Sven Hellqvist

Identification of the Sex Pheromone of the Currant Shoot Borer Lampronia capitella

Under an artificial light:dark cycle, females of Lampronia capitella were observed calling, with extended terminal abdominal segments, during the first 2 hr of the photoperiod. Extracts of terminal abdominal segments from females elicited large electroantennographic responses from male antennae. Gas chromatography with electroantennographicDetection revealed three active peaks. Based on comparison of retention times and mass spectra of synthetic standards, these compounds were identified as (Z,Z)-9,11-tetradecadienol and the corresponding acetate and aldehyde. The electroantennographic activity of the four geometric isomers of all three compounds was investigated, and the respective (Z,Z)-isomer was found to be the most active in all cases. Aldehydes generally elicited larger antennal responses than alcohols, whereas acetates were the least active compounds. A subtractive trapping assay in the field, based on a 13:26:100 μg mixture of (Z,Z)-9,11-tetradecadienal, (Z,Z)-9,11-tetradecadienyl acetate, and (Z,Z)-9,11-tetradecadienol confirmed that all three compounds are pheromone components. Subtraction of (Z,Z)-9,11-tetradec- adienol from the blend completely eliminated its attractiveness, whereas the other two-component blends showed reduced activity. This is the first pheromone identification from the monotrysian superfamily Incurvarioidea, confirming that the common pheromones among ditrysian moths (long-chain fatty acidDerivatives comprising alcohols, acetates, and aldehydes with one or more double bonds) is not an autapomorphy of Ditrysia, but a synapomorphy of the more advanced heteroneuran lineages.

A survey of Lygus parasitoids in Sweden

Abstract Lygus spp. (tarnished plant bugs) are generalist herbivores and occur as pests on a wide range of crops. In the development of conservation biological control strategies for Lygus spp. in Sweden, more information is needed on the impact of different natural enemies. In this study, we determined the occurrence and the degree of parasitism on adults and nymphs of the most common Lygus species in alfalfa, barley, red clover and oilseed rape in Uppsala in Central Sweden and in Umeå in Northern Sweden. Nymphs and adults of Lygus spp. were collected by sweep netting for estimation of their parasitism level (by dissection) and identification of parasitoid species (from reared Lygus specimens). The dominant Lygus species in both locations was L. rugulipennis (75–99%). Parasitism by Phasia obesa (Tachnidae) on overwintering Lygus adults was recorded in almost every field sampled at both locations. The parasitism level was low at overwintering sites but increased in arable fields during summer. Lygus nymphs collected in Umeå were parasitised by Peristenus pallipes (Braconidae) and in Uppsala by P. relictus, P. pallipes and P. varisae. The hyperparasite Mesochorus globulator (Ichneumonidae) was recorded in Umeå.

Biotypes of Dasineura tetensi, differing in ability to gall and develop on black currant genotypes

Variation in damage levels on certain black currant, Ribes nigrum L., genotypes, caused by the black currant leaf midge, Dasineura tetensi (Rübs.) (Diptera: Cecidomyiidae), has been observed in northern Sweden. I investigated whether this variation is due to variation in virulence among midges. From a field population of midges, I successfully selected for virulence and avirulence, respectively, on the resistant black currant genotype cultivar ‘Storklas’ (called resistant genotype). The performance of avirulent and virulent midge larvae on two black currant genotypes were studied in experiments where first or second instar larvae were artificially transferred. There were no differences in larval survival and developmental rate between the two midge types when transferred to the susceptible currant genotype ‘7801–31’ (called susceptible genotype). Larvae of the virulent strain established galls and developed on ‘Storklas’ but development was initially slower there than on the susceptible currant genotype. Larvae of the avirulent strain suffered high mortality or remained in first instar on that same currant genotype when transferred alone, but developed readily if transferred together with virulent larvae. Larvae transferred in second instar to host plants susceptible to the larvae resumed feeding and developed further to maturity. Second instar larvae were also able to establish new galls even though these galls were not as well developed as those caused by first instar larvae. Black currant plantations in northern Sweden were surveyed and local midge populations were found to be composed of either avirulent, virulent or a mixture of both midge types. Virulent midges were not restricted to plantations where resistant currant genotypes were grown. I conclude that, at least, two biotypes of the midge exist, and that those two are distinguished by the ability to gall and survive on ‘Storklas’.

Mulching with grass-clippings in cauliflower : effects on yield and brassica root flies (Delia spp.)

