Sexual generation and overwintering of the peach leaf curling aphid Brachycaudus helichrysi (Kalt.) in Himachal Pradesh, India

Autumn migrants preferred to settle on the dorsal leaf surface of peach with gynoparae being more numerous than alate males. These return migrants on peach were similar to those described by others except for a comparatively smaller processus terminalis. Among the oviparae with metatibial pseudosensoria. most (62.5%) had six antennal subdivisions; 25% possessed five antennal subdivisions and half of these were parasitised. Oviparae were bigger than those previously described on plum/damson but their processus terminalis was comparatively shorter. Ultimate instar nymphs were without pseudosensoria and had 5–seg-mented antennae, the VI segment being cleaved from the meriston during the final moult. Alate males mated with the oviparae, mating duration being 3 to 6 min. Oviparae contained, at the most, two well developed eggs at one time, and normally deposited eggs singly during November-December. Most eggs hatched within 20–28 days but those laid in December during colder weather took up to 50 days to hatch. By midJanuary most eggs had hatched. Fundatrix developmental rate was dependent on sap-flow. Overwintering occurred as the fundatrix.     

Stylet activities and potato virus Y vector efficiencies by the aphids Brachycaudus helichrysi and Drepanosiphum platanoidis

Stylet penetration activities of two aphid species were recorded electrically and compared with their efficiency of potato virus Y transmission. B. helichrysi (Kltb.) acquired the virus during 15% of single penetrations on infected leaves. These acquisitions were associated with the occurrence of cell membrane puncture by stylets, recorded during 44% of the penetrations. D. platanoidis (Schrank) punctured membranes during only 8% of penetrations, and its acquisition efficiency was less than 1%. The frequency with which aphids puncture cell membranes appears to partially determine their vector efficiency.     

Fluctuations of Vanessa cardui butterfly abundance with El Niño and Pacific Decadal Oscillation climatic variables

Annual 4th of July Butterfly Count data spanning more than 20 years are examined to explore Vanessa cardui (Painted Lady) population fluctuations with ENSO (El Niño) and Pacific Decadal Oscillation (PDO) indices. California, Colorado and Nebraska censuses exhibit a strong positive correlation with the strong El Niño events of 1982–1983 and 1997–1998 and the weaker event of 1991–1992. Regression analysis shows the population fluctuations are strongly coupled to climate variations on both short (El Niño) and longer (Pacific Decadal Oscillation) time scales. Recognizing the sensitivity to these time scales is important for predicting longer‐term global climate change effects.     

Long‐range seasonal migration in insects: mechanisms,evolutionary drivers and ecological consequences

Myriad tiny insect species take to the air to engage in windborne migration, but entomology also has its ‘charismatic megafauna’ of butterflies, large moths, dragonflies and locusts. The spectacular migrations of large day‐flying insects have long fascinated humankind, and since the advent of radar entomology much has been revealed about high‐altitude night‐time insect migrations. Over the last decade, there have been significant advances in insect migration research, which we review here. In particular, we highlight: (1) notable improvements in our understanding of lepidopteran navigation strategies, including the hitherto unsuspected capabilities of high‐altitude migrants to select favourable winds and orientate adaptively, (2) progress in unravelling the neuronal mechanisms underlying sun compass orientation and in identifying the genetic complex underpinning key traits associated with migration behaviour and performance in the monarch butterfly, and (3) improvements in our knowledge of the multifaceted interactions between disease agents and insect migrants, in terms of direct effects on migration success and pathogen spread, and indirect effects on the evolution of migratory systems. We conclude by highlighting the progress that can be made through inter‐phyla comparisons, and identify future research areas that will enhance our understanding of insect migration strategies within an eco‐evolutionary perspective.     

Wind matters: Asymmetric distribution of aphids on host plants can be explained by stems functioning as windbreaks

Understanding how abiotic factors influence organisms at present is the necessary first step to predict how species assemblages could be affected by climate change in the future. We examined how wind, a poorly studied abiotic factor, affects the distribution and abundance of two aphid species, Uroleucon aeneum and Brachycaudus cardui (hereafter black and green aphids, respectively), that live on the thistle Carduus thoermeri (Asteraceae) in a windy region of Patagonia, Argentina. First, considering the prevailing wind direction, we described the distribution of both aphid species around plant stems. Then, we performed a bi‐factorial experiment in which we cut stems with aphids to manipulate their position respect to wind (exposed/unexposed) and to control wind incidence (protected/unprotected). Finally, using the species most affected by wind, we examined possible mechanisms through which wind could affect aphids. Both aphid species were less abundant on the side of the stem exposed to wind respect to the unexposed side; and this pattern was stronger for the black aphid. When black aphids were positioned exposed to wind and without protection, their proportion changed towards the unexposed side of the stem; while green aphids showed a weaker response to wind. Laboratory experiments demonstrated that wind triggered both the detachment of black aphids and their movement towards the unexposed side of the stem. Our results showed that wind can explain the asymmetric distribution of aphids around plants and that stems can act as windbreaks. In a less windy future scenario, aphids could expand their foraging area, reaching higher infestation rates, which could affect their role in structuring ant assemblages and their status as crop pests. This work highlights the importance of testing the effects of less studied abiotic factors to fully understand how climate change could impact on the abundance and distribution of animals in the future.     

