Oviposition acceptance and larval development of Chilo partellus stemborers in drought‐stressed wild and cultivated grasses of East Africa

Maternal host choices during oviposition by herbivorous insects determine the fitness of their offspring and may be influenced by environmental changes that can alter host‐plant quality. This is of particular relevance to ‘push‐pull’ cropping systems where host preferences are exploited to manage insect pest populations. We tested how drought stress in maize and companion plants that are used in these systems affect oviposition preference, larval feeding, and development of the spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae). Five host species were tested (all Poaceae): maize (Zea mays L.), Napier grass (Pennisetum purpureum Schumach), signal grass [Brachiaria brizantha (A. Rich) Stapf], Brachiaria cv. ‘Mulato’, and molasses grass [Melinis minutiflora (Beauv.)]. Under drought stress, maize experienced as much oviposition as control unstressed maize in choice and no‐choice experiments. Similarly, larval leaf damage was not significantly different in drought‐stressed vs. unstressed maize. In contrast, oviposition occurred less on drought‐stressed than on unstressed Napier and signal grass. Oviposition acceptance and leaf damage remained low in both drought‐stressed and unstressed molasses grass and Mulato. Larval survival and development remained high in drought‐stressed maize, but not in Napier, signal, and molasses grass and Mulato, where survival and development were low in both drought‐stressed and unstressed plants. Our results indicate that herbivore responses to drought‐stressed plants depend on the plant species and that drought stress can change host preference and acceptance rankings. In particular, trap‐crops such as Napier grass may not divert oviposition from the main maize crop under drought stress conditions.     

Oviposition behavior of Diatraea saccharalis (Lepidoptera: Crambidae) on different rice cultivars in Louisiana

The sugarcane borer, Diatraea saccharalis (F.), is a pest of a variety of graminaceous crops in the southern United States, including sugarcane, maize, and rice in Louisiana. This study examined several aspects of D. saccharalis oviposition behavior on rice (Oryza sativa). The vertical distribution of egg masses on four phenological stages of rice in the field showed that D. saccharalis prefers to oviposit on the uppermost portions of rice plants, regardless of plant stage. In greenhouse choice experiments, females strongly preferred plants at the boot and panicle differentiation stages over plants at the tillering stage for oviposition. Greenhouse studies were also conducted to quantify the oviposition preference of D. saccharalis for different cultivars of. When plants were at the tillering stage, cultivars Cocodrie, Priscilla, Bengal, Cheniere, and CL161 were more preferred than cultivars Jupiter, XL723, and XP744. When plants reached the panicle initiation stage, cultivars Cocodrie, CL161, and Priscilla were more preferred than Bengal, Cheniere, Jupiter, XL723, and XP744. Females also oviposited significantly more egg masses on the adaxial surfaces of rice leaves than on the abaxial surfaces. These results will facilitate scouting and management of sugarcane borer and can be used as a foundation for the development of sugarcane borer resistant cultivars.     

Non-host plant extracts reduce oviposition of Plutella xylostella (Lepidoptera: Plutellidae) and enhance parasitism by its parasitoid Cotesia plutellae (Hymenoptera: Braconidae)

Botanical preparations, usually from non-host plants, can be used to manipulate the behaviour of insect pests and their natural enemies. In this study, the effects of extracts of Chrysanthemum morifolium, a non-host plant of the diamondback moth, Plutella xylostella (Linnaeus), on the olfactory and oviposition responses of this phytophagous insect and on levels of parasitism by its specialist parasitoid Cotesia plutellae (Kurdjumov) were examined, using Chinese cabbage Brassica campestris L. ssp. pekinensis as the test host plant. Olfactometer tests showed that volatiles of chrysanthemum extract-treated host plants were less attractive to P. xylostella females than those from untreated host plants; and in contrast, volatiles of the chrysanthemum extract-treated host plants were more attractive to females of its parasitoid C. plutellae than those from untreated host plants. Oviposition preference tests showed that P. xylostella females laid only a small proportion of their eggs on chrysanthemum extract-treated host plants, while ovipositing parasitoid females parasitized a much higher proportion of host larvae feeding on the treated host plants than on untreated host plants. These results suggest that certain non-host plant compounds, when applied onto a host plant, may render the plant less attractive to a phytophagous insect but more attractive to its parasitoids. Application of such non-host plant compounds can be explored to develop push-pull systems to reduce oviposition by a pest insect and at the same time enhance parasitism by its parasitoids in crops.     

