Seasonal Pattern Of Development Research Articles

Patterns of phytoalexins in the grapevine leaf stripe disease (esca complex)/grapevine pathosystem

Vineyards containing vines affected with grapevine leaf stripe disease (GLSD), one of the diseases of the esca complex, suffer losses in grape yield and quality every growing season. To examine the relation between GLSD foliar symptoms and levels of phytoalexins in grapevine, phytoalexin levels were monitored in the leaves of symptomatic, asymptomatic/diseased, and healthy grapevine leaves, at various growth stages, in two vineyards in Italy, over four growing seasons. At the same time, the leaf symptoms of the vines at some of those growth stages were recorded in each vineyard and in each growing season. The compounds extracted and identified were: trans -resveratrol, trans -pterostilbene, trans-e-viniferin and trans-δ-viniferin. The most common phytoalexin found was resveratrol. Amounts of all the phytoalexins were generally greater in symptomatic leaves than in asymptomatic/diseased or healthy leaves. In symptomatic leaves, resveratrol levels were greatest at pre-bunch closure, and peaks in pterostilbene occurred at the same time. Leaves of each category (symptomatic, asymptomatic/diseased, healthy) had lower amounts of these compounds at veraison and generally higher amounts at the stages of harvesting and/or the softening of berries. It seems therefore that the formation and pattern over time of the phytoalexins was linked to the growth stage of the vines. Leaf symptoms never occurred before pre-bunch closure, but became much more common from veraison to harvest. This study provides evidence of a relationship between the levels of phytoalexins, grapevine growth stage, and the seasonal pattern of development of GLSD symptoms.

Unusual pattern of embryogenesis of Caryophyllia inornata (scleractinia, caryophylliidae) in the mediterranean sea: Maybe agamic reproduction?

While knowledge of the reproductive biology of tropical scleractinian corals is extensive, information from temperate zones is limited. The aim of this study is to describe the reproductive biology of Caryophyllia inornata, a temperate species, and to increase the understanding of the reproductive strategies of Mediterranean corals. Samples of C. inornata were collected during SCUBA surveys at Elba island. Sexually active individuals displayed either male or female germ cells, showing a gonochoric sexuality. C. inornata exhibited an unusual pattern of embryogenesis. Embryos appeared throughout the whole year in males and in sexually inactive individuals, and they did not show a seasonal pattern of development, as usually expected for sexual reproduction. This observation suggests the possibility of asexual origin. These embryogenetic sexually inactive individuals were larger in size than the embryogenetic sexually active ones, and they might be senile polyps that preserve the ability to produce embryos only by agamic reproduction.

Diapause in the seasonal cycle of stink bugs (Heteroptera, Pentatomidae) from the Temperate Zone

