Quiescent Larvae Research Articles

Negative Impact of Unstable Spiromesifen Resistance on Fitness of Tetranychus urticae (Acari: Tetranychidae).

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is a phytophagous haplodiploid mite and its control is largely based on the use of pesticides. But, the short life cycle and high reproductive rate allow them to develop resistance to many pesticides. To design a strategy for resistance management, a fitness cost study was conducted on different populations of T. urticae, i.e., spiromesifen selected (SPIRO-SEL), unselected (Unsel), and reciprocal crosses. After twelve rounds of selections, T. urticae developed high spiromesifen resistance (71.7-fold) compared to the Unsel strain. Results showed a fitness cost for SPIRO-SEL, Cross1 (Unsel ♀ × SPIRO-SEL ♂), and Cross2 (SPIRO-SEL ♀ × Unsel ♂) with a relative fitness values of 0.63, 0.86, and 0.70, respectively. There was a significant increase in the incubation period, quiescent larvae, and egg to adult male and female developmental period of the SPIRO-SEL compared with Unsel strain. Moreover, resistance to spiromesifen was unstable with a decline in resistance value of - 0.05. The presence of unstable spiromesifen resistance associated with fitness costs suggests that intermittent withdrawal of its usage could potentially preserve its effectiveness for management of T. urticae.

Temperature-dependent development and reproduction of Tarsonemus confusus (Acari: Tarsonemidae): an important pest mite of horticulture.

The tarsonemid mite Tarsonemus confusus Ewing has become an economically important pest in orchards in China. This study investigated the temperature-dependent development and reproduction of T. confusus at 15, 20, 25, 30, 33 and 35°C. Eggs failed to hatch at 35°C. When temperature increased from 15 to 30°C, the developmental rate of eggs, larvae and quiescent larvae and that from egg to adulthood of both sexes significantly increased, and the time period required by females to commence oviposition significantly decreased. The lower temperature threshold (T0) for the development of eggs, larvae and quiescent larvae was between 9.3 and 12.0°C and both sexes required about 60 degree days (DD) to complete a life cycle. Females were expected to start oviposition at 12.9°C. The number of eggs laid, the number of female offspring produced and the egg hatch rate were significantly higher at 20, 25 and 30°C than at 15 and 33°C. Increasing temperature shortened the longevity of both sexes but increased the intrinsic rate of increase (rm) and finite capacity for increase (λ) with significantly shorter generation time (T) and doubling time (DT) within a temperature range of 15-30°C. The net reproductive rate (R0) was highest at 25°C. Results of this study may improve our knowledge of fundamental biology and ecology in genus Tarsonemus in general and in T. confusus in particular. Based on the local climate conditions, the applications of these results in predicting the seasonal population dynamics of T. confusus and timing the pest management are discussed.

Functional response and prey stage preference of Neoseiulus barkeri on Trasonemus confusus

The fungivorous Tarsonemus confusus Ewing is a tarsonemid mite causing a so call ‘black-dot’ symptom on the bagged apple fruit in North China, and the phytoseiid mite Neoseiulus barkeri Hughes is a cosmopolitan generalist predator of many agricultural and horticultural pests. In the present study, we evaluated the biological control potential of N. barkeri on T. confusus, by determining its functional response type to prey density of and prey stage preference on both active and quiescent life stages of T. confusus (i.e., eggs, larvae, quiescent larvae and female adults). We found that N. barkeri exhibited all three types of functional response. When fed on eggs and quiescent larvae of T. confusus, N. barkeri had a Type II functional response (i.e., inverse density-dependent predation rate); however, a Type I functional response (i.e., density-independent predation rate) was detected when N. barkeri preyed on T. confusus larvae and a Type III functional response (i.e., sigmoid density-dependent predation rate) when preyed on T. confusus adults. We further showed that the ‘constant prey’ functional response models fit our data better than the ‘depleted prey’ models, as the predator left and reencountered the previously fed prey which reduced its searching efficiency. When all active and quiescent life stages of T. confusus were available, N. barkeri significantly preferred larvae over other prey stages for feeding. Our results imply that due to its quick response to the increasing prey larval and adult densities, N. barkeri could consume a great number of active prey and is thus capable to decline the current fruit damage caused by prey feeding and to potentially prevent the prey population build-up later in the season. Furthermore, predators with Type II response may be efficient at low prey densities, thus augmentative release of N. barkeri early in the season may also suppress the egg and quiescent larva populations of T. confusus. Knowledge from this study provides insights into our understandings in the biological control ecology of N. barkeri.

