Critical Daylength For Diapause Induction Research Articles

Exploiting diapause and cold tolerance to enhance the use of the green lacewing Chrysopa formosa for biological control

Knowledge of environmental regulation of diapause in the green lacewing Chrysopa formosa, an important polyphagous predator against various pests, is essential for understanding seasonal adaptations of insects and for increasing the shelf-life and shipment of chrysopids used in biological control programs. In the present study, we identified environmental factors responsible for induction and termination of diapause and cold tolerance in this chrysopid. C. formosa exhibits a facultative, prepupal diapause within its cocoon. The free-living third instar larva is the stage most sensitive to photoperiodic stimuli. Photoperiod is the major factor governing the induction of prepupal diapause, and temperature exerts a modulating effect. Photoperiodic response curves for C. formosa showed a typical long day response over a wide range of temperatures. Critical daylength for diapause induction was estimated to be 14.3 h at 20 °C, with a shift towards short daylengths at higher temperatures. The diapause response was maximal with a short daylength of 8L: 16D at 18 °C or 20 °C, and no diapause was induced under 16L: 8D at any temperature examined. Chilling temperature had a pronounced effect on the completion of diapause termination and post-diapause development. A chilling period of 60 days or more at 5 °C was sufficient to terminate diapause in most prepupae. An increase of chilling exposure duration synchronized post-diapause development and adult emergence. What was particularly attractive is that diapausing chrysopids could be stored at 5 °C as long as 300 days with high survival and short adult emergence time. The developmental period prior to diapause was extended significantly for diapause-destined chrysopids. Prepupal diapause in C. formosa distinctly enhanced the cold tolerance. These results suggest mechanisms that could be exploited to improve shelf-life and long distance shipment of chrysopids for release in biological control program.

Diapause Induced by Temperature and Photoperiod Affects Fatty Acid Compositions and Cold Tolerance of Phthorimaea Operculella (Lepidoptera: Gelechiidae).

To find out the potential condition for diapause induction in the potato tuber moth Phthorimaea operculella (Zeller), combination of constant temperatures (15, 20, and 30°C) and photoperiods (8, 9, 10, 11, 12, 14, and 16 h) were employed from egg to adult emergence. In addition, changes in the total phospholipid fatty acid content and cold tolerance of non-diapausing and diapausing pupae were examined. The critical daylength for diapause induction were 12.43 h at 20°C and lower temperatures that can induce in 50% of population. Moreover, the composition of total phospholipid fatty acids in the pupae revealed seven major fatty acids in both non-diapausing and diapausing pupae: oleic (26-32%), palmitic (21-29%), linoleic (18-21%), palmitoleic (4-10%), stearic (9%), linolenic (7-8%), and pentadecanoic acids (3-5%) with an increase in proportion of unsaturated fatty acids in diapause state. In contrast to increase of oleic acid (C18:1) from 26 to 32% in non-diapausing to diapausing pupae, a decrement trend from 29 to 21% in palmitic acid (C16:0) was observed at the same state. Additionally, supercooling point was observed to be significantly lower in diapausing (-22.6°C) than in non-diapausing pupae (-18.5°C) and the fresh weight of diapausing pupae was found to be significantly higher than non-diapausing ones. The significance of these findings would allow us a better understanding of interrelationship between diapause and cold tolerance.

Geographic Variation of Diapause Induction and Termination in the Spider Mite Tetrαnychus urticαe: Α mini-review

In eight strains of the spider mite Tetranychus urticae Koch (Acari: Tetranychidae), originating from different localities in Europe, the critical daylength for diapause induction and termination was almost the same in each strain but varied with the latitudinal origin of the strains; critical daylength was shorter in strains originating from lower latitudes and longer in those from higher latitudes. Diapause intensity, measured as the period of chilling required for diapause termination under a short day photoperiod (LD 10:14) and 19°C, again varied with the latitudinal origin of each strain, being higher the more northern the origin of the strain. An exception were two mountain strains which showed a longer critical daylength and a deeper diapause than expected on the basis of their latitudinal origin. The number of long-day (LD 17:7) cycles required for 50% diapause termination after a certain period of chilling was higher in the northern and lower in the southern strains. These results indicate that geographic strains of T urticae may differ considerably in their diapause attributes, which may be explained as an adaptation to local climatic conditions. The great plasticity of the diapause response may, among other factors, have been responsible for the wide distribution of this mite species.

