Clip Cages Research Articles

Modification of Macrosiphum euphorbiae colonisation behaviour and reproduction on potato plants treated by mineral oil

AbstractAlthough mineral oil spray is one of the most effective ways to control the transmission of non‐persistent aphid‐borne viruses in the field, its mode of action is poorly understood. In this study, the effects of mineral oil treatment of potato plants on host selection behaviour, growth, and reproduction of potato aphids, Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae), were investigated. The effects were assessed 30 min, 1 day, and 7 days after treatment, (1) on aphid orientation behaviour by using a Y‐tube olfactometer, and (2) on aphid feeding behaviour by using the electrical penetration graph (EPG) technique. Olfactory experiments showed that the oil had a repulsive effect only 30 min after spraying. EPG experiments showed a slight modification of the aphid feeding behaviour mainly 7 days after treatment. The number of both salivation and sap ingestion events during the phloem phases were increased 7 days after treatment. In addition, irrespective of the time after treatment, xylem ingestion time was increased. Clip cage experiments were set up to assess potential effects of the oil treatment on aphid survival and population parameters. Nymphal mortality was increased on treated plants, whereas fecundity of surviving insects was enhanced. The antagonistic effects of oil treatment on aphids are discussed in a plant protection context.

Identification of Quantitative Trait Loci Conferring Resistance to Bemisia tabaci in an F2 Population of Solanum lycopersicum × Solanum habrochaites Accession LA1777

Solanum habrochaites S. Knapp and D.M. Spooner accession LA1777 have reported resistance to the sweetpotato whitefly (SPWF), Bemisia tabaci (Genn.). An interspecific F2 population of 171 plants between tomato [Solanum lycopersicum L. (formerly Lycopersicon esculentum Mill.)] and LA1777 was bioassayed against adult SPWF in a greenhouse using clip cages. A selective genotyping analysis was used with 11 resistant and 10 susceptible plants to locate resistance genes by testing them with molecular markers spanning most of the tomato genome at about 10-cM intervals. Markers in four regions were found to be associated with resistance, where three of them showed significantly strong associations and one showed a weak association through chi-square and analyses of variance. However, through quantitative trait locus (QTL) analysis using molecular markers, all four regions were identified as major QTLs with logarithm of odds (LOD) values of 4.87 to 5.95. The four QTLs were identified near the markers TG313 on chromosome 10, C2_At2g41680 on chromosome 9, TG523/T0408 on chromosome 11, and TG400/cLEG-37-G17 on chromosome 11. Multiple regression analysis produced similar results as above with fixed effects of single loci as well as interaction among some of the QTLs.

Use of Expanding Foam for Confining Thrips in Cages on Cowpea, Vigna unguiculata (L.) Walp, Flowers

Studies on insect biology often require insects to be confined on a plant surface with cages. E. A. Hartley (1923) discussed the use of glass lantern globes for caging insects on plants shortly after the beginning of the 20th century. He devised improvements in cage production that included such things as use of perforated celluloid that provided better air circulation and use of melted paraffin to reduce insect escape. A substantial improvement in cage production was the development of clip cages that enabled small insects to be caged on a small portion of the plant, i.e., branches and foliage (MacGillivary and Anderson, 1957; Guthrie and Bishop, 1960; and Mowry, 1993). These cages, however, are not without their problems. Although clip cages may work well with aphids and whiteflies, they may be unsuccessful in preventing escape of smaller insects like thrips. Further, standard clip cages are not suitable for confining certain plant structures like flowers. Salguero et al (1991) used perforated plastic bags to cage thrips on tomato blooms. Bags were secured with paraffin strips. Although this method successfully confined thrips to small blooms, the process is time consuming and difficult. Thrips are considered a major insect pest of cowpea, Vigna unguiculata (L.) Walp, worldwide with different species attacking either the blooms or foliage of cowpea (Singh and van Emden, 1 979; Jackai and Daoust, 1986). Chalfant (1976) reported Frankliniella tritici (Fitch) to be the most abundant species on cowpea. F. tritici attack cowpea flowers and can cause damage to reproductive portions of blooms resulting in premature senescence (Jackai and Daoust, 1986). The impact of thrips, especially F. tritici, on cowpea is not well defined. Although several studies have correlated F. tritici management with improved cowpea yield (Chalfant and Johnson, 1972; Sweeden et al, 1994) other studies suggest that yield increase may actually be caused by other factors such as insecticides directly inducing plant responses (Hundley, 2004). In order to define the impact of F. tritici on cowpea, known numbers of thrips will need to be confined on cowpea flowers. The objective of this manuscript is to describe a caging system that successfully confines thrips on cowpea flowers. Thrips cages (Fig. 1) were constructed by taking a square of No-Thrip Insect Screen (Green-Tek, Edgerton, WI) measuring approximately 13 cm X 13 cm and rolling it into a tube 3.5 cm in diameter. Duct tape (Duck® Brand, Henkel Consumer Adhesives, Inc., Avon, OH) strips approximately 2.5 cm wide were used to seal inner and outer seams of the rolled mesh. A 29.5 ml plastic cup (Solo Cup Co., Highland Park, IL) was placed bottom-side inward in one end of the tube. Another 2.5 cm wide strip of duct tape was used to secure the cup to the tube and tape was burnished around the juncture to ensure a seal. The end opposing the cup was also taped shut and burnished. The bottom of the cup was then removed with a carpet knife. A hole was punched in the center of the cup lid approximately 0.5 cm in diameter and a slit was created from the hole to the edge of the lid to allow placement over the peduncle of the cowpea

