A new genus and two new species of aphids (Homoptera: Aphididae) from north-west India

A new aphid genus Raychaudhuriella and two new specices viz. Raychaudhuriella myzaphoides and Rhopalosiphoninus sensoriatus are described from Himachal Pradesh, north-west Himalaya. The affinity of Raychaudhuriella gen. nov. is drawn with Aspidophorodon Verma, Cavariela del Guercio, Myazphis van der Goot, Tricaudatus Narzikulov and Vesiculaphis del Guercio. Figures and biometrical data of the new species have been provided.     

Colonization of a headwater stream during three years of seasonal insecticidal applications

We investigated recolonization by insects of a small headwater stream in the southern Appalachian Mountains that was treated along its entire length with an insecticide (methoxychlor). Initial treatment (December 1985) resulted in massive insect drift. Applications continued seasonally for three years, and drift was measured during each treatment. Taxonomic composition of the drift indicated several responses: (1) Some taxa were eliminated. (2) A number of taxa occurred only sporadically following initial treatment. (3) Early instars for some taxa showed seasonal occurrences which closely paralleled known life cycles and flight periods of adults. Groups which provided strong evidence for aerial recolonization included several Ephemeroptera, Plecoptera (Peltoperlidae and Isoperla spp.), and Trichoptera (Parapsyche cardis, Diplectrona modesta, Pycnopsyche spp., and Lepidostoma spp.). (4) Some long-lived taxa survived and exhibited distinct growth through several treatment periods. These include Odonata (Lanthus and Cordulegaster), some Ephemeroptera, and some Diptera (Tipulidae, Ceratopogonidae, and Tanypodinae). (5) Some taxa which were not present at the time of initial treatment appeared during the experiment. Chironomidae dominated the drift in all samples, and the number of genera did not decrease during the three-year treatment period. Of the 27 chironomid genera identified, only Micropsectra decreased in proportional abundance during treatment. In contrast, several genera (Corynoneura, Meropelopia, Parametriocnemus, and Tvetnia) showed little change in relative abundance. Larsia (Tanypodinae) increased in proportional abundance during the treatment period.     

The role of aquatic moss on community composition and drift of fish-food organisms

Macroinvertebrate density, biomass and drift were studied from moss-covered and moss-free channels in the South Fork Salmon River, Idaho. Insect densities were compared for 10 different substrate types and locations involving moss (Fontinalis neo-mexicana), sand, pebbles and cobbles. An ANOVA test demonstrated that insect densities varied significantly with substrate type (P < 0.05), and that total insect density in moss clumps differed significantly from densities in mineral substrates. Insect densities were 4–18 times greater in moss clumps than in mineral substrates under and adjacent to moss; sands under moss supported the lowest densities. During most tests, densities in pebble and cobble substrates adjacent to moss clumps were not significantly different from those found in similar substrates in the moss-free channel. The 20% moss-covered channel had 1.6 to 7.2 greater insect density and 1.4 to 6.1 greater biomass than did the moss-free channel for the tests conducted. Generally, midges (Chironomidae) made up over 50% of the insect community; annelids were the principal non-insect invertebrates.In spite of greater insect density and biomass in a moss-covered than in the moss-free channel, we did not demonstrate universally increased drift of the immature stages from the moss-covered channel, at least during daylight hours. As a consequence, we infer that salmonid fishes, feeding primarily on drifting insects during the daytime, may not derive increased caloric benefit from moss habitats until the insects emerge as adults.     

Wind dispersal and settling of first-instar crawlers of the cochineal insect Dactylopius austrinus (Homoptera: Coccoidea: Dactylopiidae)

Abstract. 1. The efficiency of D.austrinus as a biological control agent depends on successful colonization of the cactus weed Opuntia aurantiaca .
2. Unlike other coccoid insects, the female crawlers (first-instar larvae) of cochineal insects develop long wax fiaments on the dorsal surface of the body that reduce their terminal velocity in air and enhance wind dispersal.
3. Dactylopiid males are dispersed as winged adults and male crawlers of D.austrinus have fewer and shorter filaments than the females and they are blown a shorter distance in a wind tunnel.
4. Vertical and horizontal wind dispersal of D.austrinus from O.aurantiaca in the field is usually very limited, but was greatly improved when crawlers were launched from an elevated 'tower'.
5. Preparatory to dispersal, female crawlers climb to the top of the host plant and 'take-off' from there. This behaviour is most marked in crawlers 2–3 days old at which stage the wax filaments are best developed: the behaviour is never manifest following artificial 'dispersal'.
6. Final settling on cladodes of the host plant is a function of the age of the female crawlers and of the condition of the cladodes.
7. When given a choice, approximately equal numbers of crawlers settled on cladodes that had received high and low fertilizer treatments. More crawlers settled on cladodes that had been kept in the shade than on those kept in the sun, and on basal rather than terminal cladodes.
8. The highest percentage of crawlers settled on cladodes that were 20% dehydrated. Settling success was much lower on more desiccated cladodes.     