Diapause Induction inGratiana boliviana(Coleoptera: Chrysomelidae), a Biological Control Agent of Tropical Soda Apple in Florida

AbstractThe South American leaf-feeding beetle Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae) has been released since 2003 in the southeastern United States to control the invasive weed tropical soda apple, Solanum viarum Dunal (Solanaceae). Successful establishment of a biological control agent in temperate and subtropical regions depends on several life-history adaptations, including winter diapause. The timing of diapause allows the syncronization of insect herbivores with the phenology of plants, and field observations in Florida suggested that G. boliviana overwinters as an adult in diapause. The objectives of this study were to describe the diapause of G. boliviana and determine the effect of temperature and photoperiod on diapause induction. Compared with nondiapause adults, diapausing adults were yellow rather than green, had hypertrophied fat bodies, contained little food in the digestive tract, showed negligible ovarian development, and minimal movement of the hind wings when the beetles were placed on their dorsal sides. Although all nondiapause females laid eggs during a 30-d period, only five of 76 diapausing females laid eggs and this occurred only during the first 15 d of the treatment period. Consistent with morphological indicators of diapause, the respiration rate was 2.3 times lower and fat content was 2–3 times greater in diapausing adults compared with nondiapause adults. In a laboratory study, the critical daylength for diapause induction was found to be 12 h:28 min.

Seasonal Timing of Diapause Induction Limits the Effective Range of <I>Diorhabda elongata deserticola</I> (Coleoptera: Chrysomelidae) as a Biological Control Agent for Tamarisk (<I>Tamarix</I> spp.)

The leaf beetle Diorhabda elongata Brullé subspecies deserticola Chen, collected in northwestern China, has been released in the western United States to control tamarisk (Tamarix spp.). While beetle establishment and saltcedar defoliation have been noted at northern study sites, this species has not established at latitudes south of the 38th parallel. Critical daylength for diapause induction was measured in the laboratory and ranged between 14 h 50 min to 15 h 08 min, depending on temperature, and adults were shown to cease reproduction and enter diapause at daylengths of 14 h 30 min or less. Critical daylength in the field was measured at approximately 14 h 39 min and occurred 13 d before 50% of the population reached diapause. South of 36 degrees 20' N, the longest days of the year are shorter than 14 h 39 min, making the beetles univoltine in the southern United States. North of 36 degrees 20' N, a window of reproductive activity opens 13 d after the critical daylength is reached in the spring and closes 13 d after it is passed in the summer, allowing at least a partial second summer generation. It is predicted that south of the 38th parallel, premature diapause will increase mortality and disrupt synchrony between the life cycle of the beetle and host plant availability. This could hinder establishment and help explain the failure of this population south of the 38th parallel, providing a rationale for testing other populations of D. elongata in the southern range of Tamarix in North America.

Effects of Sublethal Concentrations of Bacillus thuringiensis on Larval Development of Sesamia nonagrioides

In the Mediterranean Basin, developed diapausing larvae of the borer Sesamia nonagrioides Lefèbvre are found consistently during autumn in transgenic corn, Zea mays L., expressing Bacillus thuringiensis Berliner (Bt) toxins derived from event 176. These larvae can feed on sublethal concentrations of Bt toxins because the expression of this corn toxin declines after flowering. To evaluate the possible consequences of this phenomenon, the effect of sublethal concentrations of the natural toxin producer, B. thuringiensis variety kurstaki (Dipel DF) on the performance of S. nonagrioides in the laboratory was examined. Larvae treated with Dipel DF showed higher mortality, longer developmental time, extra molts, and higher sensitivity to critical daylength for diapause induction than the untreated larvae. Accordingly, diapausing larvae collected in October and February in a Bt cornfield exhibited a higher number of supernumerary molts before pupating and longer diapause development than larvae collected in a non-Bt field at the same time. These results demonstrate that deployment of Bt corn in the Mediterranean may affect both the borer performance and the development of Bt resistance in addition to direct mortality caused by the Bt toxin.

