Choice Of Oviposition Substrate Research Articles

Insights into the evolution of herbivory from a leaf-mining fly.

Herbivorous insects and their host plants comprise most known species on Earth. Illuminating how herbivory repeatedly evolved in insects from non-herbivorous lineages is critical to understanding how this biodiversity is created and maintained. We characterized the trophic niche of Scaptomyza flava, a representative of a lineage nested within the Drosophila that transitioned to herbivory ~10-15 million years ago. We used natural history studies to determine if S. flava is a true herbivore or a cryptic microbe-feeder, given that the ancestral character state for the family Drosophilidae is likely microbe-feeding. Specifically, we quantified oviposition substrate choice and larval viability across food-types, trophic-related morphological traits, and nitrogen isotope and sterol profiles across putatively herbivorous and non-herbivorous drosophilids. The results of these studies show that S. flava is an obligate herbivore of living plants. Paired with its genetic model host, Arabidopsis thaliana, S. flava is a novel and powerful system for exploring mechanisms underlying the evolution of herbivory, a complex trait that enabled the exceptional diversification of insects.

<b>Breeding behaviour of the Coromandel Marsh Dart Damselfly (Zygoptera: Coenagrionidae: <I>Ceriagrion coromandelianum</I> (Fabricius)) in central India</b>

Ceriagrion coromandelianum (Fabricius) is one of the most common damselflies in the Indian subcontinent. It flies among bushes and breeds in stagnant pools, small garden tanks, tubs and ornamental cement ponds containing submerged and/or floating vegetation. The oviposition behaviour of C. coromandelianum was observed at the botanical garden of Hislop College, Nagpur, India, where small underground cement tubs are utilized to grow macrophytes. C. coromandelianum displays a refined hierarchy of preferences for oviposition and chooses floating leaves of Nymphaea nouchali (69%) over Lemna paucicostata (23%) and submerged Hydrilla verticillata (8%). In an uninterrupted oviposition bout, the female deposits 283 eggs in 16 rows (N=5) on the under surface of the N. nouchali leaf. The tiny leaves of L. paucicostata holds 7.8 eggs in 4.8 rows (N=10). In H. verticillata, the internode region of the stem can house 25.4 eggs (N=10). One or two eggs are also found neatly inserted in the thin leaf base of H. verticillata. Decaying plant material is never used for oviposition. The present investigation also clearly demonstrates that the choice of oviposition substrate not only depends upon the presence of aquatic species in the water body but also on the spatial location of the oviposition site.

Fruit flies may face a nutrient-dependent life-history trade-off between secondary sexual trait quality, survival and developmental rate

Optimal life-history strategies are those that best allocate finite environmental resources to competing traits. We used the geometric framework for nutrition to evaluate life-history strategies followed by Drosophila melanogaster by measuring the condition-dependent performance of life-history traits, including the morphology of male secondary sexual characters, sex combs. We found that depending on their rearing environment flies faced different forms of trait trade-offs and accordingly followed different life-history strategies. High-energy, high-carbohydrate, low-protein diets supported development of the largest and most symmetrical sex combs, however, consistent with handicap models of sexual selection these foods were associated with reduced fly survival and developmental rate. Expressing the highest quality sex combs may have required secondary sexual trait quality to be traded-off with developmental rate, and our results indicated that flies unable to slow development died. As larval nutritional environments are predominantly determined by female oviposition substrate choice, we tested where mated female flies laid the most eggs. Mothers chose high-energy, high-protein foods associated with rapid larval development. Mothers avoided high-carbohydrate foods associated with maximal sex comb expression, showing they may avoid producing fewer ‘sexy’ sons in favour of producing offspring that develop rapidly.

