Novel control methods for insect pests: development of a microencapsulation procedure for proteinaceous bioactives intended for oral delivery.

BACKGROUND: The objective was to develop an environmentally favourable microcapsule suitable for delivery of proteinaceous bioactive agents ('bioinsecticides') to pest insects. RESULTS: Utilising feeding bioassays, we determined that microspheres made of alginate can be produced in a variety of sizes and are palatable and non-toxic to larvae of the lepidopteran pest Lacanobia oleracea. Dehydrated microspheres were also readily ingested by larvae. Using a novel feeding bioassay and alginate microspheres containing a fluorescent marker material (coumarin 7 encapsulated in styrene maleic anhydride beads), we determined that the microspheres successfully deliver the marker to the insect gut. Moreover, the alginate microspheres rapidly break down in the alkaline conditions of the insect gut and release their contents, the beads passing through the gut in 2-3 h. Using bovine serum albumin as a test protein and western blotting, it was determined that alginate can successfully encapsulate protein, and that the microspheres can be stored in a CaCl2 solution for up to 24 days without extensive leakage. Importantly, it was also determined that alginate and the microsphere-making procedure developed do not inactivate rVPr1 (an insect immunosuppressive protein and potential bioinsecticide). CONCLUSIONS: An alginate-based microsphere has potential to deliver the proteinaceous bioactive rVPr1 to pest insects.

Can Batesian mimicry help plants to deter herbivores?

Several authors have suggested that edible plants could avoid herbivory by mimicking olfactory cues of toxic plants. However, very few studies have been carried out to test this hypothesis. The aims of the present study were to identify the volatiles of three clover species and to test whether a species lacking chemical defences, such as red clover, could avoid being grazed by rabbits by mimicking the volatiles of the cyanogenic white clover. Two main volatiles were identified in all three clover species, and a further two volatiles were present in white clover only. Rabbits presented with a choice between white clover, red clover and red clover sprayed with white clover extract ate significantly more red clover than white or white-flavoured red clover. The results suggest that the volatiles of toxic plants could be used and exploited as a source of natural, safe and effective repellents to control the impact of pest herbivores on plants.

Boosting silica levels in wheat leaves reduces grazing by rabbits.

Systemic application of sodium silicate can significantly enhance the levels of leaf silica in winter wheat (Triticum aestivum L. cv. Mercia), suggesting that this material could reduce the palatability of plants to vertebrate herbivores (e.g. rabbits, Oryctolagus cuniculus L.). A bioassay was developed using hydroponically grown wheat plants. Plants treated with sodium silicate were significantly more resistant to grazing by wild rabbits than untreated plants, with severe, potentially lethal feeding damage being reduced by over 50%. Further studies were carried out to develop more practical techniques for boosting silica levels in plants using silicon-rich 'fertilisers' including calcium silicate and calcium silicate slag (CSS). Silica levels were elevated in the plant 1.9-2.8 times over the control through the application of various silicon materials, in line with those of the hydroponic treatment. Encouragingly, levels of silica were elevated even in young wheat plants, which are most vulnerable to rabbit damage, and in a range of wheat varieties. The use of CSS is particularly promising because of its lower cost in comparison with calcium silicate, and it has a proven track record in slag fertilisation of rice and sugar cane crops. At the optimum CSS application rate of 3 g silicon L(-1) soil, wheat silica levels were approximately doubled, with no detrimental impacts on long-term growth or yield.

Masking the taste of the conditioned taste aversion agent levamisole using an ion-exchange resin, for practical application in wildlife management.

For a conditioned taste aversion (CTA) agent to be successful in wildlife management applications, the compound must not be detectable by the animal. Levamisole is an effective CTA agent when administered by oral intubation, but it is readily detected by a number of species when mixed directly in food. This paper describes the development of an ion-exchange resin complex (resinate) to mask the taste of levamisole. Two different resins were evaluated, Amberlite IRP-64 and Amberlite IRP-69, and release studies indicated that the resinate formed using IRP-64 resin would be most suitable for use in wildlife management. Although it contained a relatively low loading of levamisole (77 g kg(-1)), the results indicated that the IRP-64 resinate should be stable in the mouth and release the levamisole quickly in the acid environment of the stomach (93% of levamisole was released into 0.1 M HCl in 5 min). In a bioassay using laboratory rats (Rattus norvegicus Berk), we showed that the taste of levamisole was successfully masked in a biscuit bait using the IRP-64 resinate and that a CTA was generated to untreated bait. The use of ion-exchange resins is a new approach in the taste-masking of CTA agents and could be applied to other wildlife management applications.

Improving the persistence of a formulation of the avian repellent cinnamamide, for the protection of autumn-sown oilseed rape.

In a previous pilot field trial on autumn-sown oilseed rape (Brassica napus L), a suspension concentrate formulation of the avian repellent cinnamamide, using Acronal 4D (50 g litre(-1)) as the sticker, was shown to reduce damage by woodpigeons (Columba palumbus L). However, the persistence of cinnamamide on rape leaves was poor. This paper describes the development of a weather-resistant formulation by the inclusion of a more effective sticker. In vitro studies were used to investigate wash-off of cinnamamide, which was identified as being the major mechanism of loss in the field. Rainfastness of cinnamamide was assessed by washing deposits on glass slides and rape leaves using a 'rain-washing machine'. A number of stickers were evaluated and the effect of sticker concentration, ageing of deposits, freezing and intermittent washing on rain-fastness was investigated. None of the candidate stickers showed increased rainfastness compared to Acronal 4D. However, two of the stickers, Crovol T40 G and Emoleo L1, when combined with Acronal 4D in small amounts, did reduce wash-off compared with Acronal 4D alone. Freezing led to an increase in wash-off of cinnamamide, but inclusion of Emoleo L1 with Acronal 4D reduced this effect. Increasing the concentration of the sticker was also shown to improve the rainfastness; doubling the concentration of Acronal from 50 to 100 g litre(-1) halved the wash-off of cinnamamide.