Reproductive diapause and quiescence in a tropical rice bug, Leptocorisa oratorius

AbstractExperiments were carried out to analyze the effects of food supply and photoperiod on the induction of dormancy in Leptocorisa oratorius Fabricius (Heteroptera: Alydidae) adults in Alor Setar (latitude 6.1° N), West Malaysia. When the adults were deprived of food, they ceased oviposition, became tolerant to starvation, and their oxygen consumption rate decreased, but they did not accumulate lipid. Their oxygen consumption rate again increased when they were allowed to resume feeding. Therefore, food limitation induced quiescence in the adult. On the other hand, diapause was induced by short daylength (critical photoperiod was 12L:12D), leading to immature ovaries, hypertrophied fat bodies, lipid accumulation and low oxygen consumption rate even when food was available. However, in the study area most of the bugs probably did not enter diapause at any time of the year, because the shortest outdoor daylength including civil twilight was longer than the critical daylength for diapause induction.

Photoperiodic induction of the first and the second diapause in the bean bug, Riptortus clavatus: a photoperiodic history effect

In nondiapause adults raised under a long-day photoperiod, the critical daylength for diapause induction was between 13 and 14 h although some individuals did not respond to the short-day photoperiod and went on laying eggs. In postdiapause adults in which LD 13∶11 induced the first diapause (L13 insects), the critical daylength for diapause reinduction was between 13 and 14 h, whereas it was between 12 and 13 h in postdiapause adults in which LD 10∶14 induced the first diapause (L10 insects). Under LD 13∶11, a small proportion of L10 insects went into the second diapause after great delay as compared with L13 insects. Under LD 10∶14, on the other hand, L10 insects went into the second diapause more rapidly than L13 insects. Therefore, the photoperiod which had induced the first diapause affected the photoperiodic induction of the second diapause not only in the critical daylength but also in the speed of response. In Riptortus clavatus, the photoperiodic history influences the subsequent photoperiodic response even after a physiological state induced by the previous photoperiod was terminated completely.

EFFECT OF FOOD AND PERHAPS LARVAL CROWDING ON DIAPAUSE INITIATION IN TUFTED APPLE BUD MOTH (LEPIDOPTERA: TORTRICIDAE)1

Larvae from a laboratory strain of tufted apple bud moth, Platynota idaeusali (Walker), were reared on semisynthetic diet and excised apple leaves while exposed to naturally-decreasing daylengths. Leaf-reared larvae showed a higher incidence of diapause than larvae reared on diet. The critical daylength for diapause induction in leaf- and diet-reared larvae occurred at ca. 14.8 and 14.3 h, respectively. Larvae reared on semisynthetic diet and exposed to naturally-decreasing daylengths were subjected to different levels of crowding. As the number of individuals reared together in the same container increased, the incidence of diapause increased. Separation of the effects of larval crowding from any possible effects of the quality of the semisynthetic diet on diapause induction was not attempted.

Geographic variation in the circadian system controlling photoperiodism inOstrinia nubilalis

1. The critical daylength for diapause induction is temperature dependent in three geographic strains ofOstrinia nubilalis. Critical daylength increases as the temperature is lowered, as does the general level of diapause. 2. The critical daylength and general level of diapause are also strain dependent at two constant temperatures (20 °C and 30 °C). The northern strain shows a longer critical daylength than the southern strains. The northern strain also shows a greater tendency to diapause at both temperatures. 3. Whether or not Nanda-Hamner experiments yield positive (induction of diapause rising and falling approximately every 24 h) or negative (nonrhythmic) results is a function of the strain being examined and the temperature of the experiment. The northern strain shows a nonrhythmic hourglass response at 20 °C but circadian periodicity at 30 °C. Conversely, southern strains show a nonperiodic pattern at 30 °C but circadian periodicity at 20 °C. 4. The results from Nanda-Hamner experiments are compatible with the pacemaker-slave model for circadian rhythmicity and photoperiodism recently proposed by Pittendrigh (1981).

Induction and Termination of Diapause in the Sugarcane Borer1,2

Populations of the sugarcane borer, Diatraea saccharalis (F.), in the Lower Rio Grande Valley of Texas were found to enter facultative diapause as last-stage larvae. The peak incidence of diapause in sugarcane fields occurs in Nov. or Dec. Both induction and termination of diapause are dependent upon photoperiod and temperature. A high incidence of diapause is induced when the insects experience both low temperatures and short photophase. The critical day-length for diapause induction at 21°C is between 12 and 13 h of light. Diapause termination is accelerated by increasing both temperature and photoperiods.