Predicting economic losses from the continued spread of the Mexican rice borer (Lepidoptera: Crambidae)

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive species that originated from Mexico, and it is threatening to cause major economic losses to sugarcane, Saccharum spp., and rice, Oryza sativa L., industries in Louisiana. The insect is expected to reach sugarcane and rice production areas in Louisiana by 2008, and infest all of Louisiana sugarcane and rice industries by 2035. When all sugarcane in Louisiana becomes infested, annual yield losses of $220 million would be expected for a cultivar of comparable susceptibility to LCP 85-384 (assuming this cultivar is planted on 100% of the production area). This also assumes the use of the current practice of rainfed production and one application of insecticide, which is presently used by farmers in Louisiana. Irrigation with 30 cm of water is predicted to reduce estimated losses by 29%, whereas four applications of a biorational insecticide such as tebufenozide are expected to reduce the loss in revenue by 53%. The use of the resistant 'HoCP 85-845' would reduce the projected loss in revenue by 24%. Combining all three management tactics on sugarcane, anticipated net loss in revenue would decrease by 66%. The rice industry in Louisiana is projected to suffer from a loss in revenue of $45 million when the entire state is infested. A 77% reduction in loss in revenue is expected with one application of lambda-cyhalothrin. A quarantine on east Texas sugarcane is estimated to save the Louisiana industry between $1.1 billion and $3.2 billion (depending on management) during the time needed for the insect to fully invade the state's sugarcane and rice producing area by natural migration rather than by accidental introduction. The rapid deployment of appropriate management tactics will have a key role in reducing the anticipated economic impact of E. loftini once it becomes a pest in Louisiana sugarcane and rice.     

Oviposition specificity in single vs. cluster egg-laying butterflies: a discrimination phase in Colias eurytheme?

Summary Oviposition preferences and rates of the pierid butterfly Colias eurytheme were examined in laboratory tests. Oviposition rates with only a non-preferred host plant present were not lower than rates observed when both preferred and non-preferred hosts were present. There was no correlation between strength of preference in simultaneous choice tests and the extent to which oviposition rate declined when the preferred host was absent. The results are consistent with the hypothesis that butterflies which lay their eggs singly will accept non-preferred hosts for oviposition more readily than cluster egg-layers.     

Resistance to the Mexican rice borer (Lepidoptera: Crambidae) among Louisiana and Texas sugarcane cultivars

A 2-yr study to evaluate Louisiana and Texas sugarcane, Saccharum spp., cultivars for resistance to the Mexican rice borer, Eoreuma loftini (Dyar) was conducted in two locations in Texas, chosen for having different infestation levels. Criteria for assessment of resistance included percentage of bored internodes and adult emergence holes, the latter used to determine the relative impact of each cultivar on the potential areawide buildup or reduction of adult E. loftini populations. A recently released cultivar, HoCP 85-845, seemed to lose a portion of its resistance under heavy E. loftini infestation pressure, suggesting its value only in moderate-to-low infestation conditions. Cultivar CP 70-321 was the most resistant. Results indicated that cultivar LCP 85-384 was significantly (P < 0.05) more susceptible than NCo 310, traditionally the most susceptible cultivar commercially produced in Texas. In 2001, LCP 85-384, which now represents 85% of the production area in Louisiana, had the greatest moth production per hectare (17,052 +/- 3,956) under the lower infestation pressure, significantly (P < 0.05) higher than HoCP 85-845 (3,038 +/- 2,353). In a portion of the test at the high-infestation location, high levels of sodium and magnesium salt stress (15-30-cm soil depth) were associated with higher E. loftini damage in all cultivars except HoCP 91-555 and CP 70-321.     

