It is very important to understand that all of the bruchids that feed in seeds of Prosopis lay eggs on seed pods before or when the pods mature, thus pods that have bruchids emerge from them in storage were infested by bruchids before they were put into storage. Therefore, it is very important to reduce the numbers of bruchids in seeds as soon as possible after they are harvested and prior to or shortly after they are stored. Of course, some (probably most) Prosopis bruchids will continue their life cycle until all food materials are used up. Thus it is essential that storage areas be clean and free of places where food accumulates and bruchids may hide because uninfested pods may be attacked when placed in storage areas that have living bruchids in them.
Felker (personal communication), Felker et al. (1981) and Smith and Ueckert (1974) have used insecticides to control Prosopis seed-feeding insects prior to harvest. They did not attempt to determine the best insecticide to control insects in the field but used insecticides that they thought would reduce the numbers of insects. Therefore, most of the insecticides listed in Table 4 (page 41) have not been tested to determine how effective they are in controlling pre-harvest seed pests of Prosopis. Cadahia (1970) documented the periods of greatest activity and percent damage of the Lepidoptera that feed on flowers and fruits of P. tamarugo in Chile. He also suggested the most appropriate times for applications of insecticides. Léon (1974) compared the effects of various formulations of Endosulfan in controlling the Lepidoptera that feed on flowers and fruits of P. tamarugo in Chile. The results of the studies of Koch (1969), Cadahia (1970) and Léon (1974) are summarized in Habit et al. (1981).
The most likely time to apply insecticides to control insects that feed upon Prosopis pods is when the young pods are beginning to form (but see Smith and Ueckert below). Applications of insecticides during flowering may kill the pollinators.
Felker et al. (1981) found that Orthene 1 sprayed at three-week intervals reduced the number of bruchid emergence holes from 23 per 100 pods to one per 100 pods, but they concluded that “Malathion seems as effective as Orthene”.
Smith and Ueckert (1974) found that Prosopis glandulosa trees sprayed with Cythion increased the number of good seeds from 30% to 51%. They concluded that the reduction of pod-sucking insects and bruchids was responsible for the increase. They also found that trees treated with Cythion from flower set until pod development produced a mean of 148 pods per tree and a mean of 54% good seeds, whereas trees treated subsequent to flowering produced a mean of 104 pods per tree and a mean of 45% good seeds. Thus, the time of flower set may be the best time to apply insecticides.
The other insecticides in Table 4 are, for the most part, proven insecticides for controlling economic legume seed-feeding insects in the field.
It is emphasized here that Prosopis pods should be treated shortly after harvest to destroy the bruchid larvae in the seeds. Methods other than fumigation with chemicals listed below are to subject the seeds to extreme heat or cold. Often seeds can be subjected to low or high temperatures that will kill insects but not the seeds. Storage areas free of residual Prosopis seeds and seed-infesting insects are also essential.
Rupérez (1978) is the only scientist who has made specific recommendations for control of Prosopis bruchids in storage (Table 5, page 42). He recommended standard materials that are used for control of other stored-products insects. At present we do not know which of the insecticides (Table 5) are best suited for control of Prosopis seed pests in storage or their effects on the ability of Prosopis seeds to germinate. Probably any of the most effective fumigants for stored-products insects of legumes (methyl bromide, hydrocyanic acid, carbon disulfide, aluminum phosphide and carbon tetrachloride/ethylene dichloride mixtures) would control Prosopis insects. Research is needed to ascertain the most effective insecticides for controlling seed pests of Prosopis in storage.
Many methods have been used in attempts to reduce the numbers of insects in stored products (Table 6, page 43). Much of the research that has been conducted on the use of plants or parts of plants, extracts of plants, oils, ashes and minerals for control of bruchids has been done by scientists in India. Golob and Webley (1980) compiled a list of traditional methods to control insects of stored products and published a bibliography of research papers that describe these methods in detail. The work of Golob and Webley is of especial value for present and future control programmes of stored-products insects in countries where synthetic organic insecticides and fumigants are too expensive to be used widely. When non-economic tropical plants are developed for economic uses, these traditional methods should be investigated thoroughly for use in Third World countries.
