Marika Mänd

Population changes and phenotypic diversity of Phytophthora infestans isolates from Estonia and Finland.

In Estonia and Finland, 386 and 671 isolates, respectively, of Phytophthora infestans were collected during the growing seasons of 2001-2007. Collection was from groups of potato cultivars of different origin from field plots at two research institutions in eastern and northern Estonia and from variety trials at two locations and commercial potato fields in Finland. Mating type, pathotype based on virulence on a differential set of 11 R genes of Solanum demissum and response to the fungicide metalaxyl were determined in both countries by comparable methods. The diversity of the P. infestans populations in both countries over the monitoring period was high. In Finland, the proportion of A1/A2 mating types was almost equal throughout the monitoring period, while in Estonia the A1 population, dominating in 2001-2004, shifted towards an equal proportion of both mating types in 2005-2007. The diversity of the P. infestans population, as measured by virulence pathotypes and the number of avirulence factors per isolate, developed in opposite directions in Estonia and Finland from 2001-2004 to 2005-2007: the diversity decreased in Estonia and increased in Finland. Metalaxyl sensitivity in the Estonian P. infestans population increased while in Finland it decreased during the same period. Results clearly show differences between Estonian and Finnish populations of P. infestans in several aspects, which may derive from cropping practices. The high A2 mating type percentage during 2005-2007 in both countries points to soil contamination with oospores.

High Repeatability of Anti-Predator Responses and Resting Metabolic Rate in a Beetle

Measures of repeatability are essential for understanding behavioral consistency and individual differences in behavior, i.e. animal personalities. We studied anti-predator responses of the yellow mealworm beetle (Tenebrio molitor) and performed behavioral tests in plastic containers representing a typical laboratory environment of T. molitor. Behavioral tests were repeated in Eppendorf test tubes where we also measured resting metabolic rate (RMR). Results show that the response latency to a threatening/startling stimulus, and the total time spent in the state of tonic immobility, correlated across the tests. The behavioral responses were repeatable and RMR covaried phenotypically with personality: we found a negative correlation between response latency time and time spent immobile, a positive correlation between response latency and RMR, and a negative correlation between RMR and total time spent immobile. These correlations were also similar across trials performed in the Eppendorf test tubes and the plastic containers.

The length of discontinuous gas exchange cycles in lepidopteran pupae may serve as a mechanism for natural selection

Gas exchange is studied in diapausing pupae of Mamestra brassicae L., whose larvae are reared under identical conditions. The release of CO2 gas is recorded with infrared gaseous analyzers. Oxygen convective uptake into the tracheae and oxygen consumption rates are recorded by means of a constant‐volume coulometric respirometer. Outputs from both of these respirometry systems are combined with infrared actographs. All 3‐month‐old pupae of M. brassicae display a pattern of discontinuous gas exchange (DGE) cycles of CO2 gas release by bursts, although the lengths of these cycles varies between individuals. Some pupae exhibit long DGE cycles of at least 20 h in duration, with negligible CO2 gas release during interburst periods, and there is presumed to be a convective gas exchange at this time. As a result of a partial vacuum inside the tracheae, a large oxygen convective uptake always occurs at the start of the spiracular opening phase. Other pupae have short DGE cycles of less than 3 h in duration, with elevated CO2 gas release during the interburst period, when gas exchange is predominantly diffusive. The spiracular open phase in these pupae consists of frequent separate convective bursts of CO2 gas release, with the opening–closing rhythms of the spiracles, which are considered as O phase fluttering. The pupae with long DGE cycles exhibit extremely low metabolic rates and very low total water loss rates, whereas those with short DGE cycles have higher metabolic and total water loss rates. The pupae with long DGE cycles live approximately twice as long as those with short cycles; thus, the present study demonstrates that long DGE cycles confer a fitness benefit on pupae as a result of a lower metabolic rate associated with water economy, conferring on them a longer life.