Resistance to stem borers (Lepidoptera: Crambidae) among Texas rice cultivars

A 4-yr field study was conducted to assess the resistance of rice, Oryza sativa L., cultivars to injury from the sugarcane borer, Diatraea saccharalis (F.), and the Mexican rice borer, Eoreuma loftini (Dyar) (both Lepidoptera: Crambidae). Several cultivars showed reduced levels of injury ('CLXL8', 'XL8', 'Wells', 'Cheniere', and 'XP710' in 2003; CLXL8, XP723, Cheniere, and 'CL161' in 2004) and lower stem borer yield loss (CLXL8 in 2004) than the more susceptible 'Priscilla'. The resistant CLXL8 also had less injury and yield loss in 2004 and higher yield in 2003 than 'Cocodrie', currently the most popular rice cultivar in Texas and Louisiana. Linear regression analyses between whiteheads and main crop rice yield showed steeper negative slopes for the more resistant cultivars than the more susceptible cultivars, indicating a greater yield loss per whitehead on the resistant cultivars. Compensation from insect injury likely explains the positive associations established in our study between main crop yield and whiteheads for some cultivars. Cultivar resistance is anticipated to become a major control tactic in reducing infestations of E. loftini and D. saccharalis in the Texas and Louisiana rice industries.     

Sex‐biased oviposition by a nursery pollinator on a gynodioecious host plant: Implications for breeding system evolution and evolution of mutualism

Dioecy, a breeding system where individual plants are exclusively male or female, has evolved repeatedly. Extensive theory describes when dioecy should arise from hermaphroditism, frequently through gynodioecy, where females and hermaphrodites coexist, and when gynodioecy should be stable. Both pollinators and herbivores often prefer the pollen‐bearing sex, with sex‐specific fitness effects that can affect breeding system evolution. Nursery pollination, where adult insects pollinate flowers but their larvae feed on plant reproductive tissues, is a model for understanding mutualism evolution but could also yield insights into plant breeding system evolution. We studied a recently established nursery pollination interaction between native Hadena ectypa moths and introduced gynodioecious Silene vulgaris plants in North America to assess whether oviposition was biased toward females or hermaphrodites, which traits were associated with oviposition, and the effect of oviposition on host plant fitness. Oviposition was hermaphrodite‐biased and associated with deeper flowers and more stems. Sexual dimorphism in flower depth, a trait also associated with oviposition on the native host plant (Silene stellata), explained the hermaphrodite bias. Egg‐receiving plants experienced more fruit predation than plants that received no eggs, but relatively few fruits were lost, and egg receipt did not significantly alter total fruit production at the plant level. Oviposition did not enhance pollination; egg‐receiving flowers usually failed to expand and produce seeds. Together, our results suggest that H. ectypa oviposition does not exert a large fitness cost on host plants, sex‐biased interactions can emerge from preferences developed on a hermaphroditic host species, and new nursery pollination interactions can arise as negative or neutral rather than as mutualistic for the plant.     

Distribution ofChilo partellus (Lepidoptera: Pyralidae) egg batches on maize

Distribution ofChilo partellus egg masses was studied in field, greenhouse, and laboratory experiments. The eggs were laid in batches mainly on the lower side and the lower leaves of the plant. The egg batch size ranged from 1 to 169 eggs, with a median of 33.5 eggs per batch (average, 40.5). Oviposition ofC. partellus is described at two levels. The first level, choice of oviposition plants, followed a random distribution. The second level, number of egg batches per plant, followed an aggregated distribution in the field, where more than one egg batch was deposited on the same plant by the same female, which was found on 25% of the oviposition plants. A mechanism for egg-layingC. partellus females to perceive preceding oviposition or injured plants could not be detected. Oviposition site choice seemed to be mediated by tactile stimuli.     