Resistance to corn leaf aphid (Rhopalosiphum maidis Fitch) in tropical corn (Zea mays L.)

Corn leaf aphids (Rhopalosiphum maidis Fitch) are found throughout the year on maize in Hawaii and occasionally cause yield loss. Sweet corn inbred Hi38-71 was observed to have high field resistance to aphids and was chosen for this genetic study. An artificial infestation technique was developed using hair-pin clip cages (2.2 cm diameter) which we devised and built. The cages were applied to field-grown plants into which three wingless viviparous adults were placed. Aphid populations were classified on a 1–10 rating scale after about 2 weeks based on digital images of the cages. Mean aphid coverage ratings were 2.97 for the resistant parent and 7.28 for the susceptible parent (representing >200 insects per cage). The F1 hybrids showed similar susceptibility (6.72), showing resistance to be recessive in nature. Six generations of the cross between Hi38-71 and susceptible inbred Hi27 were artificially infested to provide a generation mean analysis of 360 treated plants over two growing seasons. A joint scaling test showed that the fit to a 3-parameter additive-dominance model satisfactorily explained the observed variability with no assumed linkage or epistasis. We conclude that resistance to corn leaf aphid in Hi38-71 is conferred by a single recessive gene labeled aph. These results concur with a previous study under uncontrolled natural infestation in a single environment. The hair-pin clip cage method was most effective in distinguishing resistant and susceptible genotypes under diverse natural growing conditions in Hawaii.

Methodology for biological studies of mealybugs (Hemiptera: Pseudococcidae).

Several methodologies have been used in biological studies of mealybugs (Pseudococcidae) in the laboratory. The objective of this work was to compare three methodologies in order to establish a pattern for development studies. The development nymphal period and mortality of the citrus mealybug, Planococcus citri (Risso, 1813), was evaluated in PVC clip cages of 10 and 30 mm in diameter attached to leaves of coffee plants ( Coffea arabica L. cv. Acaia Cerrado), and on leaf sections placed over an agar film layer. Forty mealybug eggs were individually placed on the substrate and evaluated daily. The data were submitted to analysis of variance followed by the Test of Tukey (p≤ 0.005). Differences were detected in citrus mealybug nymphal development period and mortality depending on the used methodology. The shortest period and the lowest mortality were obtained using foliar sections maintained in agar-water which appears to be a viable methodology for mealybug studies in the laboratory. The excessive insect manipulation seems to be the main negative factor in mealybug development when using clip cages fixed to plant leaves.

