Host-plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum

Sorghum midge, Stenodiplosis ( Contarinia ) sorghicola (Coquillett) is an important pest of grain sorghum world-wide. Considerable progress has been made in screening and breeding for resistance to sorghum midge. However, some of the sources of resistance have become susceptible to sorghum midge in Kenya, in eastern Africa. Therefore, the wild relatives of Sorghum bicolor were studied as a possible source of new genes conferring resistance to sorghum midge. Midge females did not lay eggs in the spikelets of Sorghum amplum , Sorghum bulbosum , and Sorghum angustum compared to 30% spikelets with eggs in Sorghum halepense when infested with five midge females per panicle under no-choice conditions. However, one egg was laid in S. amplum when infested with 50 midges per panicle. A larger number of midges were attracted to the odours from the panicles of S. halepense than to the panicles of Sorghum stipoideum , Sorghum brachypodum , S. angustum , Sorghum macrospermum , Sorghum nitidium , Sorghum laxiflorum , and S. amplum in dual-choice olfactometer tests. The differences in midge response to the odours from S. halepense and Sorghum intrans were not significant. Under multi-choice conditions, when the females were also allowed a contact with the host, more sorghum midge females were attracted to the panicles of S. bicolor compared with S. amplum , S. angustum , and S. halepense . In another test, numerically more midges responded to the panicles of IS 10712 compared with S. halepense , whereas the differences in midge response to the panicles of ICSV 197 ( S. bicolor ) and S. halepense were not apparent, indicating that S. halepense is as attractive to sorghum midge females as S. bicolor . The wild relatives of sorghum (except S. halepense ) were not preferred for oviposition, and they were also less attractive to the sorghum midge females. Thus, wild relatives of sorghum can prove to be an alternative source of genes for resistance to sorghum midge.     

Antixenosis component of resistance to sorghum midge, Contarinia sorghicola Coq. in Sorghum bicolor (L.) Moench

Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is the most destructive pest of grain sorghum, and host-plant resistance is an effective method of controlling this insect. We studied the antixenosis component of resistance to sorghum midge using multi-, double- and no-choice cage tests, and under multi-choice field conditions to quantify and understand the nature of antixenosis component of resistance to this insect in Sorghum bicolor (L.) Moench. Midge response towards sorghum panicles was influenced by panicle size and cage type used to study the orientation behaviour. Maximum number of midges were recorded at 30 and 60 min after initiating the experiment. Antixenosis shown by C. sorghicola under multi-choice field conditions to ICSV 197 and TAM 2566 was not confirmed under cage tests, while DJ 6514, AF 28 and IS 3461 were non-preferred both under field and cage conditions. Midge-resistant female parents (PM 7061 and PM 7068) were less preferred than the midge susceptible (ICSA 42 and 296A) female parents. Male-sterility did not influence host finding and acceptance by the midge females, although in one out of two tests, the maintainer lines (B-lines) were preferred over the male-sterile lines (A-lines).     

Components of resistance to the sorghum midge, Contarinia sorghicola

Studies were conducted on components of resistance to sorghum midge on four resistant (DJ 6514, AF 28, TAM 2566 and IS 15107) and two susceptible cultivars (CSH 1 and Swarna). Data were recorded on the numbers of eggs, larvae, emerged adults and grain damage in panicles of different genotypes infested with 60 midge females/panicle under no-choice conditions. The size of floral parts (glume, lemma, palea, lodicule, stigma, style, ovary and anther), rate of grain development and tannin content of grain were measured. The lengths of glume gl and 82, lemma L1 and L2, palea, lodicule, anther, style and stigma were positively associated with susceptibility to sorghum midge. Rate of grain development (between 3rd and 7th day after anthesis) was negatively associated with susceptibility to sorghum. Tannin content of grain was also negatively correlated with midge susceptibility, although there were distinct exceptions (e.g. DJ 6514 is highly resistant bur has a low tannin content).     