Oviposition Substrate of the Mountain Fly Drosophila nigrosparsa (Diptera: Drosophilidae)

The survival of insect larvae often depends on the mother’s choice of oviposition substrate, and thus, this choice is an essential part of an insect species’ ecology. Especially species with narrow substrate preferences may suffer from changes in substrate availability triggered by, for example, climate change. Recent climate warming is affecting species directly (e.g., physiology) but also indirectly (e.g., biological interactions) leading to mismatching phenologies and distributions. However, the preferred oviposition substrate is still unknown for many drosophilid species, especially for those at higher elevations. In this study, we investigated the oviposition-substrate preference of the montane-alpine fly Drosophila nigrosparsa in rearing and multiple-choice experiments using natural substrates in the laboratory. Insect emergence from field-collected substrates was tested. More than 650 insects were reared from natural substrates, among them 152 drosophilids but no individual of D. nigrosparsa. In the multiple-choice experiments, D. nigrosparsa preferred ovipositing on mushrooms (> 93% of eggs); additionally, a few eggs were laid on berries but none on other substrates such as cow faeces, rotten plant material, and soil. The flies laid 24 times more eggs per day when mushrooms were included in the substrates than when they were excluded. We infer that D. nigrosparsa is a mushroom breeder with some variation in oviposition choice. The flies favoured some mushrooms over others, but they were not specialised on a single fungal taxon. Although it is unclear if and how climate change will affect D. nigrosparsa, our results indicate that this species will not be threatened by oviposition-substrate limitations in the near future because of the broad altitudinal distribution of the mushrooms considered here, even if the flies will have to shift upwards to withstand increasing temperatures.

Response of cowpea bruchid, Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae) to cheese wood, Alstonia boonei De Wild stem bark oil extracted with different solvents

Cheese wood, Alstonia boonei De Wild stem bark was extracted with five different solvents namely: methanol, ethanol, acetone, petroleum ether and n-hexane. The extracts were tested for insecticidal activity on cowpea bruchid, Callosobruchus maculatus (Fab.). Adult mortality and adult emergence of the insects were investigated. Oviposition deterrences using dual-choice and multiple-choice tests were also investigated as well as percentage damage and weight loss at temperature of 28 ± 2 °C and 75 ± 5% relative humidity. Results showed that at the rate of 2% extract per 20 g of cowpea seeds, methanol, petroleum ether and n-hexane extracts caused 100% mortality of adult cowpea bruchid after four days of post treatment. When the bruchid had choice of oviposition substrate, they laid significantly (p < 0.05) fewer eggs on cowpea seeds treated with extracts compared to untreated seeds. There was no adult emergence in seeds treated with methanol, ethanol, petroleum ether and n-hexane extracts and 100% reduction in F1 progeny was recorded compared with untreated that had 81.86% adults emergence and 0% reduction in F1 progeny. The results obtained from this study revealed that methanol, ethanol, acetone, petroleum ether and n-hexane extracts of A. boonei stem bark were effective in controlling C. maculatus and could serve as an alternative to synthetic insecticides for the protection of stored cowpeas against bruchids.

Potency to Cowpea Seed Bruchid, Callosobruchus maculatus (Fabricius) [Coleoptera: Bruchidae], of African Nutmeg Seed [Monodora myristica (Gaertn.) Dunal] Extracted with Different Solvents.

African nutmeg, Monodora myristica (Gaertn.) Dunal, seed was extracted using: methanol, ethanol, acetone. petroleum-ether. n-hexane or water. The extracts were tested for insecticidal activity against cowpea seed bruchid, Callosobruchus maculatus (Fab.), at ambient tropical conditions of temperature and relative humidity. Results showed that steam distillate caused the highest percentage mortality (92.5 ± 0.80) at 4 days post-treatment compared to 40.0 ± 0.8 – 68.8 ± 1.0 for other solvents. However, only acetone caused significantly (P&lt;0.05) lower mortality. When the bruchids had choice of oviposition substrate, they laid significantly fewer eggs (18.8 ± 0.8) on cowpea seeds treated with steam distillate compared to 2: 32.8 ± 1.8 eggs laid on cowpea seeds treated with other solvent extracts. Significantly lower number of adults emerged from seeds treated with extracts than from untreated seeds. There was no adult emergence in seeds treated with steam distillate, therefore suggesting that steam distillate was the most potent of all biopesticide tested for insecticidal activity on C. maculatus.