Oviposição e dispersão de ninfas de Bemisia tabaci biótipo B em genótipos de tomateiro

Diversos métodos têm sido empregados para avaliar a resistência de plantas a moscas-brancas. Todavia, poucos trabalhos têm sido realizados visando determinar a dispersão de ninfas desses insetos sobre as plantas. O objetivo do presente trabalho foi avaliar a oviposição de B. tabaci biótipo B e a dispersão de suas ninfas em folíolos com e sem exsudatos de genótipos de tomateiro. Foram utilizados sete genótipos de tomateiro: LA716, LA1739, PI134417, LA462, LA1584, 'Santa Clara' e P25 (controle suscetível). A oviposição de B. tabaci biótipo B foi avaliada em gaiolas plásticas (2,8 cm²) fixadas na face abaxial dos folíolos, nas quais foram inseridos dez casais do inseto. Para avaliação da dispersão das ninfas, considerou-se o deslocamento dos insetos além do limite da área ocupada pelas gaiolas. As variáveis observadas foram: mortalidade de adultos 24 horas após a liberação, número de ovos, viabilidade da fase de ovo, período de incubação, número de ninfas e dispersão. Em folíolos com exsudato, LA716, LA1739 e PI134417 provocaram as maiores mortalidades. Adultos mortos nos folíolos desses genótipos ficaram aderidos aos tricomas glandulares, o que provocou redução na oviposição do inseto. Para dispersão, nos folíolos com exsudato, os máximos valores ocorreram nos genótipos LA716, LA462 e P25. Na condição sem exsudato, LA716 promoveu a menor dispersão das ninfas. A presença do exsudato influencia negativamente a sobrevivência e oviposição do inseto. A dispersão das ninfas também é afetada pelo exsudato, embora outros fatores possam ser importantes para o deslocamento do inseto.

Evaluation of Beta corolliflora for Resistance to Curly Top in Idaho

Curly top of sugarbeet is caused by Beet severe curly top virus (BSCTV) or closely related curtovirus species which are vectored by the beet leafhopper (Circulifer tenellus). Beta corolliflora, shown in 1969 to impart a very high level of curly top resistance to sugarbeet into the BC 2 generation, is a wild relative of cultivated sugarbeet that has not been utilized in breeding programs. The nature of curly top resistance from B. corolliflora seems to be reduced symptoms and resistance to viral accumulation. Field screening of 14 B. corolliflora accessions for resistance to curly top followed by PCR detection of BSCTV did not identify any accessions with phenotypic symptoms of curly top and 9 accessions did not have detectable virus. Clip cage inoculations followed by PCR detection of BSCTV and of related species, Beet mild curly top and Beet curly top viruses, were difficult to interpret due to small sample size but indicated that accessions BETA 408, BETA 414, BETA 528, BETA 690, and BETA 805, from Genebank Gatersleben, Foundation Liebniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany had no visible curly top symptoms or evidence of virus accumulation. Results of a preference test showed that beet leafhoppers did not

Attractiveness and host suitability of winter wheat cultivars for cereal aphids (Homoptera: Aphididae)

Cereal aphids (Homoptera: Aphididae) yearly infest winter wheat occasionally leading to significant yield reduction when biotic and abiotic factors are optimal for rapid population growth. Within the host plant complex, influences of eight winter wheat cultivars on the development of cereal aphids was studied in a two-year project focussing on the most important species in terms of yield reduction. Therefore, antibiosis, aphid settlement behaviour, and the relation of infestation and yield loss were evaluated by observing the development of isolated aphids within clip cages, by estimating the natural infestation of alatae morphs, and by measuring yield parameters. The cultivar Hybnos I significantly reduced numbers of offspring of caged Metopolophium dirhodum and Sitobion avenae at seedling stages (growth stage 13, in laboratory) in comparison to other cultivars. During later stages such as shooting and flowering (in laboratory and fields, respectively), no significant differences in aphid development were observed among cultivars. During the period of immigration, alatae of Rhopalosiphum padi and S. avenae preferred to settle on Batis (on May 25 th) and Tommi (on June 10th), respectively. At other evaluations, no significant differences were found among the cultivars and aphid species. Crop yield (kg per ha) and hectolitre weight (g per ccm) were significantly reduced with increasing aphid density in all cultivars, with highest reductions in cultivar Dekan. In contrast, only some cultivars showed significant reductions in protein content with increasing aphid density, while others were tolerant and not reacting to aphid infestation with respect to protein content. In summary, no striking indications for different aphid susceptibility could be found in the set of cultivars tested, even though they differed strongly in attributes such as colour, height, yield potential and development pattern. The results are discussed in terms of cultivar selection to improve sustainability of integrated pest management and the importance of cultivar features for aphid migration and population models.