Physiological basis for low-temperature survival and storage of quiescent larvae of the fruit fly Drosophila melanogaster.

The cryopreservation techniques proposed for embryos of the fruit fly Drosophila melanogaster are not yet ready for practical use. Alternative methods for long-term storage of D. melanogaster strains, although urgently needed, do not exist. Herein, we describe a narrow interval of low temperatures under which the larvae of D. melanogaster can be stored in quiescence for up to two months. The development of larvae was arrested at the pre-wandering stage under fluctuating thermal regime (FTR), which simultaneously resulted in diminishing the accumulation of indirect chill injuries. Our physiological, metabolomic, and transcriptomic analyses revealed that compared to larvae stored at constant low temperatures, the larvae stored under FTR conditions were able to decrease the rates of depletion of energy substrates, exploited brief warm episodes of FTR for homeostatic control of metabolite levels, and more efficiently exerted protection against oxidative damage.

Autochthonous Gnathostomiasis, Brazil

To the Editor: Gnathostomiasis is an infestation by nematodes of the genus Gnathostoma; the main source of infection is raw freshwater fish. In the past, gnathostomiasis was regarded as restricted to certain Asian and Central American countries, but increase of migratory flux and changes in alimentary habits have contributed to importing cases into areas where the disease is not endemic (1,2). We report a case of autochthonous gnasthostomiasis in Brazil.

Life tables and thermal constants of Pediculaster mesembrinae (Acari: Siteroptidae) fed on the Fungus, Trichoderma harzianum Rifai

Life and fecundity table studies on Pediculaster mesembrinae (Canestrini) (Acari: Siteroptidae) were conducted under controlled conditions (15, 20, 25 and 30°C, relative humidity 60 ± 5 %), using cohorts of 40 individually confined mites in observation arenas. Fermented wheat straw (compost) previously inoculated with Trichoderma harzianum Rifai spores was used as substrate and food source. The study started with mite eggs approximately 5 h old. The life cycle of P. mesembrinae included the stages of egg, larva, quiescent larva or nymphocrysalis, and adult; only females were observed in our population. The length of the life cycle, as well as total longevity, showed an inverse (linear) relation with temperature. Values of rm (intrinsic rate of increase) were 0.146, 0.132, 0.170 and 0.204, for 15, 20, 25 and 30°C, respectively. Developmental rates had a direct and linear relationship with temperature; and threshold temperatures ranged between -0.53 and -3.22°C. Development from egg to adult required 152 degree days.

Oxygen consumption, water, lipid and glycogen content of early and late diapause and non-diapause larvae of the burnet moth Zygaena trifolii

Oxygen consumption, lipid, glycogen, water content and dry weight are given for three corresponding larval diapause and non-diapause instars. At 20 °C, the respiration rates of diapause larvae were considerably lower (about 23%) than in corresponding non-diapause larvae. However, a body size-metabolism relationship could not be detected at a lower temperature (5 °C) in older diapause instars (L 4 and L 5 larvae). The O 2 consumption of diapause larvae (4th instar) was invariably different at 5 and 20 °C when measured at 30-day intervals during a 150-day period. The values were by one and a half times higher at 20 °C. A further intensified O 2 consumption at 20 °C indicated that the larvae were preparing to shed the diapause skin; the increase was again 1.5 times higher than in dormant larvae. O 2 consumption rates did not differ when groups of quiescent larvae were compared with diapause larvae at 5 °C, but an earlier timing of increased O 2 values and moulting indicated the different physiological state of the tested larvae. Diapause larvae contained more than twice as much lipid and twice the amount of glycogen as non-diapause larvae. The highest lipid and glycogen contents were detected in the small diapause larvae (L 3 stage), related to their pronounced respiratory rates. Lipid and glycogen were utilized throughout the whole diapause period. The glycogen content dropped more sharply at 20 °C compared to 5 °C, whereas only slight differences in decreasing lipid content occurred, indicating that glycogen is the more important energy source to survive the period after the onset of diapause. The calculated daily rates of loss of lipid and glycogen showed that the lipid and glycogen contents were sufficient for the L 4 larvae to survive an approx. 1 year diapause period at 20 °C. During the diapause period, the fresh weight ratio dropped more sharply than lipid and glycogen, implying that water loss was the main factor in decreasing body weight. The water content decreased to 61% of the initial value (4th instar). However, it was obviously not correlated to the invariable supercooling ability of dormant larvae.

