 °C the preoviposition periods of D. variabilis from Nova Scotia and Massachusetts were 27.2 and 34.0 days, respectively; at 18°C eggs hatched at 61.5 ± 2.08 and 72.4 ± 1.95 days, respectively. This decreased development time in Nova Scotia allows for the production of diapause larvae during late August.

Tufted Apple Budmoth (Lepidoptera: Tortricidae): Photoperiodic Induction of Larval Diapause and Stages Sensitive to Induction 1

A photoperiodically controlled larval diapause of the short-day, long-day type was identified in tufted apple bud moth, Platynota idaeusalis (Walker). Pupae obtained from diapause and nondiapause larvae reared at 21°C were similar in weight; however, heart rates of diapause larvae were significantly lower than those of nondiapause larvae. Induction of larval diapause was dependent upon both photoperiod and temperature. The critical short-day photoperiod at 21°C was between 1 and 3 h for a Pennsylvania strain. The long-day critical photoperiod at 21°C was ca. 14 h for both Pennsylvania and North Carolina strains. Diapause at a short daylength was averted entirely at 32°C in a Pennsylvania strain. There was no difference in the incidence of diapause in progeny of adults and eggs reared under naturally decreasing short daylengths versus a constant daylength. Sensitivity to a diapause-inducing photoperiod did not occur at any one particular stage in larval development. A maximum of 39% diapause occurred when four of the five larval instars were exposed to a short daylength, and 100% diapause occurred when all five instars were exposed to a short daylength.

Regulation of juvenile hormone esterase activity in the European corn borer, Ostrinia nubilalis

The regulation of juvenile hormone esterase in last-instar diapause and nondiapause larvae of Ostrinia nubilalis was investigated using topically applied juvenile hormone I and a juvenile hormone mimic, methoprene. The influence of the head on juvenile hormone esterase was also investigated. Both juvenile hormone and methoprene caused increases in esterase levels when applied to feeding animals. Neither the hormone nor methoprene was capable of elevating nondiapause esterase activity to levels comparable to those found in untreated prediapause larvae. The esterase levels could be elevated in the larval body, without the head, during prepupal development of nondiapause larvae and in post-feeding diapause larvae. In both cases, juvenile hormone or methoprene induced juvenile hormone esterase activity in head-ligated animals. Topically applied methoprene prolonged feeding and delayed the onset of diapause. When methoprene was applied to larvae that had entered diapause, it disrupted diapause by inducing a moult.