Interrelationship of Meloidogyne hapla and Ditylenchus dipsaci on Resistant and Susceptible Alfalfa

Simultaneous inoculations of alfalfa with Meloidogyne hapla larvae and Ditylenchus dipsaci at 16, 20, 24, and 28 C did not depress penetration of either nematode in ''Nev Syn XX'' -a selection resistant to M. hapla and D. dipsaci, ''Vernal 298'' -a selection resistant to M. hapla and susceptible to D. dipsaci, ''Lahontan'' -a cultivar resistant to D. dipsaci and susceptible to M. hapla, and ''Ranger'' -a cultivar susceptible to both M. hapla and D, dipsaci. Infection with D. dipsaci depressed growth of susceptible ''Vernal 298'' and ''Ranger'' at all soil temperatures, except for ''Vernal 298'' at 16 C. Infection with M. hapla alone did not depress growth of any of the alfalfas. A combination of M. hapla and D. dipsaci resulted in a synergistic weight depression on ''Ranger'' at all soil temperatures. Inoculation of the four alfalfas with D. dipsaci 2, 4, 6, and 8 wk before inoculation with M. hapla at 16, 20, 24, and 28 C did not influence the resistance or susceptibility of ''Nev Syn XX,'' ''Lahontan,'' or ''Ranger.'' However, galling of ''Vernal 298'' by M. hapla was affected by soil temperature, plant age, and inoculation with D. dipsaci.     

A laboratory study on the thermal tolerance of four southeastern stream insect species (Trichoptera,Ephemeroptera)

The acute thermal tolerances of four southeastern stream insect species, Ephemerella invaria (Walker), Stenonema ithaca (Clemens and Leonard), Symphitopsyche morosa (Hagun), and Brachycentrus lateralis (Say) were determined using an artificial stream enclosure. All species were acclimated at 10°C for 72 hours prior to instantaneous immersion into heated water for 96 hours. Percent mortality was recorded and the temperature at which 50% mortality occurred determined (LT5o). Data were subjected to standard statistical analysis.Thermal tolerance values were compared between species tested and to results from previous investigations using similar methodologies. The evolution and life histories of these species were also discussed in relation to their thermal tolerance values.     

Colonization of artificial substrates by stream insects: Influence of substrate size and diversity

A field experiment was performed in a New Mexico (U.S.A.) stream to investigate the relation between size and diversity of substrate and numbers and diversity of colonizing insects. Baskets with either small gravel, large gravel, or a 1 : 1 mixture of the two sizes were placed in a riffle area and colonization was monitored for 19 days.Colonization was rapid, and both total number of individuals and number of species colonizing the substrates had stopped increasing by the end of the experiment. Fewer individuals colonized baskets downstream, suggesting that the drift is a major source of insect colonists. Small substrate supported more individuals and more species than the larger stones. Total number of individuals and the number of species on the mixed substrate were between numbers on small and large substrate. These results do not support previous generalizations on the relation between substrate size and complexity and the structure of invertebrate communities in streams. Results of the study are compared with the findings of recent experimental studies and it is suggested that earlier generalizations on the role of substrate size and complexity need to be reexamined.Order of authors was determined by the flip of a coin. Reprint requests may be sent to either author.     

Sampling Bias in Roadsides: The Case of Galling Aphids on Pistacia Trees

Sampling along roadsides is convenient and is widely practiced in insect population researches. Ecological conditions in road verges are very different than those prevailing in natural habitats and they affect the annual growth of plants in semi-arid and arid regions. This in turn may improve development, survival and abundance of insects feeding on plants growing in roadsides. These trends may bias the results of sampling. To verify this assertion, we quantified the effects of growing in roadside on annual growth of Pistacia atlantica trees and Pistacia palaestina shrubs and compare two demographic indexes of nine gall-inducing aphid species on trees growing along roads with trees in the open landscape, in Israel. The annual growth of the two host plants was significantly more vigorous in roadsides than away from roads. Tests of Combined Probabilities showed that the likelihood of P. atlantica and P. palaestina to be parasitized by more galls of Fordini species is higher in roadsides than away from roads. Moreover, in the semi-dry regions of Israel, three aphid species on P. atlantica and five species on P. palaestina induced more galls in plants growing along roads than away from roads, while in the rainy Northern region, the difference was not significant between the two habitats. These results indicate a biased evaluation of population size in roadside habitat, which has to be accounted in insect–plant relation researches.