The paper reviews the data on diapause and related phenomena in stink bugs (Heteroptera: Pentatomidae). Using stink bugs as examples, the consecutive stages of the complex dynamic process of diapause (such as diapause preparation, induction, initiation, maintenance, termination, post-diapause quiescence, and resumption of direct development) are described and discussed. Out of 43 pentatomid species studied in relation to diapause in the Temperate Zone up to date, the majority (38 species) overwinter as adults, two species—as eggs, and another two species—as nymphs. Pentatoma rufipes is believed to be able to overwinter at different stages of its life cycle. Less than 5 % of pentatomid species are probably able to overwinter twice. Only five species have obligate diapause, others have the facultative one. Day-length and temperature are the main diapause inducing factors in the majority of species. The role of food in the control of seasonal development is essential in the pentatomid species feeding on plant seeds. In different species, different stages are sensitive to day-length. Some pentatomids retain sensitivity to photoperiod even after diapause, others lose it and become photo-refractory (temporarily or permanently). In Pentatomidae, such seasonal adaptations as photoperiodic control of nymphal growth rates, seasonal body colour change, migrations, and summer diapause (aestivation) are widely represented, whereas wing and/or wing muscle polymorphism has not been reported yet. In the subfamily Podopinae, induction of facultative reproductive winter diapause is under the control of photoperiod and temperature. All species feed on seeds and their seasonal development to a great extent reflects availability of food. However, the same food preferences and pattern of seasonal development are also characteristic to many species from the subfamily Pentatominae. All species of the subfamily Asopinae are predators. Among them, Picromerus bidens and Apateticus cynicus have obligate embryonic winter diapause, which is rear among true bugs. At the same time, A. cynicus and Podisus maculiventris belong to the same tribe but have different types of diapause: obligate embryonic diapause in A. cynicus and facultative adult diapause in P. maculiventris. Other Asopinae species studied up to date have facultative adult diapause controlled by photoperiod and temperature with probably only one exception: in Andrallus spinidens, adult diapause is controlled by temperature, and photoperiod plays only a secondary role. Thus, in spite of the similar habits and feeding types among Asopinae, the species of this subfamily have different types of diapause and the latter is controlled by different factors. In the subfamily Pentatominae, most species overwinter as adults and induction of their diapause is controlled by the long-day type photoperiodic response, in spite of the differences in their feeding preferences (within phytophagy). However, there are some exceptions in this subfamily, too: Palomena prasina, P. angulosa and Menida scotti have obligate diapause, which conditions univoltinism in these pentatomids. In M. scotti, only females have obligate adult diapause, whereas males remain physiologically active through the whole winter, this pattern being unusual for Heteroptera. The univoltine seasonal cycle of this species with summer diapause (aestivation) and apparent migrations is similar to that of shield bugs (Scutelleridae). According to the analysis of seasonal development, the evolution of seasonal adaptations in Pentatomidae does not directly reflect their phylogeny. However, individual genera, small tribes or even subfamilies have similar complexes of seasonal adaptations. At the same time, Pentatominae is a large and apparently collected taxon, but most of species in this subfamily have the same facultative adult diapause.

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 1. Patterns of seasonal development

AIM: To describe the seasonal pattern of development of third-stage infective larvae (L3) from eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus on pasture in the North Island of New Zealand. METHODS: Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28–31 days after deposition on 13–18 occasions, between January 2005 and July 2006. Analysis of the number of larvae recovered used a mixed model including number of eggs deposited, weight of faeces recovered (an assumed indicator of earthworm activity), site, contamination date, and position of deposited faeces, i.e. on the surface or buried. RESULTS: There was a significant effect of contamination date on development of all three species, with maximum numbers ofL3 developing between late spring (November) and early autumn (March), and minimum numbers in June and July. There were large differences between species, with H. contortus exhibiting a long period (April to October) where development was close to zero, whereas T. circumcincta developed to some extent all year round. Development of T. colubriformis was intermediate between the other two species. Burying faeces containing nematode eggs increased the number of L3 recovered compared with surface deposition (p≤0.001), although there were a small number of exceptions involving only T. colubriformis. The weight of faeces recovered at harvest, which was assumed to be an indication of earthworm activity, was correlated with the number of L3 recovered for all species (p<0.001). In a separate analysis, earthworms were assumed tohave been active if <5 g faeces remained at harvest. Where this occurred, the number of L3 of T. colubriformis and T.circumcincta recovered was reduced by 56% and 58%, respectively (p<0.001). CONCLUSIONS: A marked seasonal pattern of development was observed for all three species, with the most larvae developing in spring-early autumn and the least in winter. This seasonal pattern was most pronounced in H. contortus and least obvious in T. circumcincta. Burying faeces containing eggs generally resulted in more L3 being recovered, whilst the apparent activity of earthworms resulted in fewer larvae being recovered.

Life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae) in a first-order upland stream in central Germany

The number of immature stages and the seasonal patterns of development are basic life history features of a stream dwelling species and knowledge about these important components are essential for understanding its adaptations to its dynamic environment. The life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae), one of the dominant scrapers in the upper and middle reaches of the Breitenbach, a first-order upland stream in central Germany, was analysed. The pronotum length and the relationship between pronotum length, larval biomass and case length showed seven distinct larval instars, contrary to earlier findings from the Breitenbach. In addition to a few trichopteran species from other functional feeding groups, A. fuscipes is the only scraping caddis fly reported to have more than five larval instars. The moult increments of pronotum length and larval biomass were distinctly lower than in glossosomatid species with five larval instars. A. fuscipes is clearly univoltine in the Breitenbach. First-instar larvae were found from July to the beginning of December, and second-instar larvae from July to January. At the beginning of December the population consisted of the instars I to V, and development did not cease during winter. The sixth-instar larvae occurred mostly in January, and the seventh-instar larvae were never present before January. The prepupae and pupae occurred in April. The last pupae were found at the beginning of September, although most of the emergence took place in June and July. At least five different immature stages with different ecological demands were present at any time throughout the year. The ecological advantage having two additional larval instars compared to other glossosomatid species may be to compensate for the high rate of mouthpart wear that occurs while the larvae feed on the rough Bunter Sandstone substratum. A further advantage may be to spread the risk of high mortality under unfavourable environmental conditions.