Control of Brennandania lambi (Acari: Pygmephoroidea) by freezing: evaluation of its efficacy and effects on mushroom growth and yield

Laboratory and field studies were conducted to evaluate freezing as a control measure against Brennandania lambi (Krczal) which infests cultivated mushrooms (Agaricus bisporus) in Shanghai primarily through contaminated spawn. Laboratory experiments showed that exposure of contaminated spawn at -10° C for 24 h killed all stages of B. lambi. These mites probably died due to the freezing of body tissues during sustained exposure at -10° C for 24 h. because the supercooling points for the egg, active larva, quiescent larva, non-gravid adult and gravid adult of B. lambi were respectively -11.34, -10.96, -11.43, -7.65 and -11.20° C, whereas the freezing points were respectively -6.68, -6.84. -6.56, -3.96 and -6.75 °C. Semi-field experiments showed that compost inoculated with B. lambi-infested spawn that had been exposed at -10 °C for 24 h had no mite infestation during spawn running and thus mycelium growth was normal. Laboratory and field experiments during 1989 to spring 1990 showed that freezing spawn had no effect on mushroom yield. Further field experiments in two farms during fall 1990 showed no effect of freezing spawn on yield in one farm and increased yield in the other farm. A field experiment during 1991 to 1992 also indicated that freezing spawn -10 °C for 24 h to 34 h had no effect on mushroom yield.

Pherbina mediterranea: immature stages, biology, phenology and distribution (Diptera: Sciomyzidae)

The egg, three larval instars, and puparium of Pherbina mediterranea are described. The duration of the various immature stages indicates that this specis is univoltine and spends the winter as quiescent larvae. The biology, phenology and geographical distribution are presented. The main features of the larvae are illustrated with scanning electron micrographs. A key to the adults of genus Pherbina is given.

The Life History of a Mushroom Pest Mite, Pediculaster flechtmanni (Wicht) (Acari: Pygmephoroidea), with Studies of Alternate Morph Formation

The cosmopolitan pest mite Pediculaster flechtmanni (Wicht) sometimes builds swarming populations in commercial mushroom houses, where it feeds on “weed” fungi. Females are dimorphic, one morph adapted for phoresy. Mites were cultured on Nigrospora oryzae grown on yeast extract agar at 21–28°C ambient and at 24°C constant. Preadult stages are egg, active larva, and quiescent larva, these stages lasting about 41, 7, and 43 h, respectively, at 21–27°C ambient. Female–female cycle is about 125 h at 21–27°C ambient. Females are physogastric, each producing about 200 eggs within one to six oviposition days. Net reproduction rate is approximately 65 females per female per generation. Sex ratios are initially female biased, often becoming male biased as mothers age. Unmated females, if they reproduce, are arrhenotokous. Pronounced sexual dimorphism in morphology and behavior is shown. Phoretic and nonphoretic females also differ from one another in behavior as well as in structure. Experiments suggest that the proportion of phoretomorphs increases as cultures age; this increase is not due to attenuated phoretomorph developmental time or increasing age of the mother; phoretomorph increase probably is related to environmental factors associated with habitat deterioration; and such factors could be pheromonal or nutritive, and they may act upon any stage in the life cycle.