Evaluation of planting date, sorghum hybrid, and insecticide treatment on sorghum midge (Diptera: Cecidomyiidae) management in northeast Louisiana

The combined effect of planting date, insecticide treatment, and host-plant resistance was studied in northeast Louisiana for management of the sorghum midge, Stenodiplosis sorghicola (Coquillett), during 1994 and 1995. Significantly higher numbers of sorghum midges were observed visiting flowering spikelets of the midge-susceptible sorghum hybrid (Delta and Pine Land 'DP1552') than those of the midge-resistant sorghum hybrid (DeKalb 'DK-60'). Numbers of midges averaged 1.2 and 0.6 per flowering panicle in the susceptible and resistant sorghum hybrids, respectively, in 1994 and 1.8 and 1.0, respectively, in 1995. Midge densities increased significantly as the sorghum flowering season progressed. Sorghum midge reached peak densities during the first half of August in 1994 and 1995. The length of the flowering period in the early-planted (mid-March) sorghum was significantly longer compared with the flowering periods in the mid-April, mid-May, or mid-June planted sorghums. This resulted in prolonged exposure of flowering panicles to ovipositing midges and increased midge damage in the early-planted (mid-March) sorghum. Damage by sorghum midge was significantly higher in the early-planted (mid-March) sorghum hybrids than in the late-planted (mid-June) sorghum hybrids. The midge-susceptible hybrid produced highest yields when planted in mid-April and mid-May (optimum period) and lower yields when planted very early (i.e., mid-March) or late (i.e., mid-June). No significant differences were observed in yields for the resistant hybrid at any planting date in 1994. However, in 1995, significantly lower yields were recorded in resistant sorghum planted in mid-June. Levels of sorghum midge damage and sorghum seed yields in the untreated resistant hybrid were not significantly different than those observed in the insecticide-treated susceptible hybrid. Numbers of adult midges captured on sticky traps were positively correlated to numbers of visual estimates of ovipositing midge females visiting flowering spikelets.     

Resistance of Collard Green Genotypes to <Emphasis Type="Italic">Bemisia tabaci</Emphasis> Biotype B: Characterization of Antixenosis

Bemisia tabaci (Genn.) biotype B (Hemiptera: Aleyrodidae) is an important pest of vegetable crops, including collard greens Brassica oleracea var. acephala (Brassicaceae). The use of resistant genotypes is an interesting option to reduce insect populations and can be used as an important tool for integrated pest management (IPM). This study evaluated 32 genotypes of collard greens against the attack of silver leaf whitefly, with the aim to characterize antixenosis. Initially, a multiple-choice trial was conducted using all genotypes, in which the adult attractiveness was assessed on two leaves per genotype at 24 and 48 h after infestation. After 48 h, one leaf of each genotype was randomly selected for the determination of the number of eggs per square centimeter. From the results of the multiple-choice trial, 13 genotypes were selected for a no-choice oviposition test, following the same method of the previous test. Colorimetric analyses were also performed to establish possible correlations between leaf color and insect colonization. Genotypes HS-20, OE, and VA were less attractive, demonstrating antixenosis. Genotypes LG, VE, J, MG, MOP, HS-20, VA, and MT had less oviposition in the multiple-choice test, which indicated expression of antixenosis. In the no-choice test, genotypes VE, P1C, CCB, RI-919, H, and J had less oviposition, which also characterized antixenosis. Therefore, genotypes VE and J showed the highest resistance stability because both had less oviposition in both test modalities. Thus, the resistance to B. tabaci biotype B indicates the genotypes HS-20, OE, VA, VE, and J are promising for use in breeding programs to develop resistance to whitefly.     

Antibiosis component of resistance in sorghum to sorghum midge, Contarinia sorghicola

Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is an important pest of grain sorghum, and host-plant resistance is one of the most effective means of controlling this pest. We studied the antibiosis mechanism of resistance in sorghum to C. sorghicola in a diverse array of midge-resistant and midge-susceptible genotypes. Data were recorded on adult emergence, postembryonic developmental period, number of mature eggs in the ovary, fecundity, larval survival from artificially implanted eggs; and the tannins, soluble sugars, and protein content of 10-day old and mature grains during the 1982-91 rainy and post-rainy seasons. Adult emergence was significantly lower in the midge-resistant genotypes compared with the susceptible controls. Initiation of adult emergence was delayed by 4–8 days on DJ 6514, IS 8571, IS 9807, IS 10712, IS 19474, IS 19512, ICSV 830 and ICSV 197. Postembryonic developmental period was prolonged on DJ 6514, IS 15107, IS 3461, IS 7005, IS 19474, ICSV 831 and ICSV 197. However, the delay in adult emergence or the extended developmental period was not observed during the post-rainy season in some genotypes. These differences in the expression of antibiosis to midge in resistant genotypes over seasons may be attributed to the effect of environmental conditions on the insect development and chemical composition of sorghum grain. Amounts of tannins and proteins were generally greater in the midge-resistant lines compared with the susceptible ones (except tannins in DJ 6514) while the soluble sugars were low in the midge-resistant lines (except TAM 2566). These differences in chemical composition of the grain between genotypes and variations over seasons have been discussed in relation to the expression of antibiosis mechanism of resistance to the sorghum midge. Antibiosis to sorghum midge was also evident in terms of smaller size of larvae, lower number of eggs in the ovary, reduced fecundity, and larval survival. Midge-resistant lines have diverse effects on the biology of this insect. Antibiosis along with other components of resistance can be used to develop cultivars with stable resistance to C. sorghicola.     

