Perry L. Adkisson

Release of prothoracicotropic hormone and potentiation of developmental ability during diapause in the bollworm, Heliothis zea

In Heliothis zea, pupal diapause is not due to a deficiency of the prothoracicotropic hormone (PTTH), as it is in many other insects. However, PTTH is essential for diapause termination and adult development. Removal of the pupal brain 4 hr after larval-pupal ecdysis blocks the insects ability to initiate adult development. Transplantation of brain neurosecretory cells restores this ability, whereas other tissues such as corpora allata have no effect. In the diapausing pupa, PTTH is released from the brain within 24 hr after larval-pupal ecdysis. Subsequent removal of the brain fails to block the ability for diapause termination, because PTTH potentiates the ability for adult development. Since diapause termination is suppressed in a temperature of 21°C, the bollworm retains the ability to initiate development in 27°C whereas it remains in diapause in 21°C. Diapause continues even though pupae are supplied with additional PTTH via neurosecretory cell transplantation. Ecdysone injection and prothoracic gland-ablation experiments indicate that the prothoracic glands are the source of the prohormone α-ecdysone, and that diapause is maintained by an α-ecdysone deficiency. This evidence, in conjunction with the above results, suggests that PTTH release potentiates prothoracic gland function in the diapausing pupa which is then regulated by a temperature dependent process.

Environmental factors controlling the induction of diapause in the pink bollworm, Pectinophora gossypiella (Saunders)

Abstract Fourth instar larvae of the pink bollworm may undergo a facultative diapause at the end of the larval feeding period. Diapause larvae are heavier, have a slower rate of heart beat, and consume oxygen at about one-sixth the rate of non-diapause individuals. In addition, the diapause condition is accompanied by an atrophy of the male gonads and an increase in fat content of both sexes. Diapause in the pink bollworm is primarily under the control of the photoperiod. With the strain of moths used in this study, day lengths of 13 hr or less induced diapause whereas longer day lengths averted this condition. Diet and temperature may also exert an effect on the percentage of the population that enters diapause; however, these effects are not readily apparent except under short days. Under inductive photoperiods the greatest incidence of diapause in the pink bollworm occurred in populations reared under the coolest temperatures on diets having the greatest oil content. A possible thermoperiodic effect of lowered temperatures during the scotophase was demonstrated. The pink bollworm appears to respond to absolute rather than changing day lengths. Although the early larval instars appear to be most sensitive to diapause-inducing photoperiods, diapause may be induced in some individuals in any instar. Furthermore, the effects of short-day exposure in the early instars may be largely nullified by exposure of the subsequent instars to long days.

Controlling Cotton's Insect Pests: A New System

Cotton is more heavily treated with insecticides than any other crop in the United States. In southern Texas, this heavy treatment resulted in insecticide- resistant strains of major pests which almost destroyed the industry in the late 1960s and early 1970s. An integrated insect control program based on new short-season cotton varieties and traditional cultural practices has restored production in the area. The new system has been widely implemented because it produces greater net returns by reducing the use of insecticides, fertilizer, and irrigation.

A long-day short-day effect in the photoperiodic control of the pupal diapause of the bollworm, Heliothis zea (Boddie)

Abstract Diapause induction in the bollworm was found to be dependent upon both temperature and photoperiod. More bollworms diapaused when reared at 21° than 27°C under identical photoperiodic regimens. The photoperiodic requirement for inducing the pupal diapause, in a substantial percentage of a population under natural conditions, requires that the previous parent and egg stages be exposed to longer photofractions than the subsequent larval progeny. Results suggest that the bell-shape of the diapause induction curve in the autumn is due to the parents and eggs having one set of photoperiodic requirements and the larval stages having another. Diapause may be induced only when the critical photoperiodic requirements of all three life-history stages overlap. Thus, diapause is restricted to a relatively narrow range of photoperiods and at College Station, Texas, occurs only from late September to mid-November. This provides the bollworm with a mechanism for distinguishing between spring and autumn day-lengths. The experiments also indicate that there may be a maternal influence which initiates the individual toward the diapause condition prior to the deposition of eggs; however, this treatment may be reversed by altering the sequence of photoperiodic exposure during the developmental period from egg to pupae.