Soybean defense responses to the soybean aphid

Transcript profiles in aphid (Aphis glycines)-resistant (cv. Dowling) and -susceptible (cv. Williams 82) soybean (Glycine max) cultivars using soybean cDNA microarrays were investigated. Large-scale soybean cDNA microarrays representing approx. 18 000 genes or c. 30% of the soybean genome were compared at 6 and 12 h post-application of aphids. In a separate experiment utilizing clip cages, expression of three defense-related genes were examined at 6, 12, 24, 48, and 72 h in both cultivars by quantitative real-time PCR. One hundred and forty genes showed specific responses for resistance; these included genes related to cell wall, defense, DNA/RNA, secondary metabolism, signaling and other processes. When an extended time period of sampling was investigated, earlier and greater induction of three defense-related genes was observed in the resistant cultivar; however, the induction declined after 24 or 48 h in the resistant cultivar but continued to increase in the susceptible cultivar after 24 h. Aphid-challenged resistant plants showed rapid differential gene expression patterns similar to the incompatible response induced by avirulent Pseudomonas syringae. Five genes were identified as differentially expressed between the two genotypes in the absence of aphids.

Effect of an Alternate Weed Host, Hairy Nightshade, <I>Solanum sarrachoides</I>, on the Biology of the Two Most Important Potato Leafroll Virus (Luteoviridae: Polerovirus) Vectors, <I>Myzus persicae</I> and <I>Macrosiphum euphorbiae</I> (Aphididae: Homoptera)

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.

Effect of an Alternate Weed Host, Hairy Nightshade,Solanum sarrachoides, on the Biology of the Two Most Important Potato Leafroll Virus (Luteoviridae: Polerovirus) Vectors,Myzus persicaeandMacrosiphum euphorbiae(Aphididae: Homoptera)

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.

Soil Potassium Deficiency Affects Soybean Phloem Nitrogen and Soybean Aphid Populations

The soybean aphid is an invasive pest in the midwest United States, with frequent population outbreaks. Previous work has shown that aphid population densities are higher on potassium-deficient soybean than on healthy soybean. The experiments reported here test the hypotheses that the potassium nutrition of the host plant affects the forms of phloem nitrogen available to soybean aphids, and subsequently, their abundance. In field surveys and an exclusion cage study when aphid populations were high, soybean plants with potassium deficiency symptoms had a higher density of soybean aphids than plants without deficiency symptoms. In clip cage experiments, this effect was caused by earlier aphid reproduction and higher numbers of aphid nymphs per mother on plants growing in lower-potassium soil. In phloem exudation samples, the percentage of asparagine, an important amino acid for aphid nutrition, increased with decreasing soil potassium, perhaps because of potassium's role in the nitrogen use of the plant. Taken together, these results show that soybean potassium deficiency can lead to higher populations of soybean aphid through a bottom-up effect. A possible mechanism for this relationship is that soybean potassium deficiency improves the nitrogen nutrition of these N-limited insects. By releasing these herbivores from N limitation, host plant potassium deficiency may allow soybean aphid populations to reach higher levels more rapidly in the field.

Life history of Eretmocerus mundus, a parasitoid of Bemisia tabaci, on tomato and sweet pepper

Eretmocerus mundus is native to the Mediterranean region where it is often observed to enter greenhouses to parasitize B. tabaci on fruiting vegetables and other host crops. Fecundity on tomato and pepper was evaluated by placing newly emerged pairs (n = 15) of E. mundus on leaf discs infested with second instar B. tabaci, the preferred stage, maintained at 25 C and changed daily until death of the female. All whitefly nymphs were observed for host feeding and inverted to count parasitoid eggs. Adult longevity was estimated at 7.3±0.8 d on tomato and 10.1±1.0 d on sweet pepper. Fecundity (number of hosts parasitized) was estimated 147.8±12.6 per female on tomato and 171.1±21.5 on pepper. Incidence of host feeding (number of hosts killed) was significantly greater on sweet pepper than on tomato, 15.6±1.9 vs. 10.4±1.3 nymphs per female, respectively. No significant differences were detected in the duration of life stages between sweet pepper and tomato. Preimaginal survivorship in clip cages was estimated at 69.5±11.9% on tomato and 76.6±10.5% on sweet pepper, with no statistical differences. Net reproductive rate (Ro) was estimated at 63.8±8.2 and 51.0±4.4 on tomato and sweet pepper respectively. Generation time (T) was signifi- cantly greater on sweet pepper (19.3±0.5) than on tomato (17.9±0.4), but the estimate of intrinsic rate of increase (rm) was not statistically different at 0.216±0.005 and 0.219±0.004 respectively. These values are well above those reported for B. tabaci on any crop, indicating the potential of E. mundus to control this pest on solanaceous crops in the greenhouse.