Flea beetle (Chrysomelidae: Alticinae) species composition and abundance in different cruciferous oilseed crops and the potential for a trap crop system

Flea beetles are significant insect pests of cruciferous oilseed crops in northern Europe. A two-year small-scale field experiment was performed to determine the species complex and abundance of flea beetles (Chrysomelidae: Alticinae) associated with eight cruciferous oilseed plants: Brassica juncea (L.) Czern., Brassica napus L. var. oleifera subvar. annua, Brassica nigra (L.) Koch, Brassica rapa L. var. oleifera subvar. annua, Camelina sativa (L.) Crantz, Eruca sativa Mill., Raphanus sativus L. spp. oleifera (DC) Metzg. and Sinapis alba L. Their relative attractiveness to flea beetles was compared to assess their potential for use within a trap crop system for spring oilseed rape. Adults of six species of flea beetles were found on the test plants. Phyllotreta undulata Kutsch. was the most abundant species followed by Phyllotreta nigripes (Fabr.), Phyllotreta nemorum L. and Phyllotreta vittata (=striolata) (Fabr.), while Phyllotreta atra (Fabr.) and Chaetocnema concinna Marsh. were occasionally present. The species composition of flea beetles on seven of the investigated plant species was fairly similar but differed significantly on C. sativa. The flea beetle species discriminated between the tested host plants, with a general gradient in attraction from E. sativa > B. juncea > B. nigra > R. sativus > S. alba > B. rapa > B. napus through to C. sativa. Brassica juncea and B. nigra developed faster and at early growth stages were more attractive to overwintered adult flea beetles than B. napus and therefore had potential as trap plants to protect spring rape. R. sativus and E. sativa, despite their development rate being slower than B. napus were also more attractive to flea beetles. Thus, further experiments with a complex of attractive early season and late-season plant species (multiple trap crops) should be undertaken.

Male mealworm beetles increase resting metabolic rate under terminal investment

Harmful parasite infestation can cause energetically costly behavioural and immunological responses, with the potential to reduce host fitness and survival. It has been hypothesized that the energetic costs of infection cause resting metabolic rate (RMR) to increase. Furthermore, under terminal investment theory, individuals exposed to pathogens should allocate resources to current reproduction when life expectancy is reduced, instead of concentrating resources on an immune defence. In this study, we activated the immune system of Tenebrio molitor males via insertion of nylon monofilament, conducted female preference tests to estimate attractiveness of male odours and assessed RMR and mortality. We found that attractiveness of males coincided with significant down‐regulation of their encapsulation response against a parasite‐like intruder. Activation of the immune system increased RMR only in males with heightened odour attractiveness and that later suffered higher mortality rates. The results suggest a link between high RMR and mortality and support terminal investment theory in T. molitor.

Does Thinning of Old Apple Trees Improve Fruit Quality and Decrease Pest Incidence

The effect of thinning on fruit weight, color, biochemical composition, and on leaf insect occurrence was studied in an over 80-year-old orchard on two apple tree (Malus domestica Borkh.) old cultivars: Liivi Sibulõun and Paide Taliõun. The study was conducted to restore an old orchard for quality apple juice production. Pruning led to a significant increase in pests, but the number of natural enemies of pests and of neutral insects did not increase. The total number of arthropods was significantly higher on ‘Paide Taliõun’ in the second year after pruning. Consequently, more pests were found in both experimental years on this cultivar. Pruning significantly increased leaf SPAD value leading to a decrease in the total phenolics content of the fruit. The effect of thinning on ascorbic acid content was cultivar dependent. Fruit skin was greener, apple flesh color was yellower, and fruit weight increased by up to 60% after pruning. Among apple taste parameters, the sugar acidity ratio was not influenced by pruning but was positively correlated with skin color, especially in ‘Liivi Sibulõun’. Thinning of old apple trees does not affect the taste of apples but could reduce the impact on the healthy parameters, such as phenolic compounds.