Photoperiodic responses of certain geographical strains of Pectinophora gossypiella (Lepidoptera)

Abstract Strains of Pectinophora gossypiella were collected from El Paso (32°N) and Port Lavaca (28°N), Texas; Virgin Islands (18°N), West Indies; Villa de Cura (10°N), Venezuela; Palmira (3°N), Colombia; and Saenz Pena (27°S), Argentina. These were reared in laboratory cultures and tested with photoperiods having from 10 to 14 hr of light time/day at temperatures of 21, 27, and 32°C and on a diet having a lipid content of 1 and 5 per cent. The response curves plotted from the combined data obtained in the photoperiods having from 10 to 12 hr of light time/day showed that the incidence of diapause in each strain from highest to lowest was as follows: El Paso, Port Lavaca, Argentina, Virgin Islands, Colombia, Venezuela. Temperature had a profound effect on the incidence of diapause. The higher temperatures strongly inhibited diapause and at 32°C the percentage of larvae of all strains in diapause was very small. An increase in the lipid content of the diet produces a concomitant increase in the incidence of diapause. This was particularly true for the Virgin Islands strain. This strain also showed a strong response to temperature. The critical photoperiod was not affected by temperature or diet. It remained almost the same in the El Paso, Port Lavaca, Argentina, and Virgin Islands strains. The incidence of diapause was always limited in the Venezuela strain regardless of the experimental regimen. In the Colombia strain, a high incidence of diapause was produced only in the photoperiod having a short light fraction of 10 hr. This photoperiod, LD 10 : 14, is never encountered in nature by the Colombia strain. In all strains, diapause was prevented when the light fraction of the photoperiod was increased to more than 13 hr/day.

Role of photoperiod and temperature in the induction of pupal diapause in the bollworm, Heliothis zea.

Abstract Investigations were conducted on the bollworm to determine the photoperiodic sensitivity of the adults, eggs, and larvae in relation to diapause induction. In addition, the influence of constant and decreasing temperatures and day-lengths was determined. Adult moths, eggs, and larvae were found to be sensitive to photoperiod. A great incidence of diapause occurred when both adults and eggs experienced day-lengths of more than 11 hr and the larvae day-lengths of less than 13 hr. Temperature was found to interact with photoperiod in the induction of diapause. Periodic decreases in day-length and temperature resulted in a higher rate of diapause induction than was obtained when either stimulus was maintained at a constant level.

Photoperiodic Reversibility of Diapause Induction in an Insect.

The diapause of the pink bollworm is under photoperiodic control. Diapause is prevented when the dark phases of the daily photoperiod are 8 to 10 hours in duration. If the dark period is extended to 12 hours, diapause is induced. Intercalation of 8- or 10-hour nights may reverse the diapause induction caused by exposure to photocycles having 12-hour dark phases. The 10-hour night was much more effective in reversing induction than the 8-hour night. The intensity of diapause, in part, appeared to be dependent on the previous photoperiodic experiences of the test animals.

Photoperiod and temperature as factors controlling the diapause of the sunflower moth, Homoeosoma electellum☆

Abstract Induction of larval diapause of the sunflower moth, Homoeosoma electellum (Hulst), was found to be dependent upon both temperature and photoperiod. Diapause was induced more readily at 21 than at 27°C, but only in photoperiods having 11 hr or less of light/day. Greatest percentages of diapausing larvae occurred among larvae subjected to 10 hr or less light time/day at 21°C, regardless of the photoperiodic exposure of the parents and eggs. The incidence of diapause was extremely low when larvae were subjected to periodic reductions in either temperature or day-length. A concomitant reduction of temperature and day-length increased the percentage of diapausing larvae to some degree, but this was small compared to percentages obtained among larvae maintained in days of 11 hr or less at 21°C. Diapause termination may be influenced by temperature and photoperiod. Diapause termination required less time at 27° than 21°C. Also, larvae which were subjected to photoperiods having 11 hr or more light/day resumed development more rapidly than larvae held in shorter light periods.