Progress towards a biological control programme for glasshouse whitefly (Trialeurodes vaporariorum) on tomatoes

During 1969/74 different methods of using the parasite Encarsia formosa to control whitefly infestations on tomatoes in glasshouses have been evaluated commercially. The most effective control was achieved by the Glasshouse Crops Research Institute (GCRI) programme of timed parasite introductions at rates totalling 120000 parasites per ha (48000/acre) following the pre-establishment of a low, evenly distributed infestation of the pest throughout the crop. Other methods, including the regular introduction of parasites after planting in anticipation of a whitefly infestation or starting when the first whiteflies appear on the plants, are also described. These multiple introduction (‘dribble’) methods, gave mostly satisfactory control but were less predictable. The efficiency of the parasite is greatly impaired during the short days and low light intensities of the late winter months and alternative methods of dealing with early whitefly infestations, including the use of chemicals, are discussed.     

Host plant direct defence against eggs of its specialist herbivore,Heliothis subflexa

1. The insect Heliothis subflexa Guenée is a specialist on plants in the genus Physalis. In the present study, the physical response of Physalis leaves to egg deposition by H. subflexa is described. 2. It was observed that the leaves of Physalis plants respond to the eggs of H. subflexa, while co‐occurring non‐host plants do not. Leaves of Physalis angulata L. and Physalis pubescens L. respond to H. subflexa eggs by the formation of (i) necrotic tissue, (ii) undifferentiated cells that form a bump (neoplasm) under the eggs of this herbivore, or (iii) both types of responses. 3. Greenhouse experiments showed that 64% of eggs laid on P. angulata elicited a response, and that a response to an egg decreased the probability of hatching. Further experiments in the field with P. angulata showed that the mean response to eggs by leaves was 31%, and that this response increased as temperature increased. Field experiments also confirmed that a plant response to an egg decreased the probability of hatching and increased the probability of removal from the plant by physical dislodgement or predation. 4. Eggs that elicited a response had a 25% lower probability of hatching and a 28% lower probability of remaining on the plant, resulting in an average fitness cost of 19.3% for H. subflexa. This is the first study to show an induced direct physical defence of a plant against eggs of a noctuid moth.     

Transmission of louping ill virus between infected and uninfected ticks co-feeding on mountain hares

Abstract. Most of the data on oral infection of ticks by louping ill virus have been obtained from experiments in which animals were infected by syringe inoculation with infectious material. Using infected ticks to mimic the natural situation, we have demonstrated that louping ill (LI) virus transmission can occur from infected to uninfected Ixodes acinus feeding in close proximity on mountain hares (Lepus timidus). Under these conditions the hares developed either low or undetectable viraemias. Highest prevalence of LI virus infection was observed in recipient nymphs which had fed to repletion between days 3 and 7 post-attachment of virus-infected adults; following engorgement, 56% of nymphs acquired virus. These results demonstrate the efficient transmission of LI virus between co-feeding ticks on naive mountain hares. However, when ticks were allowed to co-feed on virus-immune hares a significant reduction in the frequency of infection was observed. Neither red deer (Cervus elaphus) nor New Zealand White rabbits supported transmission of LI virus. The significance of virus transmission between cofeeding ticks on LI virus epidemiology is discussed.     

Population dynamics of Siphoninus philyreae in California in the presence and absence of a parasitoid, Encarsia partenopea

Abstract. 1. Densities of the whitefly, Siphoninus phillyreae Haliday, remained at low levels at two sites where a parasitoid, Encarsia parknopea (Walker), was released on whitefly-infested ash, Fraxinus sp., and pomegranate, Punica granatum. Populations of S.phillyreae at control sites, where parasitoids were absent, were increasing in density at the beginning of the summer.
2. By mid-summer, E.partenopea had appeared at all four control sites, and densities of S.phillyreae declined to levels similar to those at the release sites.
3. In the absence of the parasitoid, the age structure of S.phillyreae populations was dominated by the egg stage, indicating a population increasing in density. After E.partenopea became abundant at a site, the age structure of the population had a decreasing proportion of young stages.
4. The changes in S.phillyreae age structures were explained by examining the percentage of fourth instar S.phillyreae from which E.partenopea , as opposed to adult whiteflies, emerged. After the parasitoid became abundant at a site, the majority of fourth instars produced parasitoids rather than whitefly adults. The result was that the adult S.phillyreae population declined, and few eggs were laid.
5. The dynamics of the interaction between E.partenopea and S.phillyreae were similar on ash and pomegranate.     

Preliminary studies of an integrated control programme for cucumber pests and an evaluation of methods of introducing Phytoseiulus persimilis Athias-Henriot for the control of Tetranychus urticae Koch

Preliminary investigations suggest that, when Phytoseiulus persimilis is used to control Tetranychus urticae, the major pest of cucumbers, the control of other pests and powdery mildew can be effected by means of Encarsia formosa for the control of whitefly (Trialeurodes vaporariorum), bed drenches of gamma-BHC for thrips control and dimethirimol for the control of cucumber mildew (Erysiphe cichoracearum). The parasite Aphelinus flavipes failed to control an infestation of Aphis gossypii in one trial. A comparison of different methods of introducing Phytoseiulus confirmed that the best results were obtained when an even, artificial infestation of Tetranychus urticae was established on the crop before the introduction of the predator.