Effect of arbuscular mycorrhizal fungi (Glomus intraradices) on the oviposition of rice water weevil (Lissorhoptrus oryzophilus)

Root-feeding insects are important drivers in ecosystems, and links between aboveground oviposition preference and belowground larval performance have been suggested. The root-colonizing arbuscular mycorrhizal fungi (AMF) play a central role in plant nutrition and are known to change host quality for root-feeding insects. However, it is not known if and how AMF affect the aboveground oviposition of insects whose offspring feed on roots. According to the preference–performance hypothesis, insect herbivores oviposit on plants that will maximize offspring performance. In a greenhouse experiment with rice (Oryza sativa), we investigated the effects of AMF (Glomus intraradices) on aboveground oviposition of rice water weevil (Lissorhoptrus oryzophilus), the larvae of which feed belowground on the roots. Oviposition (i.e., the numbers of eggs laid by weevil females in leaf sheaths) was enhanced when the plants were colonized by AMF. However, the leaf area consumed by adult weevils was not affected. Although AMF reduced plant biomass, it increased nitrogen (N) and phosphorus concentrations in leaves and N in roots. The results suggest that rice water weevil females are able to discriminate plants for oviposition depending on their mycorrhizal status. The discrimination is probably related to AMF-mediated changes in plant quality, i.e., the females choose to oviposit more on plants with higher nutrient concentrations to potentially optimize offspring performance. AMF-mediated change in plant host choice for chewing insect oviposition is a novel aspect of below- and aboveground interactions.     

Oviposition Preference for Water-Stressed Plants in <Emphasis Type="Italic">Orius insidiosus</Emphasis> (Hemiptera: Anthocoridae)

Plant species affect the oviposition behavior of the zoophytophagous predator Orius insidiosus. This study was conducted to determine whether manipulating plant quality, via stress, within a single plant species (Phaseolus vulgaris L.) would affect the oviposition behavior of O. insidiosus and the subsequent performance of its offspring. Plants that had water withheld (water-stressed treatment) had about 20% less total dry weight than plants that were watered to alleviate the drought stress (unstressed treatment). In comparison to unstressed plants, unifoliolate leaves and petioles of water-stressed plants had about 20 and 12% less relative water content, 54 and 29% greater sap osmotic potential, and 19 and 70% greater concentrations of amino-nitrogen, respectively. Reproductive O. insidiosus were then presented stressed and unstressed plants in a two choice test to determine oviposition preference. First instar survival on the two treatments was evaluated in no-choice tests. Orius insidiosus laid 70% more eggs per cm² on the stressed plants. The lifespan of newly-hatched nymphs was the same in both treatments. Eggs were more frequently laid on the leaf vein than the petiole of unstressed plants, whereas in stressed plants oviposition on these parts occurred at equal frequency. These findings suggest that physiological changes in water-stressed bean plants created conditions more favorable for O. insidiosus oviposition. As there was no increase in offspring performance, it is hypothesized that females chose oviposition sites near preferred feeding sites or plant tissues that were less prone to desiccation.     

Differential parasitism of Plutella xylostella (Lepidoptera: Plutellidae) larvae by the parasitoid Cotesia plutellae (Hymenoptera: Braconidae) on two host plant species

Laboratory experiments were conducted to examine host selection by Cotesia plutellae Kurdjumov when larvae of its host, Plutella xylostella (Linnaeus), fed on Chinese cabbage, Brassica campestris L. ssp. pekinensis and those fed on common cabbage, Brassica oleracea L. var. capitata were provided simultaneously, and to investigate the roles of plant and host volatiles in mediating host selection. When C. plutellae were provided with equal numbers of host larvae on plants of the two species in one arena, the parasitoid parasitized 4- to 15-fold more host larvae on Chinese cabbage than on common cabbage. This preference changed little with host density. However, an experience of searching coupled with an oviposition in a host larva on a leaf of the less-preferred plant, common cabbage, significantly increased the preference for parasitizing host larvae on this plant and resulted in twice as many host larvae parasitized on this plant than on Chinese cabbage. Dual choice tests with a Y-tube olfactometer showed that plant volatiles from Chinese cabbage were more attractive to female C. plutellae than those from common cabbage when plants of both species were either intact or infested. In parallel to the increased parasitism on common cabbage following experience, oviposition in a host larva on this less-preferred plant significantly increased the response to volatiles emanating from that plant. These results indicate that host plants may strongly influence the foraging behaviour of C. plutellae, but their differential attractiveness to the parasitoid may be altered by experience of the parasitoid.     