Oxygen requirements of larvae of the smallmouth bass, Micropterus dolomieui Lacépède

Smallmouth bass larvae became highly sensitive to oxygen deficiency on the second day after hatching and continued so to the 10th day. During this period they could not survive exposure to 1 mg O2 l–1 for 3 h at 20° C, and many were killed within 1 h. At 2 mg O2 l–1 half the larvae survived 3 h at 20° C; at 2.5 mg l–1 most survived, and at 3.5 mg l–1 all survived. Resistance to oxygen deficiency was regained by the 11th day, the majority of the larvae withstanding a 3‐h exposure at 1 mg O2 l–1. At 25° C the effects of low oxygen concentration were intensified. At 3 and 4 mg O2 l–1 and 20° C the normally quiescent larvae became very active, even swimming to the surface 5 or 6 cm above the substrate. Increasing the temperature increased this response. Smallmouth larvae were more sensitive than large‐mouth bass larvae to oxygen deficiency.

OBSERVATIONS ON THE BIOLOGY AND BEHAVIOUR OF HOMOEOSOMA FARINARIA TURNER (LEPIDOPTERA: PYRALIDAE) ON SENECIO JACOBAEA L., IN TASMANIA

AbstractThe blue stem borer, Homoeosoma farinaria Turner has a bivoltine life cycle on ragwort, Senecio jacobaea L., in northern Tasmania. Development is continuous, although the insect overwinters as a quiescent larva until the onset of warmer weather in spring. Adults are active from late November and larvae from this generation quickly complete their development during summer. Second generation adults fly from mid‐February until March. Surveys showed that infestations in ragwort were more common in the north than in the south of the State. Four hymenopterous parasites were identified during the study of which a braconid, Apantales sp., was predominant.

The hatching process in Trichuris muris (Nematoda: Trichuroidea)

Eggs of Trichuris muris hatched in the cecal contents of mice. A new method was used to calculate the volume changes in the eggs and larvae during hatching under simulated in vivo conditions. Previously quiescent larvae were activated and performed a series of purposeful movements within the egg that resulted in the head and stylet penetrating one of the polar plugs. In the final stage prior to emergence from the egg, there was significant swelling of the eggs due to endosmosis, which was critical for successful hatching. The hatched larvae were also significantly bigger than the resting larvae. Some observations on egg morphology are made, and a mechanism for hatching of T. muris is described.

Life History and Seasonal Population Growth of Oligonychus ilicis1 Infesting Japanese Holly in New Jersey 2

The life history and seasonal population growth of the southern red mite, Oligonychus ilicis (McGregor), infesting Ilex crenata ‘Convexa’ are reported. Mean developmental times (in days) at 24°C are: egg incubation, 6.5; active larva, 1.4; quiescent larva, 1.0; active protonymph, 0.9; quiescent protonymph, 0.9; active deutonymph, 0.9; and quiescent deutonymph, 1.1. Females deposit 2.4 eggs/day, totaling 36 eggs/lifetime. Adults live for 16.5 days at 24°C. Field population growth of O. ilicis was compared in random counts of mites infesting carbaryl-treated and untreated Japanese hollies during the 1977 season. Treated groups showed a 6-fold increase in the number of immature mites and a 13-fold increase in the number of adult females and eggs compared to populations on untreated hosts. Populations peaked in November at 387 females/100 carbaryl-treated leaves and 25 females/100 untreated leaves. Treated populations produced 50.9 diapausing eggs/leaf and resulted in severe injury to host fOliage as compared to only 3.8 overwintering eggs/leaf and no leaf damage on untreated hollies. Neither the treated nor untreated populations followed the seasonal population growth pattern previously described. Data suggest these differences are attributable to the adverse effects of carbaryl on indigenous predatory populations.

Developmental changes in the late larva of Calliphora stygia. I. Haemolymph.

Quantitative studies of plasma levels of protein, lipid, and soluble carbohydrate in larvae of O. 8tygia reveal discontinuities at days 6 and 10 of development. From day 3 to 6 plasma levels of protein and lipid increase sharply. After day 6, there is a decline in the concentration of plasma protein which is accelerated. at the onset of pupation. The plasma lipid concentration rises abruptly at day 10, but then declines with the onset of puparium formation. The concentration of soluble carbohydrates in the haemolymph falls slightly between days 6 and 7 of development and commences to rise at about day 10; still higher levels are reached in the quiescent larva and early prepupa.