Population structure, maturation and reproduction of the European squid, Loligo vulgaris, in the Central Adriatic Sea

This paper presents data on the population structure, maturation patterns, fecundity, reproduction, and length–weight relationships of the European squid, Loligo vulgaris, in the Central Adriatic Sea. This species is one of the most valuable commercial cephalopods in the fishery of the Adriatic Sea, yet the population structure and reproductive biology are poorly known. The data are based on the analysis of 1583 individuals caught between 1998 and 2000 along the Croatian coast. In the major part of the year the sex ratio was close to 1:1, but in certain months males outnumbered females. Males were dominant in the smallest and the largest individuals, but at medium lengths females dominated. The length–weight relationship and dorsal mantle length at first sexual maturity for both sexes is given. Male and female reproductive outputs were counted and measured. Oocytes from the ovaries and oviducts of mature females were at various phases of development. Monthly changes of maturity indices, coefficients and frequency of appearance of advanced maturity stages showed a pattern of seasonal development with low values during summer and very high values during winter and spring. The spawning peaks were between January and May, but mature individuals were caught in all months, indicating that in the Central Adriatic Sea this species spawns throughout the year.

Development, Survival and Availability of Gastrointestinal Nematodes of Sheep and Pastures in a Semi-arid Area of Kajiado District of Kenya

A study was carried out on a ranch in the semi-arid area of Kajiado District in Kenya during the period July 2000 to June 2001 to determine the seasonal patterns of development and survival of gastrointestinal nematodes of sheep on pastures. A series of plots were contaminated with sheep faeces every month and pasture samples were collected weekly for the recovery and identification of larvae. The availability of infective larvae on naturally contaminated pastures was also monitored on the paddocks grazed by sheep and around the night pen and the watering point every month from July 2000 to June 2001. The results from the examination of the pasture samples indicated that rainfall distribution was the major factor governing the development and survival of the pre-parasitic stages. No parasitic larvae were detected from the plots contaminated during the dry months from July to October 2000, but development and translocation of infective larvae on pastures occurred on plots contaminated during the rainy seasons and soon after when relatively high moisture was present in the herbage (November 2000 to June 2001). During this period, peak larval counts occurred between the first and the second week post contamination, then declined to undetectable levels between week 4 and 16 post contamination. The lack of development of infective larvae during the dry season and the relatively rapid decline of their population during the wet season presents an opportunity for the use of pasture spelling as a means of helminth control in the study area. The availability of infective larvae on naturally contaminated pastures, around the night pen and around the watering point also followed the rainfall distribution pattern. Infective larvae were consistently recovered around the watering point throughout the study period. This indicated that the point is an important source of infection for sheep, especially during the dry season when other pastures are non-infective.

Circadian rhythmicity and photoperiodism in the pitcher-plant mosquito: adaptive response to the photic environment or correlated response to the seasonal environment?

Many plants and animals use the length of day or photoperiod to cue their seasonal patterns of development, reproduction, dormancy, and migration. Among temperate arthropods, the median or critical photoperiod increases with latitude or altitude. Concomitantly, in beetles, moths, mites, flies, and mosquitoes, there is a declining expression of a rhythmic, presumably circadian-based, component of photoperiodic response. It has been proposed that the long summer days in the north select for a reduced response to light by the circadian clock, which results in this declining rhythmic expression and, consequently, longer northern critical photoperiods. However, these patterns might also be due to direct, seasonal selection on the critical photoperiod itself, which results in a correlated reduction in the rhythmic component as a result of internal physiological constraints within the organism. Using standard light duration and selection experiments, we show that evolution of photoperiodic time measurement in the mosquito, Wyeomyia smithii, results from the direct response of critical photoperiod to seasonal selection and a correlated response of the rhythmic component of photoperiodic time measurement. We conclude that expression of the circadian clock is necessary neither for the central mechanism of photoperiodic time measurement nor for the adaptive modification of critical photoperiod.