Plant architecture affects periodical cicada oviposition behavior on native and non‐native hosts

Variation in plant quality provides a basis for oviposition site selection for a variety of insects. Of the plant traits that influence plant–insect interactions, plant architecture has received little attention despite its putative role in modulating oviposition behavior. In a common garden comprised of native and non‐native plant species, we assessed how host plant architecture and identity influenced the oviposition behavior of 17‐year periodical cicadas (Homoptera: Cicadidae: Magicicada). On each host, we quantified the availability of branches suitable for oviposition and compared those measures with the branches used by ovipositing cicadas. Using this approach, we determined how the structural attributes of plants (i.e. branch diameter, length and incline) affected oviposition site selection. We then related cicada oviposition preferences to offspring performance by quantifying egg hatching success. On each host species, cicadas selectively used broader and longer branches for oviposition, suggesting that branch architecture provides a basis for oviposition behavior irrespective of plant identity. Broader and longer branches were more abundant on native than on non‐native hosts in our study, contributing to greater oviposition loads among the native species. Egg hatching success was similar among native and non‐native hosts. However, it is possible that the use of native plants for oviposition could enhance offspring output because native hosts generally contained more viable eggs per egg nest and more egg nests per plant. While previous accounts of cicada oviposition preferences have focused on differences in oviposition loads among hosts, our evaluation of within‐host branch selection by ovipositing cicadas helps to clarify oviposition preferences at a higher resolution and demonstrates that plant architecture provides an important basis for oviposition behavior. Furthermore, because branch structure can differ substantially among host species, our results suggest that periodical cicadas may be sensitive to the changes in plant composition that often result from non‐native plant invasions.     

Oviposition by screwworm flies (Diptera: Calliphoridae) on contact with host fluids

Factor affecting oviposition by screwworm flies, Cochliomyia hominivorax (Coquerel), contacting different host fluids were examined in a laboratory bioassay. Fresh bovine blood, which does not release the attractive odors involved in host finding, nevertheless stimulated as many or more females to oviposit than did the other fluids tested. These other fluids included attractive fluid from screwworm-infected wounds (a favored oviposition site in nature) and cultures of Providencia rettgeri (a bacterium implicated in attractant production). Oviposition did not vary with batch of fresh blood or frozen storage, making blood a useful standard for comparing oviposition rates among studies. Oviposition did vary with the substrate to which the blood was applied, suggesting that an interaction between tactile and chemical stimuli is important for host recognition. Both insemination and darkness during bioassay increased oviposition rates, but the magnitude of these effects was small compared with that due to substrate. Age had no effect for at least 1 wk after females became gravid.     

Fiji disease resistance in sugarcane: Relationship to cultivar preference in field populations of the planthopper vector Perkinsiella saccharicida

Populations of the planthopper vector Perkinsiella saccharicida on sugarcane cultivars resistant (cvs QUO and Q87), moderately resistant (cvs Q90 and Q124) and susceptible (cvs NCo310 and Q102) to Fiji disease with known field resistance scores were monitored on the plant (2000–2001) and ratoon (2001–2002) crops. In both crops, the vector population remained very low, reaching its peak in the autumn. The vector population was significantly higher on cultivars susceptible to Fiji disease than on cultivars moderately resistant and resistant to Fiji disease. The number of P. saccharicida adults, nymphs and oviposition sites per plant increased with the increase in the Fiji disease susceptibility. The results suggest that under low vector density, cultivar preference by the planthopper vector mediates Fiji disease resistance in sugarcane. To obtain resistance ratings in the glasshouse that reflect field resistance, glasshouse‐screening trials should be conducted under both low and high vector densities, and the cultivar preference of the planthopper vector recorded along with Fiji disease incidence.     