Oviposition and larval survival of Dasineura tetensi on four blackcurrant Ribes cultivars

Monitoring of an unsprayed infested fieldsite using watertraps in S.E. Kent revealed four generations of Dasineura tetensi (Rubs) (Diptera: Cecidomyiidae) occurring between April and September 1996. Ribes nigrum L. cultivars 'Baldwin' (susceptible), 'Ben Alder' (susceptible) and 'Ben Connan' (resistant) were sampled for eggs in the field and assessed for midge damage throughout the season. Oviposition was indiscriminate, but plant damage varied significantly between cultivars. In laboratory choice experiments, mated female midges showed no preference between susceptible shoots of 'Ben Alder' and resistant shoots of 'Ben Connan' for oviposition. Olfactory responses of D. tetensi to leaf volatiles of 'Ben Alder' and 'Ben Connan' were also tested in a 4-way olfactometer. Mated females did not discriminate between volatiles of susceptible and resistant host plants. Larvae reared on cv. 'Ben Connan' shoots were significantly smaller than those reared on shoots of cv. 'Ben Alder'. Larval antibiosis and not female antixenosis appears to be the main mechanism for resistance to D. tetensi in 'Ben Connan'.     

Identifications of two different mechanisms for sorghum midge resistance through QTL mapping

Sorghum midge is the one of the most damaging insect pests of grain sorghum production worldwide. At least three different mechanisms are involved in midge resistance. The genetic bases of these mechanisms, however, are poorly understood. In this study, for the first time, quantitative trait loci associated with two of the mechanisms of midge resistance, antixenosis and antibiosis, were identified in an RI (recombinant inbred) population from the cross of sorghum lines ICSV745 x 90562. Two genetic regions located on separate linkage groups were found to be associated with antixenosis and explained 12% and 15%, respectively, of the total variation in egg numbers/spikelet laid in a cage experiment. One region was significantly associated with antibiosis and explained 34.5% of the variation of the difference of egg and pupal counts in the RI population. The identification of genes for different mechanisms of midge resistance will be particularly useful for exploring new sources of midge resistance and for gene pyramiding of different mechanisms for increased security in sorghum breeding through marker-assisted selection.     

DNA sequence variation in the ITS-1 rDNA subunit and host relationships in sorghum midge, Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae), in Australia

Sequence variation in the internal transcribed spacer (ITS-1) ribosomal DNA subunit was examined for sorghum midge obtained from introduced and native hosts in south-eastern and central Queensland. No variation was observed relative to host plant or geographical distance for midges collected from two introduced hosts, grain sorghum ( Sorghum bicolor ) and Johnson grass ( S. halepense ); however, sequence differences were observed between midges from introduced and native hosts and among midges from a single native host, slender bluegrass ( Dichanthium affine ). No evidence was observed of introduced midges on native hosts, or vice versa. These results agree with previously hypothesised host distributions for native and introduced midges in Australia, and expand the sample of introduced hosts to include Johnson grass. They suggest that Stenodiplosis sorghicola , the principal midge infesting grain sorghum, is also the most common species on Johnson grass. This confirms that Johnson grass plays a role in the population dynamics of S. sorghicola and suggests that midges originating from Johnson grass may influence levels of infestation in grain sorghum.     