Mechanical properties of the endophytic ovipositor in damselflies (Zygoptera, Odonata) and their oviposition substrates

Damselfly females use their ovipositor valves to saw aquatic plants in order to insert their eggs into the plant tissues. Stiffness of the plant substrata is therefore an important parameter for oviposition substrate choice by females. Using a force transducer combined with a motorised micromanipulator, the bending stiffness of the ovipositor at the axial compressional load was studied in seven European damselfly species and compared to the local stiffness of seven preferred plant substrates. The puncture force of tested plant samples ranged from 105 to 1500 mN, and their local stiffness ranged from 208 to1776 N/m. The bending stiffness of the ovipositor was estimated as 173–409 N/m depending on the damselfly species. Using original and literature data, a significant positive correlation between mechanical properties of the ovipositor and preferred oviposition substrates was demonstrated. Possible behavioural adaptations to overcome high stiffness of plant tissues during oviposition are discussed.

Genetically idiosyncratic responses of Drosophila melanogaster populations to selection for improved learning ability

To what extent is adaptive evolution over short timescales repeatable? To address this question, we studied the performance of crosses between replicate Drosophila melanogaster lines previously subject to selection for improved learning response in the context of oviposition substrate choice. Of the 10 pairwise F1 crosses among the five selection lines, four performed in the original learning assay similarly to the parental lines, whereas the remaining six showed learning scores significantly below the average of the parental lines. In particular, four F1 crosses (three involving the same line) showed no detectable learning, on a par with unselected control lines. This indicates that the response to selection in some lines involved allelic substitutions at different loci. Additional assays of crosses between two selection lines indicated that the loss of performance in hybrids generalized to another type of learning assay, and held for both short- and long-term memory. Joint analysis of first- and second-generation crosses between these two lines supported the hypothesis that the response to selection in these different lines was based on the spread of recessive alleles at different loci. These results show that the evolutionary trajectories of populations of the same origin subject to uniform selection may sometimes diverge over very short evolutionary timescales.

Ecology of colonizing populations of the figfly Zaprionus indianus (Diptera, Drosophilidae) in Porto Alegre, Southern Brazil

Ecological parameters such as trophic niche overlap and niche breadth were computed from the frequency of all drosophilid species collected in 2001 and 2002, in the urban area of Porto Alegre city, Brazil. Independently of place, drosophilids community composition and components breeding or feeding sites, the highest frequencies of Zaprionus indianus (Gupta, 1970) were obtained during seasons with higher average temperatures, especially during summer. From a total of the 19,146 individuals of Z. indianus sampled, 80% were found in this season. The data of trophic niche breadth suggest a higher opportunism of adult flies in feeding substrate use, but the females are still selective in oviposition substrate choice. For the values of niche overlap, only for some species, did we find any correlation between these and species richness and/or number of resources, and the most of the correlation values considering breeding and feeding sites were positive. The colonization of Z. indianus in Porto Alegre could be leading to adjustments in the survival strategies of the resident species, but it is possible that many species have conditions for coexisting with the invader.

THE EFFECT OF LEARNING ON EXPERIMENTAL EVOLUTION OF RESOURCE PREFERENCE IN DROSOPHILA MELANOGASTER

Learning is thought to be adaptive in variable environments, whereas constant, predictable environments are supposed to favor unconditional, genetically fixed responses. A dichotomous view of behavior as either learned or innate ignores a potential evolutionary interaction between the learned and innate components of a behavioral response. We addressed this interaction in the context of oviposition substrate choice in Drosophila melanogaster, asking two main questions. First, will learning also evolve in a constant environment in which it always pays to show the same choice? Second, how does an opportunity to learn affect the evolution of the innate (genetic) component of oviposition substrate choice? We exposed experimental populations to four selection regimes, involving selection on oviposition substrate preference (an orange versus a pineapple medium). In two selection regimes the flies were selected for preference either for the orange medium, or for the pineapple medium. In the remaining two selection regimes the flies were also selected for preference for either orange or pineapple, but additionally could use past experience (aversion learning) to decide which medium it paid to avoid. Lines exposed to the latter selection regimes evolved improved learning ability, indicating that learning may be advantageous even if the same behavioral response is favored every generation. Furthermore, of the two selection regimes that favored oviposition on the pineapple medium, the regime that allowed for learning led to the evolution of a stronger innate preference for pineapple, than the regime that did not allow for learning. In contrast, of the two regimes that selected for oviposition on the orange medium, the one that allowed for learning led to a smaller evolutionary change of the innate preference. Thus, an opportunity to learn facilitated the evolution of innate preference under selection for preference for pineapple, but hindered it under selection for preference for orange. We discuss possible mechanisms for this effect.