Antibiosis and Antixenosis to <I>Aphis gossypii</I> (Homoptera: Aphididae) in <I>Colocasia esculenta</I>

Fifty cultivars of taro, Colocasia esculenta (L.) Schott (Araceae), collected from islands in Micronesia and Polynesia, eight cultivars from the University of Hawaii's taro germplasm collection, and a closely related aroid, Xanthosorna sagittifolium (L.) (Araceae), were screened for antibiosis and antixenosis to Aphis gossypii Clover. Life history data for A. gossypii were collected by assessing survivorship and fecundity of aphids caged on taro leaves in the field. Significant differences in aphid reproductive rate and longevity were observed among the taro cultivars, and cultivars were ranked from most resistant to most susceptible. Antixenosis was assayed in the laboratory in a multiround choice test where A. gossypii were offered four leaf discs excised from different taro cultivars. Additionally, field observations of aphid abundance on taro cultivars were made to corroborate clip cage studies and laboratory experiments. 'Iliuaua','Rumung Mary','Maria', 'Ketan 36', and'Agaga' were the most resistant in terms of reducing aphid fecundity and survivorship, whereas the Iliuana,'Purple', 'TC-83001', and 'Putih 24' were least preferred in aphid choice tests. X. sagittifolium consistently exhibited strong aphid resistance. Resistant cultivars identified in this study may form the basis of breeding programs seeking to combine aphid resistance with other desirable agronomic traits in taro.

Transmission of Cassava brown streak virus by Bemisia tabaci (Gennadius)

AbstractTwo whitefly species, Bemisia afer (Priesner & Hosny) and B. tabaci (Gennadius) were used in transmission experiments with Cassava brown streak virus (CBSV) (Ipomovirus; Potyviridae). Adults of whiteflies were given access to CBSV by containing them in clip cages on CBSV‐infected cassava plants. Whiteflies were then transferred, together or separately, to CBSD‐susceptible cassava plants of var. ‘Albert’ in a controlled environment. In glasshouse experiments, whiteflies were caged with CBSV‐infected and virus‐free cassava plants. Transmission of CBSV was sporadic and occurred in three of seven experiments when inoculated by B. afer and B. tabaci or B. tabaci alone, but not by B. afer alone. However, rate of transmission was low (maximum 22%) even when using high whitefly numbers of up to 120 per target plant. Successful transmission was confirmed by the detection of CBSV by reverse transcription‐polymerase chain reaction. Spread of cassava brown streak disease (CBSD) in the field in Tanzania coincided with increases in whitefly numbers; further supporting the evidence that B. tabaci is a vector of CBSV. The results of this study establish for the first time that B. tabaci is the vector of CBSV, similar to other ipomoviruses.

The use of clip cages to restrain insects reduces leaf expansion systemically in Rumex obtusifolius

Abstract. 1. Clip cages have been used widely by experimental ecologists to contain insects on plants.2. Under controlled conditions, the effect of applying clip cages alone and clip cages and the chrysomelid beetle Gastrophysa viridula on systemic leaf expansion of Rumex obtusifolius was investigated. Treatments were applied to the fully expanded fourth leaf and expansion of leaf 8 was measured over a period of 22 days.3. The application of clip cages reduced the rate at which leaf area increased and led to reductions in final leaf areas.4. Clip cages have systemic effects on plant development and these effects are sustained even after the clip cage is removed. Investigators should take this into account in designing experiments.