Leaf surface chemistry of sorghum seedlings influencing expression of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is one of the serious constraints to sorghum production, and host plant resistance is an important component for controlling this pest. We studied the expression of resistance to A. soccata in a diverse array of sorghum genotypes in relation to composition of leaf surface chemicals during the seedling stage. The sorghum genotypes IS 1054, IS 1057, IS 2146, IS 4664, IS 2312, IS 2205, SFCR 125, SFCR 151, ICSV 700, and IS 18551 exhibited antixenosis for oviposition, and suffered less deadhearts due to sorghum shoot fly, A. soccata. Compounds undecane 5- methyl, decane 4- methyl, hexane 2, 4- methyl, pentadecane 8- hexyl, and dodecane 2, 6, 11- trimethyl, present on the leaf surface of sorghum seedlings, were associated with susceptibility to shoot fly; while 4, 4- dimethyl cyclooctene was associated with resistance to shoot fly. The compounds associated with resistance/susceptibility to shoot fly, can be used as marker traits to select for resistance as well as for diversifying and increasing the levels of resistance to this pest. The role of biochemical compounds for developing sorghum varieties with resistance to shoot fly, A. soccata has been discussed.     

Effect of sorghum resistant to Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) on oviposition and development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract Helicoverpa armigera oviposition preference for, and larval development on sorghum hybrids with differing resistance to sorghum midge, Stenodiplosis sorghicola , were investigated. When H. armigera larvae were fed seed of resistant and susceptible hybrids in the laboratory there were no differences in larval and pupal sizes or the rate of development. The same result was recorded when larvae fed on panicles on plants in a glasshouse. On some sampling occasions, significantly more eggs were laid on panicles of resistant hybrids in the field. This occurred when plants were in plots and also in a mixed planting. Midge-resistance status did not affect levels of egg parasitism. In a field study using recombinant inbred lines between a midge-resistant and a midge-susceptible line, no relationship was found between level of resistance and oviposition of H. armigera . We conclude that, although midge-resistant hybrids are sometimes preferred for oviposition by H. armigera, the resistance per se does not determine this preference. Egg survival, larval survival, development and resultant damage are not significantly affected by the midge-resistance status of the host.     

Effect of insecticide application and host plant resistance on parasitization of sorghum midge,Contarinia sorghicola coq.

Sorghum midge (Contarinia sorghicola Coq.) (Diptera: Cecidomyiidae) is one of the most important pests of grain sorghum. The effects of different insecticides applied at the complete‐an‐thesis stage for insect control, and host plant resistance on the parasitization of sorghum midge, were studied. Tetrastichus spp. and Eupelmus popa are the major parasites of sorghum midge larvae. Of the several insecticides tested, monocrotophos reduced midge parasitization by half compared with the untreated control. Midge parasitization was lower on midge‐resistant genotypes. Amongst the lines resistant to sorghum midge, the levels of parasitization were higher on the moderately resistant lines IS 10132 and PM 9760 compared to those on IS 3461, IS 7005, IS 9807, IS 19512 and AF 28, etc. Parasite activity closely followed the midge population density across sowing dates. The role of these factors on the effectiveness of midge parasites in integrated pest management are discussed.     

Resistance and susceptibility of Boronia megastigma cultivars to infestations by the psyllid Ctenarytaina thysanura

Studies were conducted on 23 boronia cultivars to determine the mechanisms of resistance and susceptibility to the psyllid, Ctenarytaina thysanura Ferris and Klyver. No antibiosis effects were detected in any of the boronia cultivars investigated. No cultivar was tolerant to C. thysanura attack. However, in both free-choice and no-choice tests in the glasshouse, ovipositional antixenosis (non-preference) was detected in cultivar HC27, whereas cultivars HC4 and HC142 were most preferred for oviposition. Measurement of terminal shoot hardness of cultivars revealed variations in relative hardness. Given a choice between boronia cultivars of the same size and colour but of differing hardness of the terminal shoots, C. thysanura laid more eggs on those cultivars with softer terminal shoots (HC4 and HC142) and laid fewest eggs on harder terminal shoots (HC27). This may explain differences in the psyllid population on different cultivars in the field. Fewer eggs were laid on terminal shoots exceeding a hardness rating of 80 g/mm terminal shoot thickness.     