Experimental evolution of learning ability in fruit flies.

The presence of genetic variation for learning ability in animals opens the way for experiments asking how and under what ecological circumstances improved learning ability should evolve. Here we report experimental evolution of learning ability in Drosophila melanogaster. We exposed experimental populations for 51 generations to conditions that we expected to favor associative learning with regard to oviposition substrate choice. Flies that learned to associate a chemical cue (quinine) with a particular substrate, and still avoided this substrate several hours after the cue had been removed, were expected to contribute more alleles to the next generation. From about generation 15 on, the experimental populations showed marked ability to avoid oviposition substrates that several hours earlier had contained the chemical cue. The improved response to conditioning was also expressed when the flies were faced with a choice of novel media. We demonstrate that these behavioral changes are caused by the evolution of both a higher learning rate and a better memory.

Why 'false' colours are seen by butterflies

A combination of colour and polarized reflections helps them to choose oviposition sites. Light can be described by its intensity, spectral distribution and polarization, and normally a visual system analyses these independently to extract the maximum amount of information1. Here I present behavioural evidence that this does not happen in butterflies, whose choice of oviposition substrate on the basis of its colour2 appears to be strongly influenced by the direction of polarization of the light reflected from the substrate. To my knowledge, this is the first record of ‘false’ colours being perceived as a result of light polarization. This detection of false colours may help butterflies to find optimal oviposition sites.

Performance of Western Flower Thrips (Thysanoptera: Thripidae) on Cultivars of Miniature Rose

The performance of western flower thrips, Frankliniella occidentalis (Pergande), on cultivars of miniature rose, Rosa chinensis ‘minima’ , was measured via larval development and adult oviposition experiments using leaf and petal disks. The time for larvae to complete development on both leaf and petal disks differed significantly among cultivars, although the differences were much more pronounced on petal tissue. Developmental time was prolonged on petal tissue from cultivars with red and orange flowers and generally shortest on white- and yellow-flowered cultivars. Larvae failed to complete development on petal tissue from one red- and one orange-Howe red cultivar. In a no-choice test during 10 d, female thrips deposited significantly different numbers of eggs in flower petal tissue among cultivars, with red- and orange-flowered cultivars being among the least preferred. In choice tests comparing oviposition during 48 h in petal disks from cultivars with the same flower color, a preferred cultivar was revealed in each flower color group. In choice tests under constant light and constant dark conditions, using pair combinations of petal disks from the preferred cultivars, flower color had no effect on choice of oviposition substrate. When leaf and flower petal disks from the same cultivar were compared in choice tests, leaf tissue was consistently the preferred substrate for oviposition,

Influence of host plant abundance and insect diet on the host selection behavior of Maruca testulalis Geyer (Lepidoptera: Pyralidae) and Riptortus dentipes Fab (Hemiptera: Alydidae)

The influence of juvenile nutritional history of two legume pests, the pyralid moth Maruca testulalis (Geyer) and the alydid bug Riptortus dentipes (Fabricius) on host selection by adult and F 1 progeny was investigated on cowpea and soybean. Larval counts suggested that juvenile dietary experience in M. testulalis did not influence choice of oviposition substrate by the adults. In screen house experiments, cowpea was always selected over soybean, both by parental adults and F1 larvae, regardless of the larval feeding history. The number of adult moths in the various cowpea and soybean crop combinations was a function of the proportion planted to cowpea; moth distribution was generally unaffected by the area cropped with soybean. The choice of host by adult R. dentipes was also unaffected by the nutritional history of the nymphs. Bug distribution on the two crops varied with crop phenologies; distribution in plots of different cowpea:soybean ratios was a function of the proportion of cowpea in that treatment only when podding occurred earlier on cowpea. However, when podding was synchronized in both crops, there was no distinct preference between the two crops. These results are discussed in the light of the possibility of both pests expanding their host range in Africa to include soybean, or possibly shifting completely from cowpea to soybean.