Preformation, architectural complexity, and developmental flexibility in Acomastylis rossii (Rosaceae)

The duration of preformation and the seasonal pattern of development were studied in the architecturally complex alpine perennial Acomastylis rossii. Each leaf and inflorescence requires 3 yr to progress from initiation through structural and functional maturity to senescence. As a consequence, three cohorts of preformed organs, initiated in successive years, are borne simultaneously by each individual plant. The oldest cohort matures immediately following snowmelt, after which no additional leaves are matured until the following spring. A second cohort remains below ground in the apical bud and continues development, while a third cohort is initiated. Initiation and development of primordia proceed below ground throughout the summer and continue for at least 2.5 mo after aboveground structures have senesced. Acomastylis rossii maintains numerous dormant vegetative buds containing preformed leaf primordia in the axils of senesced leaves. Developmental preformation has been widely reported in arctic and alpine tundra environments and has been theorized to severely constrain rapid responses to environmental variation. The presence of many such preformed structures may mitigate some of the constraint on plant response to environmental variation imposed by the long developmental trajectories of leaves and inflorescences in apical buds.

Analysis of developmental preformation in the alpine herb Caltha leptosepala (Ranunculaceae)

Developmental preformation is ubiquitous among alpine and arctic tundra plant species and may cause a delay in plant morphological responses to environmental variation. The duration of preformation and seasonal pattern of development were examined in Caltha leptosepala to identify characteristics of architecture and development that may influence the timing of plant responses to environmental cues, both within a single growing season and between years. All structures in C. leptosepala are preformed: leaves are initiated one or two growing seasons before they mature and flowers are initiated one growing season before maturation. Features of development and architecture in C. leptosepala, however, appear to differ from the determinate growth patterns of other exclusively preforming species, and may allow within-season variability in the seasonal development and maturation of structures. Cohorts of leaves initiated are asynchronous with maturation cohorts, and each year the number of leaf primordia per plant at snowmelt exceeds the number to mature aboveground. Therefore, some flexibility in whether leaves complete a 2-yr or 3-yr developmental trajectory might occur. Plasticity in reproductive phenotype might also occur via the process of floral abortion. Despite developmental characteristics that might facilitate the expression of phenotypic plasticity, only slight variability was observed in the duration of preformation or in the seasonal pattern of initiation and emergence of structures. Growth patterns of C. leptosepala thus appear to be fundamentally constrained, and limitations to annual growth may assure that sufficient preformed primordia remain belowground at the end of each growing season for maturation of a full cohort during the subsequent season.

Life cycle and seasonal development of post-embryonic Argas reflexus (Acari: Argasidae) at two thermally different locations in Central Europe

Seasonal development was investigated in the pigeon tick, Argas reflexus (F.) over a 5-year period. The ticks were kept in desiccators at two deposition sites with different temperature conditions: a warmer attic and a cooler outdoor aviary. The life cycle of A. reflexus consists of the egg, larva, a variable number of two to four nymphal instars and the adult stage. In the cooler aviary, the ticks passed, on average, fewer nymphal instars than in the attic. At both locations, ecdysis of the nymphs and adults occurred only during the summer months, with peak numbers of ticks finishing the moult in August. This consistent pattern was evident irrespective of the feeding date of the preceding developmental stage or the year of observation. The results strongly suggest that nymphs II, nymphs I and larvae fed later than in mid-July, August or September, respectively, entered a state of diapause and, thus, overwintered in the engorged state. Argas reflexus nymphs II from a laboratory stock that were deposited inside the attic showed a remarkably different seasonal pattern of development, even more than 1 year after their deposition. This suggests that a circannual rhythm may be involved in the ticks' seasonal timing. Mortality of the engorged ticks (from repletion to ecdysis of the following stage/instar) was below 1.5% in most cases, irrespective of the season and the location. Unfed larvae survived for a maximum of one year inside the attic, whereas the median survival period of unfed nymphs was at least 3 years at the same location. Based on the present results, the generation time from (F1) egg deposition to oviposition in the F2 generation might be 3-11 years in Central European A. reflexus, depending on the course of development (two or three nymphal instars) and the number of gonotrophic cycles (probably up to six) of the F1. The life span of a single tick might take approximately 7-11 years or even longer.