The role of herbivore‐ and plant‐related experiences in intraspecific host preference of a relatively specialized parasitoid

Parasitoids use odor cues from infested plants and herbivore hosts to locate their hosts. Specialist parasitoids of generalist herbivores are predicted to rely more on herbivorederived cues than plant-derived cues. Microplitis croceipes (Cresson)(Hymenoptera: Braconidae) is a relatively specialized larval endoparasitoid of Heliothis virescens (F.)(Lepidoptera: Noctuidae), which is a generalist herbivore on several crops including cotton and soybean. Using M. croceipes/H. virescens as a model system, we tested the following predictions about specialist parasitoids of generalist herbivores:(i) naive parasitoids will show innate responses to herbivore-emitted kairomones, regardless of host plant identity and (ii) herbivore-related experience will have a greater influence on intraspecific oviposition preference than plant-related experience. Inexperienced (naive) female M. croceipes did not discriminate between cotton-fed and soybean-fed H. virescens in oviposition choice tests, supporting our first prediction. Oviposition experience alone with either host group influenced subsequent oviposition preference while experience with infested plants alone did not elicit preference in M. croceipes, supporting our second prediction. Furthermore, associative learning of oviposition with host-damaged plants facilitated host location. I terestingly, naive parasitoids attacked more soybeathan cotton-fed host larvae in two-choice tests when a background of host-infested cotton odor was supplied, and vice versa. This suggests that plant volatiles may have created an olfactory contrast effect. We discussed ecological significance of the results and concluded that both plant- and herbivore-related experiences play important role in parasitoid host foraging.     

Distribution of second generation European corn borer,Ostrinia nubilalis, egg masses in field corn and relationship to subsequent tunneling damage

The relationship between second generation European corn borer (Ostrinia nubilalis Hübner) egg mass numbers and subsequent field corn damage, as measured by stalk cavity numbers, was studied in 79 fields in northeastern North Carolina over three years. A mean of 0.028 egg masses per plant (645 egg masses/23400 plants) was found over the course of the study. Significant differences in oviposition rate were detected between fields and years. Ca. 85% of egg masses were deposited in a five leaf zone surrounding the primary ear; of these, 89% were found on the lower four leaves in this zone. Egg masses appeared to be distributed randomly within fields but at low rates of incidence, and oviposition was relatively uniform between sampling areas within individual fields. Under moderate to high oviposition pressure (mean number of egg masses per plant over the duration of the oviposition period >ca. 0.02), eggs laid during the early phases of the oviposition period account for more subsequent stalk damage than eggs laid during the later phases of the oviposition period. Variations in second generation egg mass numbers accounted for ca. 70% of variation in stalk cavity numbers.     

Drought‐stress and plant resistance affect herbivore performance and proteome: the case of the green peach aphid Myzus persicae (Hemiptera: Aphididae)

Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well‐watered and drought‐stressed plants of both susceptible and resistant peach (Prunus persica), the effects of both stressors on aphid performance and proteomics are tested. Overall, the influence of the water treatment on aphid performance is less pronounced than the effect of host plant genetic resistance. On the susceptible cultivar, aphid survival, host acceptance and ability to colonize the plant do not depend on water treatment. On the resistant cultivar, aphid survival and ability to colonize are higher on drought‐stressed than on well‐watered plants. A study examining the pattern of protein expression aiming to explain the variation in aphid performance finds higher protein expression in aphids on the drought‐stressed susceptible cultivars compared with the well‐watered ones. In the susceptible cultivar, the regulated proteins are related to energy metabolism and exoskeleton functionality, whereas, in the resistant cultivar, the proteins are involved with the cytoskeleton. Comparison of the protein expression ratios for resistant versus susceptible plants reveals that four proteins are down‐regulated in well‐watered plants and 15 proteins are down‐regulated in drought‐stressed plants. Drought stress applied to the susceptible cultivar induces the regulation of proteins in M. persicae that enable physiological adaptation to maintain an almost unaltered aphid performance. By contrast, for aphids on the resistant cultivar subjected to drought stress, the down‐regulation of proteins responds to an induced host susceptibility effect.     