Antixenosis mechanism of resistance in pigeonpea to the pod borer, Helicoverpa armigera

Abstract:  The noctuid pod borer, Helicoverpa armigera , is one of the most important pests of pigeonpea, and plant resistance is an important component for minimizing the extent of losses caused by this pest. To develop insect-resistant cultivars, it is important to understand the contributions of different components of resistance, and therefore, we studied the antixenosis mechanism of resistance to H. armigera in a diverse array of pigeonpea genotypes under no-choice, dual-choice, and multi-choice conditions. Antixenosis for oviposition was observed in case of ICPL 187-1, ICP 7203-1, ICPL 88039, T 21, ICPL 84060, and ICPL 332 under no-choice, dual-choice and multi-choice conditions. However, the number of eggs laid on ICPL 88039, T 21 and ICP 7203-1 did not differ significantly from those on ICPL 87 under dual-choice conditions. The susceptible check, ICPL 87 was highly preferred for oviposition. The genotypes ICP 7203-1, ICPL 187-1, T 21, ICPL 332, and ICPL 84060 can be used as sources of non-preference mechanism of resistance in pigeonpea improvement programs to breed for resistance to H. armigera .     

Categories and inheritance of resistance to Nilaparvata lugens (Hemiptera: Delphacidae) in mutants of indica rice 'IR64'

Varietal mutants can be useful for developing durable resistance, understanding categories of resistance, and identifying candidate genes involved in defense responses. We used mutants of rice 'IR64' to isolate new sources of resistance to the planthopper Nilaparvata lugens (St?l) (Hemiptera: Delphacidae). We compared two mutants that showed a gain and loss of resistance to N. lugens, to determine the categories of resistance to this pest. Under choice tests, female planthoppers avoided settling and laid fewer eggs on the resistant mutant 'D518' than on the susceptible mutant D1131, susceptible check 'TN1', and wild-type IR64, indicating that antixenosis was the resistance category. Similarly, under no-choice conditions, planthoppers laid 29% fewer eggs in D518 than in IR64, but they oviposited more in 'D1131' and TN1. Honeydew excretion was greater on D1131 seedlings but slightly lower on D518 than on IR64. Nymphal survival and adult female weight did not differ among rice cultivars. D518 showed higher tolerance of N. lugens infestations than IR64. Genetic analysis of the F1, F2, and F3 populations derived from D518 x IR64 revealed that resistance in D518 is dominant and controlled by a single gene. Despite the variation in resistance to N. lugens, both mutants and IR64 performed similarly in the field. The mutant D518 is a new source of durable resistance to N. lugens, mainly due to enhanced antixenosis to female hoppers for settling and oviposition.     

Host range and searching behaviour of Cricotopus lebetis (Diptera: Chironomidae), a tip miner of Hydrilla verticillata (Hydrocharitaceae)

A chironomid midge, Cricotopus lebetis Sublette (Diptera: Chironomidae), was discovered feeding on Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) in Crystal River, Citrus, Co., Florida, in the 1990s. Larvae of the midge mine the apical meristems of hydrilla, causing terminal branching and stunting of the plant. We investigated the fundamental host range of the midge by conducting a series of no-choice and paired-choice tests. No-choice developmental tests with neonate larvae revealed that the fundamental host range of C. lebetis included not only on hydrilla but also several other aquatic plants in different families, suggesting that this insect is not a hydrilla specialist. In paired-choice bioassays, larval colonisation of Elodea canadensis Michx. (Hydrocharitaceae) and Najas guadalupensis (Spreng.) Magnus (Najadaceae) was greater than colonisation of H. verticillata. Behavioural bioassays in a Y-tube olfactometer and in Petri dishes suggested that neonate larvae were not able to locate host plant material, whereas older larvae were successful in finding hosts. In paired-choice oviposition tests, adult females discriminated between potential oviposition sites, with greater numbers of eggs laid on E. canadensis and N. guadalupensis than on H. verticillata. This study is the first detailed account of host searching and oviposition behaviour of a phytophagous chironomid midge. The results will be used to assess the potential value of C. lebetis as a biological control agent of hydrilla.     

Seasonal incidence of Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) and its parasitoids on Sorghum halepense (L.) Pers. in south-eastern Queensland, Australia