The use of whole plants or parts of plants such as leaves, stems, seeds or roots that have only been processed by chopping or powdering, is reported from much of the world but mostly from India and Africa.
Plant extracts and oils were listed in two different sections by Golob and Webley (1980) and that scheme is followed in Table 6. The plant extracts were oils that presumably have toxic materials dissolved in them that account for their insecticidal activity. Conversely, those listed under oils by Golob and Webley kill eggs of bruchids but no mode of action is implied. Presumably the oils may act as a physical poison to the eggs or larvae, or some chemical factor in oils may be responsible for the death of bruchids. The main concern with the use of oil is that those oils which are cheaply available in a locality will be effective without imparting some rancid or off-flavour to a food stuff or affect the viability of seeds.
The works of Su (1976, 1977) Su et al. (1972 a, b, 1982) and Schmutterer (1981) are intriguing because their research involves extracting toxic chemicals from plants (e.g. citrus peels, neem seeds) and using them to protect stored products from insects.
Wood ashes and minerals are widely used for mixing with grains (Table 6). Their effectiveness varies with the silica content of the dust and their absorptive and abrasive properties. They may also fill the interstitial spaces in bulk grain or provide a barrier to the movement of insects.
Miscellaneous methods of control such as spreading a 2 cm layer of sawdust on stored legume seeds, use of fire to trap and kill insects or to heat seeds to destroy the insects in them, and use of smoke to repel or kill insects have been used.
The use of controlled atmosphere storage (Kamel 1980, Burrell 1980) is of interest because it is a technique where large amounts of seeds can be stored in underground pits which are deprived of air. The insects inside the seeds soon use up the available oxygen, carbon dioxide is produced and the insects suffocate. Variations of storage of seeds in hermetically sealed containers may include artificial introduction of carbon dioxide into the container before sealing it and the use of fungal respiration or fermentation to use up the oxygen.
A wealth of information on appropriate technologies for development with specific reference to small farm grain storage is available in the works of Lindblad (1978) and Lindblad and Druben (1976 a, b, c). These should be consulted for specific and general control of pests of stored products in developing countries.
Various predators and parasites have been recorded as attacking and killing storage insect pests. The predaceous mites in the genus Pyemotes have been observed to attack and kill eggs, pupae and adults of the bruchids Acanthoscelides obtectus and Callosobruchus maculatus. The hymenopteran Pteromalus schwenkii feeds on larvae of Callosobruchus chinensis. Dinarmus laticeps is a common pest of bruchids. Although predators and parasites may locally reduce populations of pests, they cannot be considered an effective overall method of control (National Academy of Sciences 1978).
The parasites and predators that have been reported to attack Prosopis pests are listed in Table 7 (page 47). Those reported by Koch and Campos (1978) in Table 7 attack the moth Cryptophlebia carpophagoides but all of the others attack bruchids.
Conway (1980) observed that Trichogramma spp. egg parasites were most abundant in eggs of the Prosopis bruchids Mimosestes protractus and M. amicus, probably because their eggs are exposed on the surface of the pod. Algarobius prosopis lays eggs in cracks and crevices in the pods so that its eggs are not heavily attacked. Horismenus productus (Eulophidae) is a primary parasitoid of M. amicus and A. Prosopis. Conway (1980) estimated that from 1% to 4% of bruchid larvae were parasitized by H. productus at his study sites in Arizona. Conway (1980) also found that Heterospilus prosopidis (Braconidae), a larval parasite of M. amicus and A. prosopis, parasitized from 9% to 17% of the available bruchid larvae. Another Braconidae, Urosigalphus bruchi, destroyed from 4% to 7% of the Prosopis bruchid larvae (Conway 1980). Conway estimated that the larval parasites destroyed from 17% to 25% of the Prosopis bruchids at his study sites in Arizona. In summary, egg and larval parasites have an impact on bruchids by reducing their numbers but they would have to destroy significantly more bruchids than have been reported here to be an important method of control.