Preference–performance linkage in the neotropical spittlebug Deois flavopicta, and its relation to the Phylogenetic Constraints Hypothesis

1. Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in a tropical system using the pasture pest Deois flavopicta Stal, which oviposits into the ground and not into plant tissues. The prediction that there is no oviposition preference–larval performance linkage was supported. The absence of such a link provides an evolutionary basis for eruptive population dynamics. 2. The effects of host species and host plant quality on the preference of ovipositing females of D. flavopicta and performance of their offspring on the selected host plants were tested at the population level. 3. Female oviposition behaviour was affected by the presence of the host plant. Females of D. flavopicta showed a strong preference to oviposit close to host plants. The number of eggs was higher in pots containing Brachiaria ruziziensis (121.88 ± 13.70) than in pots containing only the wet oviposition substrate (5.2 ± 1.98) or dry oviposition substrate (0.067 ± 0.067). Ovipositing females did not, however, discriminate between plants of Brachiaria decumbens and Axonopus marginatus and did not show a strong oviposition preference in relation to differences in plant quality (protein and fibre content). They did show oviposition preference for plants under the high watering regime. The mean number of eggs collected from pots with non water‐stressed plants was 60% higher than the mean number of eggs collected on pots with water‐stressed plants. 4. Although females did not show ovipositional preference, spittlebug larval performance, measured as percentage survival and duration of nymphal period, was better on plants of high protein and low fibre content. These results indicate that there is not a linkage between female oviposition preference and subsequent nymphal performance in relation to differences in protein and fibre content in the host plants. There was, however, a limited linkage between oviposition preference and nymphal performance in relation to plant water content. Females showed preference for moist sites that have high survival of newly hatched nymphs. 5. Evidence indicates that for D. flavopicta, the influences of natality and female oviposition behaviour in response to plant quality are not the major factors driving population outbreaks, which is in accordance with the Phylogenetic Constraints Hypothesis.     

Host plant preference and offspring performance of a leaf‐mining moth,Caloptilia fraxinella,on two Fraxinus species

The preference‐performance or ‘mother‐knows‐best’ hypothesis states that female insects choose to oviposit on a host plant that increases the performance of their offspring. This positive link between host plant choice and larval performance is especially important for leaf miners with non‐motile larvae that are entirely dependent upon the oviposition choice of the female for host plant location. Preference and performance of the ash leaf coneroller, Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae), a specialist on ash trees, Fraxinus spp. (Oleaceae), were tested in a series of laboratory and field experiments. Female C. fraxinella were exposed to two closely related hosts, black ash, Fraxinus nigra Marshall, and green ash, Fraxinus pennsylvanica Marshall var. subintegerrima (Vahl), in oviposition choice and wind tunnel flight experiments to determine which host is most attractive for oviposition. Caloptilia fraxinella females were inconsistent in host choice, yet performance of larvae was greater on green than black ash. In preference studies, C. fraxinella preferred to oviposit on black ash when leaflets were removed from the tree, but preferred intact green ash over black ash seedlings for oviposition and host location in a wind tunnel. In the field, however, more C. fraxinella visited black ash var. ‘Fallgold’ at leaf flush than green ash at the same sites. Age of the ash leaflet also influences oviposition in this leaf miner and females preferred new over old leaflets for oviposition. Performance of C. fraxinella larvae was evaluated in field and laboratory experiments and was greater on green ash than on black ash in both experiments based on larval survival and development time parameters. The stronger oviposition and host location preference in the field for black ash were not linked to enhanced performance of offspring, as green ash was the superior host, supporting higher larval survival and faster development. A stronger host location preference in the wind tunnel for green ash over black ash, however, suggests that under certain circumstances with this moth species, ‘mother (may) know best’.