Abstract  To quantify the role of Johnson grass, Sorghum halepense , in the population dynamics of the sorghum midge, Stenodiplosis sorghicola , patterns of flowering of Johnson grass and infestation by sorghum midge were studied in two different climatic environments in the Lockyer Valley and on the Darling Downs in south-eastern Queensland for 3 years. Parasitism levels of S. sorghicola were also recorded. In the Lockyer Valley, Johnson grass panicles were produced throughout the year but on the Darling Downs none were produced between June and September. In both areas, most panicle production occurred between November and March and infestation by S. sorghicola was the greatest during this period. The parasitism levels were between 20% and 50%. After emergence from winter diapause, one to two generations of S. sorghicola developed on S. halepense before commercial grain sorghum crops were available for infestation. Parasitoids recorded were: Aprostocetus diplosidis , Eupelmus australiensis and two species of Tetrastichus. Relationships between sorghum midge population growth rate and various environmental and population variables were investigated. Population size had a significant negative effect ( P  < 0.0001) on population growth rate. Mortality due to parasitism showed a significant positive density response ( P  < 0.0001). Temperature, rainfall, open pan evaporation, degree-days and host availability showed no significant effect on population growth rate. Given the phenology of sorghum production in south-eastern Queensland, Johnson grass provides an important bridging host, sustaining one to two generations of sorghum midge. Critical studies relating population change and build-up in sorghum to sorghum midge populations in Johnson grass are yet to be performed.     

Oviposition in Culicoides impunctatus under laboratory conditions

We present a laboratory-based examination of oviposition preference in the Scottish biting midge, Culicoides impunctatus (Diptera: Ceratopogonidae). A variety of oviposition substrates were screened in no-choice and choice bioassays for efficacy in eliciting an egg-laying response. Both upper-layer photosynthetic Sphagnum spp. moss and Juncus articulatus infusions were identified as producing increased oviposition under no-choice conditions. During choice trials against a control of damp cottonwool, upper-layer Sphagnum spp. moss produced a significantly greater egg-laying response. These conclusions are interpreted in terms of possible cues involved in oviposition site selection and assessed for future use in colonisation of this troublesome species.     

Morphological diversity and function of the stigma in Ficus species (Moraceae)

The stigma plays several roles such as pollen hydration and selection, and pollen tube nutrition. In the Ficus-fig wasp mutualism, stigmata have an additional, almost unknown, function by representing a physical interface for both plant and wasp reproduction. We used light and electron microscopy to compare the detailed morphology of the stigmata of nine Ficus species of different sections and with different pollination modes and sexual expressions. Figs were collected at the stage when the stigmata were receptive for pollination. Stigmata in actively pollinated monoecious species have well developed papillae concentrated on the adaxial surface exposed towards the fig cavity. Conversely, the passively pollinated monoecious species have the whole surface of the stigmata covered by somewhat smaller papillae. In both actively and passively pollinated monoecious species these features are consistent, irrespective of style length. In all actively pollinated gynodioecious species, the stigmata of pistillate flowers were tubular or infundibuliform whereas in almost all actively pollinated monoecious species (except F. racemosa) the stigmata were filiform, with one branch or two asymmetric branches. In gynodioecious species the short-styled flowers in “male” figs show a limited receptive surface with small papillae, while the stigmata of long-styled flowers in “female” figs are covered by papillae that extend down the sides of the style, increasing the stigmatic surface. In actively pollinated species, stigmata are cohesive, forming a common surface for pollen tube germination (= synstigma). The synstigma arrangement was quite variable: lax, cohesive or very cohesive, with entanglement by stigmatic papillae and stylar trichomes. Entanglement by stylar trichomes is common in gynodioecious species. The synstigma arrangement did not correlate with phylogeny or breeding system. This study is the first to report a very loose synstigma in actively pollinated monoecious Ficus species. Our analyses revealed that, in Ficus, the synstigma is functionally analogous to an extra-gynoecial compitum. Comparative studies will be required to test further hypotheses about the evolutionary determinants of such variation.     

Effects of larval movement behavior and density on emergence success and adult body size in a commensal midge

Changes in larval density and movement behavior of a commensal midge, Nanocladius (Plecopteracoluthus) sp. #4, were monitored for 26 weeks in recirculating laboratory streams. Adults were captured at emergence, sexed, and weighed to assess the effect of larval density and movement behavior on emergence success and adult size. The density of midges on hosts declined with time and coincided with a springtime increase in larval movement frequency. Midges residing on hosts with high spring densities emerged significantly less than midges on hosts with low densities. Resident midge density on hosts did not influence the likelihood of successful colonization by commensals and colonizers showed no preference for initial attachment site on hosts. However, colonizing midges emerged significantly less than resident midges. Similarly, successful emergers changed tube positions significantly less often as larvae relative to non-emergers. There was no difference in adult body weight of resident midges and colonists/movers, but adult males which emerged from commensal-laden (high density) hosts were significantly smaller than males from low density hosts. These data indicate larval density and movement behavior may have strong fitness consequences for commensal midges.