Abstract The effects of mulching with organic materials on yield and damage by brassica root maggots (Delia floralis and D. radicum) in cauliflower, were studied in field experiments for 3 years. Mulching with grass‐clippings consistently resulted in increased yield and reduced damage by root maggots, as measured by wilting symptoms and root damage. During one of these years, the effects of mulching with grass‐clippings on root fly population dynamics was also studied. Mulching did not reduce egg‐laying but resulted in increased egg‐predation. The number of D. floralis pupae per plant was not reduced by mulching, probably because of higher larval mortality owing to competition in unmulched plots. Mulching decreased the rate of parasitization by Aleochara bilineata (Staphylinidae), resulting in a higher number of healthy pupae per plant in grass‐mulched plots, and these healthy pupae were heavier. All these effects were most pronounced when the mulch material completely covered the ground, even close to th...

Biology of Synacra sp. (Hym., Diapriidae), a parasitoid of Bradysia paupera (Dipt., Sciaridae) in Swedish greenhouses

The biology of the sciarid parasitoid Synacra sp. was studied. The species has, in recent years, been found in several Swedish greenhouses. The species oviposits and develops in larvae of Bradysia paupera but not in Lycoriella solani. The mean developmental time was 25.4 days at 23 °C and 44.8 days at 17°C. Females produced an average of 272 viable offspring at 23°C and 290 at 17°C. The potential maximum rate of population increase was higher than that for its host at 23 °C. The possibilities for the parasitoids use as a biological control agent against sciarids is discussed.

Expression of a bimodal emergence pattern in diapausing and non-diapausing Delia floralis: a phenological survival strategy

For phytophagous insect species in regions with a variable climate, there is an inherent risk in having all progeny in one peak following the winter, during the critical period of adult development, emergence, and reproduction (Walbauer, 1978; Goulson, 1993). Temperate zone insects have developed a great diversity of phenological strategies to enhance survival under conditions of frequent annual variation in environmental conditions. One such strategy is polymodal emergence. According to published records, polymodal emergence has been observed in only three insect orders: Hymenoptera, Diptera, and Lepidoptera (Biron et al., 2002). One such species, the cabbage root fly, Delia radicum (L.) (Diptera: Anthomyiidae), has been studied intensively. The postdiapause bimodal emergence pattern of D. radicum adults was first noted by Finch & Collier (1983) who later defined the two phenotypes as follows: after diapause, the adult flies of the early emerging phenotype emerge in less than 20 days at 19 ± 1 ° C (320 ° d 4 ) while adults of the late emerging phenotype emerge after more than 30 days at 19 ± 1 ° C (320 ° d 4 + 280 ° d 7 ) (Collier et al., 1989a,b). At first it was assumed that diapause was necessary for the expression of the polymodal emergence, but this phenological strategy has been found in both diapausing and non-diapausing D. radicum pupae (Biron et al., 1998). The turnip root fly, Delia floralis (Fallén) (Diptera: Anthomyiidae), occurs sympatrically with D. radicum in northern parts of the holarctic region. The two species have a similar biology and host range, but D. floralis is mostly confined to sandy soils (Jørgensen, 1957, 1976). They also differ phenologically and in the number of generations per year: D. floralis generally has a single generation (but see Jørgensen, 1976) while D. radicum in most areas has more than one generation, with adults of the first generation emerging earlier than those of D. floralis . In the current study our main objective was to investigate, under controlled conditions, the patterns of emergence for two diapausing field populations of D. floralis from Sweden and Finland. Secondly, we investigated whether early and late emerging phenotypes are expressed in pupae in continuous development without diapause. Thirdly, we segregated and reared early and late emerging phenotypes without diapause from both the Swedish and the Finnish populations to assess changes in phenotype frequency over two generations.

Oviposition and flight period of the currant shoot borer Lampronia capitella

The currant shoot borer, Lampronia capitella (Lep., Prodoxidae), is an important pest of currants, Ribes spp., in northern Europe. Oviposition was studied in cage experiments and the flight period was monitored in field studies using pheromone‐baited traps. Blackcurrant, Ribes nigrum, was the host species in both studies. The total egg supply of females was on average 107 eggs and oviposition started 2–5 days after emergence. About 60% of the eggs were laid during the first day of the oviposition period. Eggs were laid in currant fruitlets, in batches comprising several, usually four to seven eggs. The flight period started shortly after the end of the flowering period of blackcurrant, and lasted for about 3 weeks.

Interaction between relative humidity and resistance to Dasineura tetensi in blackcurrant

1 Infestation by the blackcurrant leaf midge Dasineura tetensi and galling incidence on a susceptible (cv. ‘Öjebyn’) and a moderately resistant (cv. ‘Storklas’) blackcurrant genotype was studied in the field for two midge generations in the same growing season. On the resistant genotype gall initiation is delayed.