Host Range ofBrachycaudus rumexicolens(Patch), an Aphid Associated with the Polygonaceae

The aphidBrachycaudus rumexicolensis a recent arrival in Australia where the weedsEmex australis, E. spinosa,andRumexspecies are its recorded hosts. Host range on 114 species representing 42 plant families was assessed in the laboratory to determine the aphid species' potential as a biological control agent againstE. australis.Survival and reproductive success were measured in clip and/or dialysis-tube cages.B. rumexicolensdeveloped most successfully onEmexspp. andRumexspp. and to a lesser extent on other Polygonaceae.Lupinus albus(white lupin) andTriticum aestivum(wheat) were the only non-Polygonaceae plants on whichB. rumexicolensdeveloped to a degree similar to its usual hosts. At a field site in Western Australia,E. australisandPolygonum avicularewere the only Polygonaceae present and the primary host species ofB. rumexicolens.At peak abundance, it was found on other pasture and crop species, but at considerably lower numbers than on its Polygonaceae hosts. It was concluded that this was due to local migration and that populations would not be sustained on non-Polygonaceae plants. It was also concluded that the risk of virus transmission would not be increased by the presence ofB. rumexicolenson nonhosts.B. rumexicolensis considered sufficiently safe to use in programs aimed at augmenting the impact of biological control agents on the weedE. australis.     

Presence of a cerebral factor showing summer-morph-producing hormone activity in the brain of the seasonal non-polyphenic butterflies Vanessa cardui, V. indica and Nymphalis xanthomelas japonica (Lepidoptera: Nymphalidae)

Three species of nymphalid butterflies, Vanessa cardui, V. indica and Nymphalis xanthomelas japonica , do not exhibit seasonal polyphenism in wing coloration. To determine whether seasonal non-polyphenic butterflies possess a cerebral factor affecting wing coloration, we used a Polygonia c-aureum female short-day pupal assay for detection of summer-morph-producing hormone (SMPH) activity in P. c-aureum. When 2% NaCl extracts of 25 brain-equivalents prepared from the pupal brains of V. cardui, V. indica or N. xanthomelas japonica were injected into Polygonia female short-day pupae, all recipients developed into summer-morph adults with dark-yellow wings, and the average grade score (AGS) of summer morphs showing SMPH activity was 3.8, 3.7 and 4.0, respectively. In contrast, when acetone or 80% ethanol extracts prepared from pupal brains were injected into Polygonia pupae, all recipients developed into autumn-morph adults with a dark-brown coloration and each exhibited an AGS of less than 0.5. Our results indicate that a cerebral factor showing SMPH activity is present in the pupal brain of seasonal non-polyphenic nymphalid butterflies, suggesting that a SMPH and cerebral factor showing SMPH activity occur widely among butterfly species. This finding will improve our understanding of the presence of cerebral factors showing interspecific actions of SHPH.     

Back to Africa: autumn migration of the painted lady butterfly Vanessa cardui is timed to coincide with an increase in resource availability

1. The painted lady Vanessa cardui is a long‐range migratory butterfly that performs an annual multi‐generational round‐trip between Europe and Africa. Each autumn it returns to northwest (NW) Africa, presumably to track changes in resources that follow a predictable climate‐related spatio‐temporal pattern. 2. Data on the abundance of adult and immature stages in the Maghreb in 2014–2016 are used to test several hypotheses regarding the autumn migration of this species. 3. A strong seasonal migratory strategy was confirmed by the all but total absence of the species in NW Africa at the end of summer and the arrival of huge numbers migrants in October and November. Migration was timed to coincide with an increase in host plant availability but not with any increase in nectar sources. 4. Flower abundance was the main predictor of adult abundance in autumn, with Ditrichia viscosa, Verbesina encelioides, and Medicago sativa being key resources that attracted enormous numbers of butterflies to oases, ruderal habitats, and oueds. The distribution of immature stages was strongly predicted by host plant abundance (with traditional agriculture representing the most important breeding habitat) and latitude (most breeding occurred in the south of the region). Also, both adults and immature stages were more common inland than in coastal areas. 5. Changes in age structure of the adult population were also noted. The number of fresh adults slowly increased, indicating that butterflies did not return in a single wave and that the first offspring of the first returners were already emerging when some butterflies were still arriving.     

Adult stemmata of the butterfly Vanessa cardui express UV and green opsin mRNAs

Adult stemmata are distinctive insect photoreceptors located on the posterior surfaces of the optic lobes. They originate as larval eyes that migrate inward during metamorphosis. We used a combination of light microscopy and in situ hybridization to examine their anatomical organization in the butterfly Vanessa cardui and to test for the presence of visual pigments, the light sensitive components of the visual transduction pathway. The bilateral cluster of six internal stemmata is located near the ventral edge of the lamina. They retain the dark screening pigment and overlying crystalline cones of the larval stemmata. We found two opsin mRNAs expressed in the stemmata that are also expressed, respectively, in UV-sensitive and green-sensitive photoreceptor cells in the compound eye. A third mRNA that is expressed in blue-sensitive photoreceptor cells of the compound eye was not expressed in the stemmata. Our results reinforce the idea that the adult stemmata are not merely developmental remnants of larval eyes, but remain functional, possibly as components of the circadian input channel.This work was supported by grants from the National Science Foundation to A.D.B. (IBN-0346765) and R.H.W (IBN-9874493).