Oviposition preference of Lygocoris pabulinus (Het., Miridae) in relation to plants and conspecifics

Abstract: To predict possible locations of Lygocoris pabulinus (L) in the field during the summer, we determined their oviposition preference under summer conditions. With L. pabulinus reared on potato, oviposition preference was determined for potato, tomato or green bean. As preference may depend on larval or early adult experience, the oviposition preference of bugs reared on green bean for three generations, and of bugs captured from the field 12 h prior to the experiment was also determined. All females showed a strong preference for potato plants, on which fecundity was higher. Hence, although L. pabulinus is a generalist in its feeding habits, the summer generation seems to be an oviposition specialist. Aggregation of ovipositing females does not seem to occur; similar amounts of eggs were oviposited in plants with clip cages containing conspecifics as in plants without conspecifics. More eggs were oviposited in damaged plants than in undamaged plants. Plant volatiles released upon damage may aid L. pabulinus females in finding suitable oviposition sites.

Increased reproduction by pea aphids in the presence of secondary parasitoids

Summary1. The influence of the presence of secondary parasitoids on aphid reproduction was tested in a field experiment.2. Single pea aphids Acyrthosiphon pisum in clip cages on potted bean plants were exposed to a collection of secondary parasitoids enclosed within a small perforated bag. The aphids were exposed to volatile chemicals released by the secondary parasitoids but there was no physical contact.3. The production of nymphs was recorded over an 11‐day period. Aphids produced significantly more offspring in the presence of secondary parasitoids than in the absence of secondary parasitoids (36.9 vs. 31.2).4. This is the second reported occurrence of this phenomenon, and the reasons for its occurrence and its consequences for aphid population and community ecology are discussed.

Effect of Leaf Age and Silverleaf Symptoms on Oviposition Site Selection and Development of <I>Bemisia argentifolii</I> (Homoptera: Aleyrodidae) on Zucchini

The development of whitefly control tactics that provide a safer alternative to using pesticides requires a thorough understanding of the interaction between these insects and their host plants. In this study, we investigated the effect of leaf age of zucchini, Cucurbita pepo L., on the oviposition site selection and on the development and survival of immature Bemisia argentifolii Bellows & Perring. Also, we evaluated the effect of squash silverleaf symptoms on adult alighting and oviposition site selection, and on the development of immatures. Whiteflies oviposited significantly more on younger, hairier leaves than on older leaves when tested in a dual-choice petri dish clip cage. Time to 50% emergence was longer on younger versus older leaves, yet survival of immatures did not differ statistically between the leaves tested. In free-flight choice experiments, whiteflies (male and female) alighted significantly less frequently on silverleaf-affected plants than on healthy green plants. However, in dual-choice oviposition experiments, whiteflies did not discriminate between silvered and healthy green leaves. Further experiments revealed no differences in the development of immature B. argentifolii on healthy and silvered leaves. This indicates that the chemical and physiological changes in silverleaf-affected leaves do not have a detrimental effect on the survival or development of whitefly nymphs.

Insect clip cages rapidly alter photosynthetic traits of leaves

AbstractIn plant‐insect interaction experiments, a clip cage is frequently used to isolate insects or other small pests on a leaf. Clip cage effects on the physiology of the leaf could possibly confound experimental results. Our objective was to quantitate the effects of an insect clip cage of the type typically used for small pests such as whiteflies (Bemisia sp.), aphids (Aphis sp.) and mites (Urticae sp.) on the photosynthetic traits of cotton (Gossypium hirsutum L. cv. Coker 100A‐glandless) and muskmelon (Cucumis melo L. cv. Imperial 45) leaves. Clip cages that enclosed 11.3 cm2 of both the abaxial and adaxial sides of a leaf were attached to young fully expanded leaves. For the leaf tissue within the clip cage, incident radiation was decreased and leaf temperature was increased. After 24 h, chlorophyll content of tissue within the clip cage was significantly increased compared with non‐caged‐control samples taken from the opposite half of the same leaf. Three days after clip cages were attached to leaves, compared with controls, the tissue within the cage had a lower light‐saturated, steady‐state CO2 exchange rate (CER) and leaf soluble protein content. The cage effect on CER and soluble protein could be explained, at least in part, by decreased light‐saturated initial Rubisco activity for leaf tissue within the clip cage. We conclude that the clip cages caused physiological and biochemical alterations of leaves that could alter insect nutrition. Thus, it is suggested that clip cage effects on leaf physiology and microenvironment must be considered when interpreting results of plant‐insect interaction experiments.