Population structure, maturation patterns and fecundity of the squid Loligo vulgaris from southern Portugal

This study presents the results of an analysis of data on length, weight maturity stage, and fecundity of the squid Loligo vulgaris. The data are based on monthly sampling, between January 1991 and June 1992, from the landings of a traditional inshore fishery for squid in southern Portugal. Male squid generally have a lower weight than females of equivalent mantle length. The overall ratio of male to female squid is 1.1, with limited periods during autumn and spring when females outnumber males. Mature males occur within the broad size range 115–605 mm, whilst mature females have a more restricted size range within 175–345 mm. Immature stages I–II dominate the population during June and July, and there is progressive maturation of both sexes stage II to mature squid at stage V, between August and the following March and May in the larger males and females, respectively. There is a significant difference between the sizes at which the different sexes achieve maturity ( ML50%), with the male at 245 mm and the female at 227 mm. There is evidence that there are two size modes at which males achieve sexual maturity. It is suggested that maturation of this species takes approximately 8 months in the Algarve. A range of reproductive indices derived from gonad morphometrics in mature squid show a pattern of seasonal development with overall values for gonad maturation indices which are lower during the summer and higher during the autumn to the spring. Fecundity has been estimated by counting the total number of oocytes and ova in the ovary and oviduct of mature (stages IV–V) females. The number of eggs varied between 1441 and 14886 and fecundity was correlated positively with mantle length, body weight, and with length and weight of the nidamental gland.

Plant Development, Water Relations, and Carbon Allocation of Heart‐Podded Hoary Cress

AbstractAttempts to control the noxious weed heart‐podded hoary cress [Cardaria draba (L.) Desv.] in the Pacific Northwest have been relatively ineffective, and this species has expanded its distribution from irrigated hayland onto adjacent semiarid rangelands. The objective of this study was to define the seasonal pattern of development and biological activity of heart‐podded hoary cress growing on semiarid rangeland. The study was conducted in the field over a 2‐yr period on a terrace site that has deep Cumulic Haploxeroll soil and an adjacent upland site that has a shallow Lithic Argixeroll soil. Soil water content, phenology, xylem pressure potential and leaf conductance were measured at both sites. Aboveand belowground biomass and spring C allocation pattern, determined by labeling plants with 13C, were measured at the terrace location. Regardless of location, no heart‐podded hoary cress seedlings were found; all shoots developed from rhizome buds. The majority (76%) of heartpodded hoary cress biomass was located belowground. Although drought occurred earlier on the upland than the terrace site, phenology was similar on the two sites. Carbon was translocated to belowground tissues within 1 h of labeling and reached peak accumulation within 24 h. The greatest 13C enrichment of roots and rhizomes occurred during the flowering stage. The peak in belowground C allocation occurred at a stage when leaf conductance was declining rapidly. The short period of maximum C allocation to belowground tissue, the large proportion of belowground tissue, and the wide variation of phenology among plants at a given time may account for the difficulty in chemically controlling this species.

The ecology of Haemonchus contortus in a winter rainfall region in Australia: the development of eggs to infective larvae

The seasonal pattern of development of Haemonchus contortus eggs to infective larvae was investigated on the south coast of Western Australia. Sheep faeces containing H. contortus eggs were deposited on pasture plots at intervals over a 3-year period, and pasture grass and faeces were sampled periodically for infective larvae (L 3). The maximum recoveries occurred in late autumn and in late spring, when adequate moisture coincided with warm temperatures. Larval development was low and sporadic over the hot and dry summer period, and depressed during winter, although most egg depositions in winter yielded L 3 at some time. The proportion of L 3 recovered was related to temperature and moisture parameters, and the major constraint appeared to be the availability of moisture at pasture level. The best indicator of the suitability of conditions for the development of H. contortus was the proportion of green pasture material present, based on a visual assessment.

Seasonal Reproductive Development ofLampsilis cardium, Amblema plicata plicata, andPotamilus alatus(Pelecypoda: Unionidae) in the Upper Mississippi River

ABSTRACT Adult specimens of three species of freshwater mussels common to the upper Mississippi River were examined histologically to determine seasonal patterns of development in gametogenesis and release of glochidia. Full maturation of gonadal materials in Lampsilis cardium (formerly L. ovata ventricosa), a long-term breeder, occurred when ambient river temperatures reached 24° to 26°C, between late July and early August. By mid-August, glochidia were present in the marsupia. Glochidia were released from late May through mid-June of the following year once water temperatures reached 20°C. The long-term breeder Potamilus alatus demonstrated full gonadal maturation earlier than seen in L. cardium with reproduction completed by late July (26°C). Glochidia of P. alatus were released over a period similar to that observed for L. cardium, late May through early July of the following year. Fully mature Amblema plicata plicata, a short-term breeder, were collected from late May through early July (18° to 21°C)...

The influence of upwelling on South African west coast seaweeds

Upwelling from the Benguela Current system on the South African west coast has produced a seaweed flora distinct from that in the region east of Cape Agulhas. The origins of the major red algal component of the West Coast flora appear to be in temperate and polar regions of the southern Pacific Ocean, whereas the South and East Coast floras are more closely related to the floras of the tropical Indian Ocean and of South and West Australia. Although the West Coast flora has a high degree of endemism, recent evidence suggests that events since the initiation of the Benguela system < 12 million years ago have been crucial in its formation. Evidence on the effects of upwelling on growth and physiology suggests that rapid irregular fluctuations in temperature and nutrients on the West Coast have little effect on the strongly seasonal patterns of development, which are probably brought about by aspects of the light regime. Variations in light intensity in the sublittoral caused by upwelling or downwelling conditions appear to have relatively minor effects on seaweed production. Little is known of the effects of high concentrations of available nutrients in upwelled water, although the kelp Ecklonia maxima appears to have evolved both morphologically and physiologically to the West Coast conditions.

The pattern of growth, flowering and fruiting of guava varieties in subtropical Queensland

The seasonal pattern of development in seven guava (Psidium guajava) varieties grown in subtropical coastal southern Queensland was investigated to test the hypothesis that the growth pattern of some varieties is more suited to this environment. Leaf initiation commenced 4 weeks after defoliation by spraying with urea dissolved in water (250 g/litre) in September and continued for 22 weeks. Floral bud emergence and fruit set began 4-8 weeks later and continued for most of the period of shoot growth. Fruit took 14 weeks to reach maturity and the last fruit was harvested in mid-June when the trees passed into winter dormancy. Varieties varied in time to maturity, although the patterns and levels of leaf initiation, flowering and fruit set were similar. Yields ranged from 68.8 to 138.7 kg/tree. Differences between the varieties in yield could not be attributed to any characteristic such as the rate, timing or duration of flowering, fruit set or fruit growth. There was no variety with a different growth pattern closely related to high yields under conditions at Nambour. However, some varieties appear more suited to this environment, since they set a heavier crop which ripened before fruit quality declines in winter.

Seasonal Development of Tree-Hole Mosquitoes (Diptera: Culicidae) and Chaoborids in Relation to Weather And Predation1

Four species of tree-hole mosquitoes (Diptera: Culicidae) and 1 species of Chaoboridae in temperate north Florida commence their vernal development as embryos or larvae. Except for Toxorhynchites rutilus, all species overwinter in various prepupal stages. Overwintering populations of Orthopodomyia signifera, Aedes triseriatus, and Anopheles barberi are sparser and younger in the presence of Tx. rutilus than in its absence. Vernal pupation occurs first among Tx. rutilus, followed by Or. signifera–Ae. triseriatus–An. barberi, and then the chaoborid Corethrella appendiculata. Toxorhynchites rutilus, Ae. triseriatus, and An. barberi all pupate over a brief period, while C. appendiculata and Or. signifera pupate over a period of several weeks. The overwintering stages and the timing and variability of vernal development are interpreted as adaptations to seasonal harshness and to varying degrees of predation. The pattern of seasonal development